I've just about had it !!! I have replaced everything on the suspension (almost) and I still have a vibration at 35 and over MPH. I have new GOODYEAR wranglers (stock size) here is a list of everything I have replaced in last 6 months: tires, shocks, drag link,radius arm bushings, wheel bearings, races....
even when I get the tires balanced it still shakes. I had the truck computer aligned at a sears , still shakes, I took it back to get double checked at the sears,still shakes...... the toe/camber is right on the money,the man said its as straight aS A new truck can get, he even walked me to the computer to show me the readings.
WHAT AM I NOT SEEING??? HELP, Im tired of wearing my coffee evry morning
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77'FORD F150 XLT 400

 

Have the driveshaft checked, it could be slightly bent or for some reason need to be balanced. Check your yellow pages under driveshaft.

My suggestion.

John
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66F100s Rule
In the cool still quite of night you can hear chevies rusting away.

 

First check the u-joints for loose bearings. From there, check the drive shaft balance, motor and tranny mounts, and rear axle bearings. Hope you find it.

Nathan

 

I have checked the u joints, they seem tight, they are about 3 years old....there is no slop when trying to move the drive shaft at the tranny yoke, or at the gear casing....goint to call the driveshaft shop this morning...

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77'FORD F150 XLT 400

 

I had a perplexing vibration that sounds similar to yours. After checking u-joints and everything else, I realized the u-joints were, in fact, bad. They felt tight until I lifted the vehicle and removed driveline strain on the joints...then they were way loose. Replaced them and no more bad vibes.

 

I was on the phone with the driveshaft shop , he said there are actually two sizes of u joints (the cup that mounts to the axle yoke). there is a wrong / roght way to put them in, but most likely I would not have been able to get them on had they been the wrong size....to make things easier, Im swapping in a set of new ones this weekend possibly
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77'FORD F150 XLT 400

 

Couple of other things to check/look at, first, the driveshaft were it slides, the splines may be worn, to check, just grab both sides of the slip joint and try to lift and lower. There should be no play at this section. Other thing is the spring bushings in the rear springs, I know this sounds weird, but, when mine went, the truck would almost "hop" up and down. With the adjustable shocks, it would get worse the tighter I made them, letting the suspension take the movement when soft, placing it into the frame (and me) when tight. Mine usually had a "sweet" spot around 45 mph or so were it was the worst. Sounds like you found a good driveline shop though, most don't know that the rear most U-joint has two different size caps. You can make the single size cap U-joint work, but it will not hold centered. There is only about 1/16" difference between them (as they advised you-you cannot get these in backwards), and this can also cause some bad vibes, as well as make the joint not last very long. As previously posted, do check those rear bearings also, with the wheel off the ground, in and out with the wheel and up/down too, not to often do you hear of this, but it is possible. Good luck "vibe" hunting!

 

I have a 78 F150 4x4 that has a vibration too. Is yours a 4x4? I have beat myself to death trying to figure this out. I replaced the rear end and all its componets. My problem I believe is in the transfer case (bearings). I did the drive shaft, yoke, 3rd member bearings Note...helped out, but not a complete fix. I am going to drive mine till this vibration gets worse or breaks, then I'll know. Good luck
Paul
78' F150 Ranger 4X4 400
78 F150 Lariat 400
New to the corral...
76' F150 supercab longbed 390

 

its a 2wd , and I havent figured it out either....... YET
welcome aboard

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77'FORD F150 XLT 400