4x4 Actuator

wilbur · December 29, 2009

I am unable to engage 4WD on my 1992 K-Blazer w/ 350,000 miles on it. It was working fine on Sunday and I left it engaged when I parked it in the garage. Monday morning as I rolled down my snowy drive way and onto the unplowed county road it was obvious to me that the 4WD was not working. I tried dis-engaging/re-engaging but it made no difference. I do notice that the lever is much easier to pull into the 4-Hi position than normal. After searching this, I found the threads on the replacing the thermal actuator with an electric actuator per a service bulletin. Am I barking up the right tree? Any other diagnostic suggestions? I have owned this vehicle since new and have never had 4WD issues and all parts are original in the drivetrain, except for the u-joints on the rear drive shaft, which I replaced last weekend. All help is appreciated.

Nytemare · December 29, 2009

I am unable to engage 4WD on my 1992 K-Blazer w/ 350,000 miles on it. It was working fine on Sunday and I left it engaged when I parked it in the garage. Monday morning as I rolled down my snowy drive way and onto the unplowed county road it was obvious to me that the 4WD was not working. I tried dis-engaging/re-engaging but it made no difference. I do notice that the lever is much easier to pull into the 4-Hi position than normal. After searching this, I found the threads on the replacing the thermal actuator with an electric actuator per a service bulletin. Am I barking up the right tree? Any other diagnostic suggestions? I have owned this vehicle since new and have never had 4WD issues and all parts are original in the drivetrain, except for the u-joints on the rear drive shaft, which I replaced last weekend. All help is appreciated.

Yeah...sounds like you have an actuator problem. but the better fix is replace the thermal actuator with a mechanical one.

Contact this company

http://www.4x4posi-lok.com/

This will also allow you to disengage your front diff at your discretion, and have a 2LO mode as well. (put your T-case in 4LO without locking the front end). I have seen these used on lots of S-10's and fullsize trucks and they work awesome.

alwcurlz · January 1, 2010

Thermal linear actuator. So, this is a temperature sensitive actuator? Did they design it to be that way? I noticed on the 4x4 posi lok site that it's not available for GM trucks after 1999. Is that because it's not an issue anymore?

Nytemare · January 1, 2010

Thermal linear actuator. So, this is a temperature sensitive actuator? Did they design it to be that way? I noticed on the 4x4 posi lok site that it's not available for GM trucks after 1999. Is that because it's not an issue anymore?

They stopped using the thermal actuator and switched over to a pure electric solenoid system. I thought it was long before 99 though. You can probably replace the solenoid on those model years with a Posi-lok too I guess. I have only put in a couple in pre 95 models...an 88 s-10 and a 92 fulsize blazer, both those had a TLA system.

It worked by heating an inert gas via electric current that expanded about 1" and shuffled a plunger to connect the right front wheel to the left shaft and intermediate shaft. Big drawback...if you are going through deep water or soupy mud, and in some cases snow...it can cool off the TLA enough so that your axles disconnect...thus basically putting you back in 2wd. Also it was very slow to engage, and even slower in cold weather.

alwcurlz · January 1, 2010

Thermal linear actuator. So, this is a temperature sensitive actuator? Did they design it to be that way? I noticed on the 4x4 posi lok site that it's not available for GM trucks after 1999. Is that because it's not an issue anymore?

They stopped using the thermal actuator and switched over to a pure electric solenoid system. I thought it was long before 99 though. You can probably replace the solenoid on those model years with a Posi-lok too I guess. I have only put in a couple in pre 95 models...an 88 s-10 and a 92 fulsize blazer, both those had a TLA system.

It worked by heating an inert gas via electric current that expanded about 1" and shuffled a plunger to connect the right front wheel to the left shaft and intermediate shaft. Big drawback...if you are going through deep water or soupy mud, and in some cases snow...it can cool off the TLA enough so that your axles disconnect...thus basically putting you back in 2wd. Also it was very slow to engage, and even slower in cold weather.

Wow, what in the world?? Heated inert gas via electric current? Sounds like something from the science lab. No wonder we have new trucks with seat covers that act like lint collectors.

Nytemare · January 1, 2010

Thermal linear actuator. So, this is a temperature sensitive actuator? Did they design it to be that way? I noticed on the 4x4 posi lok site that it's not available for GM trucks after 1999. Is that because it's not an issue anymore?

They stopped using the thermal actuator and switched over to a pure electric solenoid system. I thought it was long before 99 though. You can probably replace the solenoid on those model years with a Posi-lok too I guess. I have only put in a couple in pre 95 models...an 88 s-10 and a 92 fulsize blazer, both those had a TLA system.

It worked by heating an inert gas via electric current that expanded about 1" and shuffled a plunger to connect the right front wheel to the left shaft and intermediate shaft. Big drawback...if you are going through deep water or soupy mud, and in some cases snow...it can cool off the TLA enough so that your axles disconnect...thus basically putting you back in 2wd. Also it was very slow to engage, and even slower in cold weather.

Wow, what in the world?? Heated inert gas via electric current? Sounds like something from the science lab. No wonder we have new trucks with seat covers that act like lint collectors.

LOL....well it was a great new way of actuating everything instead of the old manual hubs. It sold a lot of 4X4 trucks and SUV's. Chevy was doing this before all the others as far as I know. And it worked good for the average lay person. its the people who want to go off roading that find this system bad. Why they didn't start out with the solenoid system they have now is beyond me though.