Posted: 13 October 2009 at 21:36 | IP Logged

It's a wrecker. You feel no vibration in the steering wheel. The hood shakes, the lightbar shakes,  and you feel it in the seat. You would swear that it is a tire. Makes no difference if you are on or off the throttle or if you are in drive or overdrive. I suspect something in the output side of the trans (Allison).

Posted: 14 October 2009 at 08:44 | IP Logged

Another ? has this done it since you bought it new? if so do you have access to a wheel spin balancer that balances the tires on the truck, it could be brake rotors out of balance(just a thought).

Bad at 80km and goes away at 100km....sounds like something out of balance to me, since it goes away at a higher centrifugal speed of moving parts.

Is there any way of jacking the vehicle up and maybe driving the rear wheels to see if the vibration occurs and then maybe putting in 4wd and see if vibration happens

Posted: 15 October 2009 at 13:21 | IP Logged

We are waiting for GM to come to their senses and quit throwing parts at it. They ordered all the motor mounts and the trans and transfer case mounts. They say the transfer case needs to be mounted more rigidly because when they strap the t-case solidly to the frame the vibration is less. This fixes the result of the problem, not the cause. Bossman is going to have a talk to them with our new information regarding the problem. Hopefully they listen and we can get this thing fixed. We love the truck other than this problem.

Posted: 16 October 2009 at 19:15 | IP Logged

Got word today that GM has figured out the problem. They think the problem is in the torque convertor. We suggested that a while ago and they wouldn't listen. Hopefully they get it sorted out soon.

Posted: 27 October 2009 at 20:43 | IP Logged

Local GM dealer ordered a convertor last week. Said they wanted truck first thing Mon morning. At the end of the day they phoned us and said that they weren't authorized to work on an Allison med duty trans even though they are a med duty dealer. Tomorrow morning we have to tow our truck 230km to an authorized gm Allison trans dealer to get the convertor installed. NOT IMPRESSED WITH GM SERVICE!

Posted: 28 October 2009 at 10:05 | IP Logged

I KNOW WHAT THIS IS!

It's the same problem I had with the Hino. I really believe you are barking up the wrong tree with the converter.!!! You need to print this post and take it to your local truck tire company.

http://www.towtalk.net/forum/forum_posts.asp?TID=4848

Posted: 28 October 2009 at 17:40 | IP Logged

Thanks for the suggestion. When I had the truck at our shop i took all of the wheel off of our '06 Topkick and swapped them. Same vibration. We have had 19.5 tires mounted incorrectly before and had vibrations. The tire shop we use now is aware of that problem and are pretty good at checking them. When GM was diagnosing the truck they also took tires off of a brand new one with no luck.  I know the tires on our '06 are good because it is vibration free at any speed. We're supposed to get the truck back on Monday night, so i will post a reply if it is fixed. Thanks for all of the replies!!