How Can You Tell If Your Front Axel (4x4) Is Posi-trac?

green 788 · December 5, 2008

I have a 1996 GMC dually, 4x4 crew cab.

It has the G80 code on the glove box sticker which I'm told means that it has the posi-traction rear end.

But how can you tell (other than going out and playing in the mud) if the front end is limited slip or posi, or not?

Also, my truck has skid plates on the transfer case, and on a couple other locations underneath. Were these standard, or special order?

Any help appreciated...

Dan

2000DV4.8 · December 5, 2008

The G80 isn't a posi, it's an auto locking diff (locks the two axle shafts together instead of biasing the torque to the wheel with better traction like a LSD).

If I'm not mistaken, lockers or limited slips were never offered for the front axles of these trucks (at least not from the factory), but I'm not 100% sure on that one.

Not sure about the skidplates, does anyone know if the 1-tons were available with the z71 package?

zaac · December 5, 2008

I have a 1996 GMC dually, 4x4 crew cab.

It has the G80 code on the glove box sticker which I'm told means that it has the posi-traction rear end.

But how can you tell (other than going out and playing in the mud) if the front end is limited slip or posi, or not?

Also, my truck has skid plates on the transfer case, and on a couple other locations underneath. Were these standard, or special order?

Any help appreciated...

Dan

I'm not sure if any of them are posi. I believe posi front diff makes steering very difficult when in poor traction situations. I had a car without posi and when I turned one wheel by hand the other one turned in the opposite direction. The other car I had with posi both wheels turned the same direction. Don't take this as the gospel.

green 788 · December 5, 2008

Thanks guys...

My mechanic told me that the front end was not likely to be posi or limited slip, due to the design. He said it's better to have a conventional front end 4x4 design in most circumstances, to help keep the front end from slipping sideways when driving on slanted surfaces (like around the side of a hill).

Appreciate the help.

Dan

Z45 · December 5, 2008

Limited Slip axles are normally installed in cars. All light duty trucks with option code G80 use a Eaton Locking Rear Differential.

Limited Slip Differentials installed in cars are also option code G80

For instance

My 2008 GMC has G80 and its a Eaton Locker

My 2005 Cadillac CTS has G80 and its a Limited Slip Differential, Getrag makes the rear axle but I have no idea who makes the LSD.

The only advantage with a locking front axle would be strictly for off-road ONLY use. On highway they would be hard to steer and could be dangerous to the unsuspecting driver. Even G80 can be dangerous. I know of someone who side swiped another vehicle because he gunned it in 2wd on snow covered road and the G80 dug in and he fish tailed hitting the car next to him. Got ticketed for reckless driving. Anyone who had driven a G80 locker in 2wd on slippery roads knows very well the rear end can jump out on you very fast when one wheel gets better traction then the other, especially if the surface is not level.

asilverblazer · December 5, 2008

Skid plates were likely a stand alone option on his truck completely independent of any Z-71 option. Back then I don't think Z-71 was available on the 1 tons, it probably was an option much like skid plates are now. (Or were the last time I looked.)

Z45 · December 5, 2008

Skid plates are option code NZZ, you could order them on any 4x4. Standard on 1500 4x4 Z71 from 88-07.

Up until the new 2007 body style Z71 was only available of 1500 4x4 trucks. With the 2007 NBS they became available on the 2500 trucks but I don't see it available on 3500 series.

flyin6 · December 8, 2008

You don't have a posi, limited slip or locker in your front, GM doesn't do that. Isn't wise either for the average driver.

The serious off road crowd will add either a limited slip or a full on locker to our front diffs. I have one in my crawler truck, an ARB air locker.

You can not steer with the front wheels locked, you just go straight ahead, so you can see what a nightmare it would be for GM with a bunch of mall cruisers running into each other the moment they engaged the front axle.

If you are considering a front diff mod, and you are anything other an extreme rock crawler type, add a limited slip only if you can disengage the front drive axle while driving normally on streets. Do not bolt in a locker for a mostlu street driven vehicle.

green 788 · December 8, 2008

You don't have a posi, limited slip or locker in your front, GM doesn't do that. Isn't wise either for the average driver.

The serious off road crowd will add either a limited slip or a full on locker to our front diffs. I have one in my crawler truck, an ARB air locker.

You can not steer with the front wheels locked, you just go straight ahead, so you can see what a nightmare it would be for GM with a bunch of mall cruisers running into each other the moment they engaged the front axle.

If you are considering a front diff mod, and you are anything other an extreme rock crawler type, add a limited slip only if you can disengage the front drive axle while driving normally on streets. Do not bolt in a locker for a mostlu street driven vehicle.

10-4... thanks for the info.

Dan

uh6tdrvr · February 13, 2009

And its a IFS....so i really REALLY doubt there's a LSD in it.

green 788 · February 14, 2009

I went the other day to pick up a 6000 pound 32 foot camper that I had bought from a friend... and it was sitting in a pretty mushy wet field, about 300 yards in...

I was quite proud of the truck for getting the camper out of there. The wheels were buried in mud at times over the sidewalls of the tires (to the rims), and although the truck did hesitate and spin some like it was going to get stuck, I just kept the pedal down and it continued to pull on through.

The rear locker really is a great advantage, I was easily able to tell that. I can say with certainty that without the locking rear differential, I'd have been looking for a tractor to get me out of that field.

And the front end only pulls one wheel at a time, though it did switch back and forth between which front wheel was pulling... I'm guessing the one with the least traction was the one pulling and spinning... but the truck still came along quite well, considering the 6000 pound trailer hooked to it.

Dan

Nytemare · February 16, 2009

If you want to know for sure, jack up the front end, support it on axel stands for general safety, and get a friend to hold one tire. If you can turn the other one without his turning, you don't have any form of "Posi-trac".

But I agree with everyone else, it is highly unlikely, having an IFS and all, unless the previous owner did it aftermarket.

And like what flyin6 said....you wouldn't want one in there anyway...unless its an e-locker or ARB air locl...something that's disengage-able

killerbp79 · March 17, 2009

Im bringing back tha past!

I have a g80 rear end. How do you know if its the locker, or posi trak?

If its a auto lock, does that mean there is no switch? how does it work?

BTW its a 95 k1500

killerbp79 · March 17, 2009

i would also like to note that you can lock the front end. i did this on a previous crawler and it drove fine when not in 4 wheel. the axles wont lock up unless in 4x4....AM I CORRECT ON THIS???

green 788 · March 17, 2009

I don't know the answer to your second question...

But the G80 automatically locks both rear wheels together when one side begins spinning and the other isn't. It works in forward and reverse also. You can feel it "clunk" when the rear locks together...

Most good gear oils will already have the additive needed to make the clutches work properly, so you won't need the limited slip additive unless you use a sub standard oil. The Valvoline product (85W90) has the additive already in it, according to a Valvoline tech I spoke to.

Dan