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88-94 Chevy Silverado 4x4 won’t engage

marsk5

marsk5

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I have a 1992 Chevy 4x4. I replace my thermal actuator with the Posi lok cable and I still can’t get my 4wd to engage. I’ve replaced every sensor from the tcase to the front axle. When I put it into 4hi the front shaft spins freely. Any help would be appreciated. I’ve been trying to figure out this problem for 2 weeks now
 
marsk5 said:
I have a 1992 Chevy 4x4. I replace my thermal actuator with the Posi lok cable and I still can’t get my 4wd to engage. I’ve replaced every sensor from the tcase to the front axle. When I put it into 4hi the front shaft spins freely. Any help would be appreciated. I’ve been trying to figure out this problem for 2 weeks now
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Do you know the condition of the running gear?
Could be a problem in the axle shafts or the pumpkin or even the tcase
 
The truck runs fine in 2wd. No noises or grinding. The cable only goes about an half inch and then stops. I’m thinking there is something wrong in the pumpkin.
 
marsk5 said:
The truck runs fine in 2wd. No noises or grinding. The cable only goes about an half inch and then stops. I’m thinking there is something wrong in the pumpkin.
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I don't think it needs to go more than 1/2" but I would definitely start looking at the diff first
 
I have the Posi-lock on my '95 and it takes several inches of travel at the knob to engage the differential. I usually do it while turning at slow speed.
But you should be able to lock the front driveshaft to the gears in the transfer case in 4 Hi even if the axle disconnect is unlocked. Or locking the axle disconnect with the transfer case in 2wd will stop the shaft.
I believe that you have something wrong with the installation of the Posi-lock, (maybe) but also something not right in the transfer case shifting mechanism.
 
I’m goin to take another look at it tomorrow. Maybe I did screw up the installation somehow?? It seemed pretty straight forward.
 
marsk5 said:
I’m goin to take another look at it tomorrow. Maybe I did screw up the installation somehow?? It seemed pretty straight forward.
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Are you engaging it while parked and checking?
You need to move for things to lign up and engage.
 
As I found out, there is something wrong in my front diff. It seems like my shift fork is getting caught up on something. I jacked it and spun the tire and driveshaft and tired to get everything alined but it won’t engage
 
That's no fun. Does the t-case seem to engage? Hopefully you are good on that end.
 
Have you done any basic diagnostics on the system? Jack the front tires off the ground and see what happens.

Front tires off ground, t-case in 2wd = should be able to spin the front driveshaft by hand.
Shift the t-case into 4wd = should not be able to spin the front driveshaft by hand.
Back in 2wd, spin both CV axleshafts by hand = what happens?
 
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