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Thread: 4x4 Posi-Lok

  1. #1
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
    Posts
    3,110

    Default 4x4 Posi-Lok

    After nearly 20 years and many thousands of miles of trouble-free service, the thermal actuator quit on the front axle of my Tahoe. This is the electrical device that disconnects the passenger side axle shaft from the differential. This prevents the front driveshaft from turning when in 2WD, saving wear and tear and improving MPG.

    I was on a 4x4 trip in October, and at the end of one of the trail rides, I noticed the 4x4 light on the floor shifter was no longer illuminated. This light normally turns on when the front axle is engaged. I did some trouble shooting, and verified that the front actuator was no longer working, so no more 4WD!

    The most common solution is to upgrade to the newer electric actuator instead of replacing the original thermal actuator. The electric version is faster and more reliable, but it does require some wiring modifications, including running a new wire from a 12V + ignition source. I seriously considered this option, but I decided to go another route, and install the fully-mechanical 4x4 Posi-Lok:

    https://4x4posi-lok.com/product/psl600-4x4-posi-lok/

    This replaces the electric/thermal actuator with a mechanical version that is operated by a push/pull cable mounted in the cab. For me, there were two advantages with this option - 1. No more having to rely on anything electrical or electronic; even with the more reliable electric actuator installed, it would still require an electrical signal from the floor-mounted shifter to tell the actuator to engage. 2. The Posi-Lok will stay engaged, even with the ignition turned off; this is an upgrade in safety when using 4WD and parked on an incline; with the electric/thermal actuator, the front axle could disengage when the engine is turned off, causing a loss of traction when parked off-road, when winching, etc.

    The install was actually easier than expected, and even moving slowly due to a recent minor surgery, I was able to complete the project start to finish in about 2 hours. It works great, and is simple to use.



    New actuator installed:





    Push/pull cable mounted beneath dash:





    2WD position:





    4WD position:





    4WD indicator still works on floor shifter:





    Back on the trail again:




    I am really pleased with the product, and feel like I have a very reliable 4x4 that will work every single time I need it.

    As a side note, if you ever find yourself in an emergency situation and your actuator won't engage, just grab a 3/4" impact socket. Remove the original actuator, toss the 3/4" socket into the axle, and then reinstall the actuator. This will cause the actuator to push on the lever inside the axle and engage the front axle permanently, and makes it just like a Jeep Wrangler - as soon as you pull the transfer case into 4WD, you're ready to go! The front driveshaft will spin at all times, though. I actually did this for a few weeks while I contemplated what I wanted to do. However, I could tell my front driveshaft was not perfectly balanced, and I could feel it vibrating, especially at interstate speeds. You can actually buy a "PermaLok" that does this exact thing, but there's no need to spend over a $100 when a perfectly good socket does the job! I decided I wanted to be able to have a front axle disconnect after all.

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  2. #2
    Join Date
    Dec 2003
    Location
    Yukon Canada
    Posts
    1,690

    Default

    Thanks for the write up and information
    I will be looking at getting one for my Diesel Sub, as it will be our road trip vehicle with off road intentions.
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  3. #3
    Join Date
    Oct 2001
    Location
    Granby, Missouri, USA
    Posts
    3,110

    Default

    Quote Originally Posted by Yukon6.2 View Post
    Thanks for the write up and information
    I will be looking at getting one for my Diesel Sub, as it will be our road trip vehicle with off road intentions.
    If you purchase one, I suggest watching a YouTube video on how to install. The included instructions are confusing, and they even recommend draining the front diff fluid, which is not required at all.

    Casey
    1995 K1500 Tahoe 2 door, 6.5LTD, 4L80E, NP241, 3.42's, 285/75R16 BFG K02's; 1997 506 block; Kennedy OPS harness, gauges, Quick Heat plugs, and TD-Max chip; Dtech FSD on FSD Cooler; vacuum pump deleted, HX35 turbo, Turbo Master, 3.5" Kennedy exhaust, F code intake; dual t/stats, HO water pump, Champion radiator; Racor fuel filter

  4. #4
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,409

    Default

    Great posting

    Those thermal actuators can be a real pain.....And they never fail when you don't need the 4x4
    I have replaced a few over the years.....
    I think you made the best choice with the posi-lock.....
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  5. #5
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,077

    Default

    I miss my Warn hubs, and slogging through the muck to lock them. (Actually, as you all know, the key is to lock them before you go into the mud...)
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  6. #6
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,409

    Default

    Locking hubs are IMHO the best thing ever invented.....
    The new single wide bearing "Hub assembly" are a poor design and do not do well with big tires....
    The electric actuators (Or vacuum or ?????) are trouble waiting to happen and at the worst possible time.

    Flip the hubs in before you get into the rough stuff and then yank the lever when needed.

    In all my years with 4x4 rigs....Never had one of those fail

    Some of the "Auto lock" hubs were sketchy.....Take them off and throw them in the dirt....Get a nice set of Warn hubs....Life is good....
    I will say this....Most of the stock GM standard locking hubs were decent.

    Trying to improve on near perfection is usually a waste of time (Auto lockers)

    Now we have a button on the dash that tells the computer what to go do and then various modules and the maze of wires to make another gizmo activate the parts to get the 4x4 working.....
    What part of insanity is this ???

    With the 4x4 shifter off the floor it allowed the center console to cover the hump area.....aesthetics was more important the common sense.
    Tossing your gloves on the hump to dry by the heater vent was perfect......

    I digress....
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  7. #7
    Join Date
    Dec 2003
    Location
    Yukon Canada
    Posts
    1,690

    Default

    I agree to much BS in modern vehicals
    Locking hubs and a leaver, pretty much bullet proof compared to a new truck where a bad wire will leave you with a useless truck in 2WD
    my 04 GMC gasser has an issue with the electric passenger side window again, i fixed it about 10 years ago. I have never had a manual window give me grief since i started driving. It's always the electric ones that FU ,switch, wire, motor. Have had issues with all of them.Up here in the cold it is usually the wire that breaks by the door hinge.
    The last time it was the motor in the 04,water gets into the housing rusting the motor shaft which makes it hard to turn which then pops the circuit breaker leaving the window down.
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  8. #8
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,409

    Default

    The stuff of late use "Body control modules" to run all the accessories on the rig
    The window button just tells the BCM what you want and it activates a relay that feeds the power to the window motor......
    Far too complex.....
    Sort of like bolting a computer to a broom.....Rather sketchy

    I have rarely had issues with electric windows in the older rigs.

    Yeah the motors can die....But the more they overthink the plumbing the easier it is to plug up the drain......

    I would love to find an old square body in good shape.....The 91 Burbs and Blazers were sweet....
    The bugs were worked out and there were rarely any issues
    Actually....Get back to before the electronic transmissions (TH 400 ERA ) YEAH...Pretty bomb proof...

    Ya notice that all the military rigs (HUMMER) They do not have electronic trans or electronic injection.....That says it all....

    Just not dependable enough when the going gets tough and ya gotta get outta Dodge in a hurry....
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  9. #9
    Join Date
    Dec 2003
    Location
    Yukon Canada
    Posts
    1,690

    Default

    I need a good blazer to round out my square body collection, of course they are hard to find in any condition here
    I do have a project one, rust free but heavily damaged by the drivers door.Arizona truck that got hit hard.I would have to replace the firewall drivers door frame and floor boards,already sitting on a good frame
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

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