Subframe mounts.....poly / OE ?

[varia]

That's interesting Varia, your polybushes look like o.e bushes but just in polyurethane? They look like they would need pressing in as much as the old rubber ones? My guess is the majority of poly users including me are; commenting how easy they are to fit are using 2 part items where they do fit by hand and then. You just push the steel Bush through the middle.

https://www.akmotorsport.net/shop/al...teet-hardness/

normally im using 2 pieces alu subframe bushings. on this car, owner wanted something close to oem, so i used Alber's poly bushings.

[varia]

came out pretty good

[steve briance]

They look pretty good. How did you find drawing them in to the subframe. I see your wheel bearing puller in action, is there enough flexibility in the polyurethane for them to compress and slide through the hole without too much bother? I'm getting together parts at the moment and hadn't even considered the AK mounts as used superflex last time and fitted those by hand.

[4WDrifter]

John.

Questions:

- Similar to the OE bush's steel core which appears proud of the rubber, could you sandwich a hardened washer on top of the pojy's SS core to get the footprint you seek?

- What is the current effective installed height of the OE bush steel core vs. the poly's? In other words, do the poly's leave room for a washer up top? If they don't does it matter?

- Are the radial markings inherent to the chassis boss or the OE bush?

- Are these mark-makers perhaps to help inhibit movement?

I too lost part of my response while typing this. I fat-fingered something in the bottom-left of the keyboard.

here is a photo of new OEM bush showing radial marks.

[Lago Blue]

Thanks 4WDrifter,

Not ever having had these apart, just wondering what the original design intent here may have been.

As my alignment tech has now retired, and his replacement doesn't appear old enough to yet own a car, I should learn something about alignment.

- So if it's true that they are there to grip the chassis boss to help secure the two frames' positions, then;

Movement was likely a design concern, and it would also follow that there is available scope for them to be "out": enough to be significant?

- After bush or frame replacement, is there perhaps a method and tolerance limits for aligning what, frame to frame?

- Perhaps it is done by comparing the precise wheelbase measurements, side to side?

- IIRC, have I seen alignment results printed out with the two axles' thrust angles included, perhaps that is how thrust angle is computed?

- It may also be that where the frames are pointing would be the first thing to check?

Then only afterwards move on to the individual and paired wheel settings.

Always something new to learn!

[Mikes2]

The front right mounting point in the chassis is fixed but the other 3 have adjustment so that fixed point acts as a pivot point for the alignment - it's to allow for variations in the shells. They're never all identical

[Lago Blue]

Mikes2,

Very interesting, thanks.

- So then with the front RH point being fixed (& it being the frame rotation center-point), the adjustment is perhaps made possible as the remaining 3 points are hidden captive nuts which can slide laterally?

- It may be the rear frame points are a mirrored copy with what, the LH rear point fixed?

- In any case if I'm doing sub-frame removal at home, it would be good to note the position of its' fixed chassis point, and the range of motion available at the bush opposite the fixed one, so that at the alignment shop, if required I could point out to the tech, the fixed point & where to best tap to get movement, etc.

Found this thread about how one might proceed after replacing the sub-frames; & accommodating road crown:

https://www.s2forum.com/forum/techni...me-positioning

[Vorsprung durch Technik]

Did mine 11 years ago with 4 new Audi bushes and gave the subframe to Autopool to fit, (back of Fontain) in Iver. They asked me to pay for another bush as they destroyed one putting them in so it's not easy to do John even with the press but worth it imo. 4 new Bolts from Audi to refit it but i thought they were the stretch type?

To me those lines on the bush are for crush location to stop any movement like the lower balljoints on the 90 20V and S2.

I'm more of the opinion to use Original bushes on subframes as they're tried and tested (obviously millions of cars ran them) and poly other bit's maybe? It's not like you going to wear them out by putting 100K miles on them in the next 5 years with a limited mileage policy.

As an aside about polly bushes. There's a thread on fb about how everyone who has used the red ones on their S6 C4 lower control arms to subframe are all getting chewed up. There's no metal in the poly bush like the OE equipment. Audi engineers knew something i would say and these metal assisted bushes are made that way for a reason.

[Lago Blue]

Vorsprung,

You're certainly in good company preferring something (the OEM metalastic type in your case) other than poly bushes, as well known American automotive author Herb Adams (builder of many racers based on Detroit iron) in "Chassis Engineering" (ISBN 1-55788-055-7) said of urethane bushes that they "look great on the parts shelf". But there he was referring strictly to bushes which see rotation.

Here, the near static attachment of the sub-frames may be one place where we could more likely expect poly material to work as well as an OEM semi-solid mount?

However, it is also interesting here that the re-fitting of OEMs' has always been kept so tight and difficult, unchanged for well over a quarter century, versus the two-piece polys which have been around perhaps decades now too, are apparently easy to install and generally well liked in use, and yet at any point since, Audi and Boge could have made shell-less two-piece (poly-style) rubber originals, or even of poly of either type for that matter; but didn't. Neither has any other OEM or marque for that matter AFAIK. Like you say, they must have their reasons.

It may be that the top requirement for bushing choice (after even just a read of others OEM experience) often becomes "I'm not having to do that (again / like he did!)". Perhaps a technique for OEMs which included the freezing of the bushings and proper gear on hand to pull them in suitably lubricated straight and square, vice pushing (both suggested previously), painting the frames (save for the bush boss IDs) a dull black and doing the task outside on the hottest day of summer, at high noon; might together ease the install somewhat?

How and why do they fail (tearing / crumbling / softening perhaps due to age / fatigue / oil contamination? ); and is it (like OEM top-mounts and A-arm bushings) perhaps preventable?

[Fat Audi 80]

I was always under the impression that rubber & metal bushes were cheaper to produce in high volume which suits the manufacturers, and also that when in a production line scenario, one piece bushes allow for the subframe and suspension assembly to be offered up by a robot under the car for installation, whereas the two part poly bush does not suit production lines.

[Lago Blue]

Hmm, that does make some sense sir. I think you may have nailed it.

Screen Shot 2019-01-15 at 22.51.53.png

These particular bipedal robots look incredibly life-like, don't they? Those Germans!