Engine/Transmission (1994 - 1998) low vacuum

[dwatson1]

I'm experiencing a low vacuum problem that I've isolated to the control switch on the transfer case. When I disconnect the vacuum line going to the transfer case my vacuum holds steady when I shut the engine off. When it's connected my vacuum drops immediately. So, I assume that is where my problem is. My question is, if I disconnect this vacuum line, will it bother any other operations other than four wheel drive or does it give me too much vacuum? Thanks for your input.

 

[Bob V]

I assume you are disconnecting and plugging the (green) line to the transfer case valve. I would not recommend disconnecting this line. The CAD that is controlled by this valve does not have a detent or spring to hold it in position so it COULD possibly move, even though it is not likely. I would check all the lines between the valve and the CAD, one of them might be bad causing the leak

 

[dwatson1]

Thanks for responding. I removed the vacuum harness and checked for leaks, no leaks, so it's definitely in the control switch. On my 94 the white line delivers vac to the transfer case, from the transfer case red and black goes to the axle shift motor and the green to a vent or check valve. (the service man. shows both, witch is incorrect. If it's a vent it works. If it's a check valve it's faulty. ) It's the white line that I would disconnect. So what Bob V is saying is that the red or black vac line holds the front axle in neutral which could be a problem? Am I correct in assuming that a instant loss of vac when the motor is shut off that I have a problem? I have ask 3 dealer service managers that question and none could give a positive yes or no.

 

[MLee]

You should have three applications of brake peddle with the engine turned of before the vacuum is depleted, in the system. lest ways thats is the way it was with the older trucks.

What year are you refering to Watson1. is it the 94 you talking about? above?

 

[Bob V]

Sorry, I got that wrong, you are correct, the gray tube is the vacuum source, green is vent. have you checked that the CAD does engage when you shift to 4WD? Have you tried capping of the lines at the CAD and see if you still have the problem