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OT Pickup Truck and 4X4 Woes...

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  • Willy
    replied
    A little more time now to explain how the TLA (thermal linear actuator) works.
    I doubt if Fasttrack was having problems before or he would of mentioned it, so for now I'll assume it was just the shorting of terminals that took out the actuator circuit.

    The major problems with this type of actuator is that can be slow when cold. It locks the front axle via an actuator that first uses a heating coil to expand a gas inside a sealed container, the pressure of this expanding gas is what pushes a plunger to lock the front axles together for four wheel drive. As my earlier link stated,(the link is an ad for a system which eliminates the TLA) the problems are usually cold weather related because it takes a finite amount of time to get things warmed up in order to function. Also it can unlock at the most inopportune time. Like what happened to a buddy of mine while crossing a cold river.
    A walk pulling a winch line in 18-20 inches of ice cold water with cold wet footy toes is a good lesson to not trust this system.
    Last edited by Willy; 11-23-2009, 08:35 AM.

    Leave a comment:


  • A.K. Boomer
    replied
    Yes some are vacuum/electric and some are electric/solenoid, they are designed for disengagement of the propeller shaft as even with your 4WD lever placed in 2WD the prop shaft still rotates going down the highway (powered by the wheels not the trans.) unless you have this front diff disengagement mechanism (or auto locker hubs or manual disengage),,, spinning a prop shaft is a real economy killer due to the fact that your wipping it around at almost 4 times the wheel speed (in 85w90 wt.) --- This disconnect is still not as efficient as having auto locker or manual hubs as these not only disconnect the prop shaft but also the CV joints and or u-joint axle assemblies --- there's still some drag there because there's two - but they are only traveling at wheel speed and the movable parts inside the front diff. are minimal...

    FT for the record no matter how you cross a 12 volt bulb you cannot burn it out with 12 volts

    The reason your light is inop. is due to the fact that there is either a disconnect (burnt contacts) at a switch or the engagement unit houses the contacts for the light in which case its not being engaged so it cannot complete the lights circuit...

    Leave a comment:


  • motorcyclemac
    replied
    I believe the reason your "4x4" light isn't coming on is because the electronic actuator that locks in the front axle isn't shifting. My dad has a 99 GMC... and his truck (I think) delays lighting the little picture of the front axle till it is locked in. My Jeep is that way. It delays the 4x4 light till locked in. I suspect that the switch that lights the light is also actuated by the mechanism that shifts the front axle. This the light cannot go on till axle is actually locked in. If you want to confirm that.. Jack up both ends off the ground put it on jack stands. Start the truck and put it in 4x4. You should see the front drive shaft spinning along with the rear.. and neither front wheel spinning. If it was working correctly you should see 1 front tire and 1 rear tire turning assuming you have an "open" differential in the front and rear as opposed to a limited slip.

    Check fuses.

    Cheers
    Mac.

    Leave a comment:


  • Fasttrack
    replied
    Wow - thanks guys! Now I've got a place to start. I guess I should've thought about this a little more. Without manually locking hubs, it should've been obvious that there would be an electrical or vacuum controlled actuator. It didn't even cross my mind...

    What a great forum. Quick answers on a whole range of topics

    Leave a comment:


  • rdfeil
    replied
    Fasttrack,
    That truck has an electrical actuator for the front axle. It might have a switch on the transfer case to activate that actuator or the switch might be in the shift lever mechanism. It is possible the switch got fried, but I would expect a fuse. Automotive electrical systems are actually very well protected and an automotive fuse blowing due to a direct short can make quite a loud pop. Either way, with the electrical system out there will be no 4X4 even if the transfer case is manually shifted the front end will still be out Check all fuses first... Then dig deeper.

    EDIT: I see others type faster than me .............
    Robin
    Last edited by rdfeil; 11-23-2009, 12:26 AM.

    Leave a comment:


  • Willy
    replied
    Here's a link to how it functions.
    Not the best but I gotta go.

    http://www.4x4posi-lok.com/PDFs/TSG_chevyK.pdf

    Good luck.

    Willy

    Leave a comment:


  • Willy
    replied
    I believe your pickup has a front axle actuator that is activated by a switch when you engage four wheel drive. You have probably inadvertently shorted the circuit that actuates the plunger in the front axle to engage the front axle when you shift the transfer case.
    Check a good shop manual for the circuit if you don't find something like a blown fuse or relay.

    Leave a comment:


  • IdahoJim
    replied
    About 20 years ago I was hunting with a buddy who drove a Chevy, and he'd just had the front end worked on. We ended up in the snow, and his 4 wheel drive didn't work. A couple of weeks later he called and said the technician had forgotten to flip some switch in the frontend when putting things back together, and that's why the 4x4 hadn't worked. Apparently there was some electrical system in there. I know nothing about Chevy's 4x4 system, though. I'm assuming that my buddy's truck didn't have lockout hubs, and the wheel, or wheels, locked to the axle electrically, or maybe there is an electric valve that controls a vaccuum-operated lock for the hubs.
    Jim

    Leave a comment:


  • Fasttrack
    replied
    Originally posted by steve45
    '89? Doesn't it have a lever on the floor for the transfer case? My '89 Suburban had a lever on the floor, as did my '95.

    My 2000 Suburban is electronically controlled.
    Yes, that's correct, which is why I assumed it was "purely" mechanical. It just seems like an awful coincidence that it would go bad right after this little electrical issue. I checked the transfer case fluid level regularly (every two oil changes) and it's worked great up until now. I've only got about 70,000 miles on it...

    Leave a comment:


  • steve45
    replied
    '89? Doesn't it have a lever on the floor for the transfer case? My '89 Suburban had a lever on the floor, as did my '95.

    My 2000 Suburban is electronically controlled.

    Leave a comment:


  • Fasttrack
    started a topic OT Pickup Truck and 4X4 Woes...

    OT Pickup Truck and 4X4 Woes...

    1989 Chevy K2500

    So I was looking for an ignition on circuit to install a CB radio. I was all jammed up under the dash, my head on the floor board and my feet up in the air and a multi-meter in my hands. Well, I slipped and in the confusion my multi-meter lead crossed a couple of terminals. There was an arc and a "pop" noise that sounded like it came from the vicinity of the trans tunnel.

    I noticed later when I put it into 4X4 mode, the light wouldn't come on. I assumed that the pop I heard was the light blowing. Well a few weeks ago I was helping with Harvest and drove my pickup out into a wet field. Ordinarily, no problem with 4X4. This time, I got stuck. I leaned my head out the door and saw the back tires spinning and my front tires doing absolutely nothing. I had to drag my pickup out with another pickup - a 1995 Chevy K1500. It had no problem toodling around in the mud, since its 4X4 was working ...


    Any ideas where to start? I thought the 4X4 engagement was purely mechanical. Is it just a coincidence that my 4X4 dropped out after I accidently shorted something out, or is there a solenoid or some such that I might have burned up?

    Thanks!
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