Allison 4X4 problem

REKIII · October 13, 2005

I have a 2001 2500HD 4X4 with the 8.1/allison combo.

I purchased this truck from AZ and I live in WI so I'm trying to go through all the stuff that needs to be checked before winter, coolant flush, fullsize battery etc.

I also want to make sure the 4X4 is working properly. So on the way home from work yesterday, when I got into town and the trans was all warmed up I put it into 4X4, which it did fine as it did when I checked it when I bought it. So I'm driving through town and every time I'd give it a little gas, the one or the other front tire would chirp. So I decided to see what it was doing so I took a left and gave it a lot of gas once I was going staigh and both the front tires lit up nd it was tourque steerling like mad, I thought I was in one of my modded neons for a second.

So after that I took it back out of 4X4 and everything went back to like it always was. Is this how these 4X4's are supposed to work?

Oh and this was all on dry concrete.

Any help would be appreciated.

Thanks

Bob

asilverblazer · October 13, 2005

What were the rear tires doing, I don't believe there is a differential in the T-Case so it is a definate 50/50 split front to rear. I don't see why the front would get so much more power than the rear to cause the symptoms you describe. What comes to my mind is different ratios in the differentials, causing them to behave differently. (I doubt this is the case but still I wonder what would happen...)

silverado3500 · October 13, 2005

Sounds to me like you have an open rear differential, and one rear tire was spinning and one front tire was spinning. If your spinning your front tires, I'd say the 4x4 is working

Only other thing I could think of, is if you have different sized tires front to rear. That would do it for sure.

dewfpo · October 13, 2005

You should have NEVER done this on dry pavement! You were asking to break something.

Measure the height of the front and rear tires on pavement to get an accurate measurement. They should be the same (front and rear) to have the tires rolling the same distance. Adjust your tire pressure to get the same diameter.

When you are on a loose surface, the tires can break loose to release all this tension if the tires are different diameters, but on dry pavement.........

Oh, and did I say...... NEVER engage 4WD on dry pavement?

DEWFPO

REKIII · October 13, 2005

The tires are all the same size so I doubt, even if they are worn different that there could be enough difference to change the gear ratios to the point of what was happening.

From what I could tell the rears were not spinning at all, but I couldn't tell if they had power either, I'll have to go on gravel to check that.

Another person I talked to hear thought my transfer case might be broken causing the front tires to have all the power in 4X4 and the rears to have it in 2X4

Very frustrating.

Bob

asilverblazer · October 13, 2005

I don't think the transfer case effects the rear as far as power delivery, when engaged it sends power to the front, not by engaging / removing / re-engaging the rears power delivery. From the sounds of it, If the rears were not spinning something is causing the front to receive all the power or at least more than the rear, I guess the t-case could be messed up some how but not sure how.

k3500 · October 13, 2005

Were you in 4hi or 4 lo? The torque steer is normal on dry pavement. As far as lighting the fronts up, the front diff doesn't have a posi from the factory, so only one tire should have "lit" up. It may be possible someone put a locker in the front which would magnify the torque steer and cause the tires to chirp on dry pavement

dewfpo · October 13, 2005

The tires are all the same size so I doubt, even if they are worn different that there could be enough difference to change the gear ratios to the point of what was happening.

<{POST_SNAPBACK}>

I am talking about actual tire diameter not tire size.

I am running the stock 245's at 45 psi front and rear and on muddy forest service roads when in 4WD the rear always wants to come around the front when accellerating because there is more weight on the front and the actual rolling tire diameter is smaller in the front than in the rear even thought they are the same tire size with the same pressure. I can lower the pressure in the rears, or raise the pressure in the fronts to even out the tire diameter, then all is well.

That being said, I think what you described is normal behavior on dry pavement. The tension needed to be equalized and the tire with the least traction and most bound up energy released.

DEWFPO

REKIII · October 13, 2005

OK ,I get what you mean by diameter, regarding air pressure, that makes sense especially with the 315's I have on there.

I just went out to the gravel lot behind the office and there I couldn't get the fronts to do what they were, the rears were spinning like normal, but I could tell I was in 4X4.

I don't think both of the fronts were spinning at the same time for more than a second or 2, then the tourque steer kicked in which is caused by the power going from the left tire to the right tire.

So since k3500 says it's normal on dry (which I won't do again ) I think I'll rest a bit easier, especially after my gravel escapades a bit ago.

Oh, BTW this was all in 4hi. I'm not even sure what the process is to put the allison in 4lo everything I read says to put the trans in nuetral first which can't be done on an allison.

Thanks for all the help.

Bob

Haulin' 8.1 · October 14, 2005

I can't think of a way to say this without sounding like a jerk but to put the Allison in nuetral you move your shift lever to the spot where the "N" on the gear indicator screen is surrounded with illumination. It's just like any other column shifted auto trans in that regard. And make sure you're at a dead stop before engauging 4LO or you'll have horrific gear clash.

I also think your tourqe steering was normal for a truck that doesn't have locking diffs. If you did have a slip limiting front differential torque steer would be minimal. With an open diff like most fronts around here only one wheel can transmit torque at a time, that would be which ever one has the least traction. That's why power slaps side to side as you floor it and tires alternately spin and jerk the wheel back and forth. The rear is a solid axle so driveshaft twist always lifts the right rear tire up so it spins more. You were probably spinning your right rear constanly and the fronts took turns spinning since they are independant and equally loaded. When your steering angle changed the other wheel was "unloaded" and became the spinner until the steering went the other way and the situation reversed.

In any case your stuff seems to be working.

Vernon

REKIII · October 14, 2005

Everything you said makes sense. Thanks.

About the nuetral thing, thats all you have to do? The the other trans' have a neutral button by the select buttons too.

Thanks again.

Bob

Frozen001 · October 14, 2005

Everything you said makes sense. Thanks.

About the neutral thing, thats all you have to do? The the other trans' have a neutral button by the select buttons too.

Thanks again.

Bob

<{POST_SNAPBACK}>

Are you talking about the neutral on the 4x4 buttons??? That is neutral for the transfer-case, not the transmission. Shifting into 4lo can be tricky until you get to know how to do it on the pushbutton setups. It all depends on where the gears are... sometimes it will go right in sometimes you have to roll a bit to git it to lock up...

asilverblazer · October 14, 2005

The transmission must be put in neutral before selecting 4Lo on the push button four wheel drive selector. The neutral on the transfer case Is more for flat towing the truck (I thinnk). I have the most luck going into 4Lo with an extremely small amount of forward motion, a fraction of idle speed slow. But this is all on a half ton so yours might be different.

Haulin' 8.1 · October 14, 2005

Hmmm, if his truck is like mine there is not a button to put the transfer case into nuetral. Only 2HI, 4HI, and 4LO. The selector panel is labeled with a nuetral between 2HI and everything else but that is just to let you know you should have the trans in nuetral before engaging the 4WD.

Vernon

dewfpo · October 15, 2005

Hmmm, if his truck is like mine there is not a button to put the transfer case into nuetral. Only 2HI, 4HI, and 4LO. The selector panel is labeled with a nuetral between 2HI and everything else but that is just to let you know you should have the trans in nuetral before engaging the 4WD.

Vernon

<{POST_SNAPBACK}>

Actually, you can put the transfer case into neutral on these models by holding down the two buttons linked with the white line if you hold them down simultaneously.

DEWFPO