Truck Info:
1993 4Runner V6 Auto
4.88 gears 211k
Manual Locking Hubs
LC Coils installed 700 miles ago (but problem has been present for 10k+ miles)

Problems:
-Feels like you are sitting on top of an unbalanced washing machine on spin cycle at speed above 45 miles per hour- very bad at 65 and too scared to go any higher.

-Louder vibration under deceleration

-The vibration completely destroyed the slip yoke and only the front U-Joint on the first drive shaft (u joints only 5k old when they were wiped out)

-Destroyed only the front U-Joint on second drive shaft (U-Joint only 700 miles old)

-Rear Dif leaking very badly at pinion

Testing completed:
-No vibration when in P or N up to 4.5k RPM
-Rear driveshaft pulled and driven in FWD up to 55 miles per hour. There is a vibration but it is much different and located in front of truck. There is no vibration on decel, and no "washing machine" vibration
-No leaks detected at TC output
-TC output feels solid (no movement side to side or up and down
-Pinion feels solid (no movement side to side or up and down

Question:
From searching I am fairly certain that my rear 3rd is wiped out (so much so I have sourced another 3rd from a local u-pull already) but before I make the purchase I wanted to just get a thumbs up from the YotaHeads here. I am actually curious to know if it is common for a 3rd that has bad internal bearings to JUST cause the Yoke and front U-Joint to fail? And on 2 different shafts with new u-joints too boot! Or could a mis-aligned engine or soft/broken motor mount cause the front u-joint on 2 different shafts to go prematurely? Any guidance and wisdom would be WONDERFUL!

Thanks

 

Bump on this one?

 

have your rear drive line checked for balance. i bent mine wheelin and it had a wicked vibration as well. the bad driveline also caused the pinion seal to go bad (which would explain your leaking at the pinion.)

 

yes balance that sucker. you dont have a carrier bearing right??? i dont have a runner, but the carrier on my pickup went out and made for a terrible ride.

as far as balancing goes i wonder when it could have gone out of balance...when you changed you u joint or slip yoke?? always mark where everything is when you take it apart if you get a new balanced shaft. if you have the dline off, maybe jack the rear and spin your wheels to see how everything feels. i hope its not your 3rd.

and just for fun make sure there isnt a clump of dried mud in your wheel somewhere.

 

If you are not using one, I'd recommend a double cardan rear shaft.

Check out Roger's driveline 101 writeup:

http://www.4crawler.com/4x4/CheapTri...line-101.shtml

Another good writeup:

http://www.4x4wire.com/toyota/tech/driveline/

 

That was a really good read, I learned a lot from it.

I'd say get the driveshaft balanced before you replace the diff, check the cheap stuff first.

 

I had similar crazy vibartions at those speeds and it turned out to be a combination of a couple things, but one of them was the idler arm. Check to see if yours has any play in it. That thing just seemed to start wiggling at 45. Supposedly you can get new bushings from the dealer, but I just replaced the whole thing.