So I have an intermittent vibration at 40-45 mph, and had one at 60+ i balanced my driveshaft, did nothing, replaced a suspected bend rim, and that mostly solved the 60+ vibration, then I replaced my badly worn kingpins, and its is really smooth all the way up except for the slow vibration at 40-45, but it is not all the time, just sometimes, usually when I'm slowing down. Im going to replace my drag link tomorrow which is mildly worn, and change my rear shocks, (front shocks are new). other than that, I cant think of anything it could be, my wheel bearings are in fairly good condition, and all tires balance right. also i should add, it dose not matter if I'm in 4x4 with hubs locked or 2 hi with unlocked hubs. I put 20k on this truck per year, & have a 2000 mile trip coming up in a couple weeks, its not just something I can ignore cause its "not that bad" what am I overlooking here? Ill get back on after I change my drag link & shocks, weathers kept me inside for too long up here but tomorrow Ill just do it

 

Coasting to a stop or under braking power? Heat warped front rotors? Front drive line (front or rear) u joint? Front axle shafts u joints? Motor or trans mount? How are your front d/s splines and slip yoke? Front axle pinion bearing?

 

just coasting no brakes, and it happens if I'm locked up in 4 or unlocked in 2, so I have kind of ruled out it being any problems with front driveline, or anything thats not spinning when just in 2 high, I have all new spicer U joints on rear driveshaft. I know my front spindles aren't what they used to be, so I'm planning on replacing spindles, and bearings in the front, it just dosnt seem like that kind of vibration, it feels slow and heavy. on the bright side, by the time that i solve this problem, I'm sure nearly every moving part of my suspension will be brand new.

 

Try it this way, once you are up to speed, put it in N and let it coast to a stop while the engine is at idle. And see if you still get the vib and if it decreases as you slow down.

Maybe a flywheel or transmission issue, is it a auto? Swap the tires around (front to rear) and see if the vib moves?

 

I had a tire that was actually slightly out of round. If I jacked the wheel up to where it was scraping on the ground but I was able to roll it, there was a spot that was not touching the ground. I put it on the back and it made the issue go away. Did not seem to care about speeding up, slowing down, or maintaining.

Could be your alignment, but alignment seems to make issues worse at higher and higher speeds.

A tire out of balance has two normal harmonics on a vehicle. One is usually around the speed you are talking about, and then a second one higher at highway speeds or a little faster. Are you sure your tires are properly balanced?

 

Tires, wheels, rotors, spring bushings, all could be a factor. Let us know if you find it.

 

I am planning to replace my front spindles & wheel bearings as soon as they arrive in the mail, Ill have the rotors done when I'm at it, and Ill check all the tires again. it will happen sometimes after I hit a pothole on the road right at that speed (41-44mph) but it can happen when I'm climbing hills, 3rd, 4th, or Neutral, (T18 manual) it is most frequent when coasting in neutral, or at least thats when I feel it most. I replaced my drag link, & it did not help in the slightest with the vibration, but did take a little slack out of the steering. iv been looking all around my truck over the last few days and I think I have a bad leaf spring bushing, probably front of the front. I might get into swapping that out now too.

 

I got those front leaf bushings replaced with some poleurithane bushings, and haven't felt that vibration since, but it wasn't every time, so theres a chance its not fixed yet. I replaced the steering stabilizer a few days before which didn't help at all either, but it did make my steering feel funny, I don't like it, the truck doesn't straighten out on the road anymore, it fells better to turn, but harder to keep straight, cause you have to actively straighten it out on the road, does that seem right? it just seems like it is a little stiff. Any thoughts?