OK guys, I've searched yota tech with no definitive answer and am pretty stumped. On my way into work this morning after about 10 miles or so, going up a long hill in 5th gear the truck randomly started to vibrate bad, and would almost stop accelerating altogether. So I coasted to a side road, looked underneath to find nothing loose or obviously worn. got back in and noticed 1st and 2nd gear do not pose a problem, but 3rd through 5th accelerating hard in higher rpms it would shake bad.

A little history of the truck...about a year ago i put northwest "stock replacement" springs which gave me more lift than anticipated, which developed a bad vibration after, so after measuring the pinion angles, I shimmed the rear end and the problem went away. Fast forward to about a month ago, I put a set of factory 4.88 diffs with a detroit in the rear, did all the work myself including setting backlash and bearing preload, and have been driving around this long with no problems (no noises, humming or clunking besides the locker engaging and disengaging). I also put in a rebalanced driveshaft w/ new toyota u-joints in at the same time. So yesterday I noticed my transfer case companion flange was loose, so I tightened the locknut and drove last night and all was fine. So i'm stumped as to why at random going up a hill it just started to vibrate. Is it possible now that everything is tight in the driveline for something else to become more aggravated (tires out of balance?.) Sorry about the long post, just trying to give you guys a little background info. Any input would be greatly appreciated as this is my daily driver.

 

Bump! I just measured the stock 4.10 third member and it measures 9" from axle flange to pinion flange, while the v6 measures roughly 9 3/8". I have read that the factory 4.88 thirds have a special offset pinion, but it looks to be the same centerline as the 4.10. Could that slight length difference cause any problems? Thanks

 

Could be wrong, but I was under the impression that the factory 4.88s had a thinner ring gear, not an offset pinion. But having never seen one up close, dont go by me. And that much of a difference shouldn't cause that much vibration.

Are you sure the vibration is coming from the back? realizing as I typed that that if your hubs are unlocked and your in 2wd, nothing in the front should be spinning at all.

I would say double check all u-joints and that pinion flange.

 

It is possible that you could have lost some of the balancing weights on one or more of your tires? I have no experience with this so it is just a guess I could be total wrong.

 

Thanks for the replies, I actually found out the vibration in the higher gears was the engine beginning to misfire, because it got worse as I was driving it to a shop to have it looked at. The spark plugs were all covered in carbon, most likely because I just ran a couple cans of seafoam through the tank...hopefully. New OEM plugs and wires and it went away, whew