brake piston wont retract
 

i changed out my rotors no problem. i am now stuck on retracting the piston so i can put new brake pads in. someone help me!!!

i set the piston compressor up and nothing has happened. do i have to recondition the calipers?

If it is not new and has not been subject to regular brake fluid changes, it is possible that the piston or bore could be a little rusted and not allowing the piston to slide freely.

Have you opened the brake oil reservoir cap?

i opened the resevoir cap and nothing happened.

If you release the bleeder and it won't move back in its a piston/bore issue.

If it does move back in with the bleeder screew loosened then you have a hydrolic system issue.

Most likley frozen caliper.

The caliper piston develops a ring of rust in front of the seal. This effectively acts as a stop to the piston moving back.

You can buy caliper overhaul kits. However, don't buy anything until you have removed the caliper piston.

Loaded calipers are best bet if car is a keeper and you must do both sides.
Plus, new calipers will carry a warranty and be service free for many years.
Changing the brake fluid is always advisable every two to three years. If though, the rubber dust covers split, the piston will rust within one winter.

I am trying to prevent this by using a synthetic brake grease made by VERSACHEM...thick, sticky, clear grease.
Working in the UK, this problem was very prevalent and most calipers after 8 years on salted roads where shot away with rust.

I use a medium size G cramp to push the pistons back on the front axle
on single piston calipers..
If you take it to the bench to remove the piston, be very careful about applying compressed air to blow the piston out.

Use a lot of shop cloths to cover the complete caliper and keep fingers and body parts clear of the piston.

If you do not feel competent to overhaul with a kit, buy rebuilt or new units.
It is very difficult to get all the rust out of the seal groove and make the new seal fluid poof.
any rusting to the piston that lifts or opens the chrome finish, is cause for new calipers.

I have to ask this question...


Did you by chance remove BOTH calipers at the same time? and push one caliper in while the other was still off?

Reason i ask if you didnt know is if a piston becomes over extended you effectivly ruin the caliper and it will require a rebuild. and if both calipers are removed at the same time and one if retracted the pressure in the system pushes the other out past its max...


If not disregard this post.

i only had the left front caliper removed. i did however, stupidly, push the brake a few times while the caliper was not exposed to any reverse force.

I replaced all four of my calipers soon after buying my car - as I recall, 2 were shot and two were on the verge of going. My brake fluid looked like sour milk. The price of new calipers from MB for a 560 is frightening; so far, so good with much less expensive, lifetime waranteed Advance Auto (rebuilt by Cardome?) calipers, and nice, new, clean fluid, which will be changed religiously every 1-2 years. Much cheaper than 4 new calipers, especially DIY.

i looked at my brake fluid and it is a clear light brown.

Is this generically known as silicone grease? We often call it dielectric grease.

I got good advice from the BOBISTHEOILGUY web site where one guy says to butter all the caliper bore and piston surfaces with this grease to preclude corrosion. It won't wash out, nor interact with the elastomers or brake fluid. I just tried it on new wheel cylinders I replaced on another car. We'll see how the field trials go.

Is this the same or comparable stuff?
Top item: Caliper Slide Lube (N1052-42057)
http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1FX0MB1RS1GG0LM0QO&year=1986&make=MB&model=300-E-002&category=N&part=Brake+Anti-Squeal+Paste

I'm pretty sure it's the same stuff. I didn't see the word 'silicone' on the tube, but Sil-Glyde is another trade name tossed around when talking about silicone lubes.