Hello Everyone,

I've noticed that one of the vacuum operated climate control baffles makes a thumping sound after I finish accelerating. I can only assume there's a problem with my vacuum reserve or is this normal? It seems to come from the center vents.

 

Oh by the way, it's a 1993 XJ6.

 

It's possible you have a problem with the vacuum reserve or with low vacuum overall due to worn piston rings, etc. But regarding the noise in the center dash area, I would suspect that the plastic hinge pins that connect the inner ends of the demist flaps on top of the dash have broken, and the vacuum solenoid mechanisms are jerking the flaps with changes in vacuum. If I recall correctly, the flaps default to the open position but are held closed by vacuum. When the plastic hinge pins break, the flap is always open and as the vacuum solenoid moves, the inner ends of the flap jerk around instead of rotating open and closed as they are supposed to.

You may be able to see the actuators by removing the center vent, but to repair the flaps requires removing the dash, which isn't as difficult as you might think. See photos in the albums at the link in my signature.

I repaired both of the flaps in our '93 by drilling a hole through the broken plastic hinge pin and permanently reattaching them with plastic glue and small stainless steel flat-head screws.

Cheers,

Don

 

Make sure the vacuum check valves are installed and working!!
Check for other leaks.

bob

 

Hello folks. The engine provides a strong vacuum and the flaps are in good shape. It's just that acceleration momentarily reduces vacuum to the climate control system and the flaps snap into place as soon as the acceleration event is over. I notice the vacuum lines disappearing into the passenger side fender, so I assume that's where the vacuum reserve unit is. I will have to get in there and make sure all of the vacuum hose connections are nice and tight.

 

Yes, that's where it is, it looks a bit like an ocarina but hopefully without the holes

Larry