ok i have a case of the shakes....i have a 97 f150 4wd with a 6 inch lift and 3 inch body with 35s...i recently purchased this truck about a 2 months ago...i found out that the lift is "relaxed" meaning the torsion bars aren't extended..i recently replaced both upper control arms and ball joints and hub bearing on the passanger side that was bad....the rear leaf springs need to be re-stacked...who ever put the extra leaf obviously didn't know what they were doing....i have dont the wheel alignment rotated and balanced the tires still have the shakes...it starts right around 1500 RPM once i step on it the shakes go away until it shifts into a higher gear and they come back...now when i am driving in that 1500 RPM range and i hit a bump at the right angle the shakes turn into a wobble almost like they are going up and down. when i coasting its very very very suttle shimmy almost very smooth...i did notice that my steering wheel seems alittle loose when it is doing its regular...any ideas please help its getting really annoying

 

is it the trans- torque converter or the tires- suspension. if its the tires or suspension, it will do it at 30-40-50 MPH ext, even if coasting or in neutral. if it does at a specific engine speed, i might look elsewhere.

 

check your steering components. the lift and large tires aren't helping the suspension and steering up front, the parts will wear faster with the added stresses by the lifts.

 

it does shimmy only when i have the gas pressed...when i coast with my foot off...its a managable shimmy...like my tires are worn toed in due to never being aligned. when i get above 2000 RPMs the shaking is still there but not as bad. once it shifts then it gets bad

 

i will take a look at the steering and front end...anything specific...this is my first ford...i was a converted chevy boy to a ford man..so i am not if there is something specific to look at

 

It could be a lot of different things. Since you mention it is engine speed related, I might be looking at the rear driveshaft. The lift has changed the angle on the joints. If you have a short box, or a reg cab long box you may need to buy a CV style driveshaft. I drove a 6" lifted Expy and it definately had driveline vibes.

The suspension is another possibility. As mentioned, everthing up front is probably worn out. If you have steering slop you need to look at tie rod ends and the idler arm if you have done ball joints. One more thing to check is the pinch bolt on the steering shaft near the u-joint. If that is loose you can have a little slop.

There is also a chance you have tire issues, recently balanced or not, 35's are a pain, and it will probably never drive perfectly. Do you have a steering stabilizer shock installed? You should, Rancho sells a kit. I only have 33's and a stock suspension. Mine has a slight tire wobble at 65-70 mph that I can't get rid of with balancing. I am going to do the whole front end next and add the stabilizer if that doesn't fix it.

Good Luck

 

Thanks for the help and direction!....i do have the ext. cab short bed..no i don't have a stabilizer i will look into that...the driveshaft is all original ...i will have to take it somewhere to get it looked at....thanks a bunch