Matthew P Posted August 25 Report Share Posted August 25 Have a 1966 m20e withe slight drip, calipers were done 400 hrs ago so thinking a pinched o-ring, anyone have the correct part number? Tia Quote Link to comment Share on other sites More sharing options...
Fly Boomer Posted August 25 Report Share Posted August 25 14 minutes ago, Matthew P said: Have a 1966 m20e withe slight drip, calipers were done 400 hrs ago so thinking a pinched o-ring, anyone have the correct part number? Tia For mine, it's described in the SMM 32-40-04. I would expect yours to be close to that in the appropriate SMM. Quote Link to comment Share on other sites More sharing options...
N204TA Posted August 25 Report Share Posted August 25 (edited) The IPC shows an AN6227B-29 / MS28775-326 o-ring. How are your brake pads? I’d suspect worn pads causing the caliper piston to leak before a problem with the o-ring. Edited August 25 by N204TA 1 Quote Link to comment Share on other sites More sharing options...
Matthew P Posted August 25 Author Report Share Posted August 25 40 minutes ago, N204TA said: The IPC shows an AN6227B-29 / MS28775-326 o-ring. How are your brake pads? I’d suspect worn pads causing the caliper piston to leak before a problem with the o-ring. New pads, new calipers 400 hrs ago Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 1 hour ago, N204TA said: The IPC shows an AN6227B-29 / MS28775-326 o-ring. How are your brake pads? I’d suspect worn pads causing the caliper cylinder to leak before a problem with the o-ring. How would a worn pad cause a caliper to leak? Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 3 hours ago, Matthew P said: Have a 1966 m20e withe slight drip, calipers were done 400 hrs ago so thinking a pinched o-ring, anyone have the correct part number? Tia P/N is serial number dependent. Quote Link to comment Share on other sites More sharing options...
Matthew P Posted August 26 Author Report Share Posted August 26 Thanks Everyone Quote Link to comment Share on other sites More sharing options...
N204TA Posted August 26 Report Share Posted August 26 16 minutes ago, Shadrach said: How would a worn pad cause a caliper to leak? Worn pads require the piston to move further when applying the brakes. Eventually, it will be sticking out far enough that hydraulic fluid can leak around the o-ring. Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 13 minutes ago, N204TA said: Worn pads require the piston to move further when applying the brakes. Eventually, it will be sticking out far enough that hydraulic fluid can leak around the o-ring. IIRC the cylinder wall is the same dimension from top to bottom with perhaps a slight chamfer at the top. It should not leak as long as the o-ring is in contact with the cylinder wall. I cannot imagine a scenario where that would happen even with very worn pads. Is this something you’ve seen a lot of? I rebuilt my calipers years ago because of an o-ring failure. They do fail but it is rare. Quote Link to comment Share on other sites More sharing options...
MikeOH Posted August 26 Report Share Posted August 26 7 minutes ago, Shadrach said: IIRC the cylinder wall is the same dimension from top to bottom with perhaps a slight chamfer at the top. It should not leak as long as the o-ring is in contact with the cylinder wall. I cannot imagine a scenario where that would happen even with very worn pads. Is this something you’ve seen a lot of? I rebuilt my calipers years ago because of an o-ring failure. They do fail but it is rare. Do we need a FOIA request to get that redaction removed? 1 Quote Link to comment Share on other sites More sharing options...
EricJ Posted August 26 Report Share Posted August 26 28 minutes ago, Shadrach said: IIRC the cylinder wall is the same dimension from top to bottom with perhaps a slight chamfer at the top. It should not leak as long as the o-ring is in contact with the cylinder wall. I cannot imagine a scenario where that would happen even with very worn pads. Is this something you’ve seen a lot of? I rebuilt my calipers years ago because of an o-ring failure. They do fail but it is rare. Mine did that the last time the pads got worn down, i.e., first symptom is a little wetness around the bottom edge of the pad. These sorts of little oozy leaks seem to be a little worse with the synthetic fluid, but I've yet to see one turn into an actual drippy leak. Quote Link to comment Share on other sites More sharing options...
MB65E Posted August 26 Report Share Posted August 26 4 hours ago, N204TA said: The IPC shows an AN6227B-29 / MS28775-326 o-ring. How are your brake pads? I’d suspect worn pads causing the caliper piston to leak before a problem with the o-ring. I’ll confirm the -326 oring should be correct. Used this on my 65E a few years ago. Had the same issue confirming. -Matt Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 2 hours ago, MikeOH said: Do we need a FOIA request to get that redaction removed? Paragraph structure gets weird when posting from some mobile devices… Quote Link to comment Share on other sites More sharing options...
47U Posted August 26 Report Share Posted August 26 3 hours ago, EricJ said: Mine did that the last time the pads got worn down, i.e., first symptom is a little wetness around the bottom edge of the pad. These sorts of little oozy leaks seem to be a little worse with the synthetic fluid, but I've yet to see one turn into an actual drippy leak. The brake calipers in my Cherokee (circa 1998) were so neglected that the cylinders were corroded on the outer surface, past where the o-ring rides. The wetted area of the cylinder was fine. But, when the pads were worn down to the rivets the o-ring was now trying to seal against the rough cylinder wall surface and the leak ensued. I was able to clean up the surface with emory cloth and scotchbrite. And new break disks that didn’t wear the pads out every year. 2 Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 7 hours ago, 47U said: The brake calipers in my Cherokee (circa 1998) were so neglected that the cylinders were corroded on the outer surface, past where the o-ring rides. The wetted area of the cylinder was fine. But, when the pads were worn down to the rivets the o-ring was now trying to seal against the rough cylinder wall surface and the leak ensued. I was able to clean up the surface with emory cloth and scotchbrite. And new break disks that didn’t wear the pads out every year. When I overhauled my calipers, you could see some light, surface corrosion on the unwetted area but mine never leaked. It may have contributed to the o-rings demise, but it had been in service for forty years so it owed us nothing. I lightly honed the cylinder walls and replaced the o-rings It’s been good for 17 years. Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 @Matthew P Consider “renting” a small, spring loaded, cylinder hone from your local auto parts chain. Quote Link to comment Share on other sites More sharing options...
Matthew P Posted August 26 Author Report Share Posted August 26 4 hours ago, Shadrach said: @Matthew P Consider “renting” a small, spring loaded, cylinder hone from your local auto parts chain. Thanks, will see if they have one Quote Link to comment Share on other sites More sharing options...
Matthew P Posted August 26 Author Report Share Posted August 26 4 hours ago, Shadrach said: @Matthew P Consider “renting” a small, spring loaded, cylinder hone from your local auto parts chain. Actually, I'm not boring cylinders I'm bleeding brakes and changing o-ring on caliper Quote Link to comment Share on other sites More sharing options...
Shadrach Posted August 26 Report Share Posted August 26 20 minutes ago, Matthew P said: Actually, I'm not boring cylinders I'm bleeding brakes and changing o-ring on caliper The o-ring fits in a groove machined into the caliper piston. The piston will need to be removed to replace it. It would be a shame to go through the trouble to remove everything and not have the tools to repair. Your IA likely has a plan for such contingencies. Quote Link to comment Share on other sites More sharing options...
Fly Boomer Posted August 26 Report Share Posted August 26 17 hours ago, MikeOH said: Do we need a FOIA request to get that redaction removed? Just select the text. Quote Link to comment Share on other sites More sharing options...
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