PeachParts Mercedes-Benz Forum - View Single Post

rhodes2010 · #14 11-05-2013, 02:17 PM

Where do vacuum pump check valve parts go ?

I just had my 400,000 mile 300SD lose vacuum and only get two or three
presses on the brake pedal until hard pedal sets in.

After a long highway run I get power brakes for like one stop (two or three presses).
Then hard brake pedal.

After reading this thread my first stop was take out the vacuum pump check valve.

Nothing inside, wide open - my question is, WHERE DO THE MISSING PARTS GO ?

I am afraid to hear the answer, because inside the pump is the only place to go.

It made me think that if I were to open the front of the vacuum pump I might find some small debris
that could be removed before further damage.

I did not do this, but headed off to the junkyard and pulled the only three
vacuum check valves they had.

One was missing the guts, the other two had the parts inside .

So I come home with two check valves.
One of them seems to operate as expected with me blowing through it
so that is the one I put in.

Drove the car about two miles, up to 50mph, got feeble brake response and
car does not shut off.

Did my 75 mile commute , and brakes are only slightly better
and car does not shut off.

I have not tested vacuum at any ports yet, taking it one step at a time.

If I eventually need a vacuum pump, disappointed. Either a kit for $150usd
or a pump for $300usd.
Seems kinda steep, at least for the rebuild kit.

Do these pumps go out often ? (of course I am at 400,000 miles).

The other valve, I sprayed WD40, cleaned it up, and it looks really
good and behaves like the other one when I blow through it.
Air is allowed to flow from small end to large end, air is blocked
from large end through small end.

Any advice on removing that debris , for preventative failures sake ?

Any luck with junkyard pumps ? The cars I got my parts from said
250,000 miles on ODO, and who knows if the ODO's worked.