rebuild front brake calipers

All,

My 93 400e is making a thrumming noise from the front that goes away when I touch the brakes. I suspect a sticky front caliper.

Since new calipers are so expensive ($750) I am going to attempt a rebuild of the old ones. I have the kits.

Any input about caliper rebuild in general, or information about who could do it, would be greatly appreicated.

tia,

Jack
93 400e

[jeffsr]

Jack, does this post relate to the one you put up re the front wheel bearing noises?? You may just have a warped rotor. Does the pedal pulse at all? You should try to eliminate simpler problems before rebuilding calipers. Is the noise from one side or both. A better description of the noise would be helpful..

[Ashman]

Boy am I glad this post turned up. I myself have a small brake squeal at any speed when driving. What I have noticed is these items which may be causing the problem...

A Lip on the rotor that is quite high off the surface of the rotor around the edge. I would think this means the discs need to be replaced, and at the great prices on partsshop, even if its not the problem, it gives me more peace of mind.

Other than that, new pads and I think I will have my problem solved.

I suspect a warped or overly worn disc.

I myself will be repacing the discs and pads before I bother with looking into the calipers which are not something I want to have to rpelace just yet.

If I gotta replace the caliper, I might as well do both at the same time just to be safe hehe. of course I'm sure I could save lots of cash by doing just one caliper, I figure replacing them in pairs is just for better peace of mind. to me brakes are the most important feature on a car.

Alon

Yep, this post is the sister to the wheel bearing post. Since I am in there, I figure I will do both at the same time, especially since the brake bolts have microglue on them and need to be replaced every time you use them. Dang Germans, gotta love em.

Just had front rotors and pads done three months ago (ouch, gotta learn to do that myself.)

No pulsing or such, just the moaning ghost in the front.

That's why I am going for wheel bearings or calipers.

Thanks for the input,

Jack

[Mike Michalek]

Ashman

When it comes to brakes. Whatever you do to one side do the same to the other side.

[Ashman]

Yes Mike, thats my point exactly. If one caliper is bad, I'd replace both. Like I said. I think brakes are the most important feature in a car. there is nothing more scary than hitting the brakes and having the car not stop.

Alon

Ok, so now the problem is painfully clear.

This morning, the brake light came on. I removed the front wheels, and one of the right front pads was MUCH thinner than the rest. Stuck caliper.

Anyone ever rebuilt a caliper? Any input greatly appreciated.

Jack
93 400e 102k

[Mike Murrell]

Some MB mechanics say you should never rebuild or buy rebuilt MB calipers.

It's interesting that Caliber Mercedes in Anaheim, Calif. sells rebuilt units that they claim Mercedes guarantees. Their price for these rebuilt units in the case of a 126 car was WAY cheaper than brand new ones. I cannot say what they would get for rebuilts for your car.

You might give them a call. If you do indeed need to replace calipers, it might be better to buy something that MB stands beninds vs. attempting the rebuild yourself. Bad calipers can cost you or others their lives.

http://www.caliber.mercedescenter.com

1-800-225-4237

Sorry to disagree, but I've seen absolutely nothing wrong with rebuilding Benz calipers. Unlike drum brake wheel cylinders the seal stays put and the piston moves on the seal. You simply take it apart, clean everything up and replace the seal. If the piston and bore are corroded, THEN you replace them. I've taken several apart and have yet to find one not rebuildable. It certainly saves an unnecessary expense to at least check them before tossing them.

Good luck,

[jeffsr]

There is absolutely nothing wrong with rebuilding a caliper, unless..you don't know how to do it. There are a couple of gotcha items you have to be careful about. Make sure the pistons are returned to their original bores. If there is rust in the caliper bore, even with new seals you will still get some leakage. Get a used or new part, if there is damage. When seating the pistons back in the bores, be very careful you do not fold the seal lip over on itself when pressing the piston home. This can be a real disaster. Keep everything surgically clean whilst working, and you will be fine..

[psfred]

Jack:

I've done a number of calipers over the years, including several on my MBs. Not a real problem if you follow the instructions properly.

The only real problems are getting stuck pistons out of calipers and failing to re-assemble cleanly. Very difficult to get them together wrong!

Note that running rotors under minimum thickness will cause ATE calipers to stick -- the top of the pad will hit the retaining spring and cock the piston. You will have to tap it back toward the bottom of the caliper to get it out.

I recommend using a pair of screwdrivers to pry the pistons out rather than using air. You can also use the brake pedal to push them out if you use a clamp of some kind to hold the opposite one in. This is best for a stuck one as air pressure can cause the stuck piston to blow out at high speed -- very dangerous.

Any corrosion or crud you can't clean off with brake parts cleaner condems the caliper. Dont use abrasives of any kind, and this includes scotchbrite, on caliper bores or pistons. You will only cause leaks or sticking pistons.

And check that the brake lines aren't acting as valves and holding pressure in the caliper -- if the brakes drag and are released by opening the bleeder valve, replace the rubber brake lines on both sides.

Peter

Thanks to all for the great input. This forum is invaluable.

Some time ago, when I suspected a caliper problem, I bought the rebuild kits. I think that I will *very carefully* work towards rebuilding them myself. If I have any corrosion I will stop and purchase new hardware immediately.

I suspect that the PO did not change the brake fluid in a timely manner and excess water in the fluid caused either corrosion in the caliper, on the piston, or harmed the seals. We will see. I might have a ruined caliper.

I am also going to call around and see if I can get a handle on a good factory rebuilt caliper as a backup strategy in case the rebuild does not work.

Two questions:

1) Other than Caliber Motors, anyone have any idea where I could get a facotory rebuilt caliper for this car?

2) Where can I get the instructions on how to rebuild these calipers?

Thanks again,

Jack
93 400e 102k

[psfred]

Jack:

Usually there are instructions in the rebuild kit, but if not generic instruction can be found in any MB manual that includes brakes.

I tried to post a detailed list, but got stuck in an endless loop requesting that I log in -- probably a Mac thing.

If you do rebuild the caliper, please check brake function before you get out on the road, just as a precaution!

Peter

database administrator,

I suspect that your suspicions are correct. Very few people change brake fluid often, if at all.

You are getting some good words of wisdom on brake repair. I would like to add some more; it is a very good idea after any brake work involving hydraulics, to sit in the drivers seat and push on the pedal as hard as you can with both feet. If anything is going to fail, you want it to fail in the driveway, not the freeway.

Best of luck,

[Ken300D]

So, the general advice is to never use a hone on the calipers to clean the bore during a rebuild? Bummer. I have one that was a little sticky on one side during the last brake job. I forced it back in with a C-clamp and its doing fine. But the outer rubber seals were nearly shot and I'll want to do a caliper rebuild next time around (new rotors too).

Just to be sure, I'd like to ask: Do you get new pistons in a rebuild kit?

Also, I've seen advice that you should never unbolt the two halves of a caliper. Gee, that makes honing a little difficult. Anyone know why splitting the caliper open shouldn't be done? Leaks problems maybe?

Thanks - this is a great place to learn.

Ken
'82 300D