Hi,
This is my first post and I'm glad to be here. I have a question about a 1983 300sd I just bought. While driving today all of the sudden when I stepped on the brake pedal it felt as if there was no power assist and I had to use my full body weight to stop the car and now it is always like this. Very dangerous to drive! Anybody have any idea where I should start to look for the problem ?
Thanks in advance for any light you could shed on this.
Cheers, Steve

Easy case would be a broken plastic vacuum line supplying vacuum to the brake booster. Or a shot vacuum pump which is next to no probability.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Or a failed brake booster.

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

If the condition is intermittent, you might check the check valve on the top side of the vacuum pump. The valve has a habit of breaking internally. When it does, the components can block air flow into the pump.

Another thing to check is the master cylinder leaking brake fluid into the brake booster.

__________________
1985 CA 300D Turbo , 213K mi

Thanks for all the help. I'll check all of these things out.

Cheers, Steve

a failed mc and you are getting only the rear brakes is pretty exciting too.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Was the hard brake symptom accompanied by any vacuum-loss items such as: engine not stopping when key shut off; door locks not working; transmission acting funny? I had all these when my vacuum pump diaphragm developed a big leak. I rebuilt it with parts from Fastlane. Since you didn't mention any of these you probably have one of the problems suggested above. Steve

An '83 should have a piston-type pump.

Hi again,

Yes Sbean, I simultaneously had the problem of the engine not shutting off until I hit the stop lever next to the valve cover.
Cheers, Steve

You have a massive vacuum leak in the main line to the brake booster..........or the vacuum pump has failed.

You'll need a vacuum gauge or a Mityvac to check the vacuum output directly from the vacuum pump. Anything above 20" is fine.

Thanks Brian,

I'm taking the car in to Enrique At Mr MB in Tazana Ca. this Tuesday to have the whole vacum system checked out and any old hoses replaced. Hopefully that shop visit should do the trick.