Ok trying to figure this thing out. The guy iam going to buy the truck off of says that some one told him the pin was broken I am thinking he is talking about the acuator for the 4x4. Does anyone have any info on this does anyone no what else can cause this the parts to the actuator or other probable reasons. Also is there an easy way to tell. The truck is a 1998 3/4 4x4. Thanks in advance
4x4 does not work
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Molson02536
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The actuator on the differential is the thermal linear actuator (TLA). This part engages your front axle. Unlike old classic sierra which allow you to actually disengage the hubs, your truck separates the axle half shafts, which is why you could still see your front driveshaft moving, but no go-go.
When you engage 4X4, current is applied to the TLA which heats up and extends a pin on the section which protrudes into the diff. When the pin pushes into the differential, it reconnects the front axle. These TLA appear to be very failure prone, and they don't like cold weather. They also tend to retract if driven through cold water, and WILL retract when you shut the truck off, since power is no longer apllied to keep it hot. (When you restart the truck, the pin should re-engage...)
Replaced the thermal unit with the electric update kit, it works flawlessly at any temp and engages imediately after an initial 5 second delay at the relay. The kit comes with a wire harness, relay, and electric motor type actuator that doesnt need to heat up to engage. really simple to install, if i remember correctly, just need to tap into 1 or 2 of the wires at the t-case, run the small wire harness towards the front end , mount the little realy, replace the old actuator with the new one and connect the wires. any chevy/gmc dealer should be able to get you the correct kit for your truck.
Thanks I will check that out. So when the guy says the pin is broken is that part of the actuator or would that have to be another part I would have to buy. Also is it possible and hard to put locking front hubs on this truck. As I heard they are stronger and much better. Thank you.
Molson02536
New member
The locking hub is just a Manuel cable that replaces the electric one you have and your going to have to pull the cable to lock the from hubs. The kit as about the same price as the updated front hub actuator. Here is a link to the front 4wd to your Sierra and #19 is the actuator and #20 is the 4wd sensor indicator.
http://www.compnine.com/index.php?u...delid=6949&capuid=1&majorgroup=06&grouptype=B
Molson02536
New member
He means the Actuator is broken and needs to be replaced if he is correct on what is wrong with your 4wd system. Check to make sure the actuator is getting 12 volts when the 4wd is engaged (Brown wire), if your not getting 12 volts, then check the wire harness and fuse.
Keep me posted and we can go on from here.
http://gmcowners.com/gmc-forum/showthread.php?t=8480
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Right on thanks the hard part is I am away working and I have to send my wife down to take a look I will give her credit though she is more mechanically inclined then most guys. I figure with a bent A-arm they must have been 4x4 ing and hit something pretty good never heard of the a-arm being bent. I will let you know the out come it may be a week or two though.
hopesanddreamsracing
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im fairly new to this forum and this is my first post. but i have a 1500 z71 with the same problem. i dont know what trans or transfer case i have. other then its auto trans and manual nonlock hub transfer. but should i be looking for the same thing too.
Molson02536
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You got it, but start with the fuses and what year is your Sierra???
Keep us posted and we would be glad to help you get your Sierra running 100% again.
hopesanddreamsracing
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It's a 95. I know the linkage is good because it hose into neutral. But it dosent look like there's a fuse connection on the fuse panel along side the dash. Were would a find the engine trans and transfer code that tells me what modle I have. I know my engine is not the original but I don't know about anything else. Thanks for the help
Molson02536
New member
Here is a link to your front differential. Inspect #19 and #20, #19 is your actuator and you should be getting 12 Volts when your 4wd is engaged. #20 is the 4wd indicator switch, it indicates when your front differential is locked on not.
http://www.compnine.com/index.php?u...delid=6896&capuid=1&majorgroup=06&grouptype=B
Here is another link to your transfer-case, #8 is your transfer-case switch that provides 12 volts to your 4wd actuator to your front differential.
http://www.compnine.com/index.php?u...delid=6896&capuid=1&majorgroup=02&grouptype=B
Good luck and keep me posted, 90% of the time, it's going to be a bad 4wd actuator or the transfer-case switch. If your lucky's it my be as simple as a lose wire lead.