Brake light on dash comes on intermittently - PeachParts Mercedes-Benz Forum

yuke · #1 02-22-2012, 08:53 AM

All of a sudden my idiot brake light flickers on and off. I imagine this light is to tell you if the parking brake is on. Is there some kind of adjustment that can be made to stop this from coming on and off? I checked the parking brake and it is fully released. 85 300SD

kerry · #2 02-22-2012, 09:14 AM

Your front brake pads need to be replaced.

angusm · #3 02-22-2012, 10:25 AM

It could also mean your brake fluid reservoir needs topped up.

sokoloff · #4 02-22-2012, 11:01 AM

If it's the amber light, it's Post #2. If it's the red light, it's Post #3.

tangofox007 · #5 02-22-2012, 12:18 PM

Quote:

Originally Posted by yuke

I imagine this light is to tell you if the parking brake is on.

Consulting the owner's manual will undoubtedly yield better results than utilizing one's imagination.

Don't have one?

http://www.ebay.com/itm/Mercedes-Owners-Manual-1985-W126-300SD-Turbo-Diesel-/200714572869?pt=Motors_Manuals_Literature&vxp=mtr&hash=item2ebb855445#ht_2654wt_1398

Renntag · #6 02-22-2012, 12:38 PM

Solid advice above.

Note:
It doesnt cost anything to lift the hood and check brake fluid. If its low, so are your brake linings.

Solution:
Add fluid so as not to introduce air to the system in the short term, but be certain to check brake thickness at all four corners. Check both inside and outside pads as they may wear unevenly (another issue).
Depending on your wheel design, you may be able to check with an inspection mirror and flashlight. This can also be done from the backside of the wheel. It is always best to remove the wheels, one at a time if necessary.

Caution:
Dont waste any time since not only is your ability to stop at risk, but so are your rotors if you chuck a pad or wear down to metal.

ROLLGUY · #7 02-22-2012, 01:24 PM

I believe that if fluid is needed, then the brakes are worn enough to need replacing. If you add fluid, the reservoir will be overfilled when it is time to renew the brakes. When the brakes get replaced the caliper pistons are compressed, resulting in fluid filling the reservoir back to the factory level. If fluid has been added in the interim, then fluid will spill out when the caliper pistons are compressed to renew the linings. I suggest you inspect the rotors (measure the thickness), linings and replace them if they are out of spec. As stated above, the amber light is for the lining sensors, red light is for the parking brake/fluid level. The best thing to do is replace ALL the brake fluid when doing a brake job. The easy way is to suck a majority of the fluid out of the reservoir with a turkey baster (or equivalent tool), add new approved fluid, and then bleed the entire system. I use the one-man bleeding system using a soda bottle with a hose connected to the bleeder screw, and the other end in the bottle submerged in brake fluid. The hose is long enough that I can see it from under the car while pressing the brake pedal. Once there is no more air bubbles, that wheel is bled. I start at the wheel furthest away, and do the driver side front last.

Renntag · #8 02-22-2012, 01:58 PM

Quote:

Originally Posted by ROLLGUY

... If fluid has been added in the interim, then fluid will spill out when the caliper pistons are compressed to renew the linings.

Good point, but air entering the system is more of a risk if the car must be driven a little longer before service. A calculated risk we have all made in the past.

Quote:

Originally Posted by ROLLGUY

... The best thing to do is replace ALL the brake fluid when doing a brake job. The easy way is to suck a majority of the fluid out of the reservoir with a turkey baster (or equivalent tool), add new approved fluid, and then bleed the entire system....

LOL. so in the end, it is still better to add fluid now, then, at the time of brake service, remove the fluid from the reservoir in order to perform a system flush.
This would then negate the overflowing issue.

Perfect. The system flush is very important and the addition of fresh fluid even for the short term in good for the master.

For the newbies reading this it is critical to change out your brake fluid every 2-3 years minimum. Brake fluid is hygroscopic, meaning it absorbs water from the air. This is what destroys your brake system from the inside out. The instructions given by RollGuy above are spot on and should be followed regularly regardless if your brake linings are being replaced. Fresh fluid will keep the system in service for years to come.

Note to all: It is seldom mentioned that in an old master cylinder, there can be a build up outside the normal contact area of internal seals and cylinder walls. When system pressure is lost, or flushing/bleeding is happening, be mindful of staying in the normal travel area. It is common to damage a seal if pedal travel goes to the limit, thus pushing the seal into the "build up" area and damaging the seal. If you find that the master cylinder will no longer make pressure after repeated bleeding attempts, this may be the cause of sudden failure. It is possible to rebuild a master cylinder if replacement cost puts a new one out of reach.

ROLLGUY · #9 02-23-2012, 12:18 AM

Quote:

Originally Posted by Renntag

LOL. so in the end, it is still better to add fluid now, then, at the time of brake service, remove the fluid from the reservoir in order to perform a system flush.

Very true, and it is cheap insurance. However, if the lining and rotors are allowed to get thinner than spec, the caliper pistons will be at full extension or beyond. Having the brake warning light is a good thing, and filling up the reservoir may lead to procrastination in getting the brakes serviced before a major damage would occur. If the reservoir is filled up, be prepared to do the brakes SOON! Don't wait till the red light goes on again (well actually it will be too late by then).

Renntag · #10 02-23-2012, 01:34 AM

Sarcastic moment lost.

I was agreeing with you but making light of "Filling bad, overflow imminent....but remove fluid to do flush" So no overflow.

yuke · #11 02-23-2012, 09:12 AM

I'll check the pads + fluid on the weekend. I thought the red symbol was to warn you if you had the parking brake on. But I made sure the parking brake was not on but the light still flickered on and off as i was driving. I did replace the back pads not long ago and thought the front looked good at that time but i will check again.

Graplr · #12 02-23-2012, 09:25 AM

Quote:

Originally Posted by yuke

I'll check the pads + fluid on the weekend. I thought the red symbol was to warn you if you had the parking brake on. But I made sure the parking brake was not on but the light still flickered on and off as i was driving. I did replace the back pads not long ago and thought the front looked good at that time but i will check again.

My suggestion was going to be first check to make sure the parking brake pedal is tight. If it becomes loose and starts progressing downward it can cause the light to come on and off while driving. If that is not the case then follow the advice above. But it seems you have already done that. So then next I would check the fluid reservoir.

yuke · #13 02-28-2012, 08:45 AM

Quote:

Originally Posted by yuke

I'll check the pads + fluid on the weekend. I thought the red symbol was to warn you if you had the parking brake on. But I made sure the parking brake was not on but the light still flickered on and off as i was driving. I did replace the back pads not long ago and thought the front looked good at that time but i will check again.

The fluid was a little low topped it off and light does not come on anymore. Thanks for the replys.