I've been trying to chase this issue down for awhile now, about a year now i guess, it's best described as a shaking or vibration that comes on right at 47mph and is non-existent by 50mph, if i keep the truck in this 3mph window the vibration is persistent and steady, it doesn't get any worse but it also doesn't stop until i reach 50mph, i generally just power right through it and it's not noticeable, but i'd still like to find the cause if i can.


I wouldn't go as far to call this the infamous "death wobble" but there's definitely a noticable shimmy/shake/vibration that over takes the whole truck between 47-50mph, it's not isolated to just one area of the truck, it's not rpm specific as it occurs in both 3rd and 4th gear and also during both acceleration and deceleration.


This has occured with two sets of tires, one set stock sized 235/85's, the other set oversized 35x12.50's, both sets professionally mounted and balanced at a reputable shop, airing down the tires helps (or hides) the problem a little bit, but it's still there, just not as obvious.


The following is an assortment of things i can presumably rule out because they've either been repaired, replaced or checked out, some well before the vibration became known and some after..... front-end alignment, tire balancing, new shocks, new tie-rods, new wheel bearings, king pins have no play, the entire front-end is pretty tight, U-joints are new and installed in phase, new T-case bushings and engine mounts.


This problem just appeared out of the blue last summer, no front-end or driveline work was done to the truck prior to this, i'm sort of at a loss on this one, any ideas...

 

Same thing happens to me. But when i hit 70 it starts. Betwee 70-75 its humms/vibrates and it sounds like its from the front wheel wells. Idk what the heck it is but it stops around 75

 

Are you feeling this in the steering wheel? Or just a vibration in general? If the steering wheel is not shaking check the u-joints, they are usually the most common problem on a speed specific problem.

 

Mine is in general. Has a very loud hum and you can feel the truck vibrate a bit. Thats how i know when i hit 70.lol

 

Pinion bearing or weights fell off drive shaft would be my guess. When my 2000 F-350 did it it was the rear drive shaft out of balance.

 

It could be lots of things. First/easiest/lowest cost thing to check is tire balance and roundness. My daughter's Jeep had the shakes from 70-75 and smoothed right out at 80. Only problem is neither state troopers nor other traffic appreciate sustained running at 80. Tire balance fixed it. A good tech can check roundness visually while balancing.

 

I get a weird vibration in my F150 right at 45 until about 50. I just had the front axle rebuilt, tranny rebuilt and a new front drive shaft installed. It's still happening. I also have had two different sets of tires/rims on it and it did it with both sets. I'm tending to think it could be the rear drive shaft out of balance like "armstrongfordtrucks" mentioned in his post above.

 

maybe its just an "old ford" thing?

mine does it too, but it is a little broader in speed. usually 35-45, but like yours it is out of it by 50 for sure.

to me it feels like a bad u-joint, but i had it checked out and it was fine.

subscribing ... hoping to see if you ever figgure anything out.

 

If its a U joint ill have new ones soon cuz of new springs Ill see what happens

 

Thanks for the input so far, i'm kinda leaning towards armstrongs suggestion of an out of balance rear drive shaft, though i see no tell tale signs of losing a weight on the shaft it doesn't mean i haven't lost one.

only way to find out is remove the shaft and have it checked for balance, but in my neck of the woods i'd have to drive 4hrs to find a shop that offered that service so i probably won't be doing that anytime soon.

i may go pull a junk yard shaft this weekend and swap it in and see if the vibration is still there.

 

When my D-shaft was out of balance, it steadily got worse the faster i went. However, have you changed your wheels before / after? My 77 used to do this 55-60ish, and it was a slightly bent wheel. Tires balanced out fine, but it cause some sort of harmonic imbalance. Never caught it till i rotated my tires then i could just barely feel it in the steering. Tire was wearing fine too, also caused a bit of humming.

 

Armstrong nailed it, it was the rear drive shaft, i went to the yard this past weekend and had three shafts to choose from, one was in really great condition so $40 later it was mine, i got it installed yesterday using my old u-joints, i took it out for a spin not expecting much difference but when the truck smoothly cruised well past 50mph without any shake i knew my old shaft was the culprit.

 

Is that cool or what

 

I need to look at mine then too, I have the identical situation, 45-50 mph slight vibration.

 

Curious to hear what you find. One thing that happened with mine was the front drive shaft had a cap in the end that came loose caused a vibration and a loud clanking noise. When it was fixed it vibrated because a balance wasn't done. Just bought a new one from local wrecking yard runs great now. Good luck.