hey was wondering what a possibly could be causeing a very fast but not harsh vibration at around 75 mph, not sure if it gets worse if i go faster, but if i go say 5-8 mph less the vib goes away. could it be a ujoint or tires maybe out of balance?? or just the fact that i am getting up there in speed and things are just vibrating

 

I have the same vibration , have tried new tires and a new driveshaft from ford, next step for me is to replace pinion seal for a leak and check nut on yoke and diff bearing.

 

I had a similar situation on my F250 and it was the CV joint "knuckle" on the front of my rear driveline, they are conected together by a ball joint from one u-joint to the next. one of the two u-joints was dry and shot. I ended up taking the whole line to a shop and they replaced it all.

 

Does anyone have a lift on their trucks to cause the vibration? I have heard that the lift causes vibrations.

 

I've fought with vibrations in the past, and just recently the vibs started again (but feel slightly different than before). Still they are high speed vibrations like yours.

Mine originally started with a bad u-joint. I replaced all the u-joints, but the vibration was worse, not better, after. So I took the driveshaft into the shop and had it re-balanced. It helped a little, but it was still vibrating. I took it in, had it completely rebuilt, phased, etc, got it back on, and it still vibrated.

So I took it into another shop and they re-adjusted the center support bearing height. The rebuilt driveshaft has a larger center support, so it threw everything out of line with the old shims. Got it lined up correctly and the vibrations went away.

Now they have come back, but it feels like it's coming both from the back as well as the front of the truck. I talked to another guy the other day and he said to try some Centramatic automatic wheel balancers, as he thinks that the tire shops are unable to correctly balance my large tires. He said my symptoms sound exactly like one of his trucks, and the Centramatics completely fixed the problem. So I'm trying that next to see what happens. I think I've ruled out the driveshaft now as it's been worked on again and again so many times already. Plus the vibrations went away for a little while, now they are back with a vengance. I bet I threw a wheel balancer off or something.

 

im going to try and rebalance the wheels, might as well start with the easy stuff first

 

Too big of a lift without changing the driveshaft angles and replacing ujoints with CV joints will cause vibrations. Simplified. . . each ujoint has a max angle they can work at. . . start to exceed that angle and you start vibrating.
Timmy

 

Thats a good idea, but be aware that most tire balance machines only go up to 55mph, so it could still vibrate when you go faster. Mine used to do this pretty bad at that speed and a new set of tires cured it (the PO put 2 P tires on instead of LT and I missed that when I bought it).

 

Yep that's the problem that I have. I've even been to a few shops that can't fit my tires up on their balancer. No shops in my area can do any sort of road-force balancing with this size tire, so they only do the standard balancing, and I've found that most shops only spin up to about 45-50 mph.

 

When I had larger tires I had a hard time keeping things balanced. i ended up ditching the larger stuff and it smoothed right out. also it helps to balance and rotate every oil change too.