98 GMC Sonoma 4x4 question, Simon, anyone?

[mo' parts]

after the end of last winter, i noticed my 4 wheel drive was acting up. mostly just not wanting to dis-engage immediately. well, now its still doing that, but when it does dis-engage, its usally loud and kind of violent for lack of better terms. also it has a vibration and wanting to pull to the pass side more than normal (needs an alignment bad,lol). i know my front axle seals leak slightly, so i keep checking it. could it have gone too low at one point and messed something up? i got rid of my old 95 blazer when its 4-wheel starting acting up, so ive never had to dig into it. this one is paid off and low mileage so i plan on keeping it around for a while, and would like to fix it before it breaks lol.
any and all help is very much appreciated, as the snow has been on and off lately.

[turbovanman²]

Is it electric or manual?

The encoder motors do act up and can cause your problem but most likely, that stupid little vacuum switch is acting up. Try that first and unless you ran the front diff out of oil, I doubt you hurt it.

[mo' parts]

Is it electric or manual?

The encoder motors do act up and can cause your problem but most likely, that stupid little vacuum switch is acting up. Try that first and unless you ran the front diff out of oil, I doubt you hurt it.

thanks simon, and that was quick:clap:
it is the push button electric. it never ran empty, at least as long as i have owned it. i just clicked 70,1xx miles.

by encoder motors, are you talking about the solenoid? and where is this vaccume switch located....
thanks again

[1FastCSX289]

Just went through this with the 98 Blazer I bought. The encoder motor is on top of the transfer case. It has a big electrical connector plugging into it. The vacuum switch is also on top of the TC. It has a 3-hose vacuum connector going to it. That was the problem with mine. 15 bucks in the "Help" isle at autozone. They also have problems with the vacuum "axle solenoid" which is located under the battery on the passenger's side. Its very common for these to go bad or for the cable attaching it to the front diff to freeze up.

Heres a good diag procedure:

First thing I would do is disconnect (or cut) the vacuum line going from the TC to the axle solenoid (this will later be spliced back together with a vacuum line connector barb if you cut it). Check to see that there ISNT vacuum at this line in 2WD and there IS when its engaged in 4WD. If that is not the case, then replace the $15 switch on the TC. If it is getting vacuum at the correct time, then you want to make sure that the solenoid is engaging the front axle. Best way to do this is by putting all 4 wheels in the air and switching between 2 and 4 wheel and turning the front driveshaft by hand. BE CAREFUL and MAKE SURE THE TRUCK IS IN NEUTRAL because it has to be running to do this (or you must operate the solenoid with a vac pump). Try engaging and disengaging the axle. If the axle doesnt engage under any conditions, then the vacuum solenoid under the battery or cable is bad.

If all this works correctly, than its probably the encoder motor. Not that this it the only other possibility.....there are others, but without getting into probing around the transfer case control module for inputs and outputs, this is your best guess.

[mo' parts]

Just went through this with the 98 Blazer I bought. The encoder motor is on top of the transfer case. It has a big electrical connector plugging into it. The vacuum switch is also on top of the TC. It has a 3-hose vacuum connector going to it. That was the problem with mine. 15 bucks in the "Help" isle at autozone. They also have problems with the vacuum "axle solenoid" which is located under the battery on the passenger's side. Its very common for these to go bad or for the cable attaching it to the front diff to freeze up.

Heres a good diag procedure:

First thing I would do is disconnect (or cut) the vacuum line going from the TC to the axle solenoid (this will later be spliced back together with a vacuum line connector barb if you cut it). Check to see that there ISNT vacuum at this line in 2WD and there IS when its engaged in 4WD. If that is not the case, then replace the $15 switch on the TC. If it is getting vacuum at the correct time, then you want to make sure that the solenoid is engaging the front axle. Best way to do this is by putting all 4 wheels in the air and switching between 2 and 4 wheel and turning the front driveshaft by hand. BE CAREFUL and MAKE SURE THE TRUCK IS IN NEUTRAL because it has to be running to do this (or you must operate the solenoid with a vac pump). Try engaging and disengaging the axle. If the axle doesnt engage under any conditions, then the vacuum solenoid under the battery or cable is bad.

If all this works correctly, than its probably the encoder motor. Not that this it the only other possibility.....there are others, but without getting into probing around the transfer case control module for inputs and outputs, this is your best guess.

i will give this a try, thank you very much for the info. i'll post my results soon.

[Stevien1]

Stupid question- are all four tires the same size? Air pressure is the equal as well as tread depth?

I've overlooked that before! $$$$ :(

[mo' parts]

Stupid question- are all four tires the same size? Air pressure is the equal as well as tread depth?

I've overlooked that before! $$$$ :(

its kind of funny you ask that... the drivers side rear is a spare (not a donut)thats about 1-1 1/2 inch smaller in diameter. i do constantly check air press. though. lol
anyway, my front tires definitely have some uneven wear from the alignment issue, and im sure thats the vibration i have thats just amplified in 4 wheel. but would the smaller tire really make that much difference in dis-engaging? im sure the vibration and pulling is just alignment and tires.

[Stevien1]

but would the smaller tire really make that much difference in dis-engaging?

You better believe it! ;) Get some matching tires in all four corners before you do anything else.