The Missing ATE' Brake Caliper O-Ring

[Mike V]

I wanted to get this out there to everyone. I've discovered a bit of an anomoly during the restoration of my 81 R65. I'm in the process of rebuilding the front dual ATE' brake calipers and discovered the caliper O-ring is not referenced either graphically or by part number in the OEM fische. The replacement is NOT available anywhere; by BMW or parts suppliers, it basically doesn't exist except for physically in the caliper. I've spent countless hours doing research and think I've found the suitable replacement through an Industrial supplier. The O-ring is an EPDM composition (Ethylene-Propylene-Diene-Monomer), not a Buna-N or Viton. The EPDM composition will withstand the requirements of the glycol based exposure and falls within the required heat ranges. I have 100 of them and am happy to distribute if anyone is interested - after I test them. If any of you have any knowledge or experience with this application I would love to hear from you (mvtv@cox.net) either on this forum or off-list.

Mike V. / San Diego

[Bob_Roller]

I know it's kind of late now, but if you still have a caliper apart, could you measure the diameter of the piston, and the caliper bore .

The pistons are no longer available, and there was a posting last week about a shop in New York state that produces stainless steel pistons, but the smallest piston on the website would give a .040 in. gap all the way around, and that sounds a bit too large .

[Mike V]

Bob,

Unfortunately I have all the pistons and square O-rings installed in the piston chambers but I did measure the piston and I believe the piston was 36 mm. But this is not the piston O-ring I'm talking about, the O-ring I'm referring to is the caliper O-ring for the fluid delivery galley. I know Motobins supplied the replacement pistons for these ATE' calipers and I agree, 0.04 mm seems to be excessive to me for the piston to bore gap. My pistons were quite snug when re-assembling and I can tell you with high confidence the gap was more like 0.01 mm.

Mike V.

[Bob_Roller]

Mike,

Thanks for that info, it helps a lot !!

Did you gat a part number for the o-rings that go between the two halves of the caliper ?

Something that starts with AN , NAS, or MS .

[Mike V]

I'm preparing an article to be published in regards to this subject after adequate testing. The Industrial supplier I received the O-rings from has asked I not mention their name due to the obvious "possible" liability issues we all face in today's litigious world (I can respect that). I can give you the exact dimensions of the subject O-ring and it's composition along with temp ranges. Or contact me off-list (mvtv@cox.net) and I can send you some in the mail after I have the chance to test them. I should be able to get the brakes completely assembled and bled as soon as my brake lines are received in the next couple of days. I'm swimming in these things...the pack comes in a piece count of 100.

Mike V. / San Diego

[Rob Valdez 79 R65]

Hi Mike.  Thanks for doing this for all of us.
IIRC, I think I just ended up reusing my o-ring since I saw no other "easy" (lazy) options.

How did your caliper compare to mine when you opened it up?


_{click for uglier...}

[benita]

It's a metric Oring.Went to Ebay and bought a metric Oring set.No more problems with finding the right one.Set has all the correct ones for the carbs to.

[Mike V]

Rob,

I thought I was the only one growing balsamic vinegar in my calipers!!
Have a look at my restoration photo link. Mine sat for almost 12 years...yes brake fluid is definitely hygroscopic.

 http://s428.photobucket.com/albums/qq8/gruntyman66/81%20R650%20Restoration/Front%20Brakes%205-09/

let me know if you want me to send you some gaskets (mvtv@cox.net). With the condition of my calipers I didn't want to chance replacing them, there wasn't much overlap left for good compression and sealing.

Mike V.

[awaffa2003]

OMG! my savior! I need one!!

[Mike V]

Contact me with your address off-list and I'll send you a couple.
mvtv@cox.net

Mike V.