My truck has an uncontrollable violent bounce, normally starts around 40-45 MPH. but sometimes slower or faster. It is a 99 F150 4x4 SWB regular cab. It has a trailmaster 4" suspension, and 3" body lift. 36 X 14.5 X 16.5 Mickey Thompson Baja Belted tires on weld 16.5 X 14 wheels. I have been fighting this problem some time. The idler arm had a mild amount of play, but I have seen ten times worse, but I replaced it with the one offered by Moog that is supposed to be some kind of upgrade. Then I was told that a Cv axle could be causing this, and the drivers side looked rough, so i replaced it. Then I had three places tell me that it was my tires worn down too bad, so now I have brand new tires, and had the wheels checked before they mounted them, and now it seems worse. Can anyone please help me before I get thrown out the window at 45 MPH?

 

Have you checked the rear end? (Differential)

 

no, what would I need to check on it, I guess how would it cause the front end to bounce like that?

 

check your ball joints and tie rod ends but the tires and rims are so wide i think that could be a problem. If you could test a friends set of rims and tires to see if it go's away that could realy cross a big problem out.

 

do you know your shocks arent' bottoming out, (or topping out)? that's big tires/wheels for light duty frame/axles, my '01 4x 2 rides choppy mainly because theres no weight in the back and short wheelbase. Also these frames are riveted together at the front hangers of rear axle springs. Might make sure the rivets aren't worked loose, i did hear of a case where a frame finally cracked almost completely thru at this point on one side. the steel of the frame u-channel is thinner from that point back. So i would say it is possible your frame is seeing some excess flexing w/those huge tires.You got to think about the dynamics of all this and, funny things happen at certain frequencies/harmonics at diff. speeds. Are your shocks too stiff or too soft?
I would be carefull, it could be a dangerous situation. You could also put some weight in the bed and see what happens. By the way a long time ago i had an older f150 that the toe in was off enough that at maybe 35-40 mph that truck started hopping/jumping around in the front like crazy, finnally figured out the toe in was off. Smooth as silk after that was fixed. ..... my .02 worth..paul

 

Sorry about that - didn't see where the vibration was isolated to the front of the vehicle. In that case scratch my last post.

If you can rule out tires/wheels as the problem - you might check the to see if the "outboard front wheel halfshaft joint (fixed type) in the front wheel hub is properly seated." (taken from Fords TSP Disk) According to Ford - the most common causes of your problem are tire/wheel problems, but if those are ruled out you might take another look at your CV joints more specifically the outboard joint. Hope this helps...

 

sounds like you have "death wobble" which happens a lot to "lifted" trucks..something is loose..steering shaft from the column to the gearbox maybe?? mine was bad and replaced it but i'm not lifted..tires and wheels with too much back spaceing? try having them road force balanced..hard to find someone with a machine to do it but they are out there and do make a differance.double check all tie rods and such..worn bushings on the a arms?double check the alignment with some one knowledgable with a lifted vehicle..good luck..
had the "wobble" on an old lifted bronco and found that the rivets had pulled out of the coil towers..same on a 95 f150 4x..its scary when it starts and hard to find sometimes..let us know what you find

 

Thanks for the replys, Ive been meaning to check the column and gearbox, but only so much time in the day. I dont know if this might help, but I found the torsion bars out of adjustment, got the ride height as close to possible the same on both sides and it drasticly helped, but not completely cured, does anyone know how to adjust these properly, to the recommended height? I also got a castor camber kit, but I dont want to pay for install and another alignment until I know that the torsion bars are right.

 

Also wanted to say that the speed that the wobble starts varies with torsion bar adjustment, thought this was important. Ive been playin round all week, every time i go somewhere I will give one bolt or the other a little turn, or both, even an 1/8 of a turn makes a difference. I also was thinkin that the could have been incorrectly installed when the lift was installed. Its hard to find any place that does decent work here, Im still not confident with an alignment shop. It seems like every car I look at in this town the tires are worn on the inside. If anyone knows of a reputable front end shop within 100-150 miles of Panama City Florida, please let me know. Also wanted to say that I can drive through the wobble, and it will smooth out. Is this really smoothed out, or so fast that I cant feel it until something breaks. Thanks again for everyones help, hopefully the castor camber kit will help get those wide wheels on the ground, I'll let yall know, when I get it aligned.