Brake Caliper Question. - PeachParts Mercedes-Benz Forum

tobybul · #1 08-31-2007, 10:47 AM

I'm working on one of my D's and am wondering if I need to change my caliper if one of the inner pistons is not budging? I'm just changing pads. Thanks.

tangofox007 · #2 08-31-2007, 10:53 AM

There is a good chance that new seals and boots will restore normal function. But you won't know until you get the pistons out and inspect the pistons and bores for rust and pitting.

tobybul · #3 08-31-2007, 11:12 AM

Quote:

Originally Posted by tangofox007

There is a good chance that new seals and boots will restore normal function. But you won't know until you get the pistons out and inspect the pistons and bores for rust and pitting.

Never dismantled a caliper b4... is it a DIY'er? It seems a repair kit is available...

tangofox007 · #4 08-31-2007, 11:19 AM

It helps to have an air compressor with a blow gun. The bores cannot be honed, so all you can do is clean things up and renew the rubber components.

Often, the cause of the stuck piston is gunk that has built up due to a torn dust boot. And the square seal gets tired with age.

On the front calipers, install the heat shields before reinstalling the pistons. The instructions call for the opposite, but assume that you have the special tool for installing said heat shields.

Do not separate the caliper halves.

Brian Carlton · #5 08-31-2007, 11:30 AM

Quote:

Originally Posted by tobybul

Never dismantled a caliper b4... is it a DIY'er? It seems a repair kit is available...

You can do it yourself. But, I don't wish to minimize the effort required the first time. Getting the piston installed without binding is no easy task. Getting the pistons out is even more difficult.

If one of the pistons is frozen, you won't be able to remove it with compressed air........you'll need the hydraulic system of the vehicle. Naturally, you can't just press on the brake pedal or you'll blow the non-frozen piston right out of its bore and then you'll have to seal that bore to get the frozen one out. So, you've got to use a set of clamps and a steel bar to prevent the non stuck piston from moving until you get the stuck one out with hydraulic pressure.

Then, after the stuck one is removed, you need to rig up a device to hold air in the open bore so you can use compressed air to remove the non stuck piston.

Like I mentioned.........the job is not for the faint of heart.

tangofox007 · #6 08-31-2007, 12:03 PM

Quote:

Originally Posted by Brian Carlton

If one of the pistons is frozen, you won't be able to remove it with compressed air........

As with many things, it's a matter of degree. I have removed more than a few stuck pistons with compressed air. Often times, forcing the piston inward first will break things loose, then it will blow out.

When one is really stuck, I just reinstall the caliper on the car, leaving the pad out only on the side that is stuck. Then slide a piece of sheet metal between the piston and rotor (to protect the rotor), then apply the brakes.

tobybul · #7 08-31-2007, 12:12 PM

Quote:

Originally Posted by tangofox007

As with many things, it's a matter of degree. I have removed more than a few stuck pistons with compressed air. Often times, forcing the piston inward first will break things loose, then it will blow out.

When one is really stuck, I just reinstall the caliper on the car, leaving the pad out only on the side that is stuck. Then slide a piece of sheet metal between the piston and rotor (to protect the rotor), then apply the brakes.

thats actually what I did last night. Replaced the pad with a thinner, old pad and applied brake. Piston moved out. I plan to go back in there this weekend.

I decided to look last night b/c noticed car pulls to one side when braking. realized most like due to one piston not doing its job.

Brian Carlton · #8 08-31-2007, 12:14 PM

Quote:

Originally Posted by tangofox007

As with many things, it's a matter of degree. I have removed more than a few stuck pistons with compressed air. Often times, forcing the piston inward first will break things loose, then it will blow out.

When one is really stuck, I just reinstall the caliper on the car, leaving the pad out only on the side that is stuck. Then slide a piece of sheet metal between the piston and rotor (to protect the rotor), then apply the brakes.

Agreed. But, 125 psi will generate about 200 lb. of force on the piston.......not all that much if it's frozen.

I don't think the piston will clear the cylinder if the rotor is in the way.........but, it should certainly break it loose sufficiently to finish it with compressed air or by hand.

tangofox007 · #9 08-31-2007, 12:23 PM

Quote:

Originally Posted by Brian Carlton

I don't think the piston will clear the cylinder if the rotor is in the way.........

It won't. Nor do you want it to.

tobybul · #10 09-10-2007, 08:24 AM

I consulted a mechanic that frequently works on 123s and 126s. His advice is to replace the caliper. He said he has gone thru refurbishing a few of them with rusty pistons & cylinders but has found that they don't last very long.

Long story short, I found a good, used caliper and installed it.

Now here's a question/observation. The caliper I removed was a Bendix (must be made by Gerling? Usually, brand on the master cylinder and/or brake booster is same as caliper. No lablel on MC but BB says Gerling.) The replacement caliper is an ATE and it fits perfect. Supposedly, the brake fluid line location is different between the 2 brands but this one is the same.

Test drove and no more pull when braking.

vstech · #11 09-10-2007, 08:51 AM

that's cool. it is generally accepted here that you should have matching brand calipers on each side. front to back is not as important as side to side. they both work fine mixed and matched, but be sure and keep close track of the spring/pin for each side, they will not fit vise versa. make sure that you flush out the brake lines on the rest of the system, fresh clean fluid will prevent further brake down...

tangofox007 · #12 09-10-2007, 09:25 AM

Quote:

Originally Posted by vstech

it is generally accepted here that you should have matching brand calipers on each side.

Here is a quote from the W123 service manual:
"Calipers from different manufacturers may be installed on the rear axle."

vstech · #13 09-10-2007, 09:28 AM

I was saying that they should match side to side, but they will work mismatched.

tobybul · #14 09-10-2007, 10:18 AM

Quote:

Originally Posted by vstech

that's cool. it is generally accepted here that you should have matching brand calipers on each side. front to back is not as important as side to side. they both work fine mixed and matched, but be sure and keep close track of the spring/pin for each side, they will not fit vise versa. make sure that you flush out the brake lines on the rest of the system, fresh clean fluid will prevent further brake down...

I sat the pins side by side and they are same size. Only diff is Ate pin does not use a cotter pin to keep pin inplace at the end like the Bendix. Ate uses a tensioner sleeve at the head. Also, the Ate spring clip is just a different design but fits the Bendix just the same.