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Old 12-19-2015, 04:42 PM
Registered User
Join Date: Sep 2015
Location: Tacoma, WA
Posts: 7
Post '78 240D Brake Booster Test/Question

Hi Folks,

I've got a really hard brake pedal on the 240D lately, and am trying to do some tests to verify it's the booster or not. One test I did was to disconnect the vacuum like to the booster, then draw a vacuum directly on the booster with my vacuum pump. I can get it to pump up and hold 15hg (before my hand gets tired), but when I put the slightest pressure on the pedal (like 1/4"), all the vacuum drains out very quickly.

Sometimes it takes a while for the engine to shutdown, but I think I found a correlation between that issue and touching the brake pedal. I recently replaced the MC and put the new gasket in...that was working great for about a month. The booster had a lot of fluid in it at the time I replaced the MC, and I sucked as much out of there as I could.

Sounds to me like the booster is done, but wanted an opinion from you guys before I bit that bullet.

If I do bite that bullet, any thoughts on reman vs. new? Seems like reman would be fine.



1978 240d Automatic
1977 F-250
1966 VW Bus
1963 Thunderbird
1979 Audi 5000
1970 VW Bus
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Old 12-19-2015, 05:18 PM
Wodnek's Avatar
Vintage Mercedes Junkie
Join Date: Jun 2004
Location: Southeast Wisconsin
Posts: 1,661
It sounds to me like its done too. You had a master that leaked fluid in it, and that fluid did in the booster. Pretty much what you suspect.
1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
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Old 12-19-2015, 05:49 PM
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Join Date: Sep 2015
Location: Tacoma, WA
Posts: 7
Awesome. Thanks for the confirmation.
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Old 12-25-2015, 06:30 AM
Registered User
Join Date: Oct 2015
Location: Geneseo, IL
Posts: 80
I just did the exact same thing on my '78 240d. Replaced both the MC and booster. I used a reman. Shoot, the MB part was over $600, which is almost half what I paid for the car.

BTW, if you post questions like this over on the diesel forum you'll get a lot more response.
-Scott J
1978 240D
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