split calipers - seals - Warren?

[jpahemi]

Andy,
With all these costs, does it pay to invest in these calipers? I, know it's a challenge for you to complete this project, but , does this price justify the product? One day you'll wake up
and realize you want to upgrade to a Turbo or Big Red set-up(it's in our nature, we can't stay still, project wise) I certainly wouldn't use the compound that requires you to rebuild thes calipers frequently(option 2).
Regards,
J.P.

[jpnovak]

Andy, Thanks for tracking this down. Before you seal everything back up...

Can you make a diagram of the caliper spacers? I would like to know dimensions of the through holes, reliefs for seals, thickness etc. I had considered trying to widen an old set of calipers to fit Carrera Rotors. This would be easy if I machined my own spacers, new o-rings per your posts and longer bolts/pad retainers.

[KobaltBlau]

Just saw this...

Originally posted by Early_S_Man
Andy,

Aren't you leaving out one possibility -- pure silicone?

I'm not saying that Ate used that material in the OEM seals, but it seems like a good high-temp choice to me, probably good to 600°F???

Maybe pure silicone O-rings are a custom order, but your 'current' best sounds pretty high, and VW and Porsche used plenty of silicone O-rings in special places over the years ...

Well, your observation launched me into a search. Silicone o-rings are easy to get and fairly cheap, although I think we agree that they were probably not what the factory used. I realized there is some conflicting information out there regarding the compatibility of silicone o-rings with automotive brake fluid. The marco rubber page I linked to above shows silicone as being incompatible with automotive brake fluid.

Here are some other data points:

This site shows "doubtful" for silicone with "Automotive brake fluid":

http://www.parker.com/o-ring/Literature/07-5700.pdf

This site shows possible loss of physical properties (swell 10-20%), silicone rubber is "VMQ", under automotive brake fluid:

http://www.dichtomatik.us/Products/O-Ring-Handbook/5.pdf

This site says silicone o-rings are just great for automotive brake fluid (I think this may be an error):

http://www.efunda.com/designstandards/oring/oring_chemical.cfm?SM=none&SC=Automotive%20Brake%20Fluid#mat

Basically I have 3 to 1 saying that there is some risk of using silicone. However, considering the way my o-rings fit in the grooves (tight on the outside, lots of room between the inside of the o-ring and the passage), 10-20% swell is a non-issue. EPDM is clearly the best for fluid compatibility, but silicone is much better for temp. Hmm.

[KobaltBlau]

well, I found another compatibility guide I have from apple rubber that says silicone is good with automotive brake fluid. so it's 3 to 2 now. One thing is you're not supposed to use seals with like lubricant, i.e. silicone seals shouldn't be used with silicone lubricant like dow corning 4/111/112. I'm not sure of the composition of the permatex ultra brake lube, perhaps it would be suitable.

[KobaltBlau]

Some people discouraged me from doing this from the beginning, and they were right in a way. However, I hope that the work I have done will help someone in the future make the right choice about this sort of thing, and I am not sorry that I pursued this. At least they should understand what is involved before embarking on this journey.

The last straw -

Today I picked up some o-rings in silicone and EP. The supplier only had sulphur cured EP, but peroxide cured EP is a little better for this application due to a little higher temperature resistance. The o-ring technical salesperson I mentioned earlier in the thread recommended peroxide cured EP as the best thing short of perflouroelastomers.

I bought both silicone and EP because I hadn’t decided for sure what to use.

Next stop was AAA metric which is a metric fastener specialty store here in Denver (They’re great!) I picked up 8 property class 12.9 M8x75 socket head cap screws, class 10 nuts, and Belleville (Schnorr) type washers. When I brought them outside I realized they were smaller than the odd fasteners that came with the caliper. I figured I must have measured wrong and they were really M10. So I went back in with the odd bolt and told the salesperson that I guessed I needed M10. I had measured the diameter of the non-threaded part of the bolt, which on some bolts with rolled threads is smaller than the threads. The threads are what the size is based off of. He said “I don’t think so” and got his calipers out. Turns out these bolts are 9mm which he says are totally nonstandard. An Internet search confirmed this. Basically, the bolts are just as much of a specialty part as the caliper casting, and similar dimensioned replacements are not available.

I went back to McGuckin Hardware in Boulder, just to try some Grade 8 inch bolts (and play with metric bolts) to see if anything matched up. 5/16 is about the same size as M8, which are pretty sloppy, not the kind of thing you want in a brake component. M10 are really big. 3/8 is the closest to the 9mm holes, but it is still too big to fit through. The 9mm bolts fit very snugly in the stock spacers and calipers. The holes in the spacers and each side of the caliper could be drilled out just slightly (<.5mm) to accommodate 3/8-24x3” socket head cap screw. McMaster-Carr has these as part# 91251A436. They also have very thick grade 8 nuts as part 94895A815. The Belleville washers are 93501A031. The base quantities are a bit large (100) on the nuts and washers.

You could also drill the holes out slightly more for M10s.

So I think I’m giving up on this, but if I wasn’t, the options would be:

1. Re-use original bolts, which are suspect due to the pitting, although lots of other calipers out there might have the same pitted bolts
2. Find some good condition bolts out of some other wide ‘A’ calipers. Long shot.
3. Use M8s even though they don’t fit tightly and are smaller than the originals (I’m not comfortable with this)
4. Drill out the holes slightly and use the 3/8 hardware I described above. I think this is the best option but I’m not sure I’ll do it. I’m not as enthusiastic about this as I was.

I was pretty sure I was going to use the EP seals, since I suspect that’s what the caliper came with.

I could also try to contact Ate for bolts/seals but they definitely don’t show them in spare parts on their website.

Just for this record, did you find corrosion on through-bolts on M calipers you rebuilt, Warren?

Thanks for all the help, guys!

[jpahemi]

Andy,
I ran into this "odd sized" situation with the roll pin that secures the Bilstein cartridge to the bottom of the strut. Turns out it's a 7mm roll pin; of course no one has 7, only 6 or 8. Guess what; Bilstien only part.
Regards,
J.P.

[Early_S_Man]

Andy,

When I rebuilt the 'M' calipers, I bored out the holes slightly and used M8 DIN 12.9 Allen bolts to replace those M7 Ribe fasteners!

On the use of Dow Corning 4, 111, & 112 on silicone seals ... it is done all the time on 911 engines! The oil pump & oil cooler use silicone rectangular cross-section seals, and the oil-return tubes use silicone O-rings, and Dow Corning 111 is the preferred lube for all of those seals!

[KobaltBlau]

Interesting, J.P., thanks.

Originally posted by Early_S_Man
Andy,

When I rebuilt the 'M' calipers, I bored out the holes slightly and used M8 DIN 12.9 Allen bolts to replace those M7 Ribe fasteners!

Aha! I didn't realize this was part of your process, but it would have to be part of mine as well.

Warren, did you find corrosion on the old through bolts of these 'M' calipers?

Originally posted by Early_S_Man

On the use of Dow Corning 4, 111, & 112 on silicone seals ... it is done all the time on 911 engines! The oil pump & oil cooler use silicone rectangular cross-section seals, and the oil-return tubes use silicone O-rings, and Dow Corning 111 is the preferred lube for all of those seals!

Hmm, that's interesting too. Thanks!

[Early_S_Man]

Andy,

I did find some surface rust on the Ribe fasteners, but not the pitting you found. Maybe the climate or environment was a factor. No salty roads in Texas' winters!

[KobaltBlau]

Warren, if the bolts were not corroded, why did you go to the trouble of boring out the holes and replacing them? I'm just curious.

As a side note, I really don't know where these calipers spent much of their life, and how long they have been disassembled. So I don't know exactly what conditions caused the corrosion. However, I still think that since the holes are not sealed, many calipers may have corroded bolts. on the other hand, they aren't popping in half at track events, so I guess they're ok in terms of strength.

[KobaltBlau]

Well, I have contacted the seller and it seems that he will work with me. I've come far enough that I'd like to find a solution for others in this situation, but I probably will just send them back to him.

The other option is to bore out for 3/8 heat treated alloy steel (180ksi) socket head cap screws, as noted above, and use EPDM or silicone o-rings. I think this would be at least as good as new, so I still haven't decided for sure.

Any input?

[Joeaksa]

Andy,

If you are going to return the calipers and want to sell the bolts and seals you have purchased, pls let me know. I have a set of calipers off of my 85 model that were ready to bolt on but like you do not know their history.

Would feel better replacing the seal inside...

JoeA

[KobaltBlau]

Hi Joe,

All I have really bought is o-rings and lube which I can probably still return. However, I will make a list of everything you would need soon and post it here.

I am still trying to decide whether to drill for 3/8 and replace o-rings or not or just send them back. I will probably just send them back. less unsprung weight with the SC brakes!! or something.

[Joeaksa]

Let me know!

Thanks,

Joe

[KobaltBlau]

My original situation:
-no brake modifications form stock SC
-experiencing soft pedal toward the end of a DE session with brand new Ate super blue or typ 200
-front SC (20mm initial) rotors at wear limit

My original idea:
Since the SC rotors were at wear limit, simply buy a set of Carrera 3.2 front calipers and replace the rotors with Carrera 3.2 (24mm initial) rotors: easy, relatively cheap upgrade.

As you know from this thread, the upgrade was not as easy as expected due to receiving split calipers. With a track weekend approaching, I decided to buy another set of SC rotors for ~$75 and put them on. I also added the 993 diverters/deflectors (search for these if you don’t know what I mean) with the inside end of the diverter pushed as close to the hub as I could. I wanted to see whether the diverters would solve my soft pedal problem. I had talked to a local expert who runs a ‘G’ class 911SC race car (and drives it to work), and he said he didn’t feel like he needed carrera rotors. On the other hand, he has full brake ducts with hoses and hats etc.

On the track this past weekend, it wasn’t quite as hot as pueblo can be. I hoped it would be pretty hot so I could “torture test” the brakes along with an oil cooler air duct I added. The temps got up to about 87F, I want to “design for” about 95F. If it’s hotter than that, I can accept backing off a bit toward the end of a session.

Keep in mind that the thinner and very dry air at 5000 feet in Colorado does a poorer job of cooling brakes and oil coolers than air elsewhere. Brake fluid also boils at a lower temperature.

Here are some details on the car: brand new Ate super blue fluid, KFP Magnum gold track brake pads all around, stock but freshly rebuilt brakes, brand new rotors. Track tires, ~2650lb vehicle weight. Approx. 20 min DE run sessions. Fairly heavy braking in parts of the track (Pueblo Motorsports Park) expecially at the end of the front and back straights. US '81 SC engine and stock gears.

I experienced no fade at all this weekend under these conditions. Based on this, I will not upgrade to carrera 3.2 front calipers and rotors. The carrera 24mm rotor is significantly heavier than the standard 20mm thick rotor. If I have problems in the future, I will reconsider.

The second part of this post is how to restore carrera 3.2 calipers that have been split. I didn’t have to do this, but I now understand how. Similar procedures should apply to SC ‘A’ calipers, the only major difference is fastener length. Any information you use from this post, you use at your sole risk. I am not responsible for any failures that may occur using these parts, although I think they are the best parts to use.

Seals: you need 8 “–011” size O-rings. In all my research I came to the conclusion that “peroxide cured EP” is the best material to get these o-rings in. The temperature rating is not as high as desired but I believe this is the material that was used for the original seals. A technical salesperson told me that OEMs are still today using this material in high temperature brake system applications. NOTE that the more commonly available “sulphur cured EP” o-rings are not suitable. This is the only thing that was available at my local o-ring specialty store. Marcorubber.com is the only source I know of for peroxide cured EP, although I’m sure there are many others. You can buy 200 or more for the same price as 1 o-ring, but it’s still not that expensive.

Silicone is another possibility for the o-rings but a specialist told me he would not use it with automotive brake fluid, and its compatibility with brake fluid seems questionable based on my research. However, the temperature rating is much better. If you feel adventurous, go ahead and use silicone. I believe that the caliper will only leak moderately if the o-ring fails, and not affect braking performance drastically. However, I cannot prove this and you make changes to your brake system at your own risk.

If I used either one of these I would inspect it at the next caliper rebuild to see if the seals still looked good.

Fasteners:
option 1: you have cleaned up the fasteners and they look good with no pitting. In this case you can probably re-use them safely. You will need a ribe type bit to reinstall them, I believe a 6mm bit, available from samstag sales. The fasteners are definitely 9mm fasteners, a nonstandard size. You will also need this bit if you need to take the calipers apart and you don’t receive them with loosened fasteners.

Option 2: fasteners are shot. This is the situation I was in. M9 fasteners are not available at all (not standard). I wasn’t comfortable going down to M8s. The option is to go up in size, which requires drilling through each half of the caliper and through the spacer in between. The next size up from the 9mm original size is 3/8”. Above that you get to M10. you could use either size. I would probably go to M10. I would use an M10 metric metal drill bit to enlarge the holes to M10, taking special care to keep the holes concentric. I would not do this with a hand drill. I would use M10x75mm class 12.9 socket head cap screws with comparable nuts and a “schnorr washer,” a trapezoidal spring washer wit serrations on both sides. Consult warren’s torque spec table posted above for the proper torque. In my case, the M10 socket heads fit snugly in the recesses on the outside of the caliper, but they did fit. If there is much variation in these countersinks, the M10 heads might not fit and 3/8(x3") might be a better option. trapezoidal spring washers are not as available in inch sizes, however, and I don't feel as confident in the effectiveness split washers under higher torques. Be sure to use alloy steel fasteners, preferably with a tensile strength in the 180,000 psi or greater range. Keep in mind that these socket heads will stick out more than the original ribe button heads. I don’t think there would be any clearance issues with 16x6 or 7 fuchs, but check to make sure before you try to run a different set of wheels.

Another thing people might like to do is make SC calipers into Carrera 3.2 calipers. In this case you would need to make the spacer that goes in between the 2 halves. I believe that by far the easiest way to do this would be to take an SC spacer and make a copy 4mm thicker. You can then use the seals and fasteners mentioned above. However, if you don’t have your own mill, I would be very surprised if this was cheaper than buying a used set of carrera calipers, especially when you can sell the SC calipers with the latter option.

Hope this helps someone in the future, please report here or PM me if you restore split calipers. I would be happy to help someone do this as I would like to see the theories proven.