hi everyone, I just picked up a 1999 v10, automatic, f350, lariat, 4wd, crew cab, dually, long bed, 101k miles. As the title states, I get a vibration felt on the floor board and seat, not in the steering between 70-75 mph and under acceleration only. Ive searched here and google, and probably read every thread imaginable. Everyone who's had this issue solved it either by road force balancing, shimming the drive shaft, balancing the shaft, motor/trans mount, etc... Is there no direct way to diagnose the problem without randomly changing parts?

Some specs:
Front tires are 265/75/16 Goodyear silent armor prograde load E @60psi
Rear tires are 265/75/16 nitto terra grapplers load E @50psi

Front tread is 75%
Rear tread is about 25%


Ive changed:
Carrier bearing
Front Rotors, pads, brake lines.
Rear 3 u-joints
balanced drive shaft.
Balancing all 6 tires (not road forced)

I guess next will be 6 new tires.

 

I have the same issue but ive had it since i got my truck from my dad and he said that the current tires on it have a wierd wear pattern in them for some reason. They are do to be changed this spring and he said that he didnt have that problem before these current tires so im assuming its my tires for now. Also mine is the whole truck kind of bouncing and vibrating (more so vibrating) so i tend to not go up to 70mph. It may be similar to what you are experiencing.

 

I have a 2009 350 that gets a similar vibration in the 40-45mph range. And from the research I have done on this site and some others I have found that it is a very common problem in the newer trucks. Im not sure how far back the problem goes, but I guess dealers have told people there is nothing they can do about the common 40-45mph shake. No idea if that has anything to do with your year and speed range it occurs in... Based on everything you have replaced without any success I dont know what else it could possibly be.

 

after re reading your post i just realized you said accelerating only. If you go over 70-75 and then coast back down it doesnt shake in that range?

 

Accelerating between the speeds of 70-75 produces the vibrations. If I speed up to 75 and release the gas it decelerates perfectly smooth. The worst speed to accelerate on is 72mph, per gps.

 

Since my original post I can add balancing all 6 tires (not road force balancing), with no change.

Another revelation: today I delivered a load of 3200 pounds of tile, with rear tires at 70psi, and surprisingly with the weight in the bed there were no vibrations at the 70-75mph, in fact the truck drove perfectly fine with the weight.

Don't say drive with that kind of weight all the time.

I'm thinking it's a tire issue... I might try to find a place that can road force balancing.

 

hmm. well next time you drive her, look and see what the rpm is at when you are cruising 70-75. Try and match that in other gears and see if there is a vibration. The vibration probably wont be as noticeable, but if you pay attention you might notice it. If there is any hint of vibration at that rpm in other gears you can probably narrow the problem down to something in the motor. If it is positively only occurring based on vehicle speed and not engine speed, then it is probably a unbalanced tire. There is a slim chance that it is coming from the transmission, but most likely you would be having other symptoms if that was the case... im no expert, but i have a little experience tinkering around with buddies driveability problems and im pretty confident that this test will point you in the right direction. let us know.

 

Today I delivered 2200 pounds of flooring and again I noticed no vibration at any speed. However, I did notice the front passenger side brake smell, maybe that caliper is sticking. I'm going to replace the front passenger caliper.

Didn't mention on original post the front driver caliper was replaced about 1k miles ago, because it was stuck open.

 

While unloaded I brought the truck to 72mph then turned OD off, the vibration was still felt, but less noticeable probably because I was well over 3k rpm at that speed. Im beginning to think it's a tire issue because with the weight on the back it must flatten the rear tires and smoothen out any un-round areas.

Another possibility could be my caliper is slightly sticking (see above post). However, I can rule that out because with the weight in the back truck rides smooth. Hmm...

And another possibility could be shocks? Man this is becoming expensive. But I guess it's still cheaper than letting a mechanic do the work.

 

It sounds to me like a tire issue. Very slight possibility you have a U-joint that is failing, but I am still leaning towards tires.

 

Just changed two on the rear drive shaft and one on the front short shaft which eliminated a clunking sound when going from drive to reverse.

 

It could be tires but a couple of comments made in this thread sound very familiar to me and I have been there done that with highspeed vibrations. First off is the suspension on this truck stock? Lifted?

It does this at high speed under accelleration and if you load the truck heavy the problem goes away. Now I could buy that an out of round tire could resolve with enough weight but that doesn't explain why it doesn't vibrate at 70+ when not on the go pedal.

I think you need to take a hard look at your pinion angles. When you accellerate your rear differential will flex up slightly under that load. If these are close to out of the acceptable range, this accelleration coupled with high speeds (when you would most likely feel this type of vibration anyway) will be compounded. If you load the rear of truck heavy this will shift the weight more onto the rear axle pushing that angle down a bit. Result when the angle shifts up on the go pedal the angle stays within the acceptable range = no vibrations.

If truck has stock suspension there is still a possibiliity you have something loose or worn in your mounts or springs (carrier ?? if you have one) that can throw your angles off. The best way to test this is pull out your rear drive shaft and see if vibrations go away but in your case that's probably not a good idea since it's felt above 70mph and I wouldn't reccommend running it to that speed in 4HI. So the alternative is to get an angle measure and check the angle of your transmission output flange and your pinion output flange. The angle of your transmission vs pinion should be parallel (or with a degree or two) of each other when at worst case operating angles. This is a little drawing I did for myself a while back when trying to get my brain around this issue. If your sitting measurement of what is the Green line in my drawing is at a much higher angle (already pointing up above parallel) then when you get on the go pedal it is going up even higher and that's going to put some real stress on the driveline & ujoints and will cause vibrations above 60mph. If this is the cause you probably have some vibrations in the shaft whenever you accellerate but you can't feel them at slower speeds because the truck is absorbing them, at high speeds the vibration overcomes the vehicles ability to dampen and you can feel it.

I had this on my truck and you could feel it in the floor, console and seats but not in the steering wheel.

 

Sammie, from my best guestimate there is a leveling leaf on the front, the rear looks stock, shocks are rancho 9000 adjustables. I'm the 3rd owner so I don't have all the details. The angles do not look extreme compared to my little Nissan frontier.

Another new discovery yesterday being sick and tired of the vibes, I jacked up the front end for no reason and started taking apart the front passenger side brakes. Turns out when I spin the tire there is a scraping sound, however when I put the hub to LOCK the scraping sound disappears. So, is my hub going bad? Is it the wheel bearing? Could the scraping sound be associated with the vibration?

 

Could be your hub units yes but if it goes away when you lock in the hubs could be your needle bearings (spindle bearings) - hope for the latter - difference of $30 part or a $200 part. Both can cause vibrations, but bad hubs won't usually stop making sounds with the hubs locked. Lock your hubs and run it up to vibration speeds in 2HI and see if you still have the vibrations.

 

Don't think it's the tires because of the smoothness except under acceleration. Sounds to me like either driveshaft or rear suspension. You may have a broken spring that reacts unless enough weight to hold it. You've replaced the u-joints and dampner...how does the slipjoint look on the rear shaft. Dodge had a big problem with the slipjoint splines several years back that also caused "clunking" and vibrations. Easy way to check the rear tires is to rotate them from side-to-side and see if makes any worse or better. I really don't think is is front related because then it should show up in the steering wheel. Good luck.