Rear brakes brake unevenly - PeachParts Mercedes-Benz Forum

rotski · #1 07-06-2010, 08:50 AM

Hello, I have a 84 300TD.

Had the car in to a control of the rear brakes, and they said that the left side rotor was wobbling, so the brake difference was above 30% between the sides, which is the legal limit (live i Sweden).
All i had to do was change the rotors and brake pads and it ought to be sorted, the mechanic said. Well, i changed them (on both sides), and today as i went to check if it was ok, the difference between the sides were almost 50% (probably the same as before, but then i only got to know that it was above 30%).

When i brake hard the car goes left.

Anyone has a clue on what it might be?

vstech · #2 07-06-2010, 08:53 AM

have you flushed the brake fluid properly? is your parking brake stuck on one of the sides? are you sure it's a rear brake problem? heavy vehicle action is usually from the fronts.

rotski · #3 07-06-2010, 09:00 AM

yep, i sat inside the car as he tested the rear brakes, and i saw the difference myself in the display, to my horror.

The car isn't heavy moving to the left, i just feel it doesn't go in a straight line when braking.

Haven't flushed the brake fluid, is that the way to go?

layback40 · #4 07-06-2010, 09:29 AM

You may have a sticking caliper. When you changed the pads, did you clean around the pistons before you retracted them to put the new pads in? I would be checking the left caliper.

leathermang · #5 07-06-2010, 09:37 AM

I am impressed that that is something anyplace measures... very good... you won't see that happening here in the states... only by results of going one direction...

This is why all work on car brake systems is done to both sides of an axle.. either both fronts or both rears... a slight difference in friction ( in any of its forms in that system ) means a lot in the ability to stop straight..... IE, in your lane...

There are not a lot of components in the system... it would be possible to renew all of them at one time with a savings in labor compared to piecemealing them in hopes of correcting the errant one... but keep in mind that on cars of our age it is possible to have several of the critical items not 100 percent... so an accumulation of problems will require that all of them be addressed.... on BOTH sides of the axle...

Stretch · #6 07-06-2010, 10:42 AM

I've been recently working on my rear brakes so I'll add the following - as well as agree with what has already been said:-

Jack up the rear end - both sides.

Spin each wheel by hand and compare how they feel. If one stops more quickly than the other then you need to find out why.

In any case you need to check the parking brake and the caliper pistons.

For the pistons in the caliper it will be best to remove the brake pads and make sure that you can push the piston in smoothly. If it jerks or doesn't budge then you will probably have to take it apart and reseal (if there is excessive corrosion you'll probably have to get a better one / new one).

To help move the pistons you may need to remove the cap off of the master cylinder... wrap up this area with rags as spilt brake fluid will strip paint.

The parking brake is a simple affair. It is very nicely designed to be on a separate system from the disc brakes. It is just applied by the tension in a cable. Make sure that the cable system is operating smoothly and not sticking. Make sure that the return springs on the brake shoes are all fixed and doing their jobs properly. Make sure that when you spin the wheel by hand the brake shoes aren't engaging.

My guess is that it will probably be a stuck caliper piston. Good luck.

rotski · #7 07-06-2010, 10:47 AM

Thanks for all the tips, will try to clean around the pistons, i did not to that before i fitted the new pads, doh!