On a previous post I mentioned I was getting vacuum to the 4WD vacuum module under the battery even in 2WD. If fact there is so much vacuum that the module pulled the female potion on the module away from the cable it attaches too. After removing the 4WD vacuum switch that is screwed into the transfer case and has three vacuum lines attached to it I noticed the ball portion looks as though it is stuck in. See picture attached. The new 4WD vacuum switch has the ball about half way out. I assume that when you select 4WD a cam rolls over the ball to open the vacuum source to the vacuum module under the battery. Prior to replacing this part I was getting a substantial amount of vacuum at the module in 2WD. I could put my finger over the hose and feel the vacuum.

Now with the new 4WD vacuum switch installed the vacuum is much less, hard to tell there is any vacuum at all unless I put the hose up to my cheek. Does anyone know the amount of vacuum and how to check it correctly?

I took the three vacuum connection off the 4WD vacuum switch off while the car was running. I am getting suction from one of the vacuum lines. Slightly more than what I am feeling at the module.

Any thoughts at what I should check next.
Does anyone know what the actual vacuum should be?

Thank you...

 

I'm not familiar with the transfer cases that use the vacuum switch. However, I'm pretty sure the vacuum is what is supplied by the engine. There is a vacuum reservoir that with the help of a one-way valve that is part of a tee connector that maintains vacuum when the engine is under load and cannot supply much vacuum. I suspect that this one-way valve is just a simple differential valve, i.e., it opens to the source of greater vacuum, the engine or the reservoir.

With the new vacuum switch installed, does your 4wd system work properly?

 

Hello Christine,

Thank you for the reply. No front transfer case is not engaging still. The vacuum is not adequate to activate the 4WD module under the battery with the new 4WD vacuum switch installed. I will install the old switch and see if the original issue of having too much vacuum will repeat it self when in 2WD and 4WD.

Could you let me know where the vacuum reservoir is located.

John

 

Glad to help. I wish I knew more though.

As for the vacuum reservoir, in the later 2nd gens, 98? and up, it is located with the top and rear end of the left fender, rearward of the ABS module.

The thread on replacing the vacuum hoses in my signature has diagrams that show it.

Good Luck

 

Just to complete the thread. I replaced the new 4WD vacuum switch with another new one and that resolved the issue.

-John

 

Congrats!