split calipers - seals - Warren?

[KobaltBlau]

Thanks for your responses, Joe.

Originally posted by Joeaksa
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.

This would be especially good for protecting calipers during storage. I personally didn't have a problem (no destruction) using air, but I think using a low pressure (~30psi) air supply is better in this case.

Originally posted by Joeaksa

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.

agreed. they're ugly. As I mentioned above, probably not at all uncommon among calipers out there, including those used on the track. My caliper bodies and bores are not rusty at all. Just these bolts.

Originally posted by Joeaksa

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!

Things are not looking good for an OEM type seal, though I sure wish I could get them. I can tell you about the o-rings if they work for me, but they will not be well tested, just a they-worked-for-one-guy type of deal.

[KobaltBlau]

Here's another tidbit regarding seals:

Brand new Ate super blue or typ 200 brake fluid boils at a little over 500F. so obviously if you had seals that could do that you'd be golden (kalrez does this, but it's far too expensive to be what porsche sells for <$3 for the M calipers)

In practice, I believe that brake fluid boiling with fresh high quality fluid tends to occur in a very localized area. This localized boiling changes the pedal feel, and when I get to this point I back off. Considering the heat sink capacity of the caliper and the fluid, I don't think you see those kind of temperatures in other places like where the split seals are. I would love to do a scientific test or see data on this type of thing, but I haven't, so take what I say with a grain of salt, as an educated guess.

(quote from another thread, that I'm using as an anecdote)

Originally posted by Early_S_Man
The best set of instructions in print are in the Bentley air-cooled VW (Beetle, Bus, or Type 3) service manuals, which your local library may have copies of. They specifically mention 'brake paste' that is simply Dow Corning 111 or equivalent, to lubricate the rectangular cross-section seals, and Ate used to include a tiny 1 gram tube of unmarked silicone grease in their rebuld kits for the master cylinders!

If indeed the Ate recommended Dow Corning 111 or an exact equivalent, this is only rated to 400F.

[KTL]

Nice information and commentary on everybody involved in this thread. The fastener and o-ring stuff is good information for anyone else who attempts this work..Great information without a doubt!

Here's a picture of what my 65K mi. front calipers looked like.



Just like Warren described in the sense that the only problem was on the outer portion of the caliper bore. The outermost area of the bore was rather rusty and corroded. I cleaned them up very well with a scotchbrite pad (green) and put new seals in them. The pistons themselves were in great shape. The calipers were not split, by the way. They now work well for someone else as far as I know.

As far as getting new calipers? That's what I did. White Post Restorations certainly seems to do a nice job. I looked at them when refreshing my brake system. For the same price, you can get brandy new ATE calipers. So, I chose to go new. And, you can get a new pair of wide A calipers for less than $440. That's all i'm going to say on the pricing issue. PM me if you'd like.

[Early_S_Man]

Andy,

I reiterate ... Corvette calipers used a traditional O-ring for the same sealing application on'64 thru '82 models, so I don't believe there is a safety issue!!!

[KTL]

Originally posted by KobaltBlau
If indeed the Ate recommended Dow Corning 111 or an exact equivalent, this is only rated to 400F.

Then get the Dow Corning 112. It has a higher temperature rating. -40 to 450F.

[KobaltBlau]

Originally posted by Early_S_Man
I reiterate ... Corvette calipers used a traditional O-ring for the same sealing application on'64 thru '82 models, so I don't believe there is a safety issue!!!

Well, I thought about this before but I'm not sure exactly what you're saying, Warren. When you say "traditional O-ring", are you referring to the geometry, the material, or both?

If material: Standard Neoprene o-rings are only good for 275F, and not at all recommended for brake fluid. seems odd that they would be used here. I _will_ get these brakes very hot at the track, but I won't get them any hotter than it takes to boil fresh ATE super blue in a localized area. Perhaps corvette owners don't expose their brakes to this (ab)use?

If geometry: My groove geometry to o-ring geometry relationship is probably different from the corvette. I'm no expert in o-ring sealing, all I know is that my o-rings fit snugly against the outside of the groove and raise slightly above the surface the groove is in. They look good, but I haven't studied this interface in detail.

Thanks again Warren, I don't want to sound defensive but I do want to understand what you are saying.

Originally posted by KTL
Then get the Dow Corning 112. It has a higher temperature rating. -40 to 450F.

sorry, I guess I wasn't clear here. I probably will use 112. I was trying to say that if Ate was using 400F silicone, why would they bother to use seals good for better than 400F?

[Early_S_Man]

Andy,

I was referring to geometry, circular cross-section.

[KobaltBlau]

Got it. Thanks, Warren.

[jpahemi]

Andy,
The extremely lengthy and time comsuming process you're about to undertake after the rebuild is worth $150????
Regards,
J.P.

[KobaltBlau]

Originally posted by jpahemi
Andy,
The extremely lengthy and time comsuming process you're about to undertake after the rebuild is worth $150????
Regards,
J.P.

No, it's not. This is a losing proposition financially, when my time is considered. But I'm DIY to the core, and so I want to DIY. It's an engineering challenge, really. The only thing that still makes me want to buy new is that I may inspect between run sessions at the track and find a problem, even if I have heat tested before. This could disrupt a hard-earned weekend. I'm not really worried about the o-rings reacting to temp, I'm just not sure they are the perfect geometry for the grooves, although they are the best I can get with o-rings as opposed to the rectangular cross section seals I am supposed to have but can't find a source for.

[jpahemi]

Andy,
I know the feeling, I've found myself in the same situation with many 911 projects; it's just the safety issue with this one, and as you said the possible ruining of a DE w/e.
Regards,
J.P.

[KobaltBlau]

I just talked to a wrench in town who I really respect, and he has done this several times (amazing the information you get when you talk to grizzled old wrenches ). There's an o-ring specialty store in denver called "rocket seal" that he brings his calipers in to and they find him a good o-ring for the application. In fact, the o-rings I found at McGuckin actually came from rocket seal. Even though I think that the rings I already have are probably the right ones, I want to have an expert down at rocket seal look at the grooves and decide what they think is best. I'll report back the specs on what I end up using so that they are on record here.

So the plan now is:

1. clean and inspect both calipers and pistons carefully
2. rebuild caliper bores using genuine ATE rebuild kits and plenty of Dow Corning 112 on surfaces and seals
3. use o-rings that rocket seal recommends considering my grooves and temperature application (probably a viton of some sort)
4. use M8x75 class 12.9 socket head cap screws and nuts, with a Schorr brand belleville type washer under each nut

Inspect a whole bunch of times as I begin to use the brakes, as described above.

Bring SC calipers and rotors to the track the first time I use these on the track, just in case. Swap-over ain't easy, but I could avoid losing the whole weekend. I'd be surprised if I had trouble, since this wrench has used this type of ring before.

Ta-da!

[vash]

oh o, i detect the makings of another brake expert! cant wait to hear the results. good luck andy!

[no substitute]

Anyone know where the Dow Corning grease can be purchased? Thanks.

[vash]

grainger!

[KobaltBlau]

originally posted by Warren (I think) on some other thread:

http://www.netherlandrubber.com/adhesive/compound/compound2.html

My local auto parts store had the 4, something like 112 might be harder to find locally (although I need some).

[KobaltBlau]

further research:

Grainger has 4 and 111 but not 112

McMaster-Carr has 4, 111, and 112 (all of them), search for "silicone grease"

112 is rated for 450F vs 400F which I think is better for this app.

[no substitute]

Thanks for the info gentlemen. I found 4 at MSC, and 111 at Enco.

[KobaltBlau]

I went to rocket seals today, and they pointed out an error in my analysis. I stated above that Viton is compatible with brake fluid. In fact, standard Viton is not compatible with brake fluid. Dow has a new Viton “Extreme” (ETP) compound that is compatible with brake fluid, which is what confused me. This is a relatively new material. A major O-ring supplier online does not stock these, and basically you pay at least $423 whether you buy 10 or 100. I wasn’t able to find any other pricing online for these Viton “Extreme” o-rings.

So the question I am still trying to solve is: What are the original seals made out of? I would be quite surprised if they were made of a material that o-rings are not currently available in. Since regular Viton is out, it turns out that the best non-exotic o-ring material is Ethylene propylene rubber (EPR), of which EPDM is the most common form. EPR (specifically EPDM) is only rated to 300F (I found this spec several places), although rocket seals’ spec book showed up to 400F ok for short periods (I have no idea how long that means). My above mentioned “Trusted Mechanic” has used these seals several times, although I don’t know if they have been used on the track. He claims I’m “way overanalyzing” this (which is true) and says that the worst that can happen if the seals totally fail is a little weeping of fluid in the joints. But he says none of the ones he’s done have had any problems.

What I’m saying here is that the options I have found are EPR@300F, then the exotic options. I suspect now that the stock seals were probably EPR (for lack of anything more suitable), and that they are still OK at whatever temperatures that they see on a tracked car, since people are not having problems with this. Just for reference, the following prices apply for alternatives available at McMaster Carr. These prices are all for the –011 size, which I believe is correct for this application but haven’t verified for sure:

1. Exotic FEP Teflon encapsulated silicone (400F): $3.54 per o-ring
2. Exotic Kalrez material(600F): $22.38 per o-ring
3. EPDM: $2.66 for 25 o-rings

The price for the FEP encapsulated ones isn't bad, but there's no way the stock seals were made out of that. If the stock seals were made out of EPDM (I can't think of anything else that they could have used that would be better), then I might as well use EPDM.

For those of you that are thinking I'm nuts to touch these and should have them rebuilt or buy new, my question is ... is the seal material used in new or rebuilt ones any better than EPDM? I don't see what it could be that would be better. Here is a good chart to help understand the materials and applications:

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

keep in mind that pure Teflon, which are cheap, are not very elastic and therefore not very good in a normal o-ring application like this one.

[KobaltBlau]

Another update...

I know you guys are on the edge of your seats, so here is some very interesting additional information.

A technical salesperson from a large industrial o-ring supplier was kind enough to talk with me for a couple of minutes. He told me that he has recently spoken with several engineers running up against this problem, at least from GM and Lexus. He said there are two options here:

1. Pony up the cash for perfluorocarbon (Kalrez/Simriz/Chemraz) rings, which are good to 600F. These can be $10 _each_ even in large quantities, and are about $22 each in smaller quantities as I mentioned above (again, I need 8).

2. Use "peroxide cured EP" which I think is the same as EPDM (certainly it is an EPR), and just "replace them more often"

For cost reasons, all of the OEMs are doing #2, although who knows whether the seals will really be replaced more often. Probably won't in the life of the car. If indeed our ate OEM seals are EPDM, they seem to be lasting the life of these cars which is quite long. Also, clearly the 'M' Caliper seals that are available are not perfluorocarbon, since they are available from porsche for $2 each. If I replace my hardware and o-rings, however, I will at least have the luxury of inspecting/replacing these EPDM rings every time I do a caliper rebuild.

So EPDM it is, unless anyone can convince me otherwise.