Strange vibration

[Jobi-Wan Kenobi]

I've got a vibration when driving that I haven't been able to figure out yet. It doesn't occur until I reach 65 mph. My first thought is u-joints but they've been tight whenever I check them. But from looking at them I can't tell if they've been changed recently. I do have some radial play on the output shaft of the front axle that mates to the CV shaft on the drivers side. I would think though if it was an issue I would feel vibration in the steering wheel, which I'm not.

Anyone have thoughts on this?

 

[OR VietVet]

Need to also inspect the motor and transmission mounts. Bear in mind that the radial runout that you see, can be more at speed.

 

[Jobi-Wan Kenobi]

@OR VietVet can check them out. With the age and miles on the vehicle it's definitely possible they can be bad.

What's a good source for them if they need to be changed?

 

[OR VietVet]

RA and have heard here that Hummer mounts are better. Do a search about all that.

 

[Jobi-Wan Kenobi]

Was checking this out the other night to see how the engine mounts were. From what I was able to find with bad mounts the engine should want to lift on the drivers side while giving throttle with the brake held and transmission in gear. I don't seem to have that going on. I do wonder though if the mounts have other failure modes. Sometimes after the engine has gotten hot and I'm sitting parked in a parking lot or just moving at low speed with the engine idling there will be a (for lack of better words) kind of low frequency vibration or rumble. Not a clue of this is related to the original issue or if there's something else going on.

 

[rockola1971]

Original Ujoints?

 

[Jobi-Wan Kenobi]

@rockola1971 from what I can tell U-joints may be original expect for the one at the rear axle (this one is greasable). I can't grease it though without pulling the driveshaft down because the fitting is on the center of the U-joint and my grease gun tip can't reach it. So that may not have been greased for a while.

I checked out the transmission mount today. From what I can tell it seems to be ok. Not cracked, doesn't seem to be deteriorated. I do though have a very small amount of play on the output of the transfer case for the rear driveshaft. Should there be any play there?

 

[rockola1971]

@rockola1971 from what I can tell U-joints may be original expect for the one at the rear axle (this one is greasable). I can't grease it though without pulling the driveshaft down because the fitting is on the center of the U-joint and my grease gun tip can't reach it. So that may not have been greased for a while.

I checked out the transmission mount today. From what I can tell it seems to be ok. Not cracked, doesn't seem to be deteriorated. I do though have a very small amount of play on the output of the transfer case for the rear driveshaft. Should there be any play there?

There will be some play at the driveshaft, expecially on a well worn in drivetrain. Check your fluid level on your Tcase. If you have any non greasable Ujoints then they are original and need replaced....years ago.

 

[Jobi-Wan Kenobi]

I'm thinking even changing the one at the rear axle too. Then find all new ones that have a grease fitting on the bearing cap so they can actually be greased without pulling the driveshafts down.

 

[OR VietVet]

I'm thinking even changing the one at the rear axle too. Then find all new ones that have a grease fitting on the bearing cap so they can actually be greased without pulling the driveshafts down.

If you do, make double sure you always clean the zerk completely before you grease it. All zerks should be cleaned before greasing. If not cleaned, the dirt gets pushed in to the u-joint.

 

[Jobi-Wan Kenobi]

Finally have the chance to better check this out after a few weeks. I do have new u-joints to swap in, but I'm not so sure that's actually the issue. The current ones all feel tight. The play though I had noted at the drivers side output of the front axle where the CV shaft attaches seems to have increased, and I do also have a leak at the shaft seal. I'm not really sure what the issue with this would be. I changed the seal and the needle bearing on that side last fall because it seemed like there was a leak there. It does also seem like there's some abnormal noise from the front end when I drive with 4wd engaged (noticed that earlier this week).

 

[Jobi-Wan Kenobi]

So pulled the rear driveshaft down. The u-joint at the rear axle was actually bound up pretty good. It moved like it had detents inside the bearing caps. So this very well may have been the source of the vibration. Not sure what to think about the front axle though.

 

[OR VietVet]

So pulled the rear driveshaft down. The u-joint at the rear axle was actually bound up pretty good. It moved like it had detents inside the bearing caps. So this very well may have been the source of the vibration. Not sure what to think about the front axle though.

If it was not smooth and felt like it had detents/flat spots, you have definitely found "A" problem and may be the only problem but will need to replace the joint and road test. One thing to remember, is that if you feel it by your hand, imagine what it is going thru under a load condition.

 

[Jobi-Wan Kenobi]

@OR VietVet yea I'll have it back together tomorrow and will see how it feels. But yea very true. I'm just surprised it didn't vibrate at lower speeds.

 

[OR VietVet]

@OR VietVet yea I'll have it back together tomorrow and will see how it feels. But yea very true. I'm just surprised it didn't vibrate at lower speeds.

Lower speed=less load. Your hands moving it were nothing compared to what it goes thru at low and high speeds.