S4 Front Caliper Rebuild Problem (pics)!
 

Front inner pads were wearing less than outer by about a third, looked to be a sticky caliper piston(s) issue. I ordered the repair kits from Pelican, only supplier I could find that carried Brembo dual piston kits for the '89 928. New pistons are the correct diameter, but different configuration. ID is smaller so now my anti-squeal pads will not fit. The seals, both 36mm and 44mm, fit the inside of caliper correctly - Yay! Problem is the dust seals dont fit. Old ones were just a metal rimmed circle. New are rubber covered and mate to a groove in the caliper piston. Old dust seal's outside diameter(s) were 44.27mm for 36mm piston, and 52.27mm for 44mm piston. New are 45.8mm and 53.5mm. I can not get them to fit in the caliper recessed openings as they are cut to 44mm and 52mm respectively. I already bunged up one of the small seals trying out my BFH. :icon501: Seriously, I used the grease supplied with the kits, placed the caliper in a padded vice, used a piece of 1x wood stock sandwiched between vice jaw and seal, then tried to gently and evenly press it into the recess. It would either cock sideways or pop back out.

I called & emailed Pelican but they've gone stealth on me. Can't find anything on the net to explain it. Did find couple other suppliers who sell the same kits - look like the same dust seals from the pics.

So, does that mean the new dust seals are supposed to fit & I just haven't figured out the right technique for installing them? Or did I get the wrong sized dust seals? Here's all the info I could put together on caliper piston & seal:

Front caliper - inner section: ('brembo' in raised letters) # 20.4565.00, (88 stamped inside a circle)
Front caliper - outer section: ('PORSCHE' in raised letters) # 20.4564.00 (87 stamped inside a circle)

Original piston & seal...
Caliper piston small, 36mm outside diameter, 1.265 length
Caliper piston large, 44mm outside diameter, 1.260 length

Dust seal small, 44.27mm outside diameter
Dust seal large, 52.27mm outside diameter

Numbering on small dust seal: 20 4513 72 - 10
Numbering on large dust seal: 20 4513 82 - 11
==============================
NEW PARTS
Pelican caliper kit-36mm, 951-351-919-10-OEM
Pelican caliper kit-44mm, 928-351-919-10-OEM

Caliper piston small, 36mm outside diameter, 1.262 length
Caliper piston large, 44mm outside diameter, 1.260 length

Dust seal small, 45.8mm outside diameter
Dust seal large, 53.5mm outside diameter

Numbering on small seal: 20 4872 44
Numbering on large seal: 20 4872 48

Is it possible that the kits you got are for the rear calpiers?, The new pistons are definitly smaller in diameter at the working part, Just a thought. Hummm

Hawkeyes: try zeckhausen.com/brembo/consumables.htm#rebuild - They may be able to answer some questions if nothing else. I also found a site last week where they will swap out (I believe) your rebuildable calipers for like.....$90.00 IIRC! If I can find that site again I'll post that info too.

Paul Barrera
'91 $4

Does this help?
http://billsworkshop.com/P928S4/xpics/89%20Brakes.doc

You appear to have early version calipers. Odd. I thought all 89s should have new caliper version, but it appears the change broke part way in MY89. What is your VIN number?

I have more info coming.

From service bulletins...Note the VIN break at 282 (2nd footnote, last page). I hate it when they do that!

Bill, you are the MAN! Now the problem is obvious - the Porsche Nazi's did it to me again! :grr: I mean, how could I be so uninformed as to simply believe that my 1989 model would take parts designed for a 1989? And not even the dealer lists Front Caliper Repair Kit #95135191901 for the 1986 thru MID YEAR 1989. No, no, no, they list it for 86-87, and 88 (why not 86-88?). The part number for 89-95, to make it even more error prone, simply reverses the last 2 digits 01 to 10. Couldn't they have just agreed that 02 follows 01?

Anyway, now I have to decide whether to try and exchange my calipers for the 'new improved' model, or just order the correct repair kits. Price is approximately equal, if Paul is correct. Anyone notice any braking performance gains between the 86-88 models and the 89-95's?

Thanks,
Hawk

They changed the piston size 42mm to 44mm for more even pad wear.

Don't know if you'll see any performance change from the scraper vs dust cap, except for longevity by keeping things cleaner.

Nice job Bill your, library is awesome, with out your assitance this might not have been resolved , AAAA++++ , Stan

Hawkeyes: The place to go is rockauto.com! Go through the normal bs of make model etc, click on brakes, then calipers and you will see it. FYI for other lurkers: this is a deal where you send your calipers in, they remanufacture and send back to you. Rears are $93 and fronts are $119 plus core & shipping. This works for big brakes too but i'm confident that you probably can buy without a core at a good price too. Check it out and good luck! :thumbup: BTW I'm an old Healey 3000 ('61 & '65) and jag ('64 & 71 XKE) guy too. Got REAL tired of Lucas Electrics and BMC quality control but had a lot of fun. The 928 though, is still twice the car even with it's quirks. P.S. Stay off the bridges, man!

Paul Barrera
91 $4 a/t Black

No you can't. They will tell you they have no cores.

It's no secret that 90% of my library is the Jim Morehouse CDs. That's where this came from.

Bill, you're amazing. I'm sure glad you hang out in my neck of the woods. Don't get a big head though. Everyone agrees, a little head is a good thing. ;>)

You're screwed. You can only do the full rebuild with new pistons all around to update them to the new style. I searched a long time and never found any source for the older style. When I did my "rebuild" I ended up using all the old seals over again and just cleaning the snot out of everything. 2 seasons of auto-x later and everything is still fine.

fraggle,

Pelican carries both old and new and in-between. They just have them listed incorrectly in their catalog. The correct kit is shown as an '88, 36mm and 44mm - around $100 per caliper. The Rock Auto deal is legitimate, but you send in your calipers for the rebuild...heck, I can rebuild 'em & price is about the same. You are correct however in that one cannot upgrade the existing caliper to the new style. I'm not going to worry about it, have sent back the old repair kits for credit & Pelican has sent me the correct ones. BTW, Bill was the only person out of 3 dealerships and 2 928 suppliers to correctly identify the mid-year caliper piston design change.That is awesome...thanks a million Bill! :jumper: :jumper:

Update - Front Caliper Rebuild
 

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.:banghead:

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.:jumper: 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!

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.

Scraper Seals?
 

https://cimg5.ibsrv.net/gimg/rennlis...6f8545265a.jpg

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?

I stock all the seal kits if you get stuck.

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.

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

https://cimg6.ibsrv.net/gimg/rennlis...32edc51517.jpg
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?

QUOTE=Thom;16946549]https://cimg6.ibsrv.net/gimg/rennlis...32edc51517.jpg
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..

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.

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

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.