I have noticed that my front drive axle is not dis-engaging. I put a new vacuum switch and connector on the t-case about 2 months ago. While giving it an oil change over the weekend I noticed that the Vacuum Actuator was always sucked in whether in 4 wheel drive or 2. Leaving it in 2 wheel drive, I shut off the truck and the Actuator relaxes like it should when vacuum is removed. Start it up and it sucks back in. Is there something I am missing or could that switch be defective on the T-case?

If someone has any suggestions that would be great.

Thanks for the help in advance

Steve

 

Are the vacuum lines attached correctly to the switch?

 

Yes as far as I can tell. I changed them one at a time so I would not get them mixed up.

 

has to be something with the switch. the switch is what disrupts the vacuum going from the engine to the actuator. soooo doesnt mean the switch itself is bad maybe hoses wired wrong, or something in the transfercase didnt disengage causing it to be open. ive had a few trucks come through work where the switch is just stuck in causing it to be engaged all the time

 

What I have done and checked:
Replaced the transfercase vacuum switch and connector. I changed the connector over one vacuum line at a time as to get them back in the same spot but that shouldn't be an issue, the vent line is bigger the then 2 vacuum lines.
Checked Actuator and cable asm are working. The Actuator only disengages the front axle when the vehicle is shut off or the vacuum line is unplugged.
I am getting Vacuum to the actuator in 2wd mode and none in 4wd mode but the vacuum is not bleading off unless vehicle is switched off or line unplugged. Seems backwards to me.
Also noticed a switch or sensor of some kind t'd into the vacume line which is located at the base of the battery but not sure what it does. Didn't seem to have any vacuum at that switch/sensor which is a larger line.
I have run out of ideas. I have unplugged the vacuum line for now to not engage the front axle. My next step is to replace the transfer vacuum switch again with a GM part instead of a aftermarket prt

 

I've heard of guys installing the vacuum lines in the right order, but in the wrong positions.

https://blazerforum.com/forum/2nd-ge...uestion-75711/

 

The hoses are connected to the vacuum switch incorrectly. Try swapping the 2 smaller hoses at the switch. If it still doesn't work properly, you'll need a piece of vacuum line that fits onto the nipples of the vacuum switch. Select 2WD, unplug all 3 lines from the switch, (should be one connector). Using the spare piece of vacuum line, check each nipple, one of them should hold vacuum when you suck on the line. Leave the line connected to that nipple, (The vacuum source line from the engine will connect to that nipple after you figure out the other 2 nipples). Start the engine and select 4WD, blow into the line that you left on the nipple from the first step, the nipple that the air comes out goes to the actuator under the battery. The third line is the vent.

 

I got a chance to work on it yesterday. Pulled off the connector (oil dripping out of the connector) pulled off the line to the Actuator and Engine Vacuum.
Put a vacuum pump on and found the Actuator line and a gauge on the vacuum supply line to make sure which is which.
Also picked up another switch to bench check.
Hooked up the lines accordingly and all is well now.
Works like is should.
Thanks all for the help.

 

Glad you got her figured out, and thanks for posting back.

Oil in the vacuum lines indicates another problem. When/if the transfer case input shaft seal leaks, transmission fluid can pass into the transfer case causing the fluid level in the transfer case to rise. Once the fluid level reaches the vacuum switch, and if the seals in the switch leak vacuum, (very common) fluid will be drawn into the 4WD & HVAC vacuum systems through the lines on the switch. This will cause the HVAC actuators in the dash and the 4WD axle actuator to operate slow, and in some cases not at all.

Check the fluid level in the transmission & top off if necessary. Engine must be at operating temperature, transmission in park or neutral, parked on a level surface. Remove the fill plug, (upper plug) on the transfer case: if fluid runs out, allow it to finish & reinstall the fill plug. Then replace the vacuum switch and clean out the vacuum lines, reservoir, HVAC actuators, and axle actuator. Keep an eye on the fluid levels and if the problem returns, you'll need to replace the transfer case input shaft seal. The transfer case must be removed to replace the seal.

 

Yes I am aware of the seal problem. I have had the seals replaced not long after I got it. I am thinking that I was pulling a vacuum in the transfer case and trans pulling oil vaper up into the hoses. I am not sure how long these lines might have been switched. It has never really worked right I don't think like it is now.
I bought this from a 80 y/o lady that goes to my Church (yea I know little ole' lady) but she could not drive any more. had 70,000 miles on it when I bought it last spring. has around 96k on it now. put alot of work and money into it but it is a really nice truck. Thanks again for all of the help