Not Unbalanced Tires..what is it??

[Artum Snowbird]

Hi,
I've got a GMC 2500 4 by 4. It thumps down the road from 45 to 50 MPH range. I thought it was tires as I had one replaced a while back for it was out of round. It feels very similiar to that. The tire dealer put four new balanced Michelins on. It still has the thump. I recently had front end work done, Pitman arms replaced at the dealer. I would imagine he would have checked most of the suspension parts.

One friend has said repack the bearings possibly. It's a cream puff, never off-roaded and only has about 80,000 miles on it. Can anyone else suggest that or any other suggestions?

Camping season is here now, and I don't want to be broken down with the camper one somewhere.

thanks, Mike

[oldyeller]

bad shocks? loose sway bar? check the driveshaft ujoints and carrier bearing if it has one. Wheel bearings, check the brakes..

[MD8349]

You could have a bad wheel. I had one on my 99 and once it was replaced it drives smooth.

[cprdnick]

I would also consider the transmission. I know that's not something you want to hear, but I had the same problem at around 50 miles an hour. I didn't really know what it was until the tranny started to overheat about 2 months down the road and started boiling fluid out the vent. When I took it in to my transmission guy he ripped it down and said that the initial problem was oily sand about 2 inches of concreated sand on one certain side of the torque converter. I know you said it doesn't go off road, but it would be something to look into and have checked.

[87 STEPPER]

If you lifted your truck the pinion angle of your drive shaft may be incorrect and it will cause the problem you have.

Another thing you may want to ck into is finding a good tire shop that doe's on vehicle tire balancing some times it's the only way to eliminate an out of balance condition due to a disc/rotor.

[piecesparts]

Take a look at the front wheel bearings, there may be one that is not snugged tight and the thump you hear is the wheel flopping around on the shoft.

[Artum Snowbird]

Well I thank you all for your opinions. After dealing with one shop for the new tires, and having them balance the originals, plus the ones they replaced them with, I took it to another shop to have them check out everything underneath. They drove it, then put the wheels onto their state of the art "Road Force" balancer. Two of the tires were out of balance by 2 1/2 ounces and two had to be rotated on the rims to get them within specs for road force.

Likely the old tires just needed a proper balance and I would have been fine. What the heck, new Michelins look pretty good on it!

Now it runs smooth again.