split calipers - seals - Warren?

[Early_S_Man]

Andy,

That bore doesn't look bad at all! Yes, some rust and the cadmium has been eaten away in spots and areas, but no significant pitting at all! I have successfully rebuilt calipers that were much worse looking. A pink or gray abrasive rubber eraser will polish up the pistons quite effectively.

What I usually do when rust is present is to use a phosphate conversion compound such as Oxy-Solv or Naval Jelly ... applied very sparingly with Q-tips, and just to the bore itself, none on the exterior outside the bore. After half an hour or so, or when the bore has turned dark gray to black ... wipe out the bore with paper towel, dry, then wet, then dry again. Rinse with 90% isopropyl alcohol, and dry with paper towel or compressed air.

I always suggest liberal application of Dow Corning 4, 111, or 112 silicone grease to the bore, seal recesses, and pistons ... 100% coverage -- no gaps, when rebuilding, and ONLY Ate rebuild kits! Silicone grease is inert and stays in the caliper where you apply it, and is fully compatible with glycol or silicone brake fluids. Ate used to include a tiny 1 - 2 cc tube of silicone grease with their master cylinder rebuild kits ... called 'brake paste' by VW and Ate, it was also recommended in the official VW service manuals for air-cooled VWs written by Bentley in the early '70s. I do not use Syl-Glyd any longer, because a 10-year old tube turned dark brown in my tool box, whereas a 40+ year old container of military surplus Dow Corning 4 grease is as clear and new-looking as a brand-new tube off the store shelf!

[Grady Clay]

Andy,

Here is a source for Sahlwille RIBE sockets.

http://www.samstagsales.com/stahlwille.htm#ribe



Also, is Gahard Aschenmacher (sp?) tool dealer still in Boulder?
He may have them in stock.

The ones I have are Hazet. You are welcome to use one.
The sizes I have are 5, 6, 8, and 10.


You need to find the proper torque spec for those bolts.
They are very hard and I suspect torque sensitive.
You should hold the head stationary and torque the nut.
You need to know to lube the threads or not.

I think the reason the calipers were apart in the first place is
that they came from a commercial dismantler.
I’ve been helping a Pelican in SF find some brakes and they won’t
sell them to him other than as “cores” not functioning.
I think we all understand the liability issues, it is just a PITA.

It is prophetic that McGuckin’s has parts to fit.
It is the best hardware store in the world and a tourist
attraction for those in the know.

e-mail me if you want the tool.
I’m in SE Denver (~I-25 & Yale sorta.)

Best,
Grady
gradyclay@hotmail.com

[Eugene at Pelican Parts]

This has grown to become quite an informative thread.

Bill Verburg posted torque specs here

"The last time they were published was in '77. At that time the M8 bolts used on the A caliper was 34 NM, the M6 bolts used on the rear M was 22 NM. The late Brembos are a whole nother thing"

[KobaltBlau]

This board rocks! Thanks Grady for your information and your offer, and thanks again Warren and Eugene. My plan is to replace the cross bolts with new Din 12.9 socket head cap screws from AAA metric in denver, so I should not need the Ribe bit if I do that, since the calipers are already apart. I do indeed need to find out the proper torque spec, however. This is the problem:

Originally posted by Bill Verburg
The correct torque for the A front used thru '83 is 34NM(~25 lb-ft). The later wide A used from 84-89 will be different.

Bill, why do you say that the wide calipers would be different? They seem the same except the thicker spacer, are the longer bolts the issue? Would you guess the torque to be higher or lower?

Grady, I haven't heard about Aschenmacher, I should look into it. Interesting observation about the breakers.

Warren, bad news on those SS Mercedes caliper seals. A call to the dealer, my search of mercedes parts sources, and a few searches on mercedes equivalents of this BBS didn't turn up a source. It appears that the mercedes dealer shows a caliper rebuild kit for the SS calipers, but no separate split seals, just like PET. My suspicion is that this kit does not include the seals in question, as is the case with the ate 'A' caliper rebuild kit. Because of this, I am tempted to use the viton o-rings I found, which are rated for brake fluid and 400F. they fit snugly against the outside diameter of the hole, and are thicker than the hole. I think they would work, but I would be taking a risk that I would prefer to avoid by finding the correct seals. However, if I cannot find the proper seals, I can't see any alternative to throwing out my calipers, other than perhaps getting some used seals out of trashed calipers which seems ridiculous.

If anyone has good mercedes parts dealers to suggest, I'm all ears.

[jpahemi]

Andy,
Would it be a good idea to have the caliper halves electro-plated in yellow chromate or yellow cad.; this way you'll end up with virtually new calipers.
Regards,
J.P.

[Noel]

Andy,

This sounds like one hell of an adventure.

I think your bores look OK and I would not hesitate to finish rebuilding them. You might just try the seals from the hardware store and see if they work without leaking. However, with a 400 degree limit this may be an issue on the track. If not then use the ones from your old calipers.

Good luck.

[Early_S_Man]

Andy,

Too bad about Mercedes ... I guess they don't want owners fixing up the old cars, either!

The Corvette calipers from '64 thru '82 used a conventional O-ring in the same application, so I don't guess there is a safety issue!

As for the caliper thru-bolts ... 'M' calipers use M7 bolts, not M6!

For torque specs, I would use the DIN property class 12.9 value.

[Bill Verburg]

As for the caliper thru-bolts ... 'M' calipers use M7 bolts, not M6!

argue w/ the factory Warren. The #s are I posted are specs per factory.

Bill, why do you say that the wide calipers would be different?

Different longer bolts, different specs. Those #s are not published.

Again my advice, buy some unmolested calipers

[Early_S_Man]

Bill,

I don't have to 'argue' with anyone -- pure fact: 1972 - 1974 'M' calipers have M7 Ribe bolts ... I've had both front and rear calipers apart for replating and rebuilding!

Maybe you simply aren't aware that there are typographical errors in many factory publications, including spec books, parts catalogs, and technical bulletins!

[KobaltBlau]

Originally posted by Noel
I think your bores look OK and I would not hesitate to finish rebuilding them. You might just try the seals from the hardware store and see if they work without leaking. However, with a 400 degree limit this may be an issue on the track. If not then use the ones from your old calipers.

Thanks for the second opinion, Noel. I do appreciate it. The seal temperature issue is really a materials issue. The seals I have from the hardware store are absolutely not normal o-rings, they are viton material which makes a big difference. I have done some significant research on this, and I have found that there are only a couple of materials that o-rings are made in that can handle more than 400F, and compatible with brake fluid. The only reasonably priced one is pure PTFE (Teflon) which is not very elastic and therefore not great for this type of application. It is also white which these seals are not. The other two alternatives are a silicone core with pfa teflon jacket, and a kalrez polymer or the similar chemraz or simriz. The kalrez family o-rings are about $12 each in this tiny size, even in large quantities (these calipers have 8/axle). I didn't get a quote on the pfa jacketed silicone but the more common (but only 400F) fep teflon jacketed silicone is comparable in price to the kalrez. I also would be surprised if the kalrez or jacketed o-rings were around 15+ years ago, and if these flat seals were available in any materials o-rings aren't/weren't.

For these reasons, I believe that the OEM seals, whatever they are made of, are not better than 400F. I suspect they are viton as well, but I have no hard data. The geometry of the OEM seals might be better for sealing, this is my greater concern. I would be curious if anyone knows the composition of these or even the dust seals.

Originally posted by Bill Verburg
Different longer bolts, different specs. Those #s are not published.

Again my advice, buy some unmolested calipers

It seems to me that this would mean buying new. If I can be comfortable with the re-engineering I have done to a set of calipers, It would be rewarding to save this set. Yes, I realize safety is at stake. At a minimum, the calipers would be very carefully monitored during their first road and track use, and carefully monitored regularly thereafter.

Originally posted by Early_S_Man
Andy,
Too bad about Mercedes ... I guess they don't want owners fixing up the old cars, either!

yes

Originally posted by Early_S_Man

As for the caliper thru-bolts ... 'M' calipers use M7 bolts, not M6!

In any case, my 'A' calipers have M8 bolts. I have a good metric shop here in town so I can be sure to get the right ones if I replace.

Originally posted by Early_S_Man

For torque specs, I would use the DIN property class 12.9 value.

Sounds interesting. Where would I find this?

I took a closer look at the fasteners used in this application compared to the prospective socket head cap screws. Does anybody have an opinion on reusing these bolts, they are my 2 worst (all others are significantly better), i have not attempted to clean them up. If you think they are OK, should I just use steel wool on them or anything special?



A couple of things are interesting about the fasteners, aside from the Ribe heads. They are M8x75mm. compared to a socket head cap screw, the head diameter is about 14.6mm versus 13mm for the cap screw. The nut takes a 14mm wrench instead of a 13mm, and is 8mm thick compared to 6.5mm for a standard DIN 10.9 metric nut. All of this makes me believe that these fasteners are very high grade, and makes me want to reuse them if possible (see photo above). Eugene alluded to some of these differences in an earlier post on this thread. Given the difficulty of sourcing the seals, sourcing the OEM type fasteners is something I'd like to avoid (unless anyone has a good source).

Thanks again everyone, I'd like to make this easier for those who tread this path after me, or at least make it clear that thou shalt not tread this path

[KobaltBlau]

OK, I couldn't resist, even though it's midnight. I did some mild cleaning up of my worst two bolts (pictured above) with steel wool and brake cleaner. Here is what I found:





My camera doesn't do macro very well, and I'm sure it is hard to gauge depth from the photos, but here is my observation:

Although there is still rust present on the bolts, there is noticeable pitting on both bolts. These pits go below the original bolt surface, which I fear might have dire consequences to the strength of the bolts (stress riser?)

anyone agree?

If these bolts are bad, I have 3 options:

1. Get DIN 12.9 allen bolts. The shafts will be stronger, but the fasteners have a little less meat on the ends. maybe this is OK with iron calipers, but maybe not.

2. Try to find nice quality or new replacement bolts just like these. Seems like this could be quite the pain

3. Buy a new set of wide 'A' calipers. Bill seems to be in favor of this one, and it is the safe choice, and would save me time. It is also the expensive choice at $440, and feels like giving up. May still be the right choice, but I'd love to hear opinions on the not-so-easy options.

Thanks again!

[KobaltBlau]

here's a zoom

[KobaltBlau]

tweaked the image a bit (now I'm done)

[GeorgeK]

While this is a fascinating process, and I just love saving what others might trash, I respectfully suggest you don't re-use these calipers unless you find all the correct parts, new.
The new calipers seem expensive at 440$, but have you priced a front bumper/lower spoiler/headlight recently? And that is the *minimum damage* case if they fail.

[Early_S_Man]

Andy,

Below is a standard DIN fastener torque chart ...

Those Ribe fasteners are pitted pretty bad, and I would strongly recommend replacing them with DIN 12.9 bolts and using Schnorr washers under the nuts!

I have split and rebuilt both Ate 'L' and 'M' calipers ... reusing some bolts that were in good shape, and replacing others. no problems whatsoever! New VW Type III seals were used in every case.

Both the Clymer Porsche 912 Handbook and Bentley-written air-cooled VW service masnuals give procedures for splitting and rebuilding calipers! I don't quite understand the
myth that there is some kind of safety issue ... though safety is always of paramount concern when working on the brake system!

In 1986 I rebuild the calipers and changed pads again on my uncle's '76 Ford pickup after he had a slow brake fluid leak for several months after pads had been changed at the local Ford dealeship. What I found was that a copper sealing ring had been left off one of the banjo bolts at the last service, and the leak sprayed fluid on both rotor and pads! Was it life-threatening negligence case worthy of a lawsuit? Probably not, since the truck still stopped with only a slight pull to the right ... and my uncle seldom drove over 65 mph in that farm truck ... and only had to add brake fluid about once a month!

[Joeaksa]

Andy,

A tip for the future. Fix up a adapter from a grease fitting and screw it into the caliper. Attach your grease gun to it and pump it a few times and it will slowly push the caliper pistons out of the housings.

Messy? Well, you need to clean them out anyway and this is a lot less destructive than using air.

Agree with Warren and those bolts should be replaced. The pitting does not look good and these are a part that you want to have the utmost in confidence in on the car. I have split calipers in the past and had no problems with them. Used aircraft seals going back together with them so cannot help there, as well it was 15 years ago and forgotten the part numbers!

I have always wondered of the condition of the seals between the calipers I have overhauled and would feel better splitting them and replacing them. If you find a good replacement seal, please let us know. I have a set of 85 calipers on the bench right now ready to overhaul!

JoeA

[KobaltBlau]

Originally posted by Joeaksa
Used aircraft seals going back together with them so cannot help there, as well it was 15 years ago and forgotten the part numbers!

What were the characteristics of these seals? i.e. do you remember the material and/or their general geometry (o-rings or rectangular cross section etc)?

Thanks!

[Joeaksa]

Andy,

To tell you the truth, I do not remember! At the time you could buy the seals from the dealer or parts supplier and we just put them together with DC3 lube and they worked fine.

Your idea of finding seals and using them would be what I would do. I would get new bolts and a handful of new "o" rings, put one of the calipers together and torque it to specs. Let it sit for a few days and then take it apart. Check the "O" ring for deformation and make sure that its not been collapsed to the point where it would restrict the flow of brake fluid from both caliper halves.

If all looks well would then bolt it back together and put it on the car. The main reason I have heard in the past for not supplying these "o" rings was a product liability issue and our working on our own brakes throws this out the window anyway.

JoeA

[KobaltBlau]

This post addresses the safety concerns. I also added a disclaimer at the beginning of the thread.

To anyone considering this type of work, I urge you to carefully consider the safety implications. when Ate first designed these calipers, they undoubtedly went through several prototypes with different sealing and fastening arrangements and subjected them to a battery of tests. you, as a private individual, will not be able to do this. Ate probably also got feedback from the auto manufacturers using these parts. For this reason, heeding GeorgeK's recommendation is certainly the safe route: use OEM parts only, whether seals and bolts or new calipers.

The problem with this situation is that Ate, Mercedes, and Porsche have chosen not to make these seals available (as far as I can tell, but I'd still love to find out they do somehow). They would like you to buy a whole new caliper, which is, again, the safe choice. For myself, this fastener and sealing issue is not rocket science, and I want to try to solve the problem. Here are my rationalizations:

1. The fasteners: I would be very surprised if the original fasteners are any stronger than DIN 12.9's ~177000 psi tensile strength. I am really not worried about the fasteners. since these fasteners do not seal, undoubtedly many of the SCs and Carrera 3.2s out there have pitting just like my fasteners, even those being used on the track. I find it hard to believe that these old pitted fasteners are better than new DIN 12.9 fasteners.

2. The seals: I would really love to have the proper seals. However, I have had very little luck finding them. This leaves viton o-rings as the next best thing I have found. The ones I have fit very nicely and have the right cross section compared with the height of the groove.

I think there are 3 possible failure modes for these o-rings:

a. I stomp on the pedal while the car is still in the garage on stands and the caliper leaks.

b. I stomp on the pedal going around the block in my neighborhood and the caliper shows leaks or weeps when I inspect it right afterwards, or the next day, or the next week when I inspect it again and again.

c. When I first get the brakes really hot, the seals are damaged in some way, and leak either catastrophically or lightly. For this reason, I will be sure to do something like a track pad bedding in procedure in a very controlled environment, with plenty of runout areas and no other cars. As I explained above, I really doubt that the OEM seals are any better with respect to temp than the 400F rating that the viton rings have, simply because the materials required to exceed that are fairly exotic, expensive, and modern (detail above).

The seal area and fasteners would be inspected on first brake application in the garage, first time around the block (with no traffic), first 5 miles, first 20 miles, first week, first heat, and every track day, including every session on the first track day. If I find any leakage or fasteners turn when I re-torque them, I would toss the whole idea. I do think that the only catastrophic failures that are at all likely are a, b, and c above, and they can all be done in environments where losing even both front brakes catastrophically would not be a problem.

[KobaltBlau]

Thanks for the chart, Warren, that's really useful. But I wonder whether "friction coefficient .14" corresponds to lubing the threads or not. I'd be tempted to use some anti-seize so I know I get a good reading.

Originally posted by Early_S_Man

Those Ribe fasteners are pitted pretty bad, and I would strongly recommend replacing them with DIN 12.9 bolts and using Schnorr washers under the nuts!

Agreed. It seems Schnorr is just a brand (although perhaps the best brand) of 'Belleville' washers. I assume that you mean a washer like this one:



serrated on top and bottom and slightly conical. Do you have a source for the Schnorr brand?

Originally posted by Early_S_Man

I have split and rebuilt both Ate 'L' and 'M' calipers ... reusing some bolts that were in good shape, and replacing others. no problems whatsoever! New VW Type III seals were used in every case.

Too bad we don't know for sure what those seals are made out of. It would be really interesting to try this:

http://www.marcorubber.com/orid.htm

on the 901 part number seals for the M calipers, even though you need to know that the o-ring is either nitrile, EPDM, kalrez, or viton to get a certain result. I bet it would come out viton, but I probably won't be finding out since the tool is $75 and I can't think of another use for it.