Question-------------------------
Followup To
Question -
I have a 1986 GMC Jimmy that doesn't always go into four wheel drive. I have replaced the vacuum hose and the vacuum actuator ( the device that the cable connects to ). I am able to go into four wheel drive if I manually pull the cable and clamp it. Please give me an idea as to how to fix this.
Thank you
Dennis
Answer -
If vacuum is getting to the actuator, the diaphragm must be leaking, or there is a vacuum leak elsewhere.
Followup question -
The actuator that I replaced was new and it does pull the cable - but not far enough. If you think it might still be a vacuum leak, must I replace all of the vacuum hoses from the engine? Also, because the actuator is recieving vacuum, does that indicate that the control valve is functioning normally, or could it ( due to some spoatic malfunction ) pull the cable partially sometime and sometime full distance? Also where is this control valve located?
Dennis
AnswerHi Dennis,
A vacuum guage connected with a "T" would be nice. Full manifold vacuum would be what I would want.
I assume you tried to see if the cable was sticking.
I believe the control valve for that vacuum is under the hood, and is operated electrically by a switch on the transfer case, but I don't know that to be a fact.
To bypass all that stuff, find a manifold vacuum port, and connect the 4X4 actuator directly to it, and see what happens.
I would think the controls are fine if vacume is getting there when selected, but if it is low, as with a leak somewhere else, it won't overcome the internal spring pressure.
An 86 model probably has vacuum operated heater/defroster doors. Do they act strange, like changing when you go up an overpass, etc? That would be another indicator of a vacuum leak.
Good luck,
Van
