Self inflicted Brake calliper woes.

Shep57 · 2026-05-16T01:05:49-0600

The current 850 project has just been a long list of problems to solve, no real surprises but absolutely everything has had to be replaced or repaired. The one thing that was in reasonable good condition was the front caliper, absolutely spot on condition, just needed seals and stainless steel pistons like the dozen or more I've done over the years. It came apart easily, it got a dip in the ultrasonic to clean it up and a quick reassemble, job done, right? .........er no.......the seal fitted easily, the inner piston popped it nicely.............oh bugger! Wrong way around!!! Try as I might I can't get it to blow out with an air line, at least I know what I'll be doing today!!! Years ago I found a calliper that had a hole drilled in the blind side of the calliper with a neat well sealed screw blanking it off....... I suspect that now I know why!!!

baz · 2026-05-16T01:16:03-0600

Shep57 said:
The current 850 project has just been a long list of problems to solve, no real surprises but absolutely everything has had to be replaced or repaired. The one thing that was in reasonable good condition was the front caliper, absolutely spot on condition, just needed seals and stainless steel pistons like the dozen or more I've done over the years. It came apart easily, it got a dip in the ultrasonic to clean it up and a quick reassemble, job done, right? .........er no.......the seal fitted easily, the inner piston popped it nicely.............oh bugger! Wrong way around!!! Try as I might I can't get it to blow out with an air line, at least I know what I'll be doing today!!! Years ago I found a calliper that had a hole drilled in the blind side of the calliper with a neat well sealed screw blanking it off....... I suspect that now I know why!!!

Use a grease gun and pump it out

JimNH · 2026-05-16T05:37:38-0600

Yes! A grease gun can build up tremendous pressure.

Grandad · 2026-05-16T06:38:06-0600

How about heating the caliper for differential expansion ?

A grease gun is safer than compressed air

Shep57 · 2026-05-16T06:43:17-0600

I drilled a hole and pushed it out, tapped the hole 1/4 UNF and glued a screw in with red locktite, I'll keep an eye on it.

dobba99 · 2026-05-16T06:52:00-0600

People drilling holes in calipers to knock out stuck pistons are the people who do not understand hydraulics and can't figure out how to pump the pistons out. My favourite trick to remove a stuck blind side piston is to fit a grease nipple to the bleed screw hole and then block the ports in the caliper bore (outer piston removed)
I do this with a turned aluminum sleeve split in two, wrapped in PTFE tape and expanded against the ports with a short nut and bolt. Doesn't mark the bore and seals wonderfully. Never failed to remove said stuck piston. The longest part of the job is cleaning all the grease off afterwards.

B+Bogus · 2026-05-16T08:20:11-0600

Alternatively refit the caliper, bleed the system and use the master cylinder to do the job, perhaps?

olympus · 2026-05-16T10:08:21-0600

Shep57 said:
I drilled a hole and pushed it out, tapped the hole 1/4 UNF and glued a screw in with red locktite, I'll keep an eye on it.

No no no....

Shep57 · 2026-05-16T10:14:25-0600

olympus said:
No no no....

Too late now!

velo54 · 2026-05-16T18:07:17-0600

Probably absolute max 1000 psi. Screw will be fine. Graham

Self inflicted Brake calliper woes.

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