My 1991 350 SD is loosing brake fluid on a regular basis. About a half inch from the reservoir every couple of days. The insulation area around the master cylinder looks damp but the master cylinder and brake booster are dry. Looking at lines going from master cylinder to the ABS and from there to each wheel look good. Calipers on all four wheels are also dry. Any thoughts where the leak might be?

explain the insulation area you are talking about.
if fluid is leaking onto this insulation you will have to find the leak.
if someone is pressing onto the brake, and everything is dry, then I'd pull the MC and look into the booster for the fluid...

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1987 190D 2.5Turbo
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1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
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The insulation area I'm refering to is the bulkhead area between the engin and the brake master cylinder. There is a rubberized coating that acts a sound deading insulation. This area is damp.

I'm trying to look inside the brake booster. Have the master cylinder nuts off and am trying to force the MC out without disconnecting any brake lines. Can't seem to get it out far enough for a look see. Do I pry it out with more force or disconnect the brake lines after emtying the reservour?

Run some cotton string into the brake vacuum power booster, enough length to fully bottom out.
If the end is damp = the master is leaking/bad..

Fastlane: BRAKE MASTER CYLINDER
http://catalog.peachparts.com/item.wws?sku=0044307501


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1985 300SD
1983 300D
1984 190D
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2002 Honda Civic

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The cotton string trick worked great.
I tied a very small nut onto the string for weight.
String came out wet. Guess I need a new master cylinder.
Thanks for the help.
Are there any tricks to installing a new master cylinder?

Bench bleed the new master cylinder before installing it.


http://www.ehow.com/video_2327999_bench-bleed-master-cylinder.html

http://www.youtube.com/watch?v=ZH3PG3ZVcf0

http://www.youtube.com/watch?v=vOuDEiwiozQ

http://www.youtube.com/watch?v=lNtMx_4PBtk

The master cylinder job is complete. Thanks for all your help.

We'll have to call you Felix the Cat

Sixto
87 300D