Hello everyone, new here! I've got a '90 F250 4X4 and it's developed a shake. When I get to about 55 mph (going straight, turning, whatever) the truck develops a slight shake. It continues to worsen peaking at 70 and then going away completely at ~80 mph. I know it isn't the following: Ball joints (Brand new moog), tie rods (brand new moog), Bearings (brand new in all front end), loose castle nuts (have checked them numerous times), alignment (had it done after rebuilding front end), U-Joints (brand new + happens in 2wd & 4wd).

Some info about the shake: It is pretty consistent in that it happens every time I drive over 55 and seems to be high frequency. The truck is a standard transmission so I've put it in neutral to see if it's something to do with trans. It happens in gear, out of gear, in 4th gear, in 5th gear, idle rpm in neutral or 3000 rpm in neutral, it doesn't seem to matter. It gets WAY worse if I slowly let out on the gas. Worse as in amplitude gets bigger, frequency stays the same. I've crawled under and looked for anything obvious, taken down hub/spindle assembly and checked the bearings to make sure there wasn't a stray bad one, had the tires rebalanced (tires have less than 1000 miles on them), and tried everything else I can think of. I wouldn't describe it as a "death wobble" because it doesn't affect my driving. When the shake happens I don't feel it in the steering (my box is a little loose so it could be taking up the shake). I can feel it in the shifter on both the transmission and the transfer case, throughout the floor and on the dash, my mirrors shake so that I can't see out of them, and it makes a pretty good noise. It's almost like rumble strips on the highway, but not as loud unless I'm letting out on the gas slowly. I also checked the motor mounts visually and they look fine.

Does anyone have any suggestions for me? I'm at my whit's end here! Just a side note, I bought the truck and immediately took it for new tires as the old ones were terrible. When I had it there was no shake, but the tie rods and ball joints were shot. I don't remember the shake being there driving it back with new tires, but once I replaced all the stuff (tie rods, u joints, bearings, ball joints) it was there for sure. I had the alignment done after I changed everything and it was adjusted slightly. If I haven't replaced it, it's factory at least for the most part. Shocks are next but I can't imagine that they'd cause that kind of symptom. It is a leaf spring front suspension. Tires are 285-75R-16.

 

Sounds like a driveshaft balance problem, is it aluminum or steel, one piece or 2? The center carrier bearing on the 2-pc shaft is problematic if the truck has any lift and dried out U joints could also be the problem.

 

It's a single piece steel shaft. I crawled under to look and there's a little ATF slung around on rear output of the transfer case, so I pushed on the shaft. It's got some play that's not in the u-joint... The transfer case has a little play in the mount as well, but it is about 1/3 of the total slop. I don't have a blowup of the transfer case but I'm assuming that means a bad bearing.. Say it ain't so!

 

Some play in the output isn't uncommon, I'd suggest you drop the driveshaft and inspect the U-joints more closely before diving into the t-case.

 

I'll definitely have to take a closer look. They aren't sloppy or making any noise, but they are old.

 

you said universals are new. front universals, or all ? because it sure sounds like a bad universal in the rear drive shaft to me.

 

Just the front universals are new, I haven't done the back ones yet as they felt tight. I'll just have to pull it and replace them. Hopefully the 26 y/o rust on those bolts doesn't take an act of congress to get loose! PB blaster and a torch! it'll be next week before I get to pull it down because I'll be going out of town for the new year. Luckily this truck is a project and not a DD. It was an old fertilizer rig that I got for dirt cheap and was able to drive home safely. The guy who had it wasn't very mechanically gifted. It needs some love, but it's a solid truck and packs a 460

 

Alright, it took a while as I had some life happen, but I've got the universals changed out. Still no change in the noise. Anyone have any new ideas?

 

try moving tires front to back and see if it moves.
another thing i will do to isolate a vibration is put the truck up on jack stands and then run it up to speed. if it does not do it in 2 wheel drive, but does it in 4 wheel it is in the front axle, drive shaft, or transfer case.
by having it up in the air on jack stands,you can also look at the wheels for wobble to see if you have a bent rim, or bent axle.

 

I'll have to try that. I've got a buddy with a lift, so maybe I can get him to put me up in it. That brings up a question I've been pondering. Do the front driveshafts that go from the transfer case to the hub spin from viscosity in the system when it's rolling even if the hubs are free? I mean the problem arises at around 55 and I've wondered if maybe I have a problem that I'm not looking at with that system. I did pull out both axles to replace u-joints and my gut keeps telling me to go back to that, but I don't know what I'd be looking for. Since the problem only arose after doing all the work in the original post.

 

up on a lift is not the same as up on jack stands. on a lift the suspension us unloaded. on jack stands it will be the same as on the road, only the tires are not making contact with anything but air.
in theory the front drive shaft and axles will not turn if the t-case and locking hubs are in 2 wheel.
but in reality there is usually a little genetic energy transfered through the hub turning the axles and drive shaft.
it is possible you have a locking hub that is not unlocking.
to test the hubs, jack up the wheel and spin it. see if the axle turns or not.
if you can turn the wheel and hold the axle from spinning, the hub is unlocked. if you can not hold the axle from spinning the hub is not unlocking

 

I've tested all the hubs to see that they're unlocked when I did the ujoints so I know they're good to go.

Thanks for the tip on the jackstands, I would have stood it up on them on the frame because I didn't even think about loading the suspension. Last night was working on something unrelated and found the front shocks to be pretty loose. They had probably 1/4" of side to side play and are likely OEM shocks. I've never had anything that didn't have old shocks on it, but could that cause the problem?

 

it could, but i have never experienced it.

 

Sounds to me like one or more balance weights came off of the rims right after you had the new tires installed. I would not do anything else until I had the balance re-checked on the tires. Have a cord separate in a new tire is also not un-heard of.

 

I took it in to have the balance redone, and they rebalanced it, but as soon as i got up 55 after doing it, the same shake was there. They said it was hard to get the clips to stay tight and might need to go to stick on. I've been thinking about trying dynamic balancing with the *****. As for the separation, would there be any visual clues to that having happened?

Maybe I can get a video posted up to youtube and link it here for people to watch if I can get the sound to pick up well on a camera.