extreme drivetrain vibration. cannot drive truck

[superdub01]

ok so i have a terrible vibration (if you can call it that. more like intense drivetrain shaking) that started a few months ago and has gotten to the point where something is going to give if i drive it. on acceleration from a stop, or any slow speed the entire engine transmission and transfer case seems to move side to side quite a bit. i had a buddy accelerate while i looked underneath and could clearly see lateral movement. it gets much worse when towing.

SO, I HAVE CHANGED:
engine mounts, tranny mount, driveshaft support bearing, all u-joints. problem is exactly the same.

now some may say it is because of my lift kit, but i have had that for 4 years with no problem. the only modifications i have done since before this developed are listed above.

any ideas fellas? i really need some help here. thanks

 

[Dogman]

Have you had the driveshafts check for balance or dings also you need to check the driveshaft angles. Did you shim the driveshaft support bearing down? If not try it, get your self about 12 flat washers and put 6 on each side this will give you about a 1/2 inch of drop and see if it goes away. If it starts going away then you'll need more drop and longer bolts. For 2 or 3 bucks in washers it a starting point.

Take a look at the harmonic balancer on the front of the motor too. Make shore it not messed up. It will give some crazzy vibrations.

 

[superdub01]

i totally agree with what you are saying. however maybe you misunderstand what i mean by vibration. this is not a dynamic vibration that would be caused by a driveshaft or balancer. it is also not proportionate to engine speed, only wheel speed. and it is not a vibration, more like a very intense shaking. and very slow compared to driveshaft speed. almost like a couple guys were holding the sides of my bed and shaking them side to side as hard as they can while i accelerate. (thats the best i can think to describe it) and its not body mounts either. i do have a 4 inch spacer for my support bearing and i know it works well because i have run it for years with no problem.

thank you for the ideas! this one is tricky, i consider myself a fairly competent mechanic and i am totally stumped. any more ideas are more than welcome!!!

 

[BIG JOE]

What Dogman said, and/or a broken spring hanger.... or a broken leaf spring (in the spring pack).. maybe even a Main spring(s) ?

 

[Dogman]

Well the other thing would be put some street tires and see if it still does it. It sounds like it could be a tire problem. Let me back up. How do you rotate you tires? Front to back, like driver front to driver back and driver back to drive front one side or do you cross the back to the front and front to straght back?

 

[superdub01]

nope again. leaves and hangers are good. even removed them and checked the bushings. i am thinking maybe a tailshaft housing/ bearing, but not getting any leakage or play by hand.

 

[superdub01]

im sorry, dont mean to sound like a jerk and keep saying no thats not it, but this is like at 20 mph and under. it is not caused by something out of balance, because it isnt spinning very fast at that speed. more like something worn out. it happens at a dead crawl. UNDER LOAD. like on a hill, or towing, or if i put my foot past about 1/4 throttle. i cant even pull out in traffic

thanks again guys

 

[Dogman]

I know, It's a pain trying to tell someone what it's doing in words and it's harder for us to tell you what wrong not seeing what it's doing.
EZ thing to do, get your rear axle up on some jack stands pull the axles out on both sides (they should slide out EZ) and spin the tires by hand and see how well the tire spins. Also check the E brake at the the wheel and see if it's dragging. (Dont ask ) If the tire free spin then move to the next part. MAKE Shore the front hub ARE NOT LOCK IN, pull the rear drive shaft grab the rear yok and spin it by hand with the axles out and see if it is binding or feels ruff, if not. Then try the short shaft behind the T-case and see how it move. Your going to have to work to the front and remove parts to see what is moving freely. If all the part are moving freely then your going to dig into the T-case and trans. for something binding.

Was just looking at something here in your info on your truck.
Did you regear your truck for the 40" tires? Please tell me you did.

I think you may have smoked the clutch packs in 1st and 2nd gear in the trans. Do you get a little shutter pulling off from a dead stop?
Pull the trans dip stick and smell. Does it smell burnt, if so your going to need a new trans.

 

[DaveBen]

U-joint bad?? That would go with what you are telling us.

Dave

 

[iracemine]

I say tire or rim went bad