I have been trying to tackle this issue for 6 monthns now and I am at the brink of giving up. I have with me 1984 300D with 410k miles. It all started when I noticed the MC leaking I had it replaced with a Cardone MC from Amazon it came with a pre installed o ring seal. I picked up a brake booster from a part sales men whom I frequent when I need parts.


Anyways I installed the booster, master and bled the brakes of course. I started the car up the pedal dropped a tad bit indicating boosters I then tried turning the car off but it just continued running
(Am I loosing vacuum?) The only way I could get the car to shut off is when I press and hold on the brake pedal the engine gradually would shutdown.

I plugged unplugged the brake booster main line and clogged it with a Vacuum cap low and behold car shut off. (mhmm Bad brake booster???)

FYI

I tested the vacuum it pulls well over 21HG with my finger on the line. (Vacuum pump is good!)The transmission shifts like BUTTER! I disabled the door locks. Now when I measure the vacuum on the main line it reads 10hg low vacuum.


After tinkering with this issue I decided to check the vacuum again. It's 100% on sync and working I went ahead and bought another brake booster this time from this forums and the seller is a pretty reputable member He swore it holds vacuum.

I installed and yeild the same results. I don't know what to do!! Two defective brake boosters?? How in the lords name is that possible. Inspection is due in 2 months I really need to tackle this issue. Hell I have literally tried everything I don't know what to do.

If anyone can give me some insight on what it could be?



https://www.amazon.com/Cardone-Select-13-2326-Master-Cylinder/dp/B000EPZTPW/ref=mp_s_a_1_3?keywords=master+cylinder+w123&qid=1580160297&sr=8-3