Re-geared...i Think

[William Brown]

I bought my truck used(2004 3500 8.1 Allison dually w/22,000 mi.), somebody put a lot of money into it before I bought it (dual dynaflow exhaust, headers, CST 6" lift, fox shox, power rear window, Whipple supercharger, 33" BFG's....) Great truck, but I have A LOT of questions, when traveling at normal speeds 0-50 MPH in 4hi, there is a definate vibration. I have checked the front drive shaft, its not bent. Maybe CV's bent?? The engine is now creating

550HP/830 ft. lbs at the rear wheels. My thought was that maybe the rear was re-geared but not the front? I dont really know anything about trucks mechanical workings, so any help would be greatly appreciated. Is there any way I can find out who did the work? Please see my other post about the Allison tranny, also need help with that.

[Chestah]

I believe that if your front end was geared differently you would have larger problems than vibration.

[markw8]

There is probably a direct link between the 6'' lift and the vibration. My first guess would be rear drive shaft u-joints out of phase. Mark. I guess the fronts could also be the problem.

[wellinghurst]

I believe that if your front end was geared differently you would have larger problems than vibration.

 

A big 10-4 on that one. I am sure something in the suspension/tires is causing it.

[Silverado4x4]

I would try to contact the dealer and see if they will give you the name of the person that owned it before you. Be careful with the allison with that much HP&TRQ unless the tranny has been modded for that power then you should be ok, if not you will limp the tranny if your really getting on it hard. Limp means the tranny clutch packs pick up slipping will go into abuse mode and only let stay in 2nd if I recall correctly. If you limp it once it gets easy to do it again. As said above sounds like the front driveshaft is eather out of sync with the "U" joints or out of balance. If the gears are differant from the front and rear you would have eather broke something quick in the front or be dragging the rear wheels. The allison is a tuff tranny in stock form but doesnt handle high HP&TRQ very well unlees its been beefed up.

[William Brown]

Thanks for the help, how would I go about getting the drive shaft balanced. Is this something that an ardanary shop can do? Sorry if my questions are dumb, but what does it mean when the CV and drive shaft are out of sync? Is this an easy fix? How much damage could this cause driving through two winters?

 

Thanks again

[Silverado4x4]

The driveshaft "U" joints have to line up with each other meaning well its hard to discribe by words, look at the front driveshaft and look at the u joints as a plus sign like this + now if the front of the shift is like that and the rear of the shaft u joints are like this x then the joints are out of sync. To correct just remove the shaft from the truck and pull it apart it will slide apart. Now if its not balanced right any shop can do it if they have the equiptment or they can send it out to be balanced. The CV shafts aways turn no matter if its in 4wd or 2wd. Hope this helps.

[ws6_guy]

sounds like a d**n nice truck. 50mph in 4wd hi i thought that wasn't good for the trucks

[justin95]

If the vibration is in 4 high only you need a new front dual carden drive shaft. They are like $400 or so.

[wellinghurst]

sounds like a d**n nice truck. 50mph in 4wd hi i thought that wasn't good for the trucks

 

shouldn't hurt anything...AWD vehicles are good over 100mph. I drive 50+ in 4wd when the roads have snow on them.

[StoneyPgh]

I bought my truck used(2004 3500 8.1 Allison dually w/22,000 mi.), somebody put a lot of money into it before I bought it (dual dynaflow exhaust, headers, CST 6" lift, fox shox, power rear window, Whipple supercharger, 33" BFG's....) Great truck, but I have A LOT of questions, when traveling at normal speeds 0-50 MPH in 4hi, there is a definate vibration. I have checked the front drive shaft, its not bent. Maybe CV's bent?? The engine is now creating

550HP/830 ft. lbs at the rear wheels. My thought was that maybe the rear was re-geared but not the front? I dont really know anything about trucks mechanical workings, so any help would be greatly appreciated. Is there any way I can find out who did the work? Please see my other post about the Allison tranny, also need help with that.

Google: rpm / gear ratio @ 60 mph, you'll get the formulas that will also account for tire size.

[markw8]

With 6'' of lift, your problem is less likely to be out of balance than ot of phase. Each joint on the shaft have to operate at the same angle. If each is different, it will tend to vibrate through the shaft. At 6'' the angles are all but certain to change. A c/v joint on one end may fix this. This is similar to what justin95 suggested. Mark.

[William Brown]

With 6'' of lift, your problem is less likely to be out of balance than ot of phase. Each joint on the shaft have to operate at the same angle. If each is different, it will tend to vibrate through the shaft. At 6'' the angles are all but certain to change. A c/v joint on one end may fix this. This is similar to what justin95 suggested. Mark.

 

But wouldent the vibration be present at all times, not just in 4wd, since the CV spin reguardless? The vibration, from what I can tell, is present at all times when in 4wd, just more prevelant at differing speeds, somewhat like a washing machine when the clothes are out of balance, it will be less noticible when at top speed, but when it starts to slow it will become worse as speeds decrease until stopped. (if that made sense!!) Also the lift droppes the front diff down with the suspention, keeping geometry. The CV's are parallel with ground.

[William Brown]

Is there any thing that I would be able to see if the tranny had been beefedup? somewhat like the sticker on a computer "if removed no warranty..."

[Silverado4x4]

It will be impossibe to tell if the tranny is beefed up from the outside. Suncoast and Pacific does alot of Allison performance trannys but dont know if they put there decals or tags on the trannys if it was bought as a whole tranny.The front driveshaft and transfer case is the only thing not spinning when in 2wd. To eliminate the transfer case remove the front driveshaft and take it for a ride in 4wd and see if the viberation is there, if not then more then likely its the front shaft, as said after reinstalling the shaft and its back then the shaft is bent, out of balance, "u" joints are shot or out of sync.