Hawkeyes

Ok, now have calipers back in Baby Blue & driving! WooHoo. The saga got a bit complicated (why am I not surprised). The earlier version (thru mid '89) caliper piston & seals are over twice the price as the later model, & had to be special ordered as well. Salesperson (Pelican) thought one kit would do two caliper pistons, but turned out one kit would only do one caliper piston. So when parts finally did arrive, I only had half what I needed.

Ok, fraggle had it right. I installed what I had (big PIA getting the metal-ringed seal in the caliper BTW) in the left caliper, then cleaned & polished the tar out of the right caliper pistons. Cleaned up the seals with a little Brakleen on a rag & 600 sandpaper so all the residue was wiped away.

Voila! Brakes like a champ, no more pulling to one side, appears pads are wearing evenly again. I also replaced the front brake hoses with a set from Raybestos. Good quality stuff, made in America (unbelievable). I got to thinking that any OEM hose I purchased might just have been laying around & oxidizing for 18 years!

fraggle

Glad it all worked out. When I found the prices and requirements I went the cheap route. My rebuild was free because I didn't need to replace any parts. I was very careful & very lucky getting everything apart without damage.

When I tried to special order mine it ended up being NLA - it wasn't the piston size issue I ran into, it was the the dust covers problem.

UKKid35

In this photo which I took in 2004 showing the how I failed to remove the domed machine screws, you can see that the scraper seals appear to be missing

Am I seeing that correctly?

They were like that when I bought the car almost 20 years ago, and I've not had any problems with the seals despite the abuse on track over the last 100k miles

Does this mean that I have 42mm & 36mm pistons, and the seal kits are NLA? (car is an early '87)

I don't fancy scrapping the calipers, as they are still working fine, so what about replacing the main seals, ignoring the scraper seals?

ROG100

I stock all the seal kits if you get stuck.

Thom

The photo shows that the main (outer) seals seem to be missing.
The scraper seals are located in grooves inside each piston bore and scrape brake fluid from the pistons whilst these are being pushed out when braking.
If you have had no leak then it means the scraper seals actually.. seal. You may want to add the missing outer seals to prevent dust from damaging the pistons and the scraper seals.

UKKid35

Thanks

What I can't work out is what type of dust seals should be present

Obviously I should just pull the pads, and pump out the pistons sufficiently to understand what I have

But I'd like to have the right parts ready if that's at all possible

Thom

The main seals are like the ones on the left on that photo. The inner lip fits into the outer groove on the piston and the outer lip houses a steel ring that holds it in place on the caliper bore top, if that makes sense. The ones on the pictures are not exactly like the ones used on our calipers but you get the idea. The seals on the right are the scraper seals, with a square section. This is a warm topic to me as I have just prepped a set of big blacks for my 951.

PS: how are you doing with the Cerbera?

87m491

QUOTE=Thom;16946549]
The main seals are like the ones on the left on that photo. The inner lip fits into the outer groove on the piston and the outer lip houses a steel ring that holds it in place on the caliper bore top, if that makes sense. The ones on the pictures are not exactly like the ones used on our calipers but you get the idea. The seals on the right are the scraper seals, with a square section. [/QUOTE]

I just found this thread looking for PN's for rebuild kits for my 89 S4 calipers. My pucks are the early ones. Just reading the above post I'd offer an edit as the larger seals on the left of the pic are indeed the dust/scraper seals and not the "main seals" as noted. The square cut O-rings are the main seals. Having just removed the pucks from 4 calipers it's clear that the main seals are the ones furthest inboard on the caliper body and held in place by the outward pressure of the puck and inward pressure of the caliper body. If brake system pressure were to meet the outer seals, one pedal pulse would dislodge them instantly I'd think..

UKenGB

Although new to 928s, I'm not new to brake calipers and yes, the square(ish) section rings on the right are the actual seals that retain the fluid and these did NOT change design. However they DID change the outer dust seals. The early ones worked the same way as the main seals. Fitted into the caliper and sealed against the piston which is the only part that moves. The later calipers have a larger dust seal/cap that attaches into the caliper AND also to the reduced diameter of the outer end of the piston. There is NO sliding surface in this case and the movement of the piston is accommodated by flexing of the (larger) rubber seal/cap.

If I read the tech bulletin correctly, looks like when they updated the outer seal type, they also upped one of the piston sizes from 42 to 44mm. Certainly both changes were made and I think they were simultaneous.

I would suggest UKKid35's photo is of an early caliper with the scraper type dust seal. Nothing missing at all.

UKKid35

Thanks

The engine number ends 606, so it is indeed an early S4, and I believe the front caliper are original (unlike the rears which I have already replaced)

The thing that confuses me is the machining of the circular grove, which doesn't seem to have any function

PS hope to see you at a 928 event one day such as the ones organised by 928.org.uk

UKenGB

Mine is an '89 but has the later VIN so I should have the later calipers, but I've not actually looked at them.

By circular groove you mean the cross section of the dust/scraper ring being U shaped? Probably to create the springiness to provide the thrust onto the piston surfaces and keep them clean.

I think I've seen you on 928.org.uk? Yes, once we're able to safely mingle, I will enjoy meeting other 928 owners.