Title edited, thank you mods/admins.
Intro.
Purpose of this thread is primarily to detail how we can best create the the necessary conditions for a most reliable install that will also deliver the maximum damper service-life and performance; at the lowest long-term cost.
This thread will also provide a single place where you can list tips for installing yellow B6 and B8 type mono-tube Bilsteins into Audi B3 and B4 chassis MacPherson struts. This may be of use as, although similar to the stock arrangement (and despite the expense, is considered a worthwhile mod by many, an install that can be looked back on as successful longer-term) is a little different from how the original factory Boge's and other OEM (twin-tube) style dampers (including Bilstein B4's) were assembled into these Audi struts. Please note also that there are a few points herein which (all noted as such I believe), apply -just- to the original Boge's, original style Bilstein B4's and similar conventional OEM (twin-tube) type dampers. Finally, it may be useful to have a read through the entire thread as some points are applicable to both types of installations.
Notes on parts and special tool, compatibility and condition:
Along with dampers that fit, you will need the specific Bilstein cap-nuts and the particular matching cap-nut tool (a.k.a. the Bilstein wrench) also correctly sized both for your dampers and strut-tubes. Important because:
- Front struts of the North-American cars all had necked-down strut tube-tops requiring smaller (50mm O.D.) dampers;
- Some of the destined for Europe cars also came with front strut tubes of less than the more usual for Europe 55mm OD; and
- Early on, you may want to measure both your struts to be sure; in case they are not both the same or the expected size.
If re-using B6/8 Bilstein cap-nuts, ensure the rubber gland it carries is in very good condition, as this seal not only protects the damper's greased interior sliding interface below (chrome shaft against interior of yellow tube) from water and grit, but also keeps closed an otherwise known water entry point which can lead to hydro-locking of the strut assembly (more on this below). If the Bilstein wrench is a used one, ensure it has not been previously damaged, fits easily over the damper shaft, and engages fully onto the nuts correctly, read more below. Although new Bilsteins should come with new gland nuts (with glands preinstalled), no wrench will be included. The nuts, either with or without the required glands, the glands themselves, and the tool are all available separately from Bilstein.
Bilstein B6 : B8 M50 ring-nut , for 50mm front struts.png Bilstein B6 : B8 30mm seals, for 50mm front struts.png Bilstein B6 : B8 gland-nut complete with seal for 55mm front & rear struts?.png
Jordan's photos (from M/G) of a 50mm gland-nut w/o gland, the glands for those North-American front struts & 52mm? nuts w/glands for rears.
1.) Tools and Equipment Required:
- Confirm your Bilstein cap-nut (aka: gland-nut) wrench is of the appropriate size for your application; and is in perfect condition. If not contact Bilstein;
- Leather work gloves, a hack saw, and proper penetrating oil (not just WD-40);
- Bench-mounted vise; wooden blocks to contact, and brace the strut with. Use vise judiciously with the wood blocks to secure the strut in without collapsing the strut tube, for drilling the drain hole; and to cradle the assembled strut in, both for cutting the original cap-nut; and torquing the Bilstein cap-nut.
- Note: Stillsons, or even a small chain or pipe wrench should not be necessary and may result in strut-tube damage. If employed, use caution, and use only gently around the old cut cap nut; and only - after - it is already loose;
- Hand-held wire brush; Navel Jelly (a rust remover gel); lapping compound; varsol; lacquer thinner (or electrical contact cleaner); spray paint (primer and 2 colours which contrast with strut-tube colour; and each other, a small paint-brush);
- Loctite (blue), a 1/2" drive torque wrench;
- Nail-polish (in a contrasting colour to your strut paint) & a wax-oil type rust-proofing compound.
- Scriber, center punch and a ball-peen hammer; &
- Electric hand-drill, a small diameter pilot-hole drill bit, a 1/8th" to 10mm bit.
2.) Removal of Old Stock Damper from Strut (springs, etc. are assumed already off the strut at this point).
To get the likely seized old stock original style damper-retaining cap-nut off the strut most easily, and also prevent any possible crush damage to the thin strut-tube itself from a vice or pipe-wrenching etc., read on.
Method Outline:
In preparation for cutting the cap-nut by hand, brace the strut, cradling it in the vice using the wooden blocks such that it is held steady -without- putting any pressure on the tube. Next remove the OEM cap-nut as follows: Hacksaw the nut as indicated by the red lines in photo below, then soak with penetrating fluid; and only then, finally with just your gloved hands; easily twist it off.
Mac strut damper retaining cap-nut cut-lines 2019-05-02 at 10.06.28.png
Drawn lines in photo above are to indicate where to cut diagonally in 2 or 3 places around the outside of a seized cap-nut's circumference; to loosen the rusted threads. Once cut, penetrating oil can be applied directly into the affected threads and the nut will actually spring slightly open. Using a hand-saw only, cutting is sufficient when a series of small holes appear as you break through the roots of the cap-nut's interior threads. Done carefully, no damage to the struts threads (which are fully engaged and very close while you perform this task) will occur.
a.) How your nuts get stuck and why use this method:
Your strut cap-nuts may be fused onto the strut-tubes by years of corrosion activity. The originals were installed without anti-seize compound or Loctite. This rusting often seals the lower edge of the cap-nut on the strut closed, preventing any penetrating oil from entering. Because of the possibly very large total threaded surface area which may be involved (perhaps all ten internal threads of the cap-nut, times the diameter of the strut tube, equals a potentially huge rust grip area that) you will not easily break the cap loose from, or successfully remove it with just the vice, pipe-wrenches, and torches; without also damaging the thin-walled strut-tube. With this "no torches, etc." method, any strut damage is easily avoided.
Note: This method involves using a plain ordinary hack-saw to cut diagonally across and around the O.D. of the cap-nut as required to next get penetrating oil on -all- ten of those hidden engaged internal cap-nut threads . It's fast, simple and easy. Don't use a power saw or wheel of any sort as you will mess up your struts if you do.
b.) How to turn your OEM style nuts off with just your hand:
First cut, on a diagonal (relative to the strut axis), from the top to the bottom, around the O.D. of the cap-nut, -just- partially through to the roots of the cap-nut's internal threads. Depth-wise, stop when you have made a series of small holes appear in the bottom of the slot you have cut, through which you then apply penetrating oil. Continue to cut the diagonal slot right to the lower edge of the cap-nut and, because the original nut is a stamped part; it will then actually spring open slightly. If not loose at this point, do the cutting again in 2 or 3 spots spread around the O.D. and the nut will turn off by hand (Caution: cap-nut OD is now sharp!). By careful use of just a hand-held hack-saw, any damage to the strut tube's threads can be avoided altogether.
Here's a photo from a post in S2Central's Strut Cap-Nut Tools thread (link to complete thread near bottom of this post) where he made use of the above method:
Diagonally cut strut cap-nut.png
Here is an old post link (from 2010 on audiworld.com) which also described the task list above, and how to cut ever so slightly into the threaded interface between the cap-nut and strut-tube.
3.) Mac. Strut Body Prep:
a.) Tube-top thread re-condition as follows:
Considering what nut removal may have involved, you may want to take steps to ensure this does not happen again. However more immediately, this will also aid in the correct cap-nut torquing later on as torque consumed in turning the nut onto a rusty dirty strut-tube is automatically subtracted from the torque applied to the damper body (where you want the torque to be felt). Note also that there was a factory bulletin (see link below) which upped the torque because of issues observed due to cap-nut loosening.
- Wire brush the threads;
- Likewise Naval Jelly as per its' instructions;
- Paint (other than, but up to threaded area)
- Further strut tube thread cleaning. You may now use the just removed old and usefully cut OEM cap-nut (allowing adjustment by slightly squeezing the cut sides in as required) as an effective thread-chasing die with some lapping compound.
Note re importance of thread-cleaning: The Bilstein cap-nut recess, which secures and centers the top of the yellow damper tube, appears to have a slight taper, so any slack in its final positioning will allow the damper to wobble up top; and move out of position at the bottom! Re-condition the threads until they operate "as new", as this will best allow both proper capture of the damper top and best torquing of the cap-nut, helping to ensure the damper will remain correctly centered and fixed inside the strut-tube. Again, when applying torque to the nut, consider that any force consumed in turning the cap due to poor thread condition; is torque that is -not- applied to properly clamp the damper in place. This is not fixable later until the main springs are again removed. Another reason to do the best job possible here is the install torque spec is high; and the Bilstein wrench is (perhaps purposefully) weak. A best job done now will aid with any possible future removal.
b.) Drain Holes:
I put my drain holes on center thinking that would be the low spot and least likely to be blocked by the damper's presence, I also enlarged them to an 1/8" after finding one plugged with debris.
c.) Clean Strut Body:
Ensure no debris inside where damper fits into base; and clean tube-top external threads to best receive Loctite.
4.) Understanding Fixturing of the Mono-tube type (B6 &B8) Bilstein within the Mac-P. strut:
As Audi had BOGE produce and supply both the original struts and dampers for these cars, and we are instead installing yellow mono-tube Bilsteins whose OD is smaller than the original BOGE dampers, we need to understand the differences in how each of these are correctly secured inside the strut body. Particularly at the bottom of the strut interior, the original BOGE damper OD closely matches the strut ID, whereas the reco'd fitments from Bilstein do not.
The reason for this ID/OD mismatch is that while Bode designed their damper to easily self-position correctly in this strut, perhaps that Bilstein uses this same damper shell for fitment into other vehicles with differing struts, means that they have adapted it to fit - in a different fashion, which therefore allows them to not make a special version for just these cars. That circumstance may also explain why the orange warning label (re: strut drain-hole mod) has disappeared from more current purchases, as other vehicle applications may not all share this hydro-locking issue.
Unlike the original Boge or other OEM (twin-tube) style dampers (such as Koni), the yellow mono-tube Bilstein is held centered in place at the bottom -only- if correctly centered in the strut-tubes concave base during insertion (and held there until pressed into place with the cap-nut!). The possibility for errors here increases with the difference between your particular strut-tube's largest effective I.D. and your damper's O.D. at its' base, so perhaps less of a concern if these two diameters match (as is the case with the UrS cars), but any difference allows the possibility of misalignment (between strut-tube and damper center-axes) which will result in noise and damper movement while underway and at least, likely damage the cap-nut's gland seal; unless the following precautions are taken before and during assembly. The damper base has an abbreviated (less than 5mm) and shouldered slightly spherical protruding shape to fit the mating depression in the strut-tube base, and its correct function is dependent on three preconditions as follows:
a.) Damper base sphere must be correctly centered in the strut-tube's concave base recess;
b.) Top outer perimeter of the painted yellow tube must be correctly captured and centered within the Bilstein cap-nut recess (less than 5mm deep, see cap-nut recess and ledge in photo); &
c.) Cap-nut correctly fastened with Loctite; and done up to the recommended torque (see torque # on Bilstein wrench).
Examples of what can go wrong:
i.) Damper-base not centered in strut-base but off-set to one side and sitting up on interior base shoulder. This will allow the damper-base to rock laterally during driving which will at least make noise, very annoying (and possibly begin cap-nut loosening and vertical damper hammering); and everything must come apart to fix it;
ii.) Yellow tube-top not correctly captured in the cap-nut recess. Nut torque may relax during driving also allowing damper to both rock laterally and hammer vertically within strut. This will quickly kill the gland-nut seal; and the nut torque may deform yellow tube-top edge which may allow water entry into the strut.
Top end of yellow painted Bilstein outer tube to be captured in unique Bilstein top-nut ID Screen Shot 2021-07-17 at 16.26.35.png Photo (by fka at saabtechtalk.com ) is of a Saab unit (shown inverted) but no matter, it shows Bilstein's unique to their mono-tubes' top-nut interior which will engage, center and secure the damper's yellow painted tube at only its' very top end OD within the Audi strut tube via the nut's visible recess ID. It fits tight enough that after being final torqued, you'll notice some yellow paint removal on dis-assembly.
5.) Dry Run #1: Empty Assembly of Strut-tube & Bilstein Cap-Nut:
You want to be able to screw on and fully seat the cap-nut on the still empty strut-tube easily with just your bare hands. This will ensure a couple of things:
i.) That you have sufficient free cap-nut travel to properly capture, compress and hold the damper when installed later; &
ii.) That your final applied torque will all be employed to pressing down on the top of the yellow tube, securing the damper; and not partially lost fighting thread friction (Note: Be aware there was a factory TSB which upped the torque on the original cap-nut due to observed loosening issues which occurred here, see more on this at bottom of post).
Match-marking:
Paint-mark this fully down point on the exposed threads of the strut-tube just below the nut. This will give you an initial reference point (Ref. A in the strut tube-top photo below (photo by audi*line, thanks) that you should almost but not quite reach later with the slightly taller damper correctly in place with both its' base properly centered inside; and the yellow tube-top properly captured and centered in the cap-nut.
Strut-top cap-nut fit reference points.png
6.) Dry Run #2: Ensuring Full Correct Damper Placement, and Fixturing into Strut-tube:
a.) Unscrew the cap-nut and place the damper inside the strut-tube carefully centering its' base in the bottom of the strut-tube; (Note: Damper -must- be installed by lowering into strut whilst both are held vertical!). Note the damper will sit lowest in the strut-tube when it's base is properly centered, and -not- up on the circumferential shoulder of the strut-tube's internal base; only if both are held vertical during the assembly process.
b.) Next screw the cap-nut back on and hand-tighten fully onto the strut-tube again ensuring the yellow tube-top is properly centered and captive inside of, and -not- up on edge of, the cap's recess or catching the edge of the yellow tube.
c.) Paint a 2nd broad mark (well apart from the 1st) w/the 2nd paint colour, that can be easily seen while your working, horizontally just below the bottom edge of the nut at its' now final install position (Ref. B in above photo). The difference between these two paint marks should mirror the effective and observed height difference between the top threaded edge of the strut-tube; and the installed damper's yellow tube-top's (slightly taller) height (Ref.C).
d.) Now paint the 3rd and 4th marks vertically w/the 2nd paint colour again, one on the Bilstein cap-nut and one on the strut-tube to give you a very good 'Vernier' type indication of the nut being exactly fully home correctly capturing the enclosed damper (see Ref.D). If the top or bottom of the damper are not correctly positioned inside the strut, you will not be able to easily by hand turn the cap-nut down to this point during final assembly below (Hint: Paint this one such that you can see it in future by lifting the damper boot when the car is all back together).
Doing both the above empty assembly and the practice full vertical fixturing is going to help ensure a couple of things:
i.) With damper now in place you are here going to be able to confirm that because the cap-nut bottoms out -before- reaching Ref. A, that the damper will be effectively clamped in place (this is particularly important strut-tube effective internal length check for those who have done Mance's BBSE mod, and it confirms your dampers are the correct length if your struts are unmodified also) before the cap-nut bottoms on the strut-tube at Ref. A.
ii.) You are going to get a feel for how everything fits together properly; and by noting the new final hand installed height of the new cap-nut , which will now approach Ref.B and be complete when the two Ref. D marks align, you are able to more easily confirm success as you go during final assembly below, ensuring that the damper is correctly installed into the strut, rather than discovering it's not, after it's all back together; and you try dry driving on it. You now need to be thinking about how you are going to brace the assembled strut for the torquing of the cap-nut without damaging the strut-tube, the cap-nut, the Bilstein wrench or (see post #2 below); yourself!
iii.) Prior to final assembly is where I coated the strut tube interior with the rust-proofing. With a drain-hole of sufficient diameter, any excess will drain out the bottom without plugging the hole.
7.) Successful Final Assembly:
Involves just a few simple but carefully executed steps, including:
a.) Apply just a little Loctite in one spot & complete full vertical assembly again including bottoming cap-nut by hand into position at the above final ref. mark (see Ref.D);
b.) Brace strut for torquing and zero damage to strut and you!
c.) Torque application & see also "Bilstein Wrench Mod, from 2007" (photos in following post). You may need to re-do your assembly match-mark paint slightly after torquing.
Although Bilstein (North America) has always been very helpful in sending me wrenches (quickly and at no cost!) the wrench is a delicate stamping and it is not robust enough to remove the mono-tube's cap-nut if it is rusted, over-torqued, already damaged or if one uses the incorrect Loctite or even too much blue Loctite and/or doesn't warm-up the Loctite prior to the attempted loosening. By using the modified wrench, successful removal is more likely, but not guaranteed.
d.) Match-mark & rust proofing (nail-polish & wax-oil);
By marking the cap-nut and strut tube (see Ref. D) with a single (nail-polish?) mark in a spot you can most easily view when installed on the car, you can visually confirm your assembly in future. The wax-oil can be used to fill the remaining exposed exterior strut threads below the cap-nut.
Example of both the Bilstein cap-nut with gland & the wrench (photos below). Both the nut and seal are available separately. One can see that the wrench is only a stamped unhardened item & therefore fragile. As received, the two wrench teeth may be a little to long &/or sharp to easily/safely fit over & clear the damper's chrome shaft OD. The shiny wrench finish will help to highlight the deformation of the wrench when you are over-doing it. The corners where your square-drive fits & where the teeth emerge from the ring will deform first.
image_71419.png image_71420.png
Torquing the original style strut cap-nuts (with the 6-sided internal opening. seen in para. 2.) above, and the sockets for them:
Here is a link to an old write-up (from 2008 on audiworld.com) regarding the above mentioned factory Technical Service Bulletin re the cap-nut torque increase. This may also be of particular interest to those who may have been reading here about strut dis-assembly; and are going to be re-installing the original style cap-nut on their struts, used with conventional OEM (twin-tube) style original Boge's, and replacement Sachs, Koni's and Bilstein B4's, for instance:
Recapping cap-nut torque with the factory TSB...
Further (and a little farther off-topic), here in the 1st photo below (courtesy of Orsum) is the factory tool (both the VAG 2069 and VAG 2069A appear similar) necessary for torquing strictly the above original style cap-nuts onto the struts (Orsum rightly notes this socket's annular recess which has been cut away at the end shown to avoid any contact with the installed damper's shaft seal, which may be of particular interest to those who might be fashioning their own tool). Second photo below shows how that original style twin-tube damper's shaft seal (blue coloured) protrudes from the top of a Bilstein B4 damper body. Third photo shows a complete Bilstein B4, note the damper (just like their B6s & 8s) comes with a new strut cap-nut (not to scale), in this case it has an 8-sided welded-on top instead of the original style requiring the tool shown in 1st photo. The Bilstein P/N in this photo is for their 50mm O.D. B4 front (only as rears are 55mm O.D.) damper for B3 series 20v's ("Audi 90 (89, 89Q, 8A, B3) 2.3 E 20v Quattro (123 kW). Years of manufacture: 04/90 > 09/91. Suits Models with a Power Level of 123 kW. This equates to approximately 165 BHP").
OEM style strut cap-nut tool VAG 2069 .png Bilstein B4 damper shaft seal protruson Screen Shot 2023-04-23 at 12.01.12.png Screen Shot 2024-01-01 at 5.38.21 PM.png
For more on these two different socket sizes, P/N's and various suppliers and makers of this tool, please also see S2Central's thread here:
Tools for the Front & Rear Strut's Cap-Nuts...
Concluding Remarks:
I'd like to think that the above task list would allow one to not have to re-visit the damper install, however you may want to understand hydro-locking, these particular dampers' susceptibility to it; and know the symptoms which may indicate it's onset, I've certainly been wrong about this issue before, please also see my response to GT500's post titled "Bilstein Killed..." (from 2011) on this forum and work back to the quattroworld.com links.
I think that's most of it, hope this helps. And certainly I may have missed something, please chime in. Questions?
Lago Blue
Intro.
Purpose of this thread is primarily to detail how we can best create the the necessary conditions for a most reliable install that will also deliver the maximum damper service-life and performance; at the lowest long-term cost.
This thread will also provide a single place where you can list tips for installing yellow B6 and B8 type mono-tube Bilsteins into Audi B3 and B4 chassis MacPherson struts. This may be of use as, although similar to the stock arrangement (and despite the expense, is considered a worthwhile mod by many, an install that can be looked back on as successful longer-term) is a little different from how the original factory Boge's and other OEM (twin-tube) style dampers (including Bilstein B4's) were assembled into these Audi struts. Please note also that there are a few points herein which (all noted as such I believe), apply -just- to the original Boge's, original style Bilstein B4's and similar conventional OEM (twin-tube) type dampers. Finally, it may be useful to have a read through the entire thread as some points are applicable to both types of installations.
Notes on parts and special tool, compatibility and condition:
Along with dampers that fit, you will need the specific Bilstein cap-nuts and the particular matching cap-nut tool (a.k.a. the Bilstein wrench) also correctly sized both for your dampers and strut-tubes. Important because:
- Front struts of the North-American cars all had necked-down strut tube-tops requiring smaller (50mm O.D.) dampers;
- Some of the destined for Europe cars also came with front strut tubes of less than the more usual for Europe 55mm OD; and
- Early on, you may want to measure both your struts to be sure; in case they are not both the same or the expected size.
If re-using B6/8 Bilstein cap-nuts, ensure the rubber gland it carries is in very good condition, as this seal not only protects the damper's greased interior sliding interface below (chrome shaft against interior of yellow tube) from water and grit, but also keeps closed an otherwise known water entry point which can lead to hydro-locking of the strut assembly (more on this below). If the Bilstein wrench is a used one, ensure it has not been previously damaged, fits easily over the damper shaft, and engages fully onto the nuts correctly, read more below. Although new Bilsteins should come with new gland nuts (with glands preinstalled), no wrench will be included. The nuts, either with or without the required glands, the glands themselves, and the tool are all available separately from Bilstein.
Bilstein B6 : B8 M50 ring-nut , for 50mm front struts.png Bilstein B6 : B8 30mm seals, for 50mm front struts.png Bilstein B6 : B8 gland-nut complete with seal for 55mm front & rear struts?.png
Jordan's photos (from M/G) of a 50mm gland-nut w/o gland, the glands for those North-American front struts & 52mm? nuts w/glands for rears.
1.) Tools and Equipment Required:
- Confirm your Bilstein cap-nut (aka: gland-nut) wrench is of the appropriate size for your application; and is in perfect condition. If not contact Bilstein;
- Leather work gloves, a hack saw, and proper penetrating oil (not just WD-40);
- Bench-mounted vise; wooden blocks to contact, and brace the strut with. Use vise judiciously with the wood blocks to secure the strut in without collapsing the strut tube, for drilling the drain hole; and to cradle the assembled strut in, both for cutting the original cap-nut; and torquing the Bilstein cap-nut.
- Note: Stillsons, or even a small chain or pipe wrench should not be necessary and may result in strut-tube damage. If employed, use caution, and use only gently around the old cut cap nut; and only - after - it is already loose;
- Hand-held wire brush; Navel Jelly (a rust remover gel); lapping compound; varsol; lacquer thinner (or electrical contact cleaner); spray paint (primer and 2 colours which contrast with strut-tube colour; and each other, a small paint-brush);
- Loctite (blue), a 1/2" drive torque wrench;
- Nail-polish (in a contrasting colour to your strut paint) & a wax-oil type rust-proofing compound.
- Scriber, center punch and a ball-peen hammer; &
- Electric hand-drill, a small diameter pilot-hole drill bit, a 1/8th" to 10mm bit.
2.) Removal of Old Stock Damper from Strut (springs, etc. are assumed already off the strut at this point).
To get the likely seized old stock original style damper-retaining cap-nut off the strut most easily, and also prevent any possible crush damage to the thin strut-tube itself from a vice or pipe-wrenching etc., read on.
Method Outline:
In preparation for cutting the cap-nut by hand, brace the strut, cradling it in the vice using the wooden blocks such that it is held steady -without- putting any pressure on the tube. Next remove the OEM cap-nut as follows: Hacksaw the nut as indicated by the red lines in photo below, then soak with penetrating fluid; and only then, finally with just your gloved hands; easily twist it off.
Mac strut damper retaining cap-nut cut-lines 2019-05-02 at 10.06.28.png
Drawn lines in photo above are to indicate where to cut diagonally in 2 or 3 places around the outside of a seized cap-nut's circumference; to loosen the rusted threads. Once cut, penetrating oil can be applied directly into the affected threads and the nut will actually spring slightly open. Using a hand-saw only, cutting is sufficient when a series of small holes appear as you break through the roots of the cap-nut's interior threads. Done carefully, no damage to the struts threads (which are fully engaged and very close while you perform this task) will occur.
a.) How your nuts get stuck and why use this method:
Your strut cap-nuts may be fused onto the strut-tubes by years of corrosion activity. The originals were installed without anti-seize compound or Loctite. This rusting often seals the lower edge of the cap-nut on the strut closed, preventing any penetrating oil from entering. Because of the possibly very large total threaded surface area which may be involved (perhaps all ten internal threads of the cap-nut, times the diameter of the strut tube, equals a potentially huge rust grip area that) you will not easily break the cap loose from, or successfully remove it with just the vice, pipe-wrenches, and torches; without also damaging the thin-walled strut-tube. With this "no torches, etc." method, any strut damage is easily avoided.
Note: This method involves using a plain ordinary hack-saw to cut diagonally across and around the O.D. of the cap-nut as required to next get penetrating oil on -all- ten of those hidden engaged internal cap-nut threads . It's fast, simple and easy. Don't use a power saw or wheel of any sort as you will mess up your struts if you do.
b.) How to turn your OEM style nuts off with just your hand:
First cut, on a diagonal (relative to the strut axis), from the top to the bottom, around the O.D. of the cap-nut, -just- partially through to the roots of the cap-nut's internal threads. Depth-wise, stop when you have made a series of small holes appear in the bottom of the slot you have cut, through which you then apply penetrating oil. Continue to cut the diagonal slot right to the lower edge of the cap-nut and, because the original nut is a stamped part; it will then actually spring open slightly. If not loose at this point, do the cutting again in 2 or 3 spots spread around the O.D. and the nut will turn off by hand (Caution: cap-nut OD is now sharp!). By careful use of just a hand-held hack-saw, any damage to the strut tube's threads can be avoided altogether.
Here's a photo from a post in S2Central's Strut Cap-Nut Tools thread (link to complete thread near bottom of this post) where he made use of the above method:
Diagonally cut strut cap-nut.png
Here is an old post link (from 2010 on audiworld.com) which also described the task list above, and how to cut ever so slightly into the threaded interface between the cap-nut and strut-tube.
3.) Mac. Strut Body Prep:
a.) Tube-top thread re-condition as follows:
Considering what nut removal may have involved, you may want to take steps to ensure this does not happen again. However more immediately, this will also aid in the correct cap-nut torquing later on as torque consumed in turning the nut onto a rusty dirty strut-tube is automatically subtracted from the torque applied to the damper body (where you want the torque to be felt). Note also that there was a factory bulletin (see link below) which upped the torque because of issues observed due to cap-nut loosening.
- Wire brush the threads;
- Likewise Naval Jelly as per its' instructions;
- Paint (other than, but up to threaded area)
- Further strut tube thread cleaning. You may now use the just removed old and usefully cut OEM cap-nut (allowing adjustment by slightly squeezing the cut sides in as required) as an effective thread-chasing die with some lapping compound.
Note re importance of thread-cleaning: The Bilstein cap-nut recess, which secures and centers the top of the yellow damper tube, appears to have a slight taper, so any slack in its final positioning will allow the damper to wobble up top; and move out of position at the bottom! Re-condition the threads until they operate "as new", as this will best allow both proper capture of the damper top and best torquing of the cap-nut, helping to ensure the damper will remain correctly centered and fixed inside the strut-tube. Again, when applying torque to the nut, consider that any force consumed in turning the cap due to poor thread condition; is torque that is -not- applied to properly clamp the damper in place. This is not fixable later until the main springs are again removed. Another reason to do the best job possible here is the install torque spec is high; and the Bilstein wrench is (perhaps purposefully) weak. A best job done now will aid with any possible future removal.
b.) Drain Holes:
I put my drain holes on center thinking that would be the low spot and least likely to be blocked by the damper's presence, I also enlarged them to an 1/8" after finding one plugged with debris.
c.) Clean Strut Body:
Ensure no debris inside where damper fits into base; and clean tube-top external threads to best receive Loctite.
4.) Understanding Fixturing of the Mono-tube type (B6 &B8) Bilstein within the Mac-P. strut:
As Audi had BOGE produce and supply both the original struts and dampers for these cars, and we are instead installing yellow mono-tube Bilsteins whose OD is smaller than the original BOGE dampers, we need to understand the differences in how each of these are correctly secured inside the strut body. Particularly at the bottom of the strut interior, the original BOGE damper OD closely matches the strut ID, whereas the reco'd fitments from Bilstein do not.
The reason for this ID/OD mismatch is that while Bode designed their damper to easily self-position correctly in this strut, perhaps that Bilstein uses this same damper shell for fitment into other vehicles with differing struts, means that they have adapted it to fit - in a different fashion, which therefore allows them to not make a special version for just these cars. That circumstance may also explain why the orange warning label (re: strut drain-hole mod) has disappeared from more current purchases, as other vehicle applications may not all share this hydro-locking issue.
Unlike the original Boge or other OEM (twin-tube) style dampers (such as Koni), the yellow mono-tube Bilstein is held centered in place at the bottom -only- if correctly centered in the strut-tubes concave base during insertion (and held there until pressed into place with the cap-nut!). The possibility for errors here increases with the difference between your particular strut-tube's largest effective I.D. and your damper's O.D. at its' base, so perhaps less of a concern if these two diameters match (as is the case with the UrS cars), but any difference allows the possibility of misalignment (between strut-tube and damper center-axes) which will result in noise and damper movement while underway and at least, likely damage the cap-nut's gland seal; unless the following precautions are taken before and during assembly. The damper base has an abbreviated (less than 5mm) and shouldered slightly spherical protruding shape to fit the mating depression in the strut-tube base, and its correct function is dependent on three preconditions as follows:
a.) Damper base sphere must be correctly centered in the strut-tube's concave base recess;
b.) Top outer perimeter of the painted yellow tube must be correctly captured and centered within the Bilstein cap-nut recess (less than 5mm deep, see cap-nut recess and ledge in photo); &
c.) Cap-nut correctly fastened with Loctite; and done up to the recommended torque (see torque # on Bilstein wrench).
Examples of what can go wrong:
i.) Damper-base not centered in strut-base but off-set to one side and sitting up on interior base shoulder. This will allow the damper-base to rock laterally during driving which will at least make noise, very annoying (and possibly begin cap-nut loosening and vertical damper hammering); and everything must come apart to fix it;
ii.) Yellow tube-top not correctly captured in the cap-nut recess. Nut torque may relax during driving also allowing damper to both rock laterally and hammer vertically within strut. This will quickly kill the gland-nut seal; and the nut torque may deform yellow tube-top edge which may allow water entry into the strut.
Top end of yellow painted Bilstein outer tube to be captured in unique Bilstein top-nut ID Screen Shot 2021-07-17 at 16.26.35.png Photo (by fka at saabtechtalk.com ) is of a Saab unit (shown inverted) but no matter, it shows Bilstein's unique to their mono-tubes' top-nut interior which will engage, center and secure the damper's yellow painted tube at only its' very top end OD within the Audi strut tube via the nut's visible recess ID. It fits tight enough that after being final torqued, you'll notice some yellow paint removal on dis-assembly.
5.) Dry Run #1: Empty Assembly of Strut-tube & Bilstein Cap-Nut:
You want to be able to screw on and fully seat the cap-nut on the still empty strut-tube easily with just your bare hands. This will ensure a couple of things:
i.) That you have sufficient free cap-nut travel to properly capture, compress and hold the damper when installed later; &
ii.) That your final applied torque will all be employed to pressing down on the top of the yellow tube, securing the damper; and not partially lost fighting thread friction (Note: Be aware there was a factory TSB which upped the torque on the original cap-nut due to observed loosening issues which occurred here, see more on this at bottom of post).
Match-marking:
Paint-mark this fully down point on the exposed threads of the strut-tube just below the nut. This will give you an initial reference point (Ref. A in the strut tube-top photo below (photo by audi*line, thanks) that you should almost but not quite reach later with the slightly taller damper correctly in place with both its' base properly centered inside; and the yellow tube-top properly captured and centered in the cap-nut.
Strut-top cap-nut fit reference points.png
6.) Dry Run #2: Ensuring Full Correct Damper Placement, and Fixturing into Strut-tube:
a.) Unscrew the cap-nut and place the damper inside the strut-tube carefully centering its' base in the bottom of the strut-tube; (Note: Damper -must- be installed by lowering into strut whilst both are held vertical!). Note the damper will sit lowest in the strut-tube when it's base is properly centered, and -not- up on the circumferential shoulder of the strut-tube's internal base; only if both are held vertical during the assembly process.
b.) Next screw the cap-nut back on and hand-tighten fully onto the strut-tube again ensuring the yellow tube-top is properly centered and captive inside of, and -not- up on edge of, the cap's recess or catching the edge of the yellow tube.
c.) Paint a 2nd broad mark (well apart from the 1st) w/the 2nd paint colour, that can be easily seen while your working, horizontally just below the bottom edge of the nut at its' now final install position (Ref. B in above photo). The difference between these two paint marks should mirror the effective and observed height difference between the top threaded edge of the strut-tube; and the installed damper's yellow tube-top's (slightly taller) height (Ref.C).
d.) Now paint the 3rd and 4th marks vertically w/the 2nd paint colour again, one on the Bilstein cap-nut and one on the strut-tube to give you a very good 'Vernier' type indication of the nut being exactly fully home correctly capturing the enclosed damper (see Ref.D). If the top or bottom of the damper are not correctly positioned inside the strut, you will not be able to easily by hand turn the cap-nut down to this point during final assembly below (Hint: Paint this one such that you can see it in future by lifting the damper boot when the car is all back together).
Doing both the above empty assembly and the practice full vertical fixturing is going to help ensure a couple of things:
i.) With damper now in place you are here going to be able to confirm that because the cap-nut bottoms out -before- reaching Ref. A, that the damper will be effectively clamped in place (this is particularly important strut-tube effective internal length check for those who have done Mance's BBSE mod, and it confirms your dampers are the correct length if your struts are unmodified also) before the cap-nut bottoms on the strut-tube at Ref. A.
ii.) You are going to get a feel for how everything fits together properly; and by noting the new final hand installed height of the new cap-nut , which will now approach Ref.B and be complete when the two Ref. D marks align, you are able to more easily confirm success as you go during final assembly below, ensuring that the damper is correctly installed into the strut, rather than discovering it's not, after it's all back together; and you try dry driving on it. You now need to be thinking about how you are going to brace the assembled strut for the torquing of the cap-nut without damaging the strut-tube, the cap-nut, the Bilstein wrench or (see post #2 below); yourself!
iii.) Prior to final assembly is where I coated the strut tube interior with the rust-proofing. With a drain-hole of sufficient diameter, any excess will drain out the bottom without plugging the hole.
7.) Successful Final Assembly:
Involves just a few simple but carefully executed steps, including:
a.) Apply just a little Loctite in one spot & complete full vertical assembly again including bottoming cap-nut by hand into position at the above final ref. mark (see Ref.D);
b.) Brace strut for torquing and zero damage to strut and you!
c.) Torque application & see also "Bilstein Wrench Mod, from 2007" (photos in following post). You may need to re-do your assembly match-mark paint slightly after torquing.
Although Bilstein (North America) has always been very helpful in sending me wrenches (quickly and at no cost!) the wrench is a delicate stamping and it is not robust enough to remove the mono-tube's cap-nut if it is rusted, over-torqued, already damaged or if one uses the incorrect Loctite or even too much blue Loctite and/or doesn't warm-up the Loctite prior to the attempted loosening. By using the modified wrench, successful removal is more likely, but not guaranteed.
d.) Match-mark & rust proofing (nail-polish & wax-oil);
By marking the cap-nut and strut tube (see Ref. D) with a single (nail-polish?) mark in a spot you can most easily view when installed on the car, you can visually confirm your assembly in future. The wax-oil can be used to fill the remaining exposed exterior strut threads below the cap-nut.
Example of both the Bilstein cap-nut with gland & the wrench (photos below). Both the nut and seal are available separately. One can see that the wrench is only a stamped unhardened item & therefore fragile. As received, the two wrench teeth may be a little to long &/or sharp to easily/safely fit over & clear the damper's chrome shaft OD. The shiny wrench finish will help to highlight the deformation of the wrench when you are over-doing it. The corners where your square-drive fits & where the teeth emerge from the ring will deform first.
image_71419.png image_71420.png
Torquing the original style strut cap-nuts (with the 6-sided internal opening. seen in para. 2.) above, and the sockets for them:
Here is a link to an old write-up (from 2008 on audiworld.com) regarding the above mentioned factory Technical Service Bulletin re the cap-nut torque increase. This may also be of particular interest to those who may have been reading here about strut dis-assembly; and are going to be re-installing the original style cap-nut on their struts, used with conventional OEM (twin-tube) style original Boge's, and replacement Sachs, Koni's and Bilstein B4's, for instance:
Recapping cap-nut torque with the factory TSB...
Further (and a little farther off-topic), here in the 1st photo below (courtesy of Orsum) is the factory tool (both the VAG 2069 and VAG 2069A appear similar) necessary for torquing strictly the above original style cap-nuts onto the struts (Orsum rightly notes this socket's annular recess which has been cut away at the end shown to avoid any contact with the installed damper's shaft seal, which may be of particular interest to those who might be fashioning their own tool). Second photo below shows how that original style twin-tube damper's shaft seal (blue coloured) protrudes from the top of a Bilstein B4 damper body. Third photo shows a complete Bilstein B4, note the damper (just like their B6s & 8s) comes with a new strut cap-nut (not to scale), in this case it has an 8-sided welded-on top instead of the original style requiring the tool shown in 1st photo. The Bilstein P/N in this photo is for their 50mm O.D. B4 front (only as rears are 55mm O.D.) damper for B3 series 20v's ("Audi 90 (89, 89Q, 8A, B3) 2.3 E 20v Quattro (123 kW). Years of manufacture: 04/90 > 09/91. Suits Models with a Power Level of 123 kW. This equates to approximately 165 BHP").
OEM style strut cap-nut tool VAG 2069 .png Bilstein B4 damper shaft seal protruson Screen Shot 2023-04-23 at 12.01.12.png Screen Shot 2024-01-01 at 5.38.21 PM.png
For more on these two different socket sizes, P/N's and various suppliers and makers of this tool, please also see S2Central's thread here:
Tools for the Front & Rear Strut's Cap-Nuts...
Concluding Remarks:
I'd like to think that the above task list would allow one to not have to re-visit the damper install, however you may want to understand hydro-locking, these particular dampers' susceptibility to it; and know the symptoms which may indicate it's onset, I've certainly been wrong about this issue before, please also see my response to GT500's post titled "Bilstein Killed..." (from 2011) on this forum and work back to the quattroworld.com links.
I think that's most of it, hope this helps. And certainly I may have missed something, please chime in. Questions?
Lago Blue
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