Hi all,

I have a 1999 Blazer with the Auto-4WD (4 button) transfer case. I suspect that the front axle actuator solenoid valve relay is a bit leaky.

This is the small solenoid that hangs near the center of the firewall in the engine compartment with the two vacuum lines; one a supply and one to the transfer case actuator.

I have a Mityvac vacuum pump and intend to do a test on it by pulling a vacuum on it from the supply (engine) side. When I do this what would be a good indication that it is fine? I.e. For how long might I not notice any leak-down after getting to about 20" of vacuum?

Thanks!

 

I would think that it should hold a vacuum forever, however the vacuum line connections may leak after a bit. I had to replace this on my '02, the part gets a lot of engine heat which of course destroys the seals.
If I remember correctly it was not very expensive and unlike the ones on the TC, very easy to change.

 

Went out this morning after it warmed up to (just) above freezing and checked the solenoid and sure enough, it did leak. With my Mityvac I could only draw a vacuum of 15" whereas I could get to 20" on the other parts of the vacuum circuit. I'm sure it is the solenoid and not the hoses as I recently replaced all those vacuum lines and even secured them to the fittings with zip-ties to act as mini hose clamps.

Thanks for the confirmation of my suspicions.

Christine

 

Quick follow-up: Got my replacement 4WD actuator valve solenoid today and I tested it and the old one by connecting them both directly to my hand-vacuum-pump. (Mityvac) The new one held vacuum indefinitely at 20" Hg but the old one I could just get down to 20" but it would leak up to 15" in about 5 seconds. Haven't tested it yet with a drive but I already feel better knowing this part to my 4WD is working properly.