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Old 11-19-2005, 11:49 PM
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Join Date: Nov 2005
Posts: 7
Will a vacuum leak in door lock system impact braking assist pressure on 76 240D??

Hi folks,

My 240D always loses "boost" assist pressure during braking. Several brake shops have spent hours with the vehicle and still can't find vacuum leak. The brakes, master cylinder, and boost assist system have been checked by three separate shops and everyone is still scratching their heads with no explanation.

Today, as I was picking up axle shafts at an auto parts store, I noticed that two hollow yellow tubes running into the door are severed. I assume these tubes are used to power the master locking system in the car which is currently inoperable.

Could this obvious vacuum leak also impact the performance of my brake assist system? If not, should I replace the master cylinder or other component and forget about identifying the root cause of the problem?

Many Thanks in advance for all your help.

Kind Regards,

The 240Dork

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Old 11-20-2005, 12:22 AM
billrei's Avatar
W109, Floating on air!!
Join Date: Jan 2005
Location: Goleta, CA
Posts: 556
Plug the severed lines and see if that solves the problem. If the booster holds a vacuum then it should be fine. Your vacuum pump may also be bad. You should get at least 18" of mercury reading at idle. Your common brake shop does not know anything about diesel Mercedes vacuum systems. Find a repair shop that has experience with older Mercedes or you will be wasting your time.
Bill Reimels
Now down to one:
1972 300SE 3.5 W109 (Euro delivery)
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Old 11-20-2005, 12:36 AM
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Join Date: Nov 2005
Posts: 7
I'll give it a try.

Hi Bill,

I'll stick a couple of golf tees in the tubes, tape-up and see what happens.


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