Hey guys. I've asked this question a while ago, but I couldn't get the problem fixed.

I have a vibration that seems to be coming from the rear end. Shakes the seats and cab but not in the steering wheel. I originally thought it was the new tires/rims i put on. But it's not. Trust me its not, I exhausted that option. I changed all 3 u joints and steady bearing but it's still there. From what I can tell I didn't loose any weights on the driveshaft/drums. What could it be? Comes on strong around 60-80kmh. It seems to get worse when I let off at highway speed. And it's not perfectly constant, it gets worse at certain speeds...

It's driving me crazy!!!!!!!!

Could it be something in the axel? Differential? Shocks? Transmission (skeptical)?

I should add its a '79 F250 supercab 2wd 400

 

Possibly the carrier bearing on the rear driveshaft.

 

I changed it, it's brand new. I called it the steady bearing, my bad.

 

Axle pinion bearing? Loose rear yoke? Axle out of alinement? Ck your u bolts for being tight? Have you dropped the dif cover to see if you have any ring gear teeth in there that are broke or chipped off? How are you axle wheel bearings?

 

Can you elaborate on the axels being out of alignment?

 

I believe I remember your earlier post. Vibration at that low speed is no fun. Anyhow, a few comments that may help and diagnosis.

The sneakiest vibration I had was slightly loose fit of wheel bearings on the spindle due to a slightly under size spindle journal. I chased that for a while. Diagnosis: bearing adjustment was unusually sensitive. Bearings had to be almost over tightened to get the slop out and after running for a while it came back. Jack up and check for slop by pulling/pushing the top and bottom of the wheel after running for a while. Measure journal diameter L & R. Fix was a new spindle.

Slop in the pinion bearings or transmission rear bearings or transmission drive yoke or slip joint. If the transmission rear bearing, drive yoke/slip joint or rear differential input bearing are loose, the drive shaft can flop around. Diagnosis is check for slop and compare, if possible, with a known "good" setup.

Indexing of the drive shaft. U joints need to be in phase. The slip joint on most of these trucks is not indexed and can allow "oops". Search FTE to find the diagram on correct indexing.

Tires (and wheels). I know you have had these checked. Still... my daughter's Jeep had a set that balance changed over time and they went out of round and balance. They vibrated at 65-70 MPH and smoothed out again over 75. By the 3'rd balance job they stopped changing. Thankfully they wore out and got replaced eventually.

I would jack it up and check for slop in wheel bearings and the drive shaft. Also check drive shaft indexing. Then start and let it run with rear wheels in the air and observe tire rotation and drive shaft movements for any signs of excess movement and out of round condition or wobble in the tires.

If that does not turn up anything, I'd have the drive shaft checked and balanced by a competent drive shaft shop.

 

Meaning your u bolts are loose or have been loose at one time and caused the axle plate pin on the bottom of the block to be worn and has let the axle shift, does the truck track straight down the road?

Someone has to follow you to really know that.

I would pull the axles and then the hub and insp the wheel bearings and races.

2 9/16 thin wall socket will be needed. Be ready to replace the brakes since you have it that far apart.

X3 on all blue & white said.

 

How brave are you, I ask because there is an old farmers trick to find out what the rear end may be doing. Block your front tires, lift up and well block up your frame so that your rear tires are about 6" off the ground, or find a ditch you can hang that rear axle over. Get someone to slowly speed up and look and listen to whats happening. If you have access to a heavy enough front end loader use that to lift it. You shouldnt need much speed to find out whats happening.

 

Similar vibration on my 51 IH pickup... it is the slip yoke on the driveshaft. It's worn out and causes the driveshaft to wobble at different speeds. Changes whether or not there is a load on it too, worse when coasting or very light throttle.

Can you physically move the driveshaft up and down or side to side by hand?

 

Some times adding or taking away shims on the carrier bearing support will help. As mentioned , first see if the u-joints are in phase.