Hey Y'all, I've been getting a vibration while driving. It becomes really noticeable over 45mph...and gets worse as speed increases. Not in the steering, the wheel doesn't shake, I've had an proper alignment done at a Ford dealer by their tech certified for classics and has 35yrs of experience. tires were balanced at the same time. He did note that the original bal ljoints were getting a little stiff. along with some ever so slight play in the steering box. The tires have about half to a 1/3 tread left. but they are old. Made in 2005. But no dry-rot.

Im thinking that maybe a belt has shifted or something. But I thought that would be caught during the balancing. A buddy suggested a possible bent rim. Which I would also assume would be noticed during the balancing process. they're the 92-96 Ford aluminum 15in wheels. tires are El Dorado ZR4 Radial LTs. 31x10.50s. I havent off roaded it, nor do I remember hitting any large potholes.

So any thoughts or suggestions would be helpful. Thanks!

 

In no important order, these are the most common causes for vibration in our trucks:

- Check that EVERYTHING in the front end is properly tight, including the steering box, see that you aren't missing any bushings, is there any indication that a shock might have failed?.
- Check the rear driveshaft and u-joints.
- If there is any grinding noise while you roll check the bearings, if those check, look at the rear differential.
- Check the tires for deformation or out of balance conditions.
- Check the operation of the engine and the engine mounts, look at the harmonic balancer.
- Check the radius arm brackets, is it loose? is it cracked?.

 

Another thing to look at is cupping in the tires, it's where the rubber that is between the tread and the inside of the tire separates. you can take it to a tire shop and they can tell or try deflating them till there is no air left and look at the tread, you should be able to see a small amount of wavyness in the tread. That was one of the 2 primary causes for the deathwobble I had in TGM a while ago. I wish I had taken a picture of the tread on my old tires when I had them replaced but I must have forgotten.

 

Check pinion flange at the rear diff. and the slip-shaft in the rear DS (the OEM units are sealed with a boot but it doesn't keep grease from getting out over time).

Check axle pivot brackets and bushings (2)
Check radius arm brackets and bushings (2)

A side note: Does the vibration manifest more while coasting or with the driveline under load? The double-cardon U-joint at the front of the rear DS manifests early failure symptoms by causing a vibration but usually begins as a vibration only when coasting (driveline not under load).

 

Since the wheels are aluminum, I would rule them out. I have never heard of that brand of tire...I would recommend to have a "road force variance done test" on the tires, but you say they are about half to a 1/3 left.....I wouldn't spend the money to have that done. Ruling out any other mechanical problem...and by what you're describing......I would say it's time for tires. Usually dealers will have a balancing machine that does that test. Call around!

 

Are they able to do a road force test on 31s? My experience with tire balancing machines they normally wouldn't allow any offroad tires, studded tires, or over sized. These might be stock size but they are still good sized. Just a thought.

 

I know the old Hummer dealership down here could do Hummer tires. I worked at a Jeep dealership and we had one. Dealers just like to charge dealership prices!! I know the purpose of the test was initially so dealerships could warranty and or test factory installed tires through whoever the maker of the tire was...Goodyear...BF Goodrich....Kuhmo ect. That way the dealerships and the auto maker could charge tire company with replacement tires and have proof the tire was defective and not to factory tolerances. We saw lots of them down here too!!

 

I see. The dealership I worked for mainly delt in Buicks and GMCs. nothing crazy, and if there was tires that were big or knobby, they outsourced them to Shwabbies down the road.

 

I don't believe it is Engine RPM related...I've ran it up to 55mph in 2nd to make sure. Shocks are Brand new and I've checked them to make sure they are tight.

The thing is now, I seem to have 2 separate vibrations. The one I originally posted about...Becomes noticeable at 45mph and worsens as speed increases. It is there if I accelerate or if I'm cruising.

The 2nd vibration...it's loud, and it only appears when I start to back out of the throttle....Feels like its coming from right under the floor. I've been driving it with the front driveshaft out. My front diff has alot of play and needs rebuilt. So I thought that it was causing the vibrations. No change.

I did take a look at the Rear U-joints...but thats about it...looked lol. I think I did change them when first bought it almost 4 years ago. I'll look into them more when I get home from work.

Motor Mounts are the Solid ones from JBG. Has a newer Trans mount.

I dont know about the Radius and Axle Pivot bushings...I took it to the Local Ford Dealer for the balancing and alignment. The tech is ASE cert. 35yrs of exp. and is Ford Classics cert. The only thing he noted other than the age fo the tires..The ball joints, which are the originals. were starting to get a little stiff. and there is some minute play in the steering box.

Ill get some pics of everything and post.

 

Is it possible for a torque converter to become unbalanced? Or maybe the flywheel or something...

 

grab your Tcase handle while driving i bet your rear DS needs some attention. make sure tcase is full of fluid and the rear diff as well, might even change fluid in both just to be certain.

last could be a bent axle shaft.

 

Try changing the load in back by a couple hundred pounds and drive before/after on the same section of road at the same speed to see if the vibe changes.

This will check the driveshaft slip joint. Loaded vs empty will change the slip joint position and if it's this it'll change the vibe behavior. I had such a vibe - it changed speed over time as the slip joint wore further.

I think I had this issue around 80k miles, in my case I drove the truck empty a lot and that's when the vibe was evident.

It was hard to home in on because when you put it on a lift the suspension droops and brings the driveshaft to an un-worn spot.

HTH,
- Jeff

 

Well, I believe I found the issue. Me and my buddy jacked the rear of the Bronco up over the weekend. Chocked it, started her up and dropped in 1st and let it idle. the smaller, rear section of the driveshaft is bent, quite severely, and also the pinion yoke, not the actual pinion, has some slop. Only thing I can think that could have caused it would be, That the pinion nut was not properly tightened down, allowing for the slop in the yoke, and over time...The shock from gear changes, off roading and abuse, and general old age. weakened the shaft.

So its looking like a new driveshaft, since these are trans and year specific. The local shop cant make one. JBG sells them for $240 new. But also looks like a new pinion yoke at the minimum axle-wise. the gears in it now are not what it rolled out of the factory with. So I think whoever did it was not that thorough, Cause My front 3rd member is just as bad.

 

wont you need a new crush sleeve otherwise it may throw your gear setup off when you tighten it down?

 

I didn't take that into consideration, I'll have to look into it some more. I still have to pull the drive shaft out and really look at it all. Either way, it got more expensive then I was planning on lol.