Boxerworks.com

Hey all:

New to the forum but have been the owner of an 84 R100 since it was new in May 84. Taking it down for reconditioning.

My issue is that the right caliper weeps brake fluid when the brake is applied. The left does not. I have tried applying additional torque to the bolts to no avail. I have also tried "milling" the mating surfaces by gently rubbing the caliper halves over #600 grit placed on a piece of glass as suggested by the superb videos posted by Brook Reams.

My last resort will be to apply Hylomar to the o-ring that is supposed to seal the hydraulics twixt the two halves.

Any suggestions?

Thanks in advance.

Tom B

Just rebuild the calipers with OEM kits. It's brakes! I've tried some aftermarket that didn't fit well.

Thanks for the reply Zombie Master. The weeping still occurs after I rebuilt with new Brembo parts. Will try again. But good advice on not using aftermarket parts for brakes.

My only question, really, is how sure are you that the weep is from the interface between the two halves of the caliper. It isn't unknown for alloy castings to have a degree of porosity or casting flaws that could allow explain the problem and why you haven't been able to cure it.

If you are sure of that, I think the only way forward, given what you have done already, would be to take the two halves to a good machinist and ask him to face the mating surfaces. Noy sure whether they would be happy doing it, they might decline, but it's the only way I can see of getting a better match than emery and glass.

Personally, I would be very reluctant to use a sealant at that point and I don't know what sealant if any would be long term resistant to brake fluid.

In the ultimate, it may be better economically and practically to source a replacement caliper.

Rob

Could it be that torquing the bolts causes distortion. When you face them up again try a little less torque.

Thanks to all that have replied!

Barry: Yes I was very reticent to add more torque to the two caliper bolts, as that same torque sealed the left front caliper perfectly. Should have recognized that something was amiss, but figured why not give it a try. I remember using around 45 ft lbs which is within the Clymer’s recommended torque of 43-46 ft lbs. For you metrics that is around 61 N-m. I probably torqued the right caliper to around 47 ft lbs. Not much more than was called for. Dry threads.

Rob, the weeping seems to originate from the vicinity of the o-ring and spreads along the top mating surfaces of the caliper. It gives that illusion that the caliper halves are spreading, hence my bright idea of additional torque. And I agree that using a sealant is not the preferred way. I was hoping that someone had tried that and it worked. There is the outside chance that the o-ring is not correct (too small diameter or too thin), even though it was from a Brembo kit. I overhauled the calipers separately and did not compare the kits. I have some new o-rings from a Ducati store that they swear are the same ones. I’ll try those first.

Failing there, I will try to find a good machine shop. I live in a small town in Southern CO, not much here. I think that that there may be a drive to Denver in my future. Not a bad drive, but I would rather ride it though. If that does not work, then a used caliper is in order.
Thanks for your thoughts. Much appreciated.

Tom B
Woodland Park CO

TBexp[2] wrote: ↑Wed Aug 04, 2021 6:40 pm the weeping seems to originate from the vicinity of the o-ring and spreads along the top mating surfaces of the caliper. It gives that illusion that the caliper halves are spreading, hence my bright idea of additional torque.

When I did my dual piston Ate caliper I was faced with no recommended torque value being available. Ate didn't provide a figure because they didn't approve splitting the caliper due to potential warping on reassembly.

Not an exact science but I had a stab at calculating clamping forces and concluded that even at 15 ftlbs the clamping force exceeded 1 ton which was well in excess of the likely hydraulic pressure. A different caliper I know but it suggested a low torque value would work and it did.

Any chance the small o ring could've been slightly displaced on reinstallation?

Steve:

That is a very real possibility. I used a dab of Brembo seal conditioner to hold it in place, but maybe it slipped, maybe the seal conditioner was a bad idea. I will try again after I finish the rear part of the bike.

Thanks for the suggestion.

Tom

The mating surfaces of the two halves must be reasonably smooth. No big deal.
What really matters are the surfaces of the recesses that the o-ring fits in.
These surfaces, AND THE O-RING, must be impeccably CLEAN and DRY.