Rear brake caliper question, outer adjuster appears to be leaking, will not tighten to set clearance Options

[DRPHIL914]

my calipers were all fully restored by PMB performance around
5 years ago of so, when we did all new hard and soft lines. The whole system was replaced then, and i check and set clearance yearly. last year i had to do a new master cylinder so i did that ans set the clearance right before Werks Reunion last May.
now it’s time again and i noticed when i pulled the wheel there is a very small amount of fluid leakage around that outer adjuster, and after i loosened the lock but i turned the inter adjuster but it didn’t tighten up the pad at all it just spins! there is way too much space there and it needs to be in quite a bit.

any thoughts here? am i going to need to send this in?

@EricShea

[nditiz1]

I am told there is a small o ring behind the nut that can sometimes get pinched and not seal correctly. See if maybe it's not flush. I think it only leaks a little when adjusting.

[GregAmy]

...and the o-ring gets easily damaged if you allow the shaft to work inward as you're trying to retract the pads.

The little circlip on the thread is intended to keep that from happening, to stop the shaft from working inward, but sometimes it gets lost or damaged (or you horse the nut across it, damaging it) allowing the shaft to work inwards and the o-ring to unseat. If the circlip doesn't catch then as you screw in the shaft, instead of retracting the piston you're screwing the shaft inward...until the oiring around its shaft comes out of its seat.

The thin nut is just a locknut to keep the shaft from turning. You should not remove it entirely, defintely not across that circlip.

You might get away with re-seating the o-ring back into its bore by using a screwdriver to gently pry back the pad into the caliper as you screw in the threaded shaft. But do it slowly and carefully...otherwise the calipers have to come out.

I hate the design. but it is what is it...

[PatMc]

If fluid is leaking past the outer adjuster...the seal between the small o-ring on the adjuster and the caliper body has failed...that doesn't necessarily mean the o-ring is bad, but possibly the sealing surface of the outer caliper body or the adjuster shaft could be degraded such that the o-ring simply can't seal. The outer o-ring is pretty small and there isn't a lot of allowance for dimension deviation. We scrap a lot of outer half castings that are too far gone, even though they'd probably pass the pressure test.

As far as the inner adjuster not doing anything...keep in mind you're turning a gear, which in turn drives the adjuster. If you spin the gear clockwise, the adjuster shaft is spinning counterclockwise attempting to draw the piston back away from the rotor. Once you hit the limit of travel, everything will just spin. If the piston is sticking in the bore, it's possible the mechanism has pulled out of the piston...try running the inboard adjuster clockwise to run the piston out until it starts moving, then grab some channelocks or a clamp or something and without turning the inboard adjust, try and squeeze the piston in to re-seat it over the adjuster mechanism.

That being said....if the outer adjuster is leaking, the calipers will have to come apart for, at the very least, a cleaning....but it's likely the o-ring was rolled during installation or stuck at some point and was subsequently damaged upon a recent attempt to adjust the outer piston.

End of the day, those calipers should be rebuilt or exchanged for a set of quality rebuilt units...

[DRPHIL914]

If fluid is leaking past the outer adjuster...the seal between the small o-ring on the adjuster and the caliper body has failed...that doesn't necessarily mean the o-ring is bad, but possibly the sealing surface of the outer caliper body or the adjuster shaft could be degraded such that the o-ring simply can't seal. The outer o-ring is pretty small and there isn't a lot of allowance for dimension deviation. We scrap a lot of outer half castings that are too far gone, even though they'd probably pass the pressure test.

As far as the inner adjuster not doing anything...keep in mind you're turning a gear, which in turn drives the adjuster. If you spin the gear clockwise, the adjuster shaft is spinning counterclockwise attempting to draw the piston back away from the rotor. Once you hit the limit of travel, everything will just spin. If the piston is sticking in the bore, it's possible the mechanism has pulled out of the piston...try running the inboard adjuster clockwise to run the piston out until it starts moving, then grab some channelocks or a clamp or something and without turning the inboard adjust, try and squeeze the piston in to re-seat it over the adjuster mechanism.

That being said....if the outer adjuster is leaking, the calipers will have to come apart for, at the very least, a cleaning....but it's likely the o-ring was rolled during installation or stuck at some point and was subsequently damaged upon a recent attempt to adjust the outer piston.

End of the day, those calipers should be rebuilt or exchanged for a set of quality rebuilt units...

@PatMc

Thanks for your response, i think you are correct about the o-ring seal not being seated and probably happened during adjustment, and also what i had done was turned it counter CW and drawn the piston out, but once i realized this , once the new pads were placed in i was able to get the venting set correctly and lock it into place, some pressure on the pedal and a short drive and right now no leaking, so it may be reseated, but will watch this closely. My only question is, can that o-ring be replaced with out removing and rebuilding the caliper?

Thanks .
Phil

[GregAmy]

...can that o-ring be replaced with out removing and rebuilding the caliper?

I don't think so. The piston has to come out, which means the caliper has to be split. Even if you thought about trying it with the caliper on the car, you'll have to bleed the brakes anyway, so may as well just remove and split the caliper.

I suggest that if you don't have any leaking you're probably OK. Just keep an eye on it. Might want to do a quick bleed on it too. - GA

[PatMc]

@PatMc

Thanks for your response, i think you are correct about the o-ring seal not being seated and probably happened during adjustment, and also what i had done was turned it counter CW and drawn the piston out, but once i realized this , once the new pads were placed in i was able to get the venting set correctly and lock it into place, some pressure on the pedal and a short drive and right now no leaking, so it may be reseated, but will watch this closely. My only question is, can that o-ring be replaced with out removing and rebuilding the caliper?

Thanks .
Phil

In order to replace that o-ring, the outer piston needs to come out. Not that tough really...get it on the bench (in a vise), remove the jam nut retainer clip, remove the jam nut, pop of the boot retainer ring and free up the boot, then use a punch or a 4mm allen key in the outer adjuster and hammer the piston and adjuster out...clean things up, replace the o-ring, then put it back together.

squirt some brake cleaner on it and dry things off real good and keep an eye on it. Leaks don't typically solve themselves. When the jamb nut is tight, it's pulling the adjuster flange against the inside of the casting...so in theory, if the surfaces are machined perfectly (which they're not) it shouldn't leak when the jamb nut is tight...but it does, and that's why the o-ring is there. I'd replace the o-ring at the very least, but recommend tear down, inspection, and new kits installed.

Has the fluid been changed/flushed at any point since the these were installed 5 years ago?

[DRPHIL914]

@PatMc

Thanks for your response, i think you are correct about the o-ring seal not being seated and probably happened during adjustment, and also what i had done was turned it counter CW and drawn the piston out, but once i realized this , once the new pads were placed in i was able to get the venting set correctly and lock it into place, some pressure on the pedal and a short drive and right now no leaking, so it may be reseated, but will watch this closely. My only question is, can that o-ring be replaced with out removing and rebuilding the caliper?

Thanks .
Phil

In order to replace that o-ring, the outer piston needs to come out. Not that tough really...get it on the bench (in a vise), remove the jam nut retainer clip, remove the jam nut, pop of the boot retainer ring and free up the boot, then use a punch or a 4mm allen key in the outer adjuster and hammer the piston and adjuster out...clean things up, replace the o-ring, then put it back together.

squirt some brake cleaner on it and dry things off real good and keep an eye on it. Leaks don't typically solve themselves. When the jamb nut is tight, it's pulling the adjuster flange against the inside of the casting...so in theory, if the surfaces are machined perfectly (which they're not) it shouldn't leak when the jamb nut is tight...but it does, and that's why the o-ring is there. I'd replace the o-ring at the very least, but recommend tear down, inspection, and new kits installed.

Has the fluid been changed/flushed at any point since the these were installed 5 years ago?

yes, yearly , and last year a new MC was installed so the whole system was flushed and refilled.

[Sycolyst]

If, in fact, you need to rebuild the caliper it's not that hard to do. PMB has a YouTube video that is very good. I did all 4 of mine and they came out great. Very simple design.