BPG_Austin

If my HVAC diaphrams are leaking, does it effect the rest of the vacuum system? Does a leaking diaphram cause the AT vac line to not function properly and effect shifting harshness becuase of lack of vacuum? Should I fix (or temporarily plug) the offending vac lines to close the system?

Ben

Marine Blue

I had a leak in my 87 I believe at the diaphragms which did weird things to the car. The HVAC didn't operate correctly so I was getting warm air through the center vent while other vents blew cold. The cruise control didn't hold speed either, it worked briefly and then as vacuum changed it would stop working. The engine operated correctly but the flappy wouldn't have enough vacuum to change at high RPM (it worked fine at idle and startup) My car was a 5spd so I can't help with the transmission diagnosis, I'm sure someone can though.

aggravation

I think there is a check valve in the branch of the vacuum system that feeds from the engine compartment in to the hvac controls so it might be that the transmission isn't affected by a leak at the hvac pods.
I don't have an auto so I'm not sure where the tranny gets its vacuum from but I have read where people had problems with the tranny due to vacuum loss.

I'd cap the line off going into the center console to the hvac control center and see if it helps.

chrly924s

The tranny gets it's vac right off the front of the intake. There's a plug there on 5 speeds. My transmission would shift correct or consistant no matter what I did. When I put a whole new exhaust on and got rid of the cat, it cleared right up and shifts great. must be a part blocked cat effecting engine vac.

ROG100

Ben,
I sent you a selection of parts yesterday and they will be with you this morning.
Lack of vacuum will effect your shifting.
As already said you can plug any offending actuators down in the center console on the drivers side.
I also have repalcement diapragms for most of the actauators as well.
You also want to check the non return valve (blue and black) near the booster.
Do you have a Mighty Vac?
Roger
Roger

BPG_Austin

Thanks all for the input. I have a mighty vac and know which vac acuators are not functioning properly. I just had not considered that this is one large system, not individual systems. When one goes bad it effects everything else?
Roger, I installed a new check valve by the booster not long ago, should be working fine. I"ll plug in your assorted parts and plug off 'bad' vac lines and see how it effects my shifts. Again, thanks for everyones help.

BG.

Alan

The check valve has to work the other way - it allows vacuum to build in the HVAC but should not allow engine vacuum loss to affect the HVAC. If the HVAC vacuum lines are wide open it will have an effect on vacuum elsewhere - depends how bad your leak is how much effect you see. To verify the effect simply remove & plug the vacuum feed to the HVAC in the engine compartment (at the check valve).

Alan