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· Registered
1976 MBZ 450SL
8 Posts
Discussion Starter · #1 · (Edited)
This concerns my very clean 1976 R107 SL with just 107k miles. The RED brake WARNING light is now illuminated on the dash. This warning light came on when brake pedal traveled almost all the way to the floor and had to be pumped up. Once pumped up the pedal remained firm and the car seemed to stop properly except for a hard pull to the left. This pull went away after applying the brakes a few times and the still firm (normal) pedal stayed present. No brake fluid is leaking anywhere; the master reservoir remains full of fluid to the max mark. I drove the car a few times and the brakes functioned normally except for the warning light still remaining on. Then about a week later the brake pedal went near the floor again. It pumped up nicely again and it has held for about 4 months. Right after that 2nd time, I decided to change the very dirty brake fluid present in the reservoir. Using a turkey baister, I sucked the old fluid out of the master's reservoir and replaced it with fresh fluid. A few months passed and the car has only been driven a dozen or so times since the 2nd drop of the brake pedal. The pedal still remains firm but the brake warning light is still on.

I purchased this car only 3 months prior to all this happening (about a year ago now). Prior to the low pedal and warning light, I thought the car was somewhat of a slug, it lacked power. It felt like it was very heavy but having never owned a Mercedes 450SL or really ever driving one much prior, I had no idea of how it should really have felt. Since the to the floor (almost) pedal issue occurred the car now has nice power, it appears the brakes used to drag prior to the dropped pedal. I am confused because I never smelled that brake burning smell that should have been present if the brakes were dragging. I drove about 1000 miles(mostly 6-10 mile trip)s prior to loosing the brake pedal, I did take the car on the freeway a few times so if the brakes were dragging a burnt brake smell should have been present.

Is this a failing master cylinder???? What else to look for???

· Premium Member
1975 450SL
2,443 Posts
This is one of those situations where there are so many things that could be wrong, you don't want to say anything definite. From the original post, I'd agree to start with a complete brake system flush. He could have a brake hose that swelled inside and created a "one way valve", he could have a caliper problem, or a master cylinder problem. Without 'being in front of it', it's a bit hard to tell. He could even have had a E-brake problem.

One thing to remember / watch out for, is that on these two chamber brake fluid reservoirs, the overflow from the first chamber fills the second one. An older reservoir is discolored enough to make it hard to see the levels in both chambers. You could have one empty or an air bubble in the system somewhere.

If you want to start a Do It Yourself hobby, finding info online about brake systems isn't hard. A few tools and maybe a CD ROM manual could start you down a strange and wondrous path. If you want to, you could go to the local library, and probably find a book or two to look at.

Keep in touch with us here, whatever you do.


· Outstanding Contributor , Bob's Your Uncle!
83 280 SL- 5 speed-The PIG
35,861 Posts
So many things could contribute.

Low brake fluid introducing air to the system.
Low brake fluid??? = worn brakes or a leak.

Or a bad master cylinder.

Sounds like you need a brake system check up.
Fluid, master, calipers/pads, and brake lines.

Or you could remove the light bulb from the warning light.
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