Vibration

[Kroozer74]

I tried a search for this but couldnt find much.

I have a 76 fj with a 4" lift and 33's.
I recently replaced my pinion bearings and adjusted my 3rd member. Reinstalled it and it works great except for when im in 4th gear running down the highway over say 40mph it starts to have a vibration like the u joints are going bad, but they are fine because i checked and greased them real good when i did the 3rd member. But if i push in on the clutch the vibration stops. So it is vibrating only when its under a load
What could cause this?

It has a newer clutch in it maybe 3 years old.
Could my driveshaft be out of balance or clutch out of adjustment? Something in the rear end??

Thanks

 

[paraseeba]

What is the angle of your drive shaft? I know they say you don't want to be over 10 degrees.

 

[ColonelMustardFJ40]

Wow. Vibrations are bad. If it wasn't there before your repairs and it is present after them, have to go with something you've done when it was reassembled. Rear gears can be grenades and a lot can be destroyed from a bad vibration. I would definitely recheck your work. Best to you!

 

[pb4ugo]

Could it be your pinion bearings went bad because the vibration was present b4? I'd check the driveline & drive shaft angles.

 

[Kroozer74]

Well the vibration was way worse before the repair because my pinion bearing was shot. But now it only does it at higher speeds and under a load. Could it be my pinion angle? I wouldnt think with a 4" lift it would effect it.

 

[NikP]

I wrestled with the same type of issues. I had the drive line balanced by two different companies and replaced u-joints both times. I finally had the drive line company install a CV joint and wedged my diff to accommodate.

I've been smooth ever since.

It could be a u-joint. I thought might were good and when I took the drive shaft to be balanced they told me there was some play in them even though they had less than 4000 miles on them. With a 4 inch lift, everything gets amplified.

 

[FJsnoozer]

Mine did this, I had a dS bolt on the pinion that was backed all the way out. The mud made it look tight.

It would also flutter under full load in first a the weight transfer caused the pinion angle to change.

 

[pb4ugo]

Well the vibration was way worse before the repair because my pinion bearing was shot. But now it only does it at higher speeds and under a load. Could it be my pinion angle? I wouldnt think with a 4" lift it would effect it.

Yes. Did you install the lift or the PO? A vibration or poor drivelines angles could have caused the pinion bearings to fail. Your current vibration my have been the reason your bearings failed in the 1st place. Is the pinion close to parallel w/the driveline output (=)? What's your driveshaft angle? Be sure to check the ujoints with driveshaft out. Check & make sure the slip joint spline doesn't wobble. Check Tom Woods site, it has good info on driveline angles.

 

[Fast Eddy]

Are you sure your u-joints are properly aligned? Sounds like what you're describing.

 

[peesalot]

splines on slip part of driveshaft are worn a little. Mine is the opposite, only vibrates when you let off gas, say like when you get to your offramp while going down freeway.

 

[cjgoode]

Make sure your drive shaft is in phase, search here it has been discussed many times. Cannot remember exactly what the alignment of the ends of the drive shaft should be, but that is a common cause of this problem.

 

[Roboosfj40s]

If I am not mistaken the pinion stock angle is 5 degrees? Chime in guys and gals coz I forget, do you ever forget? I do. lol

 

[Kroozer74]

I installed the lift when i got the cruiser about 5 years ago. Drove it through high school then bought another truck and just drive it every now and then. But i never had any vib problems until that pinion bearing went out. But i did drive it probably more then i should have with that bearing out maybe it tweaked my u joints. I guess ill pull the shaft and take it to a shop and let them look at it and see if maybe the u joints are just worn or something!

 

[lostmarbles]

Are you sure your u-joints are properly aligned? Sounds like what you're describing.

Make sure your drive shaft is in phase, search here it has been discussed many times. Cannot remember exactly what the alignment of the ends of the drive shaft should be, but that is a common cause of this problem.

Yep.

Driveshaft yokes should be aligned like this:

 

[Degnol]

I fought this after installing 4" of lift. Can be lack of spline engagement or the need for shims. After retubing the driveshaft and installing 7* shims to rotate the pinion down, all is well.

 

[AlexJet]

mine is the opposite, only vibrates when you let off gas, say like when you get to your offramp while going down freeway.

This is exactly what I'm battling on my 4Runner with 5" lift now. I have replaced the driveshaft to the different one as mine had worn out yoke. Now planning to replace U-Joints for Spicer ones.
Good note on pinion bearing. I should check that one as well. If I just spin the flange with removed driveshaft, would I feel the bearing gone bad on the pinion?