shudder in 4X4 on snow

[Jim Leap]

Hello,

Today I drove my 91 (5 speed with limited slip) up a very steep snow covered road. I had chains on the front wheels and no weight in the bed. Every time the road got steep the truck would start shaking pretty hard. Slowing down or speeding up didn't seem to change the shaking. I am guessing this has something to do with the limited slip differential. I recently serviced the rear axle but neglected to put in the recommended additive for the limited slip. Could this be the problem? The U-Joints are good. Any advice or suggestions would be greatly appreciated.

[IowaCummins]

i get this problem every year. i think its just the weight and slipping of the truck doing so. seems like it happens with out my plow on regular weight, but with the weight of the blade it goes away?

[KTA]

Check your front CV real good and see if it isnt loose.

[Jim Leap]

Thanks for the replies. The CV is new and the U Joints on both drive lines are in good shape. The shaking was definitely similar to what would be caused by a bad CV. The shaking was so bad that I ended up parking the truck and going the rest of the way on snowshoes. I can't imagine what else it could be but I definitely need to get it figured out. I was almost tempted to pull the rear drive line to isolate the problem but the snow was pretty deep and I didn't have my tool box.

[KTA]

Is the entire cv new or just the u-joints in it? Is the truck lifted at all?

[Mark Nixon]

How loose are your chains on the truck?
If they aren't properly installed, the crossbars will "roll" under the tires and give the same effect as what you describe.
Deeper snow on the surface, plus an uphill grade will compound the problem.

Tire pressure is also very critical.
I once had a very bad traction problem pulling with chains through the Rockies, it would pull real hard to the right and get the truck really squirrely.
Later on I realized it was because the driver's side outer tire had gotten a nail in it, and gone flat in the time after I put the chains on.
Since it was a dual wheel and it was snowy, it was hard to tell that the tire was low, so I thought I had brakes hanging up on the trailer.
Kept air in the tire and never had a problem after that.

Mark.

[Richie O]

Have you ever chained up the front before? If so did it do the same thing? Chains on the front are not going to be smooth. You will feel them chatter through the snow. It might have just been digging hard on the hills. As far as the rear posi i don't suspect you would feel any issues with that in the snow. Mine chatters on hard dry ground around corners, but on slippery surface it is smooth due to tires slipping. I only run chains on the rear with some weight in the back.

[Jim Leap]

Thanks for the replies. Much appreciated. I'll try to answer all the questions here. The truck is stock - no lift. The tire pressure was good and the chains fit really snug. The CV was rebuilt not replaced but it is real tight. This was the first time I have run chains on the truck. The conditions were pretty challenging since there was a layer of old snow on the road that was frozen solid and it was covered with about a foot of cold fresh snow. I went up the road early in the morning. I only had the vibration in the steeper parts of the road but the vibration was really bad. This is a non maintained forest service dirt road. I attempted to go back up the road later in the afternoon when the snow had warmed up a but and the vibration was less but still not at all acceptable. Something is not right. Seems like the solution should be obvious. needless to say I am anxious to get this figured out and fixed. I have been up that road numerous times in similar conditions in my 55 Willys PU with the front chained up with no problems.

[Jim Leap]

I was under the truck yesterday changing oil and greasing the steering and drivelines and I looked from the engine area back toward the transmission and noticed that there was a gap between the top washer and top insulator on the transmission mounts. The top insulator was free to spin around the spacer. Don't know why I didn't notice this earlier. Anyway, I went ahead and ordered new insulators. I'll install them today. I am thinking this could very possibly have been the cause of the vibration when I was pulling hard up a snow covered road. In retrospect the vibration kind of felt like the transmission/transfer case were jumping around a little. I think the combination of high torque and sloppy mounts could cause this kind of vibration. Any thoughts/comments?

Thanks,

[bmoeller]

In retrospect the vibration kind of felt like the transmission/transfer case were jumping around a little. I think the combination of high torque and sloppy mounts could cause this kind of vibration. Any thoughts/comments?

Thanks,

It is possible. Had a similar problem with my KW last summer. The trans was moving around and causing driveline vibrations under load. The drivers side mount was visibly shot, and got the set for the pass side as well. Was a good thing too. The steel plate in it was broke in half, and couldn't been seen til I went to pull it out and the other half almost hit me in the face when I jerked on it. Not small mounts with a 525hp Cat in the truck. Would've left a mark.

Something else to consider, is the chains making and breaking traction in the deep snow. Even a farm tractor with chains can get plenty of power hop and a bit jumpy as the tires try to climb out of the snow. Worse when there is some hard pack under the fresh stuff. It can beat you around pretty good.

[Jim Leap]

Replaced the transmission mounts yesterday. It is a different truck with the new insulators. I'm pretty sure the warn insulators were a factor in the vibration/shaking on the snow. Now I need to replace all of the cab mounts. They are pretty shot too and with the transmission firmly mounted I'm getting some of the engine vibration transferred to the cab.

[bmoeller]

Make sure the exhaust isn't touching the frame anywhere. It'll cause vibrations to be transferred to the cab as well.