Hi Good People,
I have a 1985 300D, unknown mileage (ODO stopped at 118k)
I recently had problems with the vaccum lines, causing the ignition and door locks to malfunction. I secured the vaccum lines from all leaks and everything works well again.

The problem now is there is a slight squeal coming from the left front of the engine.
Here is the breakdown:

I noticed before the vaccum lines started leaking, that while driving, a loud squeal would occur once in a while.
Then the vaccum lines started leaking and the ocassional loud squeal went away.
Now after i repaired the vaccum lines this squeal is now constent but not as loud.
Could this be a sign of Vaccum Pump Failure?

Squealing is usually belts that are loose, check all of those first.

You can check to see if you vac pump is dying or dead using a Mity-Vac. If you don't have one you should be one it's a must for work on these old diesels. To check you vac pump. Plug you mity vac into one of the tees on the main vac line comming from the vac pump and going to the break booster. Plug the other Tee if you have two. Start the car. Your mity vac should read between 20"-25" Hg. If it's lower than that remove the main vac line from the break booster. I think it's a 13mm nut. Then plug the end of the main vac line you just removed. I usually lick my thumb and seal the end tightly that way. If you mity-vac still reads low your pump is dead or dying. If it goes up to where it should be then it's your break booster. If you vac pump it bad you can rebuild it. As long at the internals of the pump are okay. Which they probably are as long as you are getting any vac.

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I am going to purchase a mity-vac and run this diagnostic that you suggested. I will post my findings. Thanks for the info.

can you hear the noise with the car idling? if so, find it. it could be the brake booster, or any # of hoses and fittings that could be letting in slight amounts of air that is whistling.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

IF you had a vacuum pump showing it's age and ready to die, even if it pumps enough to keep the vacuum using components working acceptably, it might start failing to give the needed boost to the power brakes... so how well does it brake after repeated applications or pulsing the brake pedal?... or does it get harder and harder to apply the brakes when you do such a test?
Regards,