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Old 12-15-2000, 07:40 AM
Registered User
Join Date: Oct 2000
Location: Jacksonvill, FL, USA
Posts: 125
I have a vacuum leak in the 300SD to the point that it is affecting the brakes. It will shut off but it takes about 20 to 30 seconds. I have shut off the vacuum to the locking systems for the doors. I have already replaced the A/C Servo. I am convinced that there are relatively minor leaks just about everywhere. I am willing to start replacing parts. Is there a recommended philosophy to use when approaching this challenge?

Other than this issue, the car is running great. Over 300,000 miles and it is running better than most new ones. I really want to hang on to this one. So, I am willing to put some sweat and bucks into it.

Again, any feedback would be appreciated.


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Old 12-15-2000, 08:34 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
My first point would be that the system is designed such that a total failure of all systems will not affect the brakes. In other words if you just pull the two small vacuum source lines from the large power booster source line and leave them open the leaks should be small compared to source vacuum and the booster should see sufficient vacuum to do its job.

Since you mentioned the brake problem, I assume that your source vacuum is POOR! This needs to be the first step. With no leaks, vacuum in the line to the booster should be over 20in. Vacuum should drop maybe 5in with a brake application but rapidly recover as the pedal is held (one second plus or minus). This should be done by removing the supply lines and attaching the gauge to one of them (plug the other). After verifying the system vacuum proceed with each system one at a time by reinstalling the lines to the booster line. The single line branches and has check valves, at the first branch only hook-up one side (plug other). Do this for the four possible directions the vacuum goes. Brown = fuel shut-off, Green = A/C, Yellow = door locks and Black = cruise control.

I would start with the Brown to verify that important system. Next add door locks and if they have no history I would replace all three door chambers (they all should have failed by now). They can be purchased for a fraction of the MB list of $92 (we would sell 3 for less than $150).
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 12-15-2000, 03:17 PM
Jay Jay is offline
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Join Date: Aug 2000
Location: Breinigsville,Pa.
Posts: 299
Tref, does your car have an EGR valve? They are known to leak.

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