Caliper Piston Removal

[Rick Wall]

I plan to rebuild my C brake calipers. I read comments that forcing the pistons out with a grease gun is the safer process. I have two naïve questions. First, should the grease gun fitting attach to one of the bleeder fitting holes, or the flexible hose fitting. Second question, how to clean the remaining grease from the inner plumbing of the caliper once the pistons are out?

[David Jones]

Go to your local hardware store or Harbor freight and pick up a mini grease gun and a couple of grease cartridges. Remove the grease fitting and the male fitting of the grease gun will fit the threads of the caliper connections. Plug one caliper threaded hole with a bleed nipple and use the grease gun on the other to force the piston out. Wash the caliper in your solvent wash tank or in a bowl with mineral spirits or paint thinner.
https://www.harborfreight.com/grease-gu ... 95575.html

[WilliamVaughan]

The concern is that compressed air stores potential energy. Grease alone (without air) doesn't. The stored energy is proportional to the air pressure. When the piston finally breaks free, it can get launched really fast and smash things or hurt people.

[Greg Bryan]

I made a grease nipple by adding it to a caliper bleeder screw - it didn't occur to me that the grease gun thread was same or similar to the bleeder screw thread. The excess grease was easy to wash out as stated above.
Mine were very stuck from sitting for many years and would not blow out with compressed air even though I tried.
Also, someone had powder coated the calipers and that was very hard to remove. The correct coating is zinc dichromate.

[Dick Weiss]

Remove the caliper from the carrier and hang it w/the hose still connected
I've removed caliper pistons (1-@ a time w/the other one blocked) using the brake pedal just enough to get it out; Yes, you hafta catch some fluid, but depress the pedal about a 1/2" to prevent draining the reservoir. Clean the bore if needed, add the square O-ring and dust seals, and install the piston--making sure the relief is aimed in the proper 20 degree direction! Block the piston and remove the other piston per above. Re-install the caliper and continue on the next one.

Otherwise, remove the caliper and its hose connection (for benchwork) and use a mini/3-oz light-weight grease gun (Blocking each piston per above); I use a small Porta-power hydraulic pump w/its oil.
The rear caliper(s) will need a little more work to disconnect the steel brake line to remove the caliper from its carrier and rotor. R & R the pistons per above. Top up the reservoir, flush out each bleeder and start bleeding the calipers starting w/the longest distance (to the rear) and go forward and ending w/the left front and keeping the M/C from getting empty!!! You may need to bleed the system twice and even after a drive to seat-in new pads(?) to get a pedal "feeling"; Calipers may act differently vs. drum brakes
during the 1st 50-100 miles.

[Harlan Halsey]

I have used the grease gun method, I even have a fitting which screws into the hose thread, but that method takes a lot of grease and is very, very messy. And I was never sure that I got all of the grease out of the small passages.
Now, I drain the caliper and clamp it in a bench vise. Close the bleed screw. Put a block of wood between the calipers with about 1/4" clearance. Then put 100psi air to the hose connection briefly with a rubber seal. One piston will move and clamp the block. Repeat with thinner blocks until the piston just comes out. Now put the piston lightly back and hold it with a C-clamp. Repeat the process with the other piston never allowing more than 1/4" travel. When a piston comes out the air will blow a little brake fluid so cover with a cloth.
It is true that air pressure can do real damage unless the piston is constrained. It is also true that a simple grease gun can easily develop a pressure of several thousand psi. However I have never had a piston so stuck that 100 psi air wouldn't do it easily.

[Vic Skirmants]

"never had a piston so stuck that 100 psi air wouldn't do it easily."
You don't live in the great salt-north!
One important thing to add to the discussion: Be sure to "exercise" the pistons! The square cross-section O-ring needs to flex into position, otherwise the piston gets pulled back slightly upon brake release. You'll never get a good pedal until you wear the pads down somewhat.
After brake bleeding, remove one pad and substitute an old thin one, then pump the brakes. Push the piston back and repeat. Do this at least two times for each piston. You will notice an improved pedal with each one you do. Yes, it's tedious; but you can't do it any other way that I'm aware of.
I've been preaching this for close to 50 years, and can't believe it still is a mystery to everybody.

[DonCichocki]

After a caliper rebuild I had the soft pedal situation. Followed Vic's advice and now a perfect pedal. Thanks Vic!

[Vic Skirmants]

Thanks for listening, Don!

[Rick Wall]

Thanks everyone for your detailed advice, always appreciated. Because the car was last driven in 1972, I am in the process of replacing all lines in the car, including the tunnel hard line. I would have used Dick's first suggestion, but all parts are now on the bench, plus the flexible lines were collapsed. The old pads were still thick, so all the pistons are still recessed in the calipers. I will try David's Harbor Freight grease gun plan first, then consider using air to remove if no success. Obviously I need to plug the flexible hose hole on the caliper with a bolt. I will exercise the pistons as Vic points out. Thanks again.

[Emil Wojcik]

I used compressed air for one caliper and after the piston shot out fast enough to dent the piece of wood I had it aimed at, I decided that wasn't a good idea...scared the crap out of me. Did the next one with grease and it worked just as well and was much safer albeit a bit messy.

[Geoff Fleming]

My own, personal method of removing the pistons, is to use an old master cylinder, with reservoir attached, mounted on a block of wood with an old brake pedal assembly fastened., It is very easy to now pump the brake pedal on the board and have the pistons come free. Of course, you do use some brake fluid and will need a splash pan underneath the caliper to catch the fluid once the piston is free. The piston comes free without any drama, such as found with compressed air.
I use a small C clamp on one of the pistons to prevent both from moving simultaneously. No grease to clean out from the caliper. Since I had the old parts sitting around, unused, I felt it was best to utilize them to my advantage. Have used it for many years with great success.
Vic's mention of the 'great salt North' is well heeded!

[David Pateman]

I will try David's Harbor Freight grease gun plan first, then consider using air to remove if no success.

Please do not use compressed air. I continue to use a master cylinder and pedal box combo to hydraulically force pistons out. More force can be generated hydraulically than by compressed air, and it is far safer. If hydraulics cannot do it, then compressed air would be the equivalent of a bomb. There is no great need to struggle; just send calipers to PMB for restoration. Replating is generally better than trying to paint.

[Vic Skirmants]

If a grease gun won't do it, I guarantee compressed air won't either.

[Wes Bender]

... but the excitement factor is much higher with compressed air.