Truck is an 02 FX4 4.6L with 8.8 locker rear end

I got new tires six weeks ago; went from Michelins to Firestone Desination A/Ts. The ride was definitely stiffer, as expected, but didn't notice any extra vibration.

Three weeks ago it was time to replace the rear pinion seal. The leak had been very gradual, like almost nothing, then a week after adding fluid and pulling a trailer 1200 miles it was dripping from the right wheel well, spring, wheel, etc. I didn't have time to deal with it so I added more fluid and drove it for another week.

When I finally got around to fixing it, there was a .020" deep groove worn in the bearing surface on the right axle shaft. When all was said and done, I replaced axle bearings and seals, right axle shaft, front pinion bearing, crush sleeve, pinion seal, pinion flange, and pinion flange nut.

First drive on the highway I noticed a slight shimmy in the seat of my pants, which felt like it was coming from the rear. It was more noticeable on some roads than others. Went to a different Firestone dealer to have the wheels re-balanced. Front left was out 1oz, front right was out 2.75oz. The vibration was immediately, significantly worse, and could also be felt in the steering wheel. Then went to yet another dealer yesterday and they road-force balanced all wheels, but the vibration still feels pretty much the same. Also they pointed out some slop in the steering link, and the outer left tie-rod.

The more I drove it yesterday, the more I started to suspect the rear shocks, but those checked out fine. When I got home I jacked it up and inspected and found two issues:
1.) The new axle has twice as much lateral slop as the stock one (0.045" vs .090")
2.) Even though the left axle shaft showed no signs of wear when it was all apart, there is some play between the bearing and bearing surface on the axle.

Questions:
1.) Could the play in the left axle cause that much vibration? After all, I didn't notice any when the right axle was worn down.
2.) Could an issue with a differential bearing cause vibration that feels like an out of balance tire?
3). Whats the likely-hood of it being a defective tire? Wouldn't the road-force have discovered that?
4.) Is the additional lateral play in the new axle anything to worry about?
5.) Could it be an issue with the drive shaft not playing nice with the new pinion flange?
6.) Could the right rotor have warped from heat build-up when the axle bearing wasn't getting proper lubrication?

PLEASE HELP

 

If they rebalanced them and added that much weight and it gets worse, to me it sounds like an incompitent tire shop.
I am not too sure about the axle play you have, I would think that you would want as little as possible but the .09" I do not believe is much to worry about.
How are your U-Joints on your driveshaft?
Your brakes cause more heat than that worn out bearing.

Take it back to the original tire shop and have them spin the tires on the rim and re-balance them. Do you have aftermarket rims?

 

I am going with option number 3. Yes road force balance would discover that. Ask to see the results from it, I would say it shouldn't be more than 8kg out. They may be hesitant to do that because if it is no good they need to replace it. They could also try putting your tire at 180* from where it is now on the wheel.

 

Thanks for chiming in guys. And sorry for the looonngggg post. To answer your questions:

Yes I have aftermarket wheels, though not really sure what difference that makes.

I have not checked the driveshaft. Not sure how to unless its just a matter of giving it a wiggle and feeling for play.

I'm replacing the rotors and pads this week along with the steering idler arm (which has a significant amount of play) and I will go from there. If the vibration persists, I may break-down and to go to a suspension shop in town that I trust. I would surely get an unbiased opinion about the tires there.

 

Take it back to the tire shop and have them "clock" the tires on the wheels so they will balance out using less than 1 oz of weights.

 

Are the rims the same ones with the Michelins and afterwards? If the rims are new, they could be out of round or not hub centric.

Inspect the rest of the suspension and make sure everything is within spec.

 

Roadie- The rims haven't changed.

Did the brakes and idler arm yesterday. Will see how it feels on the highway today. If the vibration persists, (and I suspect it will) I'm going to try the spare in place of the wheel with the most weight and see how that feels. Then at least I have some concrete evidence to present when I go back to Firestone.

 

I just went thru the same thing with Firestone. New tires replaced very worn out Michellins and had shimmy at about 40 mph and bad vibration at 60 mph. I checked and found left rear tire .250 out of round. They replaced with no problem. Two days later the vibration back at right rear This time they wanted to blame my wheel as having a problem. On road force balancer .230 lateral runout. They still said wheel. (Did I mension I am an auto teacher and an ASE master tech) I knew better as I had checked the wheel. I finally told them to dismount the tire and spin only the wheel and that if the wheel was the problem I would pay for a mount and balance. I left a few minutes later with a new tire.. No amount of re-clocking the tire would have fixed the issue. ( they tried). What happens to the average consumer with no mechanical training?

 

Finally got around to trying the spare tire; boy was that a waste of time. It must be bent because the vibration got worse.

Anyway, I went back to the original Firestone store, and was pleasantly surprised. The tech took it out on a new stretch of highway nearby, came back, and clocked the right rear wheel. Then he took it back out on the highway to test his work, and called it done. Then the manager said if I still wasn't satisfied, that they would replace the tire. I haven't had it on the highway yet, but I have noticed a difference at lower speeds already.

Will update if anything changes.