Vibration while engine braking (2 Viewers)

[wer1952]

I have a 1995 FJ80, mostly stock. 268K miles. When decelerating without using the brakes, basically using engine braking, at speeds over 50 mph the truck vibrates as if running over a rumble strip, until the speed drops below 50 mph. It only happens in Drive and Overdrive, and gets worse at higher speeds. It does not happen in second gear, or when I put the transmission in neutral. If I coast in neutral, with the engine rpm dropped to about 1000, it briefly vibrates when I put the transmission back in Drive and the rpm comes back up. It almost seems like the engine speed and wheel speed are mismatched. Has anyone experienced this?

 

[voodu3]

I’d start with the u joints in the driveshafts. The driveshafts could need grease.

 

[Broski]

I’d start with the u joints in the driveshafts. The driveshafts could need grease.

^^^This
And if it’s a 95 it’s a FZJ

 

[Mark W]

Lack of grease can kill ujoints, obviously. Adding grease after they are sick will not make them better. Anyway, I too would check ujoints first and replace as needed.

Mark...

 

[robnicko]

to check U joints properly remove the shafts from the vehicle. Also look for lateral movement in the joints as well and when removed clean out all the old grease from the slip joints & refresh with new moly grease

 

[Broski]

Better yet pull the rear shaft and lock the center diff and take it for a spin If the vibration goes away, you know it’s the rear driveshaft.

 

[Mark W]

I have never encountered a ujoint that was worn enough to cause vibration that could not be discerned by simply sliding under the rig and checking it in situ. Push it side to side on each axis. Twist it back and forth on the rotation plane While you are there, check the output flanges of the T/C and the pinion flanges of the diffs for any slop too. Takes approximately 2.83 minutes to complete the check of all four driveshaft ends.

It *is* possible to have a seized or at least very stiff joint. Theses are harder to detect on the vehicle. This failure mode only occurs when the lubrication is totally inadequate (non-existent usually) and will only persist for a short time before the ujoint self clearances to the point that it no longer binds. Followed very quickly by it eating itself from the inside out and failing catastrophically.

The slop in the bearings at the T'C and diff that I mentioned checking for above... this obviously can also cause drivetrain vibrations.

Mark...

 

[wer1952]

Wow, thank you all very much. You are clearly all much more mechanically inclined than I am, but I am lucky that there are a few old-school shops around here that work on trucks from before the time they became electronic wonders. No matter what, the drive shafts and u-joints seem worth looking at, and if nothing else, it is probably good practice to have them serviced. Thanks again.
And, OK, FZJ it is. Thanks.

 

[LandLocked93]

+1 u/j's are worth looking at.
But also shaft yokes slip joints (the joint appearing as the large shaft component connected to the small shaft component). They too should be greased.
By and large, I think u/joints get more maintenance over time than the yoke slip joint itself. Which then wears more as a result.
Yoke Slip joint wear will certainly manifest as the vibration of which you speak; especially if the shafts are installed backwards or out of phase following any sort of drive line service by shop that may not specialize in drive line service.
Ask me how I know.

edited to correct terminology (brain fart)

 

[WACruiserJack]

Im currently chasing down vibrations in my 97 fzj80 as well. Are there any abnormal sounds you hear when the vibrations occur and when they don’t? The shafts and u-joints are good places to check, as others have said, and grease if they seem dry. Motor and transmission mounts could be checked too as this is your motor and transmissions suspension. These are old trucks at this point and old rubber can look okay on the surface but be degraded out of a reasonable spec. Also how are your differentials and axels doing? Does the diff oil look topped up? And if it’s drained how metallic does it look? I think you’d hear growling/humming too if your diff gears were bad but worn out gears could also contribute to vibrations.

 

[mrsleeve]

Drive plates on the front hubs can cause some vibes while coasting in gear or load aka engine braking but felt more at all speeds other than very slow. Though I agree check all your u joints and slip yokes 1st, from what you describe that’s my 1st thought as well

 

[wer1952]

Im currently chasing down vibrations in my 97 fzj80 as well. Are there any abnormal sounds you hear when the vibrations occur and when they don’t? The shafts and u-joints are good places to check, as others have said, and grease if they seem dry. Motor and transmission mounts could be checked too as this is your motor and transmissions suspension. These are old trucks at this point and old rubber can look okay on the surface but be degraded out of a reasonable spec. Also how are your differentials and axels doing? Does the diff oil look topped up? And if it’s drained how metallic does it look? I think you’d hear growling/humming too if your diff gears were bad but worn out gears could also contribute to vibrations.

Thanks for the reply. There are no strange sounds at any time. In fact, the truck drives like a dream, hums along just fine.
Transmission fluid was changed about 20K miles ago and looks pristine.
The only thing is this vibration, and the fact that it only happens in Drive or Overdrive. Not in second gear where obviously the RPMs are much higher.

 

[mrsleeve]

Thanks for the reply. There are no strange sounds at any time. In fact, the truck drives like a dream, hums along just fine.
Transmission fluid was changed about 20K miles ago and looks pristine.
The only thing is this vibration, and the fact that it only happens in Drive or Overdrive. Not in second gear where obviously the RPMs are much higher.

trans mount on the rear cross member finally give up the ghost ???

 

[wer1952]

To all who replied, thank you so much. There was a bad u-joint. It was fixed, and the truck drives perfectly fine again.
Thanks again for your help and making diagnosing the problem so much easier. If you are ever in the Palo Alto area, drop me a line, I will buy you a drink.

 

[Brindleboxer]

Does the drink offer count if I didn't reply but read the posts throughout?

 

[wer1952]

Does the drink offer count if I didn't reply but read the posts throughout?

If you bring your Cruiser all the way from Gig Harbor, sure....