Disc brake cylinders

[WarDamnEagle]

Okay full disclosure, this question doesn't pertain to my 55. But the front discs on a 55 and an 80 are pretty much the same....and if I ask this question in the 80 section I will open myself to 10% of the internet.

There's a longer story here that I will share in due course but let's start with the short story. Middle son has been driving the 80 and when youngest son was home he used it for a quick trip and said the passenger side brakes were rubbing. Boy were they. I would say 1/4" of the disc on one side was gone. The other side looked fine. So I installed new rotors on both sides but cannot get the two pistons on the side with the highly worn rotor to compress. I even tried a 4T porta power and no dice. They will wiggle back and forth with a pair of channel locks so they aren't 100% stuck, at least not in all directions. The opposite side cylinders compressed no problem and all 4 compressed on the driver's side without issue.

I have read that they can "pop out" but there is no brake fluid leaking (assumption on my part that fluid would be leaking?). FSM says to just pop them out with air to rebuild them and to just push them back in with the new seals and cylinders, which is exactly what I did on my 55 calipers. The only theory I have is that the first seal ring traveled out but not the second and now the seal ring that is out is somehow preventing the cylinder from compressing back.

I have new calipers on the way so I can just change them but thought I would throw the question out in case someone else has encountered this issue before. Thanks.

 

[YukonCruisers]

When this has happened to me, I've always replaced the part. But your piston could be slighlty at an angle and catching as opposed to seized - you could try opening the bleeder valve to relieve some back pressure, tapping the brakes to move forward and then press back again, but sounds like its jammed pretty good.

 

[WarDamnEagle]

When this has happened to me, I've always replaced the part. But your piston could be slighlty at an angle and catching as opposed to seized - you could try opening the bleeder valve to relieve some back pressure, tapping the brakes to move forward and then press back again, but sounds like its jammed pretty good.

I agree with the "jammed pretty good" assessment. I will probably just replace both calipers and throw these in the spare parts bin. If they are at an angle it is impossible to see with the eye. And whatever is causing the issue is affecting them both equally.

 

[PabloCruise]

Can you get the pistons out of the caliper?

 

[WarDamnEagle]

Can you get the pistons out of the caliper?

I haven't tried. I replaced the calipers and tossed those into a box for "later".

Part of the rest of the story is I found the driver's side caliper top bolt loose with evidence that someone had held it in place with RTV. I had a dealership replace the calipers years ago so I am guessing they are the culprits. I took a flyer on trying to drill it out by hand to install a helicoil as I really didn't want to pull the knuckle to put it on the drill press. At first it didn't work and I stripped two bolts trying to get it to bolt up. Thinking the helicoil was misaligned I ordered two new knuckles and everything to do a complete front end rebuilt hand ncluding all the bearings.

Well of course the knuckles are on national backorder with no ETA so I cancelled that entire order. I did find them available in the UAE and Japan so I ordered a pair (from Japan) and before reordering everything else I took a second look at the helicoil. Rightly or wrongly, I decided I had installed it a tad too deep so I pulled that helicoil and reinstalled a new one (18mm length works for our pigs and my 80 if anyone needs that information). Two days later the new calipers showed up with new bolts and miraculously I was able to get the bolt in and tight. So I just left it at two new calipers, rotors, and pads for now. I will just hold onto the knuckles for spares when they show up.

 

[PabloCruise]

I haven't tried. I replaced the calipers and tossed those into a box for "later".

Part of the rest of the story is I found the driver's side caliper top bolt loose with evidence that someone had held it in place with RTV. I had a dealership replace the calipers years ago so I am guessing they are the culprits. I took a flyer on trying to drill it out by hand to install a helicoil as I really didn't want to pull the knuckle to put it on the drill press. At first it didn't work and I stripped two bolts trying to get it to bolt up. Thinking the helicoil was misaligned I ordered two new knuckles and everything to do a complete front end rebuilt hand ncluding all the bearings.

Well of course the knuckles are on national backorder with no ETA so I cancelled that entire order. I did find them available in the UAE and Japan so I ordered a pair (from Japan) and before reordering everything else I took a second look at the helicoil. Rightly or wrongly, I decided I had installed it a tad too deep so I pulled that helicoil and reinstalled a new one (18mm length works for our pigs and my 80 if anyone needs that information). Two days later the new calipers showed up with new bolts and miraculously I was able to get the bolt in and tight. So I just left it at two new calipers, rotors, and pads for now. I will just hold onto the knuckles for spares when they show up.

Man, caliper bolts love to F with you, don't they???

 

[WarDamnEagle]

Man, caliper bolts love to F with you, don't they???

Tight tolerances and fine threads. Sounds like an apt description for other things like occasionally like to F with you.

 

[RUSH55]

Okay full disclosure, this question doesn't pertain to my 55. But the front discs on a 55 and an 80 are pretty much the same....and if I ask this question in the 80 section I will open myself to 10% of the internet.

There's a longer story here that I will share in due course but let's start with the short story. Middle son has been driving the 80 and when youngest son was home he used it for a quick trip and said the passenger side brakes were rubbing. Boy were they. I would say 1/4" of the disc on one side was gone. The other side looked fine. So I installed new rotors on both sides but cannot get the two pistons on the side with the highly worn rotor to compress. I even tried a 4T porta power and no dice. They will wiggle back and forth with a pair of channel locks so they aren't 100% stuck, at least not in all directions. The opposite side cylinders compressed no problem and all 4 compressed on the driver's side without issue.

I have read that they can "pop out" but there is no brake fluid leaking (assumption on my part that fluid would be leaking?). FSM says to just pop them out with air to rebuild them and to just push them back in with the new seals and cylinders, which is exactly what I did on my 55 calipers. The only theory I have is that the first seal ring traveled out but not the second and now the seal ring that is out is somehow preventing the cylinder from compressing back.

I have new calipers on the way so I can just change them but thought I would throw the question out in case someone else has encountered this issue before. Thanks.

View attachment 4197109

So what’s the question?