4WD not disengaging

[firecadet613]

I've got a '95 Blazer.  I will have it in 4-Hi and then put it in 2-Hi and it doesnt seem to be disenganing?  Any idea whats causing this and what can be done to fix it?

 

Thanks,

 

Joe Thomson

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[Frank S]

You can try disconnecting the battery for about 10 minutes and see if it will revert to 2wd.It may work if it's a switch problem but if not I'd say your actuator or vacuum switch is bad.

[firecadet613]

It does eventually come out of 2Hi.  It just takes a while.  It will be in 4Hi, I press the button for 2Hi, the 2Hi button lights up, but I can still hear that it is engaged.  A few minutes later it comes out of 4Hi.  I do not know if the tcase fluid was ever changed, could that be it?  It has 80,000 miles on it.  I heard about a new blue tcase fluid.  Thanks for all your help so far.

[bassdog]

Not sure if this will work, but you can try it.

 

When shifting out of 4wd, try backing up about 10 - 15ft. It should be disengaged at that point.

 

Course it could be something electric...

 

 

bassdog

[CMNT81]

There is a TSB out for the vacuum actuator switch as well as a vacuum bypass kit on 95+ Blazer's.  What you need to determine is whether it's a hub disengagement problem or whether it's a physical gear disengagement problem via the elctric servo motor.

 

If it's on the vacuum side, it could be the above mentioned TSB.  Also, I've seen (and personally had) vacuum lines come loose, rest against exhaust components (when I had it in 4wd) and then when I put it back into 2wd, the hubs wouldn't disengage due to the vacuum leak.  So what I'm saying is check for vacuum leaks.

 

If it's on the electronic servo side, it could simply be jammed all the way up to a frozen servo motor.

 

One question though, did you have it in 4wd, shut the vehicle off, let it sit overnight in cold weather then the next day it wouldn't disengage?  If so, it's simply frozen from moisture then freezing while left in 4wd.  This is why you are suppose to disengage it when you are pulling into your driveway if your garage isn't heated.  

 

Disconnecting the battery won't do anything to the 4x4 system as that isn't PCM controled.  disconnecting the battery will only put the PCM in an "idle re-learn" procedure.

[CMNT81]

Also, as an FYI, it IS normal for GM's pushbutton style "Insta-Trac" vehicles to take their time shifting out of 4wd.  Aside from backing up, another way to manually kick it out quicker is after you push the 2wd button, let off the gas for a few seconds then resume pressing the gas.  This allows the engine's torque to be taken off the drive gears therefore allwing the system to disengage faster.

 

Fluid won't make a difference.