Stuck piston

ScottST

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Joined
Aug 25, 2024
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46
Age
61
Location
Indiana
Hello,

I have my rear caliper off and was planning on cleaning it and reinstalling it. Unfortunately, the middle piston is stuck.
I have a compressor but I’m wondering if there’s another way to unstick it.
Also, will I ruin the seals when I pull them?
I also removed the rear tire so I could install a new caliper bracket.
The bearings seemed smooth so what else should I address before I reinstall it? Grease the drive gear? Does it require “special” grease.
How about the axle. It has some pretty sticky grease on it so, should I clean it off and apply new?
 
Strike the stuck piston question. Compressed air got them out
 
If the middle piston is stuck, then it is likely that you need new seals and new piston anyway.

The best way is to push them out while there is still fluid pressure. Probably too late for that. Compressed air is what I normally use - but I've never had one stuck. At least you don't have to worry about air escaping via the other piston bore, like you do for the outer 2 pistons.

There are 4 bearings in the rear wheel. If you want to check the other two, you have to pull out the plate that holds the final drive spline. It is locked in place by a very large circlip. Easy to get out - pry it gently from one end and ease it away a bit at a time. These seem quite fragile in comparison tot he main wheel bearings.

The drive splines need the correct Moly Paste. It's not cheap. Loctite 51048 or Loctite LB 8012 (either - they are different codes for the sam stuff) they seems to be the easiest to get hold of. That or Rocol Dry Moly Paste.

Axle - it is just to protect it so a smear of general purpose grease is all that is required. Or if you've been applying the moly paste with an old toothbrush, then wipe it off on your axle. Not the threads.
 
If the piston is not all the way in and stuck, clean the area around it very well, lubricate it with DOT4 and push it is with a C-clamp. Then used compressed air to ease it out. I would keep the C-clamp in place to keep from shooting it across the room. I would use new seals on reassembly.

As for drive spline grease, see the discussion in this forum. I used Loctite LB 8012 low friction lubricant.
 
I wonder how many uses that is? I can’t see myself needing to do this job again for a long time if ever.
I’m not a distance rider
 
Still required to lube the splines at intervals, the paste can dry.
It's not just miles, but time that affects the stuff. And it's really cheap insurance compared to replacing a wheel and driveshaft.
 
ScottST said:
I wonder how many uses that is? I can’t see myself needing to do this job again for a long time if ever.
I’m not a distance rider
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I certainly hope that you will do enough riding to need to replace the rear tire at some point. The maximum interval for re-application of this lubricant is every time that the rear tire is replaced. An argument can be made for it to be done every time that the rear wheel is removed regardless of whether that is for a tire change or not.
 
ScottST said:
How much time?
Click to expand...
When it was explained to me, time was not the factor, I never asked. One could put some in a dish, lightly covered, report back when it dries.
It's a commonly accepted theory that a non ridden bike will decompose faster than a ridden one.

I certainly did not intend to give you something to worry about... plenty of bikes are wintered over for months with no ill effects, save the riders getting cranky. One of Larrys superpowers is to keep the ST world rolling, fear not Scott.
 
Sorry I didn’t bring this thread to a solution. I rebuilt the rear caliper with the help of IGOFAR. New pistons, seals, pads, all calipers cleaned thoroughly, SMC and a complete brake bleed and I have fantastic brakes!
 
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