Bilstein into Macpherson strut install

[Davi123]

The only other thing I noticed was the slotted bush nut slight (photo) protruded the SKF top mount rubber when torqued up. I wonder whether they are all standard or come in different heights as that would help close up the gap

[Nuvo]

9mm is way too big a gap in my opinion, are the slotted nuts fully engaged into each top mount? For reference, I have Bilstein B6's installed with original OEM Boge top mounts (with Mance Mount Savers installed) and they have 3 to 4 threads visible above the top nut.

I haven't seen that particular "Shock absorbing ring" before so I can't comment on that. I used two large rubber washers used in plumbing applications which serve to protect the black plastic outer rings on the stut stop from getting hammered, they also act as a dust boot to keep things clean inside the top of the top mount. HTH.

edit: Ah hold on a sec, the white washers that you've fitted, are they sandwiched between the strut stops and the top mounts so that the washers are fixed in place or are they free to rotate?

[Davi123]

Hi Nuvo, I will check the coil top plate is hard on the damper but I'm 99% sure it is. I did install these brass washers (photo below), which I understood from another thread were required, these would take up a bit of the top thread. This might explain why you have more thread showing above the nut. The brass is 2.5mm thick

[Lago Blue]

Hi Paul,

Good questions and I see some good answers already re your latest brain-teaser sir, perhaps I can also add something. It may be that this is in part an understanding front-mounted top-mount operation question. I suspect that the protruding threads and the 9mm clearance share root cause. Forgive me if I detail stuff you've already seen or known.

Q: Your concern about the 9mm of clearance would ordinarily indicate the mounts are collapsed, except these mounts have seen almost zero use, correct?

Q: I could not find a picture of your listed mounts' P/N (was this the number on the mount's bearing perhaps?), the Auto Doc UK listing for a B3 Audi 90 2.3 20v (I picked the heaviest engine that I saw listed) was P/N SKF VKDC 35100 T (link below)

https://www.autodoc.co.uk/skf/1363685#top-strut-mount

Q: The mount at the above link looks like a typical later version top-mount (as to overall mount height, but know that height tells one nothing about its' performance), with a vertical walled cavity on top (similar to the photo below), the wall's presence (or its' absence when the mount is collapsed) should be visible while still installed in the fender. With the car's weight still on the wheels, if you remove just the strut's top Nyloc and the large "domed" or cupped-washer (a.k.a. the retainer, its' actual function, other than sadly as a mount wear indicator is to simply keep the strut from falling out of the fender at full rebound) again, with the car's weight still on the tires, what do you see? The deep top cavity of a new mount should easily nearly subsume the retainer's height.

The internally threaded slotted nuts date back at least to the earliest water-cooled VWs w/MacP struts, and all are the same height. When torqued, this nut must still protrude slightly above the floor of the mount's top cavity (the flat area immediately surrounding where the installed slotted nut would go in the photo below) for steering to function. That protrusion ensures the sunken portion of the retainer is supported above the mount cavity floor and prevented from touching; such that it can rotate with steering changes without binding on the always stationary mount cavity floor.

Sachs P/N suffix 355A top-mount top cavity photo
Sachs top-mount top cavity photo Screen Shot 2025-08-25 at 2.34.42 PM.png

Q: Do the white washers you've added have a small enough centre-bore (i.e.: 14mm) that they add to the stack height of items surrounding the damper shaft and held under the very top Nyloc, or are they large enough internally to be simply captive on the exterior of the conical 'cup' of the retainers? Perhaps you added these to effect what the hard black plastic OEM damper rings do, (one is seen on the complete factory retainer in the last photo below), and that are missing from your retainers, correct? I suspect the white washers may be impeding the bottom of the retainer from contacting the top of the slotted nut, and therefore giving you both a less than normal thread protrusion; and a false mount wear indication. It may also be that the white washers are impeding and/or damping your steering somewhat.

Q: Even a lessor quality freshly mounted new top-mount, regardless of brand or overall height should at least initially if only briefly give your chassis (a B4 w/ factory strut bar, correct?) a gap of about 1.5 to 2.0mm or less between the painted fender turret top surface and the underside of the retainer when measured as follows (from Mr. Audi 90 Top-Mounts himself, Mance Etheridge) (...and this is the edited/shortened version!):

Firstly, "Comparative measurements (to those listed below) must be taken at the 12 o'clock position of the strut tower bore while standing directly "beside" one of the front tires and looking directly across the engine bay at the other strut tower and drawing an imaginary line between (the) centers of both. The measuring spot is the closest point to the opposite strut tower (where the designed vertical gap is the greatest). It's also (to be measured from) the lowest point between the retainer and the strut tower (fender turret) flat area that surrounds its bore-hole. That is because the retainers DO NOT sit flat/parallel to the strut tower tops due to (factory design intent) of the caster/camber arrangement, so all measurements must be taken at the same spot or comparisons are futile."

Secondly: Clearances listed for new Boge (P/N suffix 355 A) mounts, and the black plastic dampening ring removed for the measurement. Note Pre B4 chassis vs B4's:

"Pre-B4 chassis with new Boge Mounts:

Initial gap: 4 to 4.5mm
After 200-300 miles: 5 to 5.5mm
1,000 miles: 6mm
Eminent failure: 8mm
Total failure: 8.5mm

For B4 chassis gaps, subtract 2.5mm (due to strut bar brackets) from the above numbers."

The risk is, as the gap grows, the remaining mount strength is decreasing, leaving it evermore vulnerable to complete failure by successively lesser impacts. How quickly that clearance distance changes (grows larger/worse) depends on the original mount specification and quality (If not the latest/strongest mount, then which older/lighter car was it really intended to be used on), mileage, age, the number of moderate impacts and especially just single severe high-impact shock loads (think pot-holes) which bottom the spring and/or the bump-stops. For further, see posts #39, #40 and #64 in the "Wanted: Volunteers..." thread (link below) re comparative mount strengths, most recent reco'd mounts, their availability and why. That thread also provides some details re Strut-Stops, the mount reinforcement mod Tractor Dave kindly mentions earlier in this thread.

https://www.s2forum.com/forum/member...55#post2083755

Indeed the clearance under the retainers I run is even larger in comparison as Dave mentioned, but more importantly it is over a decade on, unchanging and without downside. My retainers no longer indicate top-mount wear, because none is taking place. In any case, some clearance is necessary (its' a feature not a bug), and further, know that the exterior measure of a mount's uninstalled height is not a very useful discriminator or performance predictor when choosing mounts. High strength and resilience are what seems to work best.

Q: As your car has the 2.5mm thick strut tower plates for mounting the factory strut bar, which reduces the expected clearance by at least that amount, the 9mm does indeed look odd. Other than the above, I'm at a loss. One wouldn't be the first to have put the mounts on upside down, but I doubt that is the case here. Similarly, you likely haven't ever used an air gun to take the top nuts off either, correct?. The only other thing I can think of is that if the car is lowered onto its' tires without then rolling the car forward or back sufficiently, all the mountings may remain stressed since tire friction and the track change during that suspension travel puts good deal of lateral force on them not otherwise relieved, but I wouldn't expect that to cause your results either. Are the top-mounts fully seated up in their receivers in the fender turrets? Probably, it is doubtful that they would fail to self-relocate during the last car lowering even considering if the (perhaps mis-indicated?) retainer gap clearance you list were true.

As for the protruding threads above the Nyloc, I would expect to see 3 threads, to put the fastener "in safety", this is industry standard as the end of the threaded shaft is chamfered, and by moving safely past that onto full height threads, we fully engage the nut's locking ability.

Damper shaft top end of a Bilstein type B6 or 8 for B2, 3 or 4 chassis
Audi 90 type Bilstein B6:8 top end of damper. Screen Shot 2025-08-25 at 11.45.43 AM.png

If you measure the height of the threaded section of the bare top end of the damper shaft (photo above), and subtract the thickness of the Nyloc and everything to be held under it, that will tell you what to expect the protrusion to be. The small OEM convex when installed "brass 2.5mm washer" you show (post #48) provides the most favourable engagement with the underside of the domed upper spring-plate (as it is subject to a good deal of asymmetric spring load from underneath, it is probably a good idea) vs the bare and square edged damper shaft alone, however some folks omit or loose it, and interesting to me is that it's absence does not lower the car (as it's not in the load path)!

Your photo shows perhaps 1/2 a thread proud of the Nyloc. Three threads showing would require the nut move down a total of 4.5mm from flush (as the thread is M14x1.5). Minus the 1/2 thread already showing leaves 3.75mm which is just over 1/8" to go. I'd guess your white washer is likely no thicker than that.

3 threads showing above the Nyloc requires the nut move down 4.5mm from flush (or just under 3:16%22) Screen Shot 2025-08-27 at 8.35.21 PM.png

It has been a good many years since I've mod'd not the top-mounts but what they're installed with. The stock OEM arrangement is weak, mine over a decade on are dare I say bullit-proof, but IIRC I'd expect to see this many threads with the stock arrangement (photo below).

A stock B4 chassis strut tower w/ the factory strut bar bracket and a worn mount
Audi 90 B4 stock strut top attachment Screen Shot 2025-08-25 at 6.17.35 PM.png

The yellow "Suspension Shock-Absorbing Ring" in your post #45 above, is shown in I believe a VW engine bay. I also believe those cars have a different bearing arrangement in their top-mounts which allows their alloy cupped washer in that case; to always remain stationary. This may explain how that installation could tolerate a snug yellow ring under the retainer; and still allow steering. Finally, despite appearances, know that we suffer no performance penalty under any circumstances for the gap our arrangement requires.

[Lago Blue]

Bilstein Damper P/Ns

For clarity, I've cut and pasted these B4, B6 and B8 damper listings for the Coupe from a PDF of a 2011 Bilstein catalog which lists our cars more thoroughly than their current on-line catalog.

Key to choosing a front strut damper P/N is the Audi MacP. strut O.D., as some cars had the necked-down to 50mm top-ends. This insures one gets the correct I.D. req'd Bilstein top-nuts that come with the dampers you buy. It would also be good to know you have two front struts of the same O.D. See also earlier in this thread post #16. Note VA = front axle and HA = the rear.

The B6's and B8's come with their own internal (hidden) bump-stops. You'll need the appropriate Bilstein wrench for these two as well.

One can run stock springs on a B8, but one shouldn't run lowering springs springs on a B6.

Bilstein new PNs explained 2 Screen Shot 2025-09-08 at 8.23.11 PM.png

Bilstein catalog Fr and Rr columns header axle Screen Shot 2025-09-07 at 4.37.08 PM.png

Bilstein catalog Coupe listings header 1 Screen Shot 2025-09-07 at 3.40.49 PM.png
Bilstein catalog re B4 6 and 8 damper listings for S2 CQ w: 50 or 55mm Fr struts incomplete Screen Shot 2025-09-07 at 3.38.04 PM.png
Bilstein catalog re B8 damper listings for S2 CQ w: 50mm Fr struts Screen Shot 2025-09-07 at 3.28.51 PM.png

[Solfella]

Forgive me, I have many questions.

So, I am a right in thinking there are a possible 3 alternatives for the S2?
But if I want the B6 there are only 2 variants xxx 059 and xxx 868?
Is there anyway of knowing which of these is suitable without visually inspecting the current shocks?
And by the looks of it, the xxx 172 are the rear option, assuming I do not want the shorter ones?
On that latter point, didn't the S2 come out on lower springs from factory and does that mean I actually need B8s?

Thank you in confusion

[Lago Blue]

Those are good questions.

Particularly as I've never owned an S2 (just B3 7A and B4 V6), I'm going to ask the readers with direct experience here to please either confirm (or especially contradict!) my answers as we are reaching the edge of my limited knowledge, thank you.

Q: So, I am a right in thinking there are a possible 3 alternatives for the S2?

If you mean B4s, 6s or 8s, for the front struts, know that the B4s (simply a low pressure twin-tube gas unit) are meant to be a near stock replacement, their caps are sized for 50mm struts, and it is most likely your car still has its' 55mm struts.

Q: But if I want the B6 there are only 2 variants xxx 059 and xxx 868?

Re fronts, probably just the xxx 868 in your (55mm?) case.

Q: Is there anyway of knowing which of these is suitable without visually inspecting the current shocks?

Yes, eyeball the struts just below the cap-nuts, are they necked down to 50mm or not (see photos below).

Q: And by the looks of it, the xxx 172 are the rear option, assuming I do not want the shorter ones?

Yup, B6s and any of the OEM springs are a great combo.

Q: On that latter point, didn't the S2 come out on lower springs from factory and does that mean I actually need B8s?

Yes slightly lower, but not so low that B6s won't work with your stock (correct?) springs, no. IIRC, notes similar to below used to appear in some of the older Bilstein print catalogs. I'm thinking those early S2 press releases might say exactly how much lower.

BILSTEIN B6
These shock absorbers can be used in conjunction with your standard height springs or a lowering spring of upto 40mm. If you are planning on lowering more than 40mm we recommend to use a shortened shock absorber such as the Bilstein B8 Shock absorbers.
No German TUV registration required.

BILSTEIN B8
Bilstein B8 dampers have the same quality and damping power as the Bilstein B6 Shock Absorbers but with shortened piston rods. These shock absorbers are ideal when used with a lowering spring of more than 40mm.

50mm (are necked down in diameter just under the top cap-nut) and 55mm front struts are not:
50mm Fr strut Screen Shot 2025-09-08 at 1.05.16 AM.png
55mm strut Screen Shot 2025-09-08 at 1.01.16 AM.png


Photo below: Q: Where to measure? A: Just below the threads.

Audi S2 Fr Strut 55mm OD measurement Screen Shot 2026-06-18 at 7.49.09 PM.png

[Solfella]

Thank you Lago Blue - really helpful

Once I work out how to PM you I will reach out about your Strut Stops too

PM sent, I think