Brief review and critique freeing caliper pistons

[lakeview]

So I have several projects going on which means I try to group together similar jobs. Last week I rebuilt 2 sets of 34mm forks, installed brass bushings in two swing arms and changed steering head bearings in three bikes to tapered. I have a pair of two piston front calipers to rebuild and read up on the techniques before I started.

Mounted a master cylinder near on my work bench and started to free up the caliper pistons. One came out easy, I then butterflyed that caliper and was able to get the other out. By then, my finger tips were all wrinkled from the brake fluid. (Gloves had come off about ten minutes in). The two remaining halves spent overnight in vinegar.

Next I took them out and hit them again with penetrating fluid and tried again with the master cylinder to get the pistons out, nothing. Then tried air pressure, no go. Another overnight in Evaporust. Brake fluid under pressure finally spat the second last one across the bench.

I went to Canadian Tire and got an 8 mm grease zerk that fit into the bleeder hole, blocked off the other hole with a cardboard gasket and a piece of metal bolted over it and started pumping grease. About 15 pumps and the piston is almost out, one last little squeeze and the piston is finally free! There was about a tablespoon of grease that finger-wiped out from the caliper and went right back into the cartridge. I had been worried about grease all over the place, but didn't happen.

So, the take away on this tale to you members just starting, read the tech section and try it! Don't be a sceptic like I was. The regular contributors here have done it before so follow their lead.

And those of you with post counts way up there, thank you for your input, guidance and often, patience. Even the most callow questioner may turn into a valued contributor.

 

[angus67]

Rite on! I've never tried the grease approach, always used air.
So grease doesn't go flying? Guest-a-mate on how much pressure u used? Did the piston just slob out? Or did it pack a punch?

 

[lakeview]

Using grease the piston just sort of gave up and wimped out, no explosion. I was using an old style manual grease gun and it took at least 15 lever pumps to get it to start moving. Once it was moving, you could see the progress of it coming out and slow up on the last couple strokes.

My attempts at using air on the half with the bleeder were tough as the only way to get the air to it was to back off the bleeder a bit and use that to put the air through. Even with a rag "gasket" over the bleeder, I was never really sure if air was actually going in or just leaking around, plus I was using my little 2 gallon unit as my big one was out in the cold garage.

 

[gggGary]

Good to hear that the forum is being used in such a great way! Minor point for next time. When removing stuck pistons I apply rust buster on the outside then begin by C-clamping the piston IN a bit. That gets it freed from the years old, rust, gunk bond, then start trying to get it moving OUT. Some back and forth really reduces the effort needed. I have used grease in the past but with the push in to start air, has gotten out some REALLY ugly lumps. Push it out a little. Stop, C-clamp the piston back into the caliper a bit, more lube, go back to pumping it out. Giving back your hard gotten gains by pushing it back in seems counter intuitive, but it really works, speeds things up and reduces damage to parts.
A rubber tip blow gun makes for easy sealing when using air pressure. And don't forget to wrap it in a rag....

 

[lakeview]

Well the C-clamp and rust buster got a work out in that episode as well and counter intuitive it is for sure. I think all the tricks and tips contributed to that last lump coming loose.

One thing about C-clamps I have read in your previous posts that still eludes me is their use on fully assembled later brakes that have seized up to get the wheel rolling so the bike can be rolled out into the light. To me, there does not seem to be any access to back the pad off with a clamp on a fully assembled caliper on a wheel. ?

 

[gggGary]

C-clamp won't always work. Better chance getting the clamp in there with mags. Truth be told I am still looking for the magic retracter to "get em to the light of day"! I'm pretty sure even if I build the perfect retracter I 'll forget to bring it along, and'll still be dragging them out kicking and screaming. I have a real challenge early caliper I can send you...........

 

[lakeview]

No thanks, I am old enough to know to pick my battles lol.

 

[fredintoon]

Rite on! I've never tried the grease approach, always used air.
So grease doesn't go flying? Guest-a-mate on how much pressure u used? Did the piston just slob out? Or did it pack a punch?

Hi angus,
the average el-cheapo side lever action grease gun will develop over 1,000 psi.
Lotsa pressure but very low flow so nothin' spurts.
It'd only spurt if there was air in the line and if those guns get airlocked they don't deliver any pressure.

 

[CDNTX650]

I used a grease gun to separate mine. It worked well. No flying grease. But a bit messy. Worked well though.

 

[lakeview]

Here is a couple pictures of my grease gun method. The last caliper I had to open up was really stuck, a c clamp would not even move either piston. I soaked the caliper for a couple days in vinegar and then made a block off plate from a handy bracket. With the grease zerk in place of the bleeder, the piston gave up quite easily. For the other side with the brake line going in, I tapped the inside of the brake fitting to take a 6 mil grease zerk and was able to pump it out as well. For all their stuck-ness, only one piston appears pitted, I will see what it looks like after it comes out of another vinegar bath.