I am attempting to diagnose a vac. leak. The motor is slow to shut down. The shut off valve is new and functioning properly.

The only system that I can find that does not hold vac. pressure is the white plastic unit behind the ALDA. The vac. line to the tranny comes off of this unit and that line holds pressure perfectly.

I am officially stumped. Can anyone with experience with this throw me a bone?

Thanks.

Beuller... Beuller...

MCCAN,

This is the vacuum valve and controls the vacuum to the auto trans. It won't hold a vacuum because it isn't supposed to, that's how it varies the vacuum. There is a 3 legged tee connection to the valve. One leg has a restriction in it. This leg must be connected to the vacuum supply. If is not, you car ruin the transmission. The restriction leg should be marked with a plastic clip.

Have you checked the vacuum of the vacuum pump with a vacuum gage? How do the brakes work? If they seem normal, the vacuum pump is probably OK. How long does the vacuum exist after you shut off the engine (not motor)? If the vacuum decreases rapidly, you have a leak someplace.

Check the vacuum, using a vacuum gage when you turn off the key, of the line going to the shutoff valve. If the vacuum isn't very high there you may have a leak in the key switch.

P E H

Thanks for the clarifications. The three way "T" is in place, and the tranny is smooth as silk. The switch behind the key that controls the shut off checks out. Doors, trunk and gas door all check out. Since I am having difficulty with the A/C center vents, I am going to have to head in that direction. I am not having favorable thoughts re: going behind the push button panel...
Thanks again for coming between me and potential disaster.

Sounds like low vacuum -- check that you have at least 11" vacuum at idle on the mail vacuum line. If not, you have a serious leak or a bad vacuum pump.

AC blowing up the windsheild is a dead giveaway for a vacuum leak.

The little white box may also control the EGR valve.

Check all the vacuum line connectors for leaks and old age -- if they don't seal on the hard plastic lines you can lose enough to cause problems.

Check the restrictors (if any) in the green (Climate Control) lines and the brown (shutoff) lines, too -- they can get plugged.

Also, does the shutoff work properly if you pull a vacuum on the brown supply line with the hand pump? If not, you have a leak in that system. If it does, I'd suspect low supply vacuum.


Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Hey, Peter, what little white box?

Oh, yeah. I read it on the fly and missed my own reference. No EGR on the 79. Prob. is probably in the HCU (no monovalve on this vintage) or under the dash.