Spongy Brake Pedal and No ABS - PeachParts Mercedes-Benz Forum

EricSilver · #1 09-14-2003, 02:17 AM

Car: 1989 260E

While recently removing and reinstalling my front brake pads, I forgot to uncap the brake fluid reservoir before pushing back the piston on one caliper (front, driver side). Upon discovering this, I immediately unscrewed the cap and continued on my work.

Since then, my normally rock-solid brake pedal has become softer. Braking is otherwise normal, with the pedal maintaining a consistent position and not sinking into the floor or anything. It just requires more foot pressure and travel distance than before.

I assumed this was because of air in the system so I had the fluid bled and flushed today, but the softness persists. I now suspect that the ABS may not be functioning as I cannot get it to engage on hard braking. I did manage to lock the front wheel while pullig into a parking space with a patch of oil, but that "test" is inconclusive.

I read in another thread that it is a common problem for the ABS to lock, and the solution is to drive backwards and slam on the brakes a few times to get the ABS to engage. But I would think that driving in forward would accomplish the same thing -- or is there some special voodoo involved in activating the ABS in reverse?

EricSilver · #2 09-14-2003, 02:26 AM

FYI: When the ignition key is turned to position 2, the ABS light illuminates normally, then shuts off, with all the rest of th indicator lights, when the engine starts.

EricSilver · #3 09-14-2003, 06:32 PM

Anyone have any good thoughts on this? There is not a great deal online about it.

EricSilver · #4 09-14-2003, 10:30 PM

Hmm, after successfully engaging the ABS on some wet leaves tonight, it sees the system is operating normally. Apparently, my new tires are so sticky that it is extremely difficult to lock the wheels.

Perhaps when my brake fluid was bled, some air still remains? Also, I noticed the reservoir fluid level is well above the Max line. In fact, it seems to be up to the cap. Would draining some make a difference?

y2kimmel · #5 09-15-2003, 11:48 AM

The min and max marks on the brake fluid reservior are there because as pads wear - the amount of fluid in the reservoir decreases (as the pistons extend further due to thinner pads).

I'm not sure fi it would help - but getting your fluid level to the "max" mark after installing new pads should be done.

If you've had your brakes bled - it's strange that the shop would overfill the reservoir.

Perhaps you've got a stuck piston somewhere?

Sorry I'm not much help.

Troy
1995 E420

EricSilver · #6 09-15-2003, 11:58 AM

Hi Troy,

Apparently it is not a common problem. Also, unless I am hallucinating, it seems my pedal is firming up a bit, particulalrly after engaging the ABS yesterday. I'll see what transpires over the next few days.

I asked the reservoir question because until now, I had always been below max but above min. I know little about the brake system, and wondered whether that pocket of air would impact performance. (The sponginess has occured around the time I first topped off the reservoir.)

Eric

EricSilver · #7 10-12-2003, 12:17 PM

Well, since opening this thread, the brakes have returned to normal. I have no explantion.

stevebfl · #8 10-12-2003, 07:11 PM

The reason is because it took a while to break in the new pads to the old rotors. In the beginning only the high spots hit. As the pads wear to conform with the surface the brake action is restored.

EricSilver · #9 10-13-2003, 12:34 AM

You know, now that you mention the high spots, I noticed the jerky, oscillating feel has stopped, and braking is now smooth again. (I had thought my rotors were warped.)

Funny how this correction just crept up on me without my noticing it. One day, there it was.