Hello all, I have a 97 f150 4.6L RWD and am getting a serious vibration above 50mph. The following has been done.

4 new tires mount and balanced. I needed these tires, and got the a month or so ago, when the vibrations started, I took it back and the said they were still in balance.
Driveshaft rebuilt by a driveshaft shop (3 new Ujoints and Carrier Bearing)
The driveshaft shop that rebuilt it informed me that it was still vibrating after the rebuild of the driveshaft. So they pulled the driveshaft and diagnosed it and said it seems as if it's a transmission problem.
The transmission was replaced at 40K miles the truck is currently at 101k. I do not feel any slipping gears or loss of power. I also do not hear any whining or anything of that matter.

I am not 100% sure its the transmission, and don't want to take it to a transmission shop and spend thousands trying to diagnose it on a 25 year old truck..

Any other ideas on what it could be? It only does this as soon as I hit 50mph or so.

Thanks.

 

Damaged suspension ?
Damaged/loose wheel bearings ?
Broken/loose engine mount ?
Alignment problems?

 

Im gonna be honest, I am not a mechanic by any means. I did jack up the truck, and there is no play in the any of the wheels, as far as checking bearings and tie rods in the front.
I am wondering why the drive shaft shop would refer to it being a transmission issue. When they pulled the drive shaft and diagnosed it, it had to be on a lift i'm assuming.
Have you heard of transmissions causing vibrations at higher speeds only?

'

 

It's possible.

 

Maybe they should have checked the balance?
Did you check it to see if it is running absolutely true, with no runout (bent)
The rear axle yoke, is it tight? not loose on the shaft like if the pinion bearings are toast?
Out of round tires? Check the lateral and radial runout

 

Did the vibration start after the tires or the driveshaft? Which was done first?

 

The tires were done before the vibration. Had them on there a month before it started. This started happening driving home from work on the interstate. Since then I’ve had the tires rebalanced and driveshaft rebuilt to try and fix the issue.

 

Did you jump any curbs after the new tires? If so, might be a bent rim. How much payload do you load? I.E. over load of stone or dirt or concrete etc... If so, could be a bent axle. Was your transmission rebuilt or did they install a used one? Did they change out the torque converter? Could be the torque converter. Did you jack the front up to check the play in the bearings? I don't know if the 2 wheel drive has the sealed bearing hub assembly, but if so, it could be one of those. Jack it up and wiggle up and down and side to side and see if you get play. Jack it up and crawl under it to make sure none of the shops dropped it off the lift. I bought my 4x4 used and from day one had a vibration at 40 miles per hour. I am convinced one of the rear axles is bent. Bought it with about 80k miles and now have 205k miles. Still has the vibration. Funny thing is, it seems to go away from between 45 and 70mph. Vibrations and electrical issues are a PITA. Good luck and let us know what you find to be the problem.

 

I have checked the bearings, as for as payload, the heaviest thing I haul is an atv, so nothing heavy has been loaded in this truck. The trans was replaced about 11 years ago/50k miles ago. I do plan to switch the tires back to front, so I can see if the vibrations change location to see if its a wheel issue, just havent got the time yet due to work.

Update: I was talking to a buddy of mine about the issue, and he said it sounded like a torque converter. He suggested I try a product called "Instant Shudder Fix" to see if it would do anything. I put the 2 oz tube in the truck and as I was going home it felt like nothing had changed. I ended up getting on the interstate and got up to 70mph, then let it come back down to 50mph, then boosted up to 70 mph again. I did this about 15 times. About 20 miles in I noticed I wasnt getting as much vibration. Turned around and drove it back home on the interstate. By the time I was hitting the exit ramp, the vibrations was nearly gone. I'll take it back out in the morning to see if the changes held up, but right now it's feeling 100x better than it did before.

 

Just a suggestion. I was chasing a vibration in a 300SRT I have. New tires and rims. Nope. New aluminum driveshaft. Nope. Alignment. Nope. Suspension in good shape. I had given up. Around 80 mph, it would vibrate and I figured when it got bad it would show.

Then I replaced the harmonic balancer. BOOM! Vibration is gone.