Dual piston caliper rebuild

Greetings, all,

I'm in the process of extracting the pistons from my calipers for a rebuild and am totally confused as to how to get the second piston out once the first one is removed.

Using a c-clamp I was able to get one piston out using the pressure in the master cylinder, but if I put it back in to build pressure and remove the second one, there isn't enough room to both have the re-inserted piston in and have clearance to extract the second one. I hope all that makes sense: I get one piston out, to maintain system pressure and get the other one out, the first one has to go back in - zero sum game.

Need help. Thanks.

 

There should be a Bleeder on both sides.

Pull the Bleeder.
Insert a Zerk Fitting for a Grease Gun.
Hit that side with some High Pressure Grease.

Out she'll come.

 

That works well but if your grease gun keeps popping off as my old one did, you can just reconnect the master cylinder, reinsert the removed piston (if they are connected, Rick knows these bikes much better then I do)and hold it in about 1/2" with two C-clamps and a bar of flat stock across the face and use the master cyl to pump the other piston out. Then remove the c-clamp and remove the first piston.

jeff

 

insert the first piston. put a block of wood inside the caliper. thin enough to leave room so that both pistons pop out. take out the bleeder and pump compressed air into the caliper. the wood allows the pistons to pop out but not enough to fly out at ya.

since the first one is popped out. it might be easier coming out then the second piston. in which case use a c-clamp to hold the first one in JUST enough to hold pressure so that the second one pops out.

 

As a last resort, you can spray around the Caliper with a solvent that will ruin the Seal and make it spongy.
Then the Piston should blow right out of there.

You are going to have to replace the Seals and have considerable work to do cleaning-up that Caliper, anyway.
The reason its stuck is because the Seal has gunk in the channel holding--n to the Piston.
That all has to go.

A Grease Gun or High Pressure Air usually does the trick.

You can look at the Front of the Piston and look for the Shadow that stays exposed to the elements and "Grab" onto the Shadow marking with Pump Pliers or Lock-on's.

 

You have to be real careful grabbing with pliers, where the piston WAS riding and where it WILL BE riding with new pads are quite often vastly different... I ruined one myself that way.

It's also been my experience (on the last 3 XJ calipers I've done) that compressed air, even at 125psi, is often useless. If that happens, the grease gun trick is the best and safest bet.

 

Make sure the Piston is not C0CKED to one side of another.

Just being out of position a little bit causes binding that is hard to overcome.

 

125 won't even get the tires off my car.

most of your big shops run 2 50 gallon compressors at 175. i run my home compressor at 160.

 

I did mine one at a time. Just finish one side first, and you'll have more than enough pressure to push the second piston out.

 

Dig, guys, I'll give it another go as soon as it's warm enough to get outside again. Had one day above freezing and now it's below 20 again. C'est la.

I guess I was confused because it didn't look like there is enough clearance for one piston held in by a c-clamp and room for the moving piston to come out far enough to pull out by hand. I'm using a fairly small c-clamp, but it still takes up room in the caliper body gap. I don't want to use pliers for fear of damaging the piston. Isn't there a tool specifically designed to extract pistons from calipers?

BTW: I've only tried to remove pistons from one caliper so far and neither one was seized. Both were moving pretty freely when I pumped the brake.

 

If the Piston won't budge from the Hydraulic Pressure supplied by the Bike's Master Cylinder you sometimes need to employ creativity.

Try pushing it out with a line hooked-up to a high-pressure grease gun ... or,

Bring the Caliper and the Banjo Bolt and Washer to an Automotive Brake Specialty Shop

(Have a real pretty girl bring it in and they'll "Stop-the-Music" and fight over who gets to do it.)

Or, ... My personal favorite.

On the way to the Brake Shop ... stop-off at Duncan Donuts and get a few Medium Blacks with all the fixings on-the-side.
Hit the Brake Shop with the rack of Coffee's and stuff in one hand ... and your Brake Caliper in the other.

Tell the busiest, dirtiest, sweatiest guy, wrestling with the most thankless brake job in the place, that God answered his prayer and sent you with Coffee for him and his pals.
Blacks, with all the fixings on-the-side.
One's just for you!

Oh, by the way ... while you're enjoying the Coffee ...
God also wants you to hook-up this little Caliper to the high-pressure and get the Caliper Piston out!
He sent me to see the right guy; right???

 

PMSL You're one smooth operator Mr Comatic!

 

I used a heat gun and a special slide hammer I made that uses a rubber expansion plug to remove the pistons.

 

Sounds good...photos?

 

I just rebuilt my twin piston xj 900 calipers last week with kits supplied by Len. First, resist the urge to separate the two halves, especially when it comes time to clean out the grooves! My rear caliper has two bleeder screws, but both front calipers only have one. It is freezing here also, so the calipers were removed and in the warm basement. I used a very small air compressor, applying air carefully to the line fitting, leaving the bleeder in place. One piston will move more easily than the other, so proceed carefully so as not to pinch the fingers! Once the "less stuck" piston popped, I pried out the two seals and replaced the piston in the now naked bore. More compressed air was used while holding the unsealed piston in place with a pliers and protective rag. You can apply a lot of air pressure to the stuck piston when the other piston is held firmly to the bottom of the bore, surprisingly little air bypasses the missing seals. That was all that was required to extract the opposite piston. Once the second piston is out, the first one will fall out of the bore. Worked flawlessly on my 6, sticky, 28 years, never been apart caliper pistons.

Dave

 

Just wanted to say that I have one of those air pumps that plug into your car, and it popped all the pistons out REAL quick. The first caliper I used a grease gun, and then used the pump to blow out all the grease. Then im like.. Hey! I'll just stick this in there. Worked every time
-Chris

 

+ One --> Grease Gun

 

Grease gun worked great for me also!!!!!!
Just finished the rebuild today
Life Is Good - Welllllllllllllllll - time to bleed the system.