I have an 84 300sd. Both the shut-off valve and brakes fail intermittently. Yesterday when I check the mail line for a crack, I was getting vacuum on the mail line but today no vacuum from the main line. If I drive the car a few files sometimes my brakes will work and other times I have to use all my strength to stop the car.

Is there an adjustment on the vacuum pump or is it time for me to remove the working vac pump from my 83 240d part car and install in on my 84 300sd?

Any advice?

Thx.

pete

There's about a dozen things that could be wrong.

With it being intermittent, it sounds like you may have the main check valve sticking or going bad. Follow the black plastic line back to the hard line. Where that hard line attaches to the vac pump, there is a check valve in that connection.

If it was consistent, you would have a leak or a bad pump.

__________________
'85 300TD "Puff The Magic Wagon" - Rolling Resto
'19 Mazda CX-9 Signature - Wife's sled
'21 Morgan 3-Wheeler P101 Edition
'95 E300d - SOLD
'84 300TD "Brown Betty" - Miss this one
'81 240D "China Baby" - Farm grocery getter

Vacuum Pump Rebuild Thread
http://www.peachparts.com/shopforum/showthread.php?p=1927867

Vacuum diaphragm replacement ?
http://www.peachparts.com/shopforum/showthread.php?t=187795

"Hen's tooth" 1985 300D vacuum filter dark black
http://www.peachparts.com/shopforum/showthread.php?p=1265296

Climate Control:
http://www.peachparts.com/shopforum/showthread.php?t=142408

Diesel Injection Pump Timing Device threads
http://www.peachparts.com/shopforum/showthread.php?t=239595



Run away diesel, why does it happen?
http://www.peachparts.com/shopforum/showthread.php?t=101404

These pics are dirty!
http://www.peachparts.com/shopforum/showthread.php?p=1469677





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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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x2 on the Check Valve when I nad an intermittent probem.
It is under were the Main Vacuum Line screws into the Vacuum Pump. You can screw it out, inspect it and I cleaned mine with WD40 because I was afraid Brake Cleaner might eat up the Valve Disc.
And, that worked for me.

__________________
84 300D, 82 Volvo 244Gl Diesel

Thanks for all the replies. It was the check valve.

I unscrewed the valve out of the vacuum pump with a 22 mm socket and the small round piece of metal that is supposed to reside in the valve was sitting at the the bottom of the vacuum pump. I hope the vacuum pump didn't suck something else into it.