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1982 300SD 126
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7 Posts
Discussion Starter #1
I need some assistance troubleshooting a vacuum issue on my 300 SD. I drove back home the other day and my car wouldn't shut off, then drove it a few hours later and brakes were hard.

Took the vacuum line off at the brake booster and heard air release when I took that line off. When I tested line before the booster I was getting a constant 20 inches of vacuum before the brake booster. The car then shut off
and I was able to brake once before I was back to having hard brakes and car not shutting off again.

I also did a test on the vacuum by the injectors where I was getting 15 inches of vacuum that dropped off as I opened the throttle. Appreciate any help anyone can give me. By the way, where can I find a vacuum diagram?

Thanks,

John
 

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Premium Member
2012 CL550 4MATIC Coupe
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9,992 Posts
Didn't we just answer this a couple of weeks ago? Different person?

PM Me your email and I will point you to the manuals.

Sounds like the check valve in the vacuum line is bad. That is what goes out on those. If that had gone bad then when the engine is under load it does not keep vacuum in the booster.
 

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1982 300SD 126
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7 Posts
Discussion Starter #3
vacuum pump/hard brakes

Different person, I saw your reply just wanted to make sure it was the exact same issue. sent you a pm as I was also asking about the door locks.

I do appreciate the prompt replies.

Thanks,
JohnP
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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10,152 Posts
I understand there are different vacuum values depending on which nipple you test. Also, the vac by the injectors, if you are referring to the Vacuum Control Valve, it should have lower vac and decrease with more rpm.
But hard brakes are a different story.
 
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