Driveline vibration issue

[sparkzaflyin]

OK.... 1972 CJ5 , T-15 , Dana 20 , Dana 44 rear pumpkin. Replaced u joints at rear drive shaft, rear diff half low. Filled diff to hole with GL5 with Limited slip additive (Sta Lube 80W90) Vibration only occurs at 55mph, smoothes out at 60mph. Transfer oil good, tranny oil good. this has only been occurring within the last month and seems to be getting worse. Any ideas? Thanks in advance for any direction!

 

[Torxhead]

Your recent vibration issues could be from placing the driveshaft back in a bit different. Possibly from the leaf springs sagging a bit more also. Do you have a constant velocity u-joint?

 

[WHATROAD]

Anything that could have changed the angle of the line to the diff. bent axle, spun diff.?

 

[sparkzaflyin]

Your recent vibration issues could be from placing the driveshaft back in a bit different. Possibly from the leaf springs sagging a bit more also. Do you have a constant velocity u-joint?

Leaf springs seem good. Standard Spicer driveshaft with standard u joints as well. I made sure to index the driveshaft before I removed it. New u joints are in phase too. Maybe the Transmission mount moved some on me, I'm a fan of using the skinny pedal sometimes. The shaft angle visually looks ok, but I haven't measured it to be sure. I replaced the u joints because of the vibration issue. It started before I replaced them.

 

[sparkzaflyin]

Anything that could have changed the angle of the line to the diff. bent axle, spun diff.?

Diff hasn't moved, I don't think I have a bent axle, it's a gravel road off-roader at best.

 

[Lumpy Grits]

Did you remove the slip spline while doing the u-joint R&R?
If you did-You may have the front and rear u-joints out of 'phase'/alignment. You may think they are aligned. But a flat surface, may show otherwise-BTDT
What amount of lift are you run'n?
LG

 

[tarry99]

Did you remove the slip spline while doing the u-joint R&R?
If you did-You may have the front and rear u-joints out of 'phase'/alignment. You may think they are aligned.
LG

What Lumpy said........or What made you think the vibration was from the driveline? Could very well be tires out of balance.

 

[sparkzaflyin]

Did you remove the slip spline while doing the u-joint R&R?
If you did-You may have the front and rear u-joints out of 'phase'/alignment. You may think they are aligned. But a flat surface, may show otherwise-BTDT
What amount of lift are you run'n?
LG

Didn't remove the slip spline. I have a one inch body lift, looks to be stock suspension, shackles, etc. otherwise. I think I'll check the driveshaft on a flat surface to be sure.

 

[sparkzaflyin]

What Lumpy said........or What made you think the vibration was from the driveline? Could very well be tires out of balance.

The "seat of the pants" feels like its coming from the rear half of the truck. Ill check to see if I'm missing any weights.

 

[Lumpy Grits]

Do a tire rotation and see what that does.
LG

 

[sparkzaflyin]

Here we go.... upon further closer inspection it seems as if my Transmission mount has collapsed some. The torque stud bushing also isn't flat, its compressed on one side towards the centerline of the tranny. My motor mounts are compressed as well towards the rear of the truck. I think that is probably my problem, new parts on the way, motor mounts, torque stud assembly and tranny mount(OEM rubber mounts). Thanks everyone for your feedback. Question: my frame is boxed in at the crossmember bolt locations. Does anyone know if those bolts are welded in place? The boxing in was probably aftermarket. I hope the PO has the wherewithal to weld them fast before boxing. It looks like I have to support the tranny with a jack and then remove the crossmember to remove the mount.

 

[Lumpy Grits]

Pricey-But well worth it.
I've run these for 20+ years.
Engine-
https://www.mountainoffroad.com/bomb-proof-motor-mount-kit-pre-99-cj-with-amc-6-cyl.html

Tranny-
https://www.mountainoffroad.com/transmission-mount-66-95-yj-cj.html

The OEM stuff you find today is from China, and it's a pile of

The OEM frame used nut-plates.......

LG

 

[sparkzaflyin]

Okay, vibration issued solved by installing new tranny mount. Question: How much do I tighten the top compression nut for the upper half of the torque bushing?

 

[Torxhead]

Thanks for the update. For me, I use all poly bushings and tranny mount and keep them fairly tight. Since I have watched the gear shifter bounce around going up steep and rocky hills.

 

[Lumpy Grits]

Come down 2-3 full turns on that nut.
LG