How do you remove a piston from a caliper?

[willie]

I was able to get the piston out of one side (half) of the caliper by using the master cylinder to pump brake fluid in to the caliper. But, naturally, once one side came out, the other no longer had any pressure behind it. I have split the caliper in half so I'm left with the one side that has a piston in it. I've tried compressed air but it didn't budge. I'm open to suggestions.
Willie

 

[Agemax]

is it far enough out the caliper to get a pair of mole grips on it? soak it in wd40 or similar than grab it with the grips. try and clamp it on an edge or lip that does not come in contact with the seals, just in case you scratch it (unless you plan on replacing it,which case it doesn't matter)
pull it out with a side to side twisting motion. it should ease out ok

 

[cowboyup3371]

What Agemax said or use a pair of screwdrivers to gently pry up on the lip of it until you can get in there with a set of pliers to finish pulling out.

 

[Johno]

I was able to get the piston out of one side (half) of the caliper by using the master cylinder to pump brake fluid in to the caliper. But, naturally, once one side came out, the other no longer had any pressure behind it. I have split the caliper in half so I'm left with the one side that has a piston in it. I've tried compressed air but it didn't budge. I'm open to suggestions.
Willie

Compressed air!

 

[bluewool]

Grease gun.

 

[jeff.saunders]

The last resort is to drill a largish hole (8mm-10mm) in the piston, tap a thread in the hole, insert a bolt and jack the piston out. While this destroys the piston, it is about the only way if compressed air doesn't budge it.

 

[willie]

Thanks guys. Hard to believe but the piston doesn't have a groove or lip to get a screwdriver on to pry. Its also not out enough to getta grip with a visegrips. The other piston was in good shape and NOS parts for a '77 RD400 are tough to find. I tried compressed air before but it didn't budge. I'll try that again tomorrow. I've thought about using a grease gun and feel it would work IF I could figure out how to connect to one. So, Bluewool, it was your idea. How do you suggest I hook up the grease gun, without sacrificing a brake line and banjo?
Thanks again,
Willie

 

[Maddevill]

Compressed air should work. You may have to up the pressure. Keep a towel wrapped around it so it doesn't fly across your garage and punch a hole in your wall.

 

[bluewool]

I put the grease nipple in where the brake line goes. Did it on the rear master for the 1150 and a couple of front calipers for rd350. Maybe I got lucky but the nipples were the same thread pitch as the brake line.

The pistons are available from HVCcycle

Here is a link to a RD400 parts list

 

[Wizard]

C Clamp

C Clamp

If your loose piston is still in place, (or put it back in), put a C-Clamp on the loose one, so it can't move anymore, put hydraulic pressure back in there, make the stuck one pop out.

 

[bwringer]

Assuming it's a caliper that's in halves you bolt together (no idea about the RD, going on GS knowledge here), you disassemble the halves and then block the hole that feeds the other caliper half. I use a chunk of old inner tube and a c-clamp.

 

[willie]

Assuming it's a caliper that's in halves you bolt together (no idea about the RD, going on GS knowledge here), you disassemble the halves and then block the hole that feeds the other caliper half. I use a chunk of old inner tube and a c-clamp.

It is indeed the kind that bolts together. I was thinking of trying the very same idea. That oughta work.
Wizard's idea would work also, thanks if I want to wait until I replace the seals in the half that I was able to remove the piston from. Then I could reinstall that piston, limit its travel with a C-clamp, and drive it out using hydraulic pressure from the master cylinder. Either way, I think the C-clamp is the key to making it happen.
Thanks guys and happy new year.
Willie

 

[hampshirehog]

You don't even need the C clamp - just a couple of short bolts or similar that you put against the free piston on one side and against the body on the other.

 

[rustybronco]

I put the grease nipple in where the brake line goes.

Or, Make a block off place for the side to side fluid transfer port, install a bolt into the brake line port to close it off, then loosen the brake bleeder and put the grease gun fitting over the open bleeder and pump away.

You can also block the transfer port off, pack the caliper with chassis grease and repeatedly screw a bolt into the brake line port - refilling with grease as necessary. It's a slow method but it works.

 

[bluewool]

Or, Make a block off place for the side to side fluid transfer port, install a bolt into the brake line port to close it off, then loosen the brake bleeder and put the grease gun fitting over the open bleeder and pump away.

+1 That may actually have been what I did.. I know I had to install the nipple in the 1150 master. It's been 15 years since I did the rd callipers.

 

[willie]

Or, Make a block off place for the side to side fluid transfer port, install a bolt into the brake line port to close it off, then loosen the brake bleeder and put the grease gun fitting over the open bleeder and pump away.

Another great method. Unfortunately, if memory serves me right, for once, the bleeder nipple is on the side opposite the side with the brake line port. And, as my luck would have it, the side that is stuck is the side with the brake line port. I'll have to wait until I return to work on Wed to try the compressed air approach. One way or the other I'm confident that I'll pop that piston out, thanks entirely to the responses to my post.
Further proof that the members of this board are incredibly helpful (and appreciated).
Willie

 

[Wizard]

Ballistic

Ballistic

I would be nervous about using Compressed Air.
It would need a lot of PSI.
Once it gets moving the piston can go Ballistic, just like a Potato Gun.
Wrap some wire around it, so it doesn't go into the wall, or you.
Still like the C-Clamp method better, so easy.

 

[Agemax]

if you havent tried it already, push the piston back into the caliper before trying to blow it back out again. it may just break away the ring of rust and crud thats stopping it from moving now. plenty of wd40 or similar to help ease the situation

 

[Agemax]

I would be nervous about using Compressed Air.
It would need a lot of PSI.
Once it gets moving the piston can go Ballistic, just like a Potato Gun.
Wrap some wire around it, so it doesn't go into the wall, or you.
Still like the C-Clamp method better, so easy.

compressed air is fine as long as you wrap the caliper in rags or hold it face down flat on a soft surface (pile of rags) and hold tight when blasting

 

[willie]

Although I like your idea re: pushing the piston back in to the caliper, cleaning the crud from the bore and pressurinzing it out, I was worried about losing the headway I'd made by getting it out as far as I did before the other piston popped out. At this point I doubt it would take any more effort/pressure to move it the entire length vs the remaining 1/2" so maybe I will try pushing it back in. As for Wizard's concern re: it going ballistic...I was definitely planning on wrapping a rag around the caliper to prevent the piston from becoming a projectile. I've done this before and found the rag also prevented contaminated brake fluid from being sprayed all over the place.
Willie