I have a 96 Tacoma with a Dana 44 front and Ford 9 Rear. I had 38.5 Thornbirds and dropped down to 35 BFG's for daily driving. Since I dropped down, whenever my speed gets to about 50-55 I get a terrible vibration. The vibration comes from the rear to center of the vehicle and I cannot feel it in my steering wheel. I was thinking tire balance, or u-joint I just swapped my Spool for a Detroit Locker in the Rear and noticed just a hair of slack in one of my U-Joints. Anyone got any other ideas. I am going to get my tires balanced here in a week or so so I can either rule that out or fix it, U-Joint too.  

this seems to be a big problem with a lot of toyotas. both my friends camrys did the same thing. they replaced the steering components and swithed the front and back tires and it worked good after that. dont really know if this pertains any relevance to you but its a thought  

It would start with a drive shaft inspection and maybe balance too and make sure ujoint angle are good and match because Ujoint are not constant in velocity and when run at angles they have to be equal on opposite on either end to cancel out velocity differences. Failure to do this can lead to strong vibrations are certain speed were drive shaft kinda resonates.  

Thanks, I did notice some slop in the rear drive shafts front ujoint. I am going to replace them and see if that changes anything. If not I will move onto getting my tires re-balanced. If not I was thinking that maybe when I was wheeling there is a chance I could have done something to knock my dtive shaft out of balance.  

I do not think is it a tire balance issue. I think it is either ujoints, balance or ujoint angles. I am leaning toward ujoints and their angles because of lift needed for tires. Also unless you are running some 5.13 or deeper gears you are placing a higher average torque load which will aggravate the problem.  

I do have 5.13 gears. I didn't have the vibration until I dropped down from my 38.5's to 35's. My pinion angles are pretty well lined up with the drive shafts. That is why I am leaning toward bad u-joints too.  

Have you tried checking your wheels for bends? If there's none, take your car to a wheel shop and have all of your wheels/tires high speed aligned. That should fix your problem. Also check for bubble in your tires. Broken radial belts will also cause the same trouble.

To have a great and safe car make sure that it is well-maintained.  

I had to have my tires shaved because nothing I did corrected the problem.  You can balance them but it will not work as the actual tire is out of round.
This can be a defective tire and it would have to be replaced or you can call around and find a shop that will shave them for you.  Most shops do not like to shave tires, but with large tires with large tread it really is not a safety issue.  

I had boy number 3 born the 10th so I have been out of the loop, I am changing my u-joints as we speak so I should know in a while, also, I noticed my tranny mounts were missing their bolts, that too will be fixed. (there is something to be said for loc-tite)  

vibration isn't as bad as it was, I think now it is a tire issue.  

I would not be so sure. I think you have u-joint angle issues and the bad joints and mount bolts were amplifying it.  

sorry if i'm repeating myself i wrote something yesterday but i don't see here today. when a toyota rim is built the mounting holes are used as the actual center of the rim, the hole in the center is not. when it comes time to balance your rims and tires a special machine or adapter is required to balance the tire using the mounting holes. most dealers know about this but don't use the machine because of the extra cost involed. gadgetonline.com has the whole explanation. when i had my 35's mounted the tire guy showed me that there is an indicated "heaviest point" on each tire, usually indicated with a small dot. if you put only your rim on the balance machine you will be able to find it's heaviest point also, then you need to mount both points directly opposing each other and you will have a much easier time balancing with a conventional machine. i had the same vibration for the longest time this solved it for the most part, then i noticed my steady bearing was worn out. now the truck is vibration free.  

hmm..... something else to look into. Thanks