55+ vibration - Help

[tdangle]

New update: Since the rear end is an open diff type, I raised one side off the ground and run it up to about 50 MPH per the speedo. I know the tire is running 2x as fast. Same vibration. if I drop the speed to 25 on the speedo, no vibration. So this leads me to driveshaft speed at 50 is when vibration starts. did the same thing with a factory steel wheel, no change. Tried the other side and same thing.

Took video of the drive shaft at the trans, carrier bearing and rear axle. Nothing looked out of place.

Rear end has a weird noise especially when slowing down during this test. I starting to think something is amiss with the Dana 60 rear end. Oh and incase if was missed in an earlier thread, driveshaft has been fully rebuilt and balanced twice, once when it was rebuilt and the other when it was shortened for my new trans.

[Accelo]

Vibration is same in 3rd or OD or neutral. Accelerating or decelerating no change.

This statement eliminates the motor and transmission as they change speed and the vibration remains. Only transmission issue related this this would be the output shaft bushing. I am assuming it is tight, but would like to hear from you on this one.

I unbolted the driveshaft from the rear end and by hand turning the yoke took up all the slack or free play in the piñon gear

This is common, if you are referring to radial play, on an open differential. The spiders have slack. This is from the axial play between the spider gears. The only method to measure gear back-lash is to have the cover off and physically retain the pinion when measuring the ring gear at the outside diameter.

Things you may try;
Sounds like you have had two different sets of tires on the truck with the same results. Let’s assume it's not the tires. The axles have been touched upon. If you look closely at the outside diameter while they are on the jack stands and rotating you may be able to see any axial or radial run-out. Since the road force balance would identify this if it was in the tires or wheels any movement would be attributed to the axles. If you haven't rotated the front tires to the rear also try that. Check for radial & axial play in the axles by lifting up on the tires while the truck is supported off the ground by jack-stands on the axle.

I am assuming you also ran the truck up to speed with both the tires rotating, while it was on the jack stands. This should have reproduced the same vibration. If it didn’t, I would watch for run-out on the OD of the tires. With luck you may be able to tell the difference between driveline induced vibration and tire vibration. As the one frequency will be four times higher than the other. Tires are the usual suspect as they are a much heavier rotation mass.
Check the driveline U-joints are phased correctly. Typically, the spline is indexed so it is impossible to get incorrect but you have done you do-diligence on all the normal items this should be on the list.
If you still have the issue after all this work I would likely go after the differential bearings. Start with the differential. Sometimes the fit will denigrate and this causes looseness with out the rumbling associated with bearing noise.
Changing the 90W and looking for debris in the oil would be an easy first step. You could confirm the back lash at the same time.
Cheers

[tdangle]

Double checked index. Drive shop put yellow dots when balancing and I have in in correct. I did drain and install new fluid really should have taken my time and checked a few things while open. I’m suspecting play in the spider gears or shaft. Not sure how an axle could be bent as this is a full floating axle, but I will check it also
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[garyd1961]

I'm a tire guy and all I can add is rotate your tires front to rear. If it's a tire problem the vibration should move from your seat to the steering wheel. I know you said you tried balancing your old tires and it still vibrated but I have seen more than one set of new tires that were so out of round you just couldn't balance them.
Oh, I forgot to say I had a 383 that someone left the bolt out of the balancer and started to wobble on the crank. Also double check to make sure you have the right flexplate for the motor, internally balanced vs externally balanced.

[tdangle]

Originally Posted by garyd1961

I'm a tire guy and all I can add is rotate your tires front to rear. If it's a tire problem the vibration should move from your seat to the steering wheel. I know you said you tried balancing your old tires and it still vibrated but I have seen more than one set of new tires that were so out of round you just couldn't balance them.
Oh, I forgot to say I had a 383 that someone left the bolt out of the balancer and started to wobble on the crank. Also double check to make sure you have the right flexplate for the motor, internally balanced vs externally balanced.

It would be great if it was the tires. Unfortunately it isn't. Same vibration with old tires, new tires, rebalancing, road force rebalancing, swapping out wheel and tire with another set. And not engine speed related. Same vibration in 3rd and OD at the same speed, also if I shift to neutral. No vibration in steering wheel, def coming from back. Jack up and put rear end on jack stands same vibration at the same indicated speed on the speedo. At this point I'm starting to think it is in the rear end. Uggg.

[BigBird05]

Since you are chasing gremlins, what about the transmission output shaft bushing?

[tdangle]

Originally Posted by BigBird05

Since you are chasing gremlins, what about the transmission output shaft bushing?

Vibration didn't change when I installed a different trans in. Went from 2004r to a built 7004r

[SCOTI]

I know you swapped wheels front to rear for validation. What about checking to see if the vibration is still apparent w/no rear wheels? Was there any notable difference? Try again w/no drums.

[tdangle]

OK, I think I found the source of the vibration. While I was installing pinion shims to raise the pinion a couple of degrees, I found that the leaf spring bushings are pretty much shot. when I unbolted the rear end from the leaf springs much to my surprise they had a lot of play in the bushings. Looks like the bushing had froze and was pivoting on the bolt. needless to say I have Hugh gouges in the brackets. that the leafs bolt to. I'm going to fill with weld, and install new bushings first and see if it's fixed.