intermittent brake problem - PeachParts Mercedes-Benz Forum

fz500sel · #1 10-07-2003, 12:48 AM

I tried a search but "brake problem" in the query turned up too many hits for me to look thru all of them. Sorry.

Vehicle is my 1990 350 SDL. It has 190K on it and it has bent connecting rods.....NO not really. (just figured that someone would say something about that problem)

Anyways, in the last week it has developed a wierd intermittent problem with the brakes. It only happened within the first 2 minutes of driving. When I went to apply the brakes the pedal was instantaneous hard to push. Not as though the pads were worn and I had to push the pedal really far down. It was hard from the initial point where I applied my foot to it. The car did stop but after I kept pushing very hard on it. The problem would then go away and wouldn't happen again the rest of the ride. Each time the car has sat for an extended period (6 hours +).

I bought the car less than a year ago, and had initial brake work done on it. I had all of the pads replaced and also the drivers side rear caliper replaced. System has been flushed and new fluid installed also.

This was all done in February of this year.

Any ideas what could be causing this problem? It has not become a real big problem but I guess any kinda' braking problem is actually a big problem since it involves safety.

sixto · #2 10-07-2003, 12:57 AM

Bent connecting rods will do that... no, not really.

It could be the engine vacuum pump telling you it's tired. Better have it checked because when a 603 vacuum pump goes it usually takes the timing chain with it. It's not a difficult DIY if you're into that sort of thing.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

haasman · #3 10-07-2003, 01:44 AM

I agree with sixto, bent rods ....

Seriously it is a vacuum problem. It seems your pump does generate a vacuum but it takes a while. Next startup, just let it run for the few minutes to get sufficient vacuum .... but in the long-term you need to find the leak.

With the 82 300SD I had, it turned out to be a brittle connector off the main vacuum line from the vacuum pump to the the brake booster. I was of course, all ready to replace the pump ($), the booster ($) etc and a friend told me to check the tube as it was a common problem. He was right and I bought him a great lunch with all the money he saved me. Check your vacuum lines.

Haasman