Brake help needed

[Lostyankee]

Also posted on Diesel page.
1979 300 SD.
Booster does not assist brakes.
I have 25" vacuum to the booster, pulsating 14 - 16" vacuum on the small line comming off the vacuum pump, booster holds 10" vacuum for 10 minutes.
In desperation I disconnected and plugged all other vacuum lines (trany, ALDA, doors, trunk, HVAC, ign. switch and no imporvement.
Reconnecting the ign. switch ... engine shuts off 0-2 seconds after key is trined off.
The only item I believe I have not tested is the vacuum pump to booster check valve.
Advice?
This problem is really getting my goat.

[senorunimog]

Sounds like a leaky booster to me. My dad had a similar problem with his 88 landcruiser. His booster developed a leak to the point where he had to stand on the brakes as hard as he could, and it still wouldnt stop the thing. Replaced the booster and all was well again.

[Lostyankee]

Drat. Looks to be a big project with lots of $.
Online shoping reveals a large price range and a bit of confusion on which will fit a 79 300SD.
Autopartswharehouse:'Prior' brand: $110 + S&H 1979 - 1979 Mercedes Benz 300SD Body 300D & 300CD.

Nextag.com:#N4000-12140 Brake Booster
ATE $516.04 Vehicle:1979 Mercedes Benz 300SDFits Engine - Chassis:
617.950 — 116.120
Description: 9" diaphragm
Spacer bushing 123 292 01 50 may be needed. Requires (1) 123 292 01 50 bushing.

Partstrain: ATE $507.29
Even taking into consideration Prior vs, ATE ... there is a large $ differantial!

Fastline: ATE $617!
What gives???????????????
This is an old, crusty, was dependable MB, not a showroom trinket.
While I do sometimes buy from Fastline and enjoy (?) this forum, I do not throw $110.00 around on a whim.
Is the Prior brand reliable?

[rs899]

Prior? Never heard of it. Have you looked into rebuilt boosters?

I think the bushing they may be talking about is where the pedal fits into the fork. For that reason it would be ideal to take your off, take it to a parts house and compare it with the one you are about to buy.

I replaced my leaker with one from a 77 280se in a boneyard. The hole in the pedal was too big (or was it small?) for the hole in the fork. I got it to work but it didn't really matter anyway because THAT used one was bad too. So, I was about to buy a rebuilt one from autozone or advanced for about $110 and found a W126 one just laying inside a car at upullit for $6. I tried that one and it worked like a charm. But I would recommend a rebuilt one- I got really good at R&Ring these (also had W123 booster problems at the same time). It's a tight fit. You might want to think about removing your driver's seat unless you like working on your head...

Rick

[Mark DiSilvestro]

Never heard of 'Prior'. Made in China?
For under $200 at a local parts store, I was able to find a Lucas replacement for the failed ATE booster in my '72 W114 250. In the past, I've had good luck with used ones, but '70s cars are now scarce in my local salvage yards.

Happy Motoring, Mark

[david s poole]

be aware that a lot of the 126 boosters will fit and work .just compare size and the fittings. david poole dallas tx.

[riethoven]

I had a 1966 BMW 2000CS that had a bad brake booster. When you pressed the pedal you could hear the vacuum leak. I was able to order the diaphragm and install it myself for a few dollars. The booster had bayonet fittings and was really hard to get apart. I know that many modern ones are crimped so they can't be repaired.