Caliper O-ring part number

[Matthew P]

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

[Fly Boomer]

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.

[N204TA]

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, 2024 by N204TA

[Matthew P]

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

[Shadrach]

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?

[Shadrach]

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. 

 

[Matthew P]

Thanks Everyone

 

[N204TA]

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.

[Shadrach]

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.

[MikeOH]

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?

[EricJ]

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.

 

[MB65E]

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

[Shadrach]

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…

[47U]

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.

[Shadrach]

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.

[Shadrach]

@Matthew P

Consider “renting” a small, spring loaded, cylinder hone from your local auto parts chain.

[Matthew P]

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

[Matthew P]

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

[Shadrach]

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.

[Fly Boomer]

17 hours ago, MikeOH said:

Do we need a FOIA request to get that redaction removed?

Just select the text.