Hi there guys, I just recently bought an '81 280CE and I've hit my first hiccup. When I picked up the car the brakes felt a little odd, spongy and almost as if they very slightly pulsed, not as much as they do with modern Benz ABS, but there was a subtle vibration. The brakes did consistently stop the car for the 5 mile drive home through town, up and down hills, etc.

The next day I decided to drive it a little further to see what was and wasn't working (this is a restoration project). I drove 17 miles to my office with little issue, the brakes seemed to stop fine, although they were again spongy. I made it home, 17 more miles, and had no problem (other than the exhaust behind the catalytic converter falling off.

A few days later, I patched the exhaust so that I could temporarily drive the car around town (it had sat idle for more than 4 years), I did the requisite fluid changes, plugs and wires, air filter, etc, and then I headed out towards my office. About 2/3 of the way through the drive, I noticed that the brakes were softer than before, and eventually there was almost no pressure and I had my foot hard to the floor before I could get the car to come to a stop.

Here's where it's odd: I got to the office and figured I would have the car towed home (I have AAA anyway) so I thought I should move it to a more conspicuous spot in the lot before more employees arrived. I went outside (maybe an hour after I had arrived) started the car, put my foot on the brake and it was fairly firm, still spongy, but nowhere near as soft as when I pulled in.

I though maybe it was a fluke thing and drove home. 2/3 of the way through the drive, the same exact thing happened again, it went to the floor.

I went to Napa and got a new master cylinder and swapped it out. Here I'm willing to admit that I didn't do a fantastic job bleeding the brakes (I was alone with a homemade bleeder) but I got what I believe to be MOST of the air out of the system.

I started the car and immediately the brake pedal was firm, appropriately firm. I was confident, so I decided to drive it around town for a few to see how it performed. 10 minutes or so into the drive, the spongy pedal feel returned, and 2 minutes after that it was even softer than before, right to the floor with little or no pressure. This was also the first time that I heard a sound, I can only describe as a creaking-type sound, although I can't say for sure where it came from, I want to say the drivers side.

I should also note that at no time did I see any fluid leaking from any of the wheels, nor any other part of the vehicle.

So my question is this: Has anyone had anything similar? If so, what was the cause? I'm assuming my half-assed approach at bleeding is at least partially to blame, but why would the vehicle initially have pressure and then lose it?

Thanks in advance for any and all help, I certainly need it!!

-Sean

 

check if any leak to be sure change brake oil pipes and check you booster

 

Thanks for your reply! At this point I'm assuming it's a brake booster issue. I replaced the master cylinder, but I'm still getting soft pedal followed by "dead" pedal after about about 15 or so minutes of driving. Prior to that, the car seems to be fine, although the pedal is still spongy. One quick question though, what part are you referring to when you say to check the brake oil pipes?

 

Sounds like you have a sticking rear brake calliper. The sticking calliper overheats the brake fluid causing it to boil. This will make the brake pedal soft and then it goes to the floor. If it was a front brake binding you should feel it pulling to one side. I would remove the rear wheels and check for a blue colour disc rotor.

 

Thanks Swatty! That was awesome information, I'm going to take a look at the rear brakes over the next week. That would certainly explain the noise that I head, if the caliper is sticking and causing the fluid to boil, I could have heard it click

 

Hey Swatty, thanks again for your suggestion, you were dead on the money! I took the rear right wheel off and immediately found blueing on the rotors and a beat old caliper stuck in place. Swapped it out and all seems right with the world.

Thanks again!

Sean

 

Glad you got it sorted