I heard the same hissing sound at my feet when I had a torn booster diaphragm in other cars, and often the leak would close as you pushed the pedal and suddenly increase the braking and almost throw you thru the windshield.

I repaired the booster in my 65 Chrysler. It was real easy to take apart and the tear was in a hardened part where the vacuum hose connects (gas fumes, not a problem in 300D). I cut a new diaphragm out of neoprene rubber sheet (no parts available). Didn't have the correct folds, but seems to work when I hooked to vacuum and moved the rod by hand. However, I installed a booster from a 74 Mopar I had.

I haven't tried taking a 300D Girling booster apart to try the same. I expect it is simpler inside since doesn't have a bellows around the master cylinder rod. The MC to booster interface is a vacuum seal, and a potential leak source. I took the booster off both of my 300D's. Both had brake fluid inside, but no vacuum leaks. I drained the fluid and installed rebuilt MC's. I also switched to DOT 5 brake fluid (seems to start arguments from the unschooled).

Yeah I believe my MC is fine, I think the only time I've ever added fluid was when I changed the calipers up front. I guess this might be a chance to bleed all of the old stuff out and replace it with new fluid, since I've read it loses efficiency over time or something

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1982 300D Turbodiesel, daily driver. Mods so far: Fram 8038 paper filter, 4 brake light mod, Gen II w126 (front) rotors/calipers, boost turned up to 12lbs, non-egr manifolds, water/methanol injection, 4-speed manual
1980 300SD Turbodiesel, project car, nearly ready to hit the street

1974 240D, New paint

I'll be swapping out boosters sometime by next weekend or so

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1982 300D Turbodiesel, daily driver. Mods so far: Fram 8038 paper filter, 4 brake light mod, Gen II w126 (front) rotors/calipers, boost turned up to 12lbs, non-egr manifolds, water/methanol injection, 4-speed manual
1980 300SD Turbodiesel, project car, nearly ready to hit the street

1974 240D, New paint

I have a similar problem. There is a hissing sound coming from the back of the brake booster where the push rod goes in. The sound disappears and vac. actuated stuff starts to work when pressure is applied to the brake pedal. This makes me think that there is a bad seal somewhere in the brake booster. I have tried 3 used boosters and the problem is still here. Am I missing something here? Is there an adjustment that can fix this? Am I installing the booster wrong?

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1980 300TD with 1985 300TD Turbo motor and 240D 4 speed.

Bill, I recently replaced the booster on my 300D with a TRW (Lucas?) unit. The old one had "G" vaguely stated on the cover probably a Girling.

Below are the images of the booster taken apart.

Left: front cover
Middle: diaphragm (?)
Right: rear cover



Diaphragm:


Close up of diaphragm and rear cover:


Reason for replacement: hissing sound on shut off and booster not holding vacuum when tested directly.

New and old unit:


Slightly different boot design:

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

When I hear a hissing sound at my feet I get out and check for snakes...
If a mouse can get into your car... a snake can follow it looking for a snack.
The joys of living in the country.... that and dirt daubers filling every hole in your tools....

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1980 240d ,

chain elongation, cam marks reference:
http://www.peachparts.com/shopforum/showthread.php?threadid=10414

http://www.peachparts.com/shopforum/diesel-discussion/305365-9-degrees-chain-stretch.html

evap fin cleaning:

http://www.peachparts.com/shopforum/showthread.php?t=156207&highlight=evaporator

A/C thread

http://www.peachparts.com/shopforum/diesel-discussion/297462-c-recommendations-mb-vehicles.html