ok, heres a good one. friend of mine has a 04 150 with 22"s, the truck has developed a violent shake in the rear. so bad that he has to pull off the road and stop, at that point he takes off and its gone. its random, usually above 50 mph. other day it happenned 3 times before he got home. any thoughts?

 

What was done to truck prior to the shakeing, Has he had the 22's for long time? Is the shaking the whole back of truck or truck bed. Have you checked the shocks and leaf springs? Is the rear tires warped or weights on tired fell off, see if they are still balanced.
Any more detail about what was done prior to shaking, any curb checks, pot holes ect...

 

theres been nothing done to the truck except wheels and tires. the fact that its random leans me away from weights and warped rims. i was in it last night and it started shaking, the vibration in the seat was unlike anything i've ever seen. he pulled over and it stopped and didn't do it again the rest of the trip. the truck only has about 55 k on it, the wheels have been on over a year. would a missing weight or bad tire be random?

 

when was the last time he checked his lug nuts?

 

The gear oil has begun to brake down/modifier dilution. Replace it w/spec and don't forget the modifier. - To many under-carriage washes lol.

 

Have him check the e-brakes. 04s are notorious for having the e-brakes cause heavy vibrations. The seem to rub at times and that causes the vibration. In my case all it took was adjusting the e-brakes a bit looser.

 

the tire could be out of balance

 

thanks for all the input, he went and had all the tires balanced and rotated. have to wait and see. never thought of the e -brake, if it happens again, he's going to check that. hey jbrew, is it possible for gear oil to brake down with fairly low miles? whats the modifier?

 

Well it SHOULDN'T need to be changed yet IMO. But there's a chance it's been contaminated. If the breather was compromised somehow and/or the pig was submerged in water/ mud when 4wheeling at some point..? That could do it real quick.

I would check out the breather line condition and check the diff fluid level and color. If questionable - better change it.

Check out the manual for specs. The little one in the glove box should have the spec. You didn't post the engine size, so I'm not going to guess. Just check out the book in the box.