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Old 05-01-2006, 10:51 PM
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Join Date: Aug 2005
Posts: 30
85 300SD brakes and now Vaccum Booster?

Hey All,

I have an awesome 85 300SD with around 215,000 miles on it. The brake fluid had been getting low and I narrowed it down to a leaking brake line with a hole by one of the mountings. Replaced the line (and I didnt leave it at the shop after they told me I needed a new master cylinder and that the hoses were fine, more reason to DIY) BUT now I am having tell-tale vaccum booster problems.

I replaced the hose and started it up and the pedal felt soft because there is air in the system. All is good, it doesn't feel mushy like before when there was a leak. However, when I went to shut it off with the brake depressed, the engine kept running for a while after i pulled the key out!

I know this is usually a problem with the vaccum booster. How can I go about diagnoising the problem? It certainly wasn't like this before I changed out the line. Could this be a problem because there is air in the brake lines?

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Old 05-01-2006, 11:21 PM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,093
Are you sure that a vacuum line didn't get knocked loose? I would suspect that first. Was this something that happened all of a sudden? Usually booster leaks I have seen in the past were more of a gradual thing. Better to check the simple things first, if I recall, that booster is very pricey!

84 300SD 350K+ miles ( Blue Belle )
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Old 05-02-2006, 12:39 AM
Ara T.'s Avatar
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Join Date: Sep 2004
Location: Santa Rosa, CA
Posts: 2,075
Check all your 4 way connectors and such, it took me a while to figure out one of mine had broken, leaving me with a 3 way connector.
1985 CA 300D Turbo , 213K mi
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Old 05-04-2006, 11:41 AM
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Join Date: Aug 2005
Posts: 30
OK so I pressure bled the brakes and now everything is hunky dory. Perhaps the air in the brake lines was causing the pressure booster some trouble, I'm not sure but it stops when I tell it too now which is nice. My friends would really make fun of me if I had to open the hood and press that big red switch everytime I wanted to stop my car

Thanks for the advice though. I was actually close to trying to take the master cylinder and brake booster apart which would have been bad. Usually, it is probably something simple!
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