Vibrations on a Stock TJ

[brokeX4]

Howdy everyone,

I am a little reluctant to post this while I am still working through the myriad of vibration posts. However, the constant theme in those are around lifts. My jeep is sitting on stock springs and older shocks (ranchos on the way). When I bought the Jeep I noticed a good bit of vibration that starts around 35mph in 3rd gear (I have 3.73 gears). Then the vibration goes away as I shift into the next gear but comes back at around 2600 to 2800 rpm. When at highway speeds (65 building to 70 mph) vibrations are non stop. The vibrations seemingly get stronger as you work your way through the gears.

My best description of the vibrations are that they are felt in the floor board and pedals. Not so much in the steering wheel. Feels pretty rear biased.

The suspension doesn't seem to be sagging. All control arms have been replaced with crown units (fresh bushings). Same with track bars. I have also replaced the u joints front and rear with spicer units. Additionally, I replaced the motor mounts and trans mount with crown replacements. Just replaced the wheels and tires. Had them balanced by a shop I trust and don't feel like that is it (though I am glad to have them rebalanced). My plan is to get the jeep into my garage tomorrow to get drive line angles but I have a hard time believing it would be that since it is bone stock. I also feel like driveshaft balance is something to look at though it seems unlikely with how stubby this is.

Has anyone faced this with a stock TJ? I feel like I am taking the right steps but I am far from a Jeep expert let alone a TJ expert.

Thank you all and I will get those drive line angles posted when I have them.

 

[Mike_H]

I assume the vibes were present before you changed U-joints? I’d make sure they are seated in their yokes all the way and the straps are tight. You might need to put it on Jack stands and watch the the yokes rotate. Your may have a bent one.

Another relatively easy thing to try is switching wheels and tires with a Buddy and go for a drive. See if the vibes change or go away. You shouldn’t have angle related vibes (or any vibes at all) on a factory stock rig.

 

[AndyG]

The above post is great -

If it is stock I’d pull my front drive shaft and see what happens - or disconnect it at the front pinion and strap it up (do not do not engage 4wd) and drive it -

You may have lost a balancing weight or have a slightly bent shaft- happens fast with a misplaced floor jack.

There is no pat answer....vibes can be elusive, so be persistent.

 

[brokeX4]

The above post is great -

If it is stock I’d pull my front drive shaft and see what happens - or disconnect it at the front pinion and strap it up (do not do not engage 4wd) and drive it -

You may have lost a balancing weight or have a slightly bent shaft- happens fast with a misplaced floor jack.

There is no pat answer....vibes can be elusive, so be persistent.

Thank you. I should have noted that I tested removing each drive shaft and running the jeep around the block. With the front only, smooth as ice. Rear only, vibrations.

But I’m going to take mike h’s advice and check u joint seating (heck I may just replace again). Then if that persists I’ll have the drive shaft checked out

 

[AndyG]

Thank you. I should have noted that I tested removing each drive shaft and running the jeep around the block. With the front only, smooth as ice. Rear only, vibrations.

But I’m going to take mike h’s advice and check u joint seating (heck I may just replace again). Then if that persists I’ll have the drive shaft checked out

Good move- I’d do the same- might get it rebalanced - weights can come off too. Keep us posted, when you share, we all learn.

 

[Necro]

What is the frequency of the vibration? Same speed as the engine? Same speed as the tires? 3-4 times as fast as the tires? Could be flywheel but doubt it if it went away with no rear driveshaft. Also doubt it's tire or rim related if it went away when you removed the rear driveshaft. I'm 99% sure it's drive shaft related if it went away and came back with the rear driveshaft. But there is a small chance it might be t-case related. What's the pinion angles? What kind of shape is the slip yoke in? Can you shake it (the driveshaft) around and see if there is any looseness anywhere? Check the tailshaft/slip yolk, and the pinion of the rear axle.

 

[brokeX4]

What is the frequency of the vibration? Same speed as the engine? Same speed as the tires? 3-4 times as fast as the tires? Could be flywheel but doubt it if it went away with no rear driveshaft. Also doubt it's tire or rim related if it went away when you removed the rear driveshaft. I'm 99% sure it's drive shaft related if it went away and came back with the rear driveshaft. But there is a small chance it might be t-case related. What's the pinion angles? What kind of shape is the slip yoke in? Can you shake it (the driveshaft) around and see if there is any looseness anywhere? Check the tailshaft/slip yolk, and the pinion of the rear axle.

Slip yoke looked fine when I was under there last. Will shake it around again and get those pinion angle measurements this afternoon.

Also realized I didn’t answer a prior question. Vibrations were present prior to replacing u joints. When I came to this forum and saw that was a good first thing to check I swapped them.