Grinding/Thunk on Accel and Decel What could it be?

[mgriff67]

Hi everyone,

I got my 1994 fj80 not long ago and it’s got its quirks. The big one is like to address now is this thumping/grinding noise that happens on acceleration and deceleration. It only occurs when the pedal is at the very end of its return travel or beginning of acceleration. There is a notable thump that occurs when both accelerating and decelerating. I can’t tell if it’s from the center diff, transfer case, but I jiggled the driveshaft and there wasn’t any play in the U joints. Anybody able to shine some light on the situation? Thanks!


Here is a link to a YouTube short of the noise:

 

[Themcfarland]

I bet ya its either the Joints or you have a loose pinion nut /busted seal/dry gears.
ujoints are typical .
I say ujoints as you are taking the slack out of the shaft when your pedal is where you describe it..

 

[NelsonCruiser]

When checking the u jounts park on level ground and set the handbrake after you put the truck in park before you let off the foot brake. Then climb under the truck and wiggle the drive shafts. This will make sure there isn’t any load in the driveline, preventing them from binding when your trying to wiggle them.

Be aware if your handbrake were to fail the truck will roll a few inches. Be mindful and keep your extremities clear.

 

[RollinYotas]

Have you grease the u joints and shafts? Is there play in the front differential bushing?

 

[PeterTheBeater]

Could be so many things, I’ve went down this rabbit hole with my truck. Grinding like that sounds like a drive shaft. Do you have a lift installed?

 

[robnicko]

unbolt the drive shafts and check the uni's when theyre not attached to the flanges, its the best way to determine the needle bearings are not shot / binding which can be hidden when bolted in place

 

[mgriff67]

Could be so many things, I’ve went down this rabbit hole with my truck. Grinding like that sounds like a drive shaft. Do you have a lift installed?

Yes I do, 4” on 35” KO3s

 

[george_tlc]

4" lift, do you have a DC shaft at the front end? And yes, pull the shafts and check uni's by hand. Also check slip joints. And as was asked, have you pumped grease into them - and if so, did the sound change in any way. Leave the front shaft off and go for a drive and report if sound changes.

Of course, this is just for the shafts, you may have issues elsewhere. But start with the relatively simple.

EDIT: Once you pull the front shaft, you need to lock the center diff, either via the dash switch (if installed), or putting into low range and pulling the fuse and then back into high range. Search for details.

cheers,
george.

 

[Devils Paw 80]

X2 on above. These are full time 4WD trucks and the front driveshaft is relatively short, not great news for the u joints with a 4" lift.

You might need one of these. SLEE - Front Double Cardan Shaft - All New Parts - Slee Off Road - https://sleeoffroad.com/products/sle-80-fcv/