Is it possible to unstick a frozen brake caliper? - PeachParts Mercedes-Benz Forum

tyl604 · #1 03-11-2016, 11:09 AM

1981 300SD. Before I change my front brake caliper, I wonder if there is really any way to get it unstuck. The piston just does not seem to want to move. I can barely get it to go back in so I can replace the pad which is worn down to the bone. Wondering if the piston has come out too far to go back in?

Is there an alternative to changing it out?

Renntag · #2 03-11-2016, 12:00 PM

It is always possible to rebuild calipers, but they are also so cheap that it is silly to not just replace them. Keep in mind the down side to poorly operating brakes. It's not just your ability to slow down but also a sticky caliper will use up fuel and brake material thus costing your more money.

If you are compelled to rebuild, try soaking the piston to caliper area with a penetrating oil on the outside and on the inside through the fluid port.

We typically use compressed air to push the piston out. Hydraulic pressure will to the same as well. just pump the brakes with the caliper loose and perhaps just the outboard pad to catch the piston as it pops out.

Word to all, this type of issue is avoided by regularly flushing the system every one to two years. Hydraulic fluid absorbs water and thus corrodes over time as it becomes contaminated.

Best of luck.

Carpenterman · #3 03-11-2016, 12:20 PM

x2. I used to fiddle around with rebuilding calipers, but the time and unpredictability of the repair just don't add-up compared to buying a new one.

It was always a time-consuming problem to remove stuck pistons. Most of the time the calipers were un-repairable. The problem is the corrosion of the bore and piston. The bores can sometimes be reconditioned with fine sandpaper, but the pistons are chrome-plated and any corrosion of the chrome means a throwaway.

If they are frozen, they are junk.

tyl604 · #4 03-11-2016, 12:21 PM

Not talking about rebuilding. Wondering if I can get the piston pushed back in so I can put in new pads. I already have a rebuilt caliper and the core charge is only $4 so I might just keep it and experiment with rebuilding it.

For now I just wonder if I can get away without all the labor of replacing the existing caliper. And take the new caliper back.

I could hardly get the piston to push back enough to get out a very worn pad.

charmalu · #5 03-11-2016, 12:47 PM

Just a note to the wise.

If you are going to replace the Calipers, do not buy them from O`Reilly`s.
I just went through this on my 80 240D.
They may say they are ATE`s, and maybe they sort of look like an ATE, but when bolted on, the Rotor will not turn.
http://www.peachparts.com/shopforum/3552003-post23.html

Go to NAPA, and you will get ATE`s with the MB star. Painted a nice Purdy shinny black. Come with new brake hardware.
Around $67 and a $35 core if you don`t have cores to give them.

http://www.peachparts.com/shopforum/diesel-discussion/374065-w123-front-brake-calipers-run-around-auto-parts-store.html

Charlie

ah-kay · #6 03-11-2016, 01:04 PM

Have you tried to loosen the bleeding nipple? I always do that when I try to push the piston back in. I put a good spanner between the worn pad and the rotor, and turn it with another spanner slowly. It will push the piston back. Then tighten the bleeding nipple again. Top up the fluid reservoir if necessary. It always works for me. Give it a try, nothing to lose.

tyl604 · #7 03-11-2016, 01:18 PM

AK - will try that. I actually bent the top ear on one pad trying to get it to push the piston back. Just worried that I cannot break loose the two big 35 year old bolts that hold the caliper on.

What do I torque them to? Is it 85 foot pounds?

ah-kay · #8 03-11-2016, 01:28 PM

My method will not damage the piston as the worn pad is a buffer and turning the spanner will apply force evenly and squarely to the piston. Unless the piston is tilted already :-) I do not know the torque of the 2 bolts holding the caliper, I do not normally look at the spec unless it is engine related. A long breaking bar will always does the job as long as you use the right socket ( use 6 points rather than 12 points ). The issue is that you might not have enough leverage unless the car is on a lift. Jacking it up or on a small ramp limit the breaking bar travel.

tyl604 · #9 03-11-2016, 01:34 PM

Do not understand. Put a spanner/wrench in front of the old brake pad and then turn the wrench with another wrench? Do not know what you mean.

Dan Stokes · #10 03-11-2016, 01:40 PM

I'm not clear if the caliper is frozen or just extended as the pad wore. If it's just extended you can push it back in with a big C-clamp. I have one I bought many years ago just for this purpose though I keep finding other uses for it. Sometimes it can be difficult to push the piston in even on a good caliper. I often find that I have to turn the screw on the C-clam a little, wait for the pressure to decrease a bit, turn it more, repeat.

If you have multi-piston calipers just leave the piston-side pad in place and push all the pistons back together.

If it's seized I agree with the guys - cheaper, easier and more permanent to install a rebuilt unit.

Dan

t walgamuth · #11 03-11-2016, 01:52 PM

I push the pads back in with a larger screwdriver....just drive it between the rotor and pad with a hammer and pry. If you can push the cylinder back in it may well work. I have done it many times....once or twice though I had to replace the caliper which I did with a used one, IIRC and another time with a new rebuilt one.

tyl604 · #12 03-11-2016, 01:53 PM

Have tried with the C clamp but cannot get enough purchase to make it work. I am hoping that it is just hyper extended. Will try opening the pitcock to relieve the pressure on the brake fluid.

Just not sure I have enough strength to bust the bolts loose.

What about torque settings? Anyone know?

leathermang · #13 03-11-2016, 02:12 PM

There used to be available a ' tiny ' scissors jack for EVENLY pushing the pistons back into the bores.... If you had not opened the bleeding nipple already... that may have been your only problem.. otherwise... if that does not work as a solution I really lean towards Renntag and Carpetman's positions....
No matter what you do wear goggles....

Charlie Foxtrot · #14 03-11-2016, 02:30 PM

A failing brake hose is one of the hidden problems associated with stuck piston in the caliper. If opening the bleeder allows the piston to be pushed back into the caliper, you have a bad hose. The hose is acting like a check valve. A thirty+ year old hose that is suspect should be replaced.

leathermang · #15 03-11-2016, 02:43 PM

In WHunter's post...notice the expected safe life of the rubber hoses....and that is with proper brake fluid change out schedule... and delamination is mentioned....

http://www.peachparts.com/shopforum/diesel-discussion/296023-front-brakes-wont-bleed-even-vac.html