Brakes "Sticking" - rebuild ? - PeachParts Mercedes-Benz Forum

tivoliman · #1 09-11-2004, 06:56 AM

Car: 1993 500SEL and 1992 190E 2.6

The brake pads are wearing uneven. This suggests to me that a caliber (piston) is “sticking”, or just not moving smoothly.

My choices – rebuild or replace.

I’ve been told FastLane has the rebuild kits for the calibers.

Is rebuilding the brake calibers a “big” job? With some American type cars, years ago, I simply removed the brake calibers and pumped the breaks – soon the piston popped out. I replaced the rubber and reassembled all.

Do the Mercedes follow the same design?

Pictures and hints are appreciated.

Your thoughts and comments are appreciated.

nglitz · #2 09-11-2004, 10:41 AM

I'm not familiar with your particular model, but if it's a single piston caliper, the piston will probably pop out, just as you said.

However, a little lubrication on the sliders might solve your problem.

If the calipers aren't leaking, you probably don't need to rebuild the caliper and it wouldn't help anyway. Your issue is the lateral sliding of the caplier and it sticking instead of sliding.

Wire brish & lube. "Never sieze" for lube between two cast iron parts or silicone grease if it slides on pins. :p

Slick,

psfred · #3 09-11-2004, 11:00 AM

Uneven meaning?

Describe the uneven-ness, there are several different types with different causes.

Peter

tivoliman · #4 09-14-2004, 01:56 PM

By uneven wear i mean that the brake pads are not the same size.

On the same wheel - one pad may be 1/8 inch, while the other is 1/4 inch (not exact numbers), but both sides are thinner than new brakes.

Thanks

psfred · #5 09-14-2004, 06:35 PM

The pads normally are a bit different in thickness. Sometimes it's the outside, sometimes the inside that's thinner, probably due to the greater exposure of that side to road dirt, etc.

However, if there is a full 1/8" difference, I would check for a sticking piston on that side, or one dragging on the worn side, there shouldn't be that much difference.

Peter

tivoliman · #6 09-14-2004, 10:59 PM

please suggest how to get the piston not to stick?

Thanks

psfred · #7 09-15-2004, 07:20 PM

Bill:

Change brake fluid every two years. Use only good pads, and never let the rotors run too thin (usually get two sets of brake pads per set of rotors, roughly 60,000 miles).

Comletely clean all the brake dust, rust, and corrosion out of the pad slot on the calipers each brake pad change (and major service, 30,000 mile interval) and lubricate the pads, this prevents them getting stuck and dragging.

You will need to rebuild the calipers (actually just change the piston seal and dust boot/heat shield) about every 15-20 years, depending on milage.

The very worst thing you can do is let the rotors get too thin -- on the dual piston ATE calipers, this cuases the backing plate on the pad to hit the antirattle spring, both greatly reducing braking power and forcing the pad and piston to cock upwards in the bore of the caliper. Since the piston is then stuck and won't move, it overheats, cooks the dust boot and lets in water and dirt, and usually also hardens the psiton seal, so if you do manage to get the piston moving again, it won't retract properly, more drag and heat.

Peter

Cigar Havana · #8 09-16-2004, 10:13 PM

I had the same problem on the rear brakes of a 1989 420 SEL.
Here is what I did:
1. removed calipers, to the bench,
2. punched out pins, removed old pads and anti-rattle spring;
3. drained as much brake fluid as I could out of the caliper
4. clamped one piston in, with a c-clamp;
5. applied air pressure to fluid hole in caliper
6. non clamped piston pops out, watch your fingers and eyes, its speed is proportional to air pressure applied.
7. One of the pistons would not come out with air pressure, so after removing the rubber boot, applied heat to the piston, not the caliper. Let it air cool 15 min. then water cooled it and tried the air again. I had one real bad one, had to heat and cool 3 times about.
8. Flushed caliper with brake fluid.
9. Used a nylon scrubbing pad to clean pistons and interior of calipers, flushed with brake fluid, wiped clean with paper towel.
10. Replaced rubber ring inside
11. Compress piston with c-clamp, about 1/4" from the bottom, do not put on the new rubber yet, you are at step 4, now do the other piston, step 5+.
12. Replace rubber boot, dust seal only after both pistons have come out. Compress both pistons down fully.
13. Tape fluid hole closed until read to install.
14. Install new pins, pads, rattle spring. Use shims on the back of the pad, use brake anti-seize on the pad slides, and on the pack of the pads. Put nothing on the pad surfaces.
15. Install calipers, new rotors are nice. Bleed brakes.

tivoliman · #9 09-17-2004, 09:12 AM

Thank you very much for the detailed description.

tangofox007 · #10 09-17-2004, 10:30 PM

I had the same problem (very uneven pad wear.) It turned out that the aftermarket brake pads that I had installed were defective. On one pad, the friction material was slightly misaligned relative to the steel backing plate. (The pad extended past the edge of the plate.) This caused the pad to jam in the caliper. In the future I will only use ATE parts on the brakes.