From five years ago, I hope bama got it fixed. Either that or they're VERY patient!
Be nice if all the posters that had the similar issue would have followed up too. Hope they all got rid of the vibration.
Surprising how often it's a driveshaft though. Especially the double-cardan type on some of the trucks.

I wonder if some of them had the hubs locked and the front was causing a vibration?

Paul

 

I have a '79 F250 4x4 that under load has a vibration at 55/ stops at 60. I did have new 17" aluminum wheels put on and a new clutch installed, at which time I noticed the issue.New U-joints/drive shaft and pinion seal. The old pinion seal had been installed backwards! No hum in the DANA 60 rear end. New gear oil in np205 along with new gear oil in the differentials didn't make any difference. Still have the vibration -- will change np435 transmission oil next and report. With the hubs unlocked vibration still occurs so I assume it doesn't involve the front drive line.

 

Yeah, likely not. But even a new shaft could have some issues. Luckily driveshafts and u-joints are a lot more reliable than most modern replacement parts. But you just never know.

Is yours the single-joint at each end type of shaft? Or does it utilize the double-cardan style joint at the transfer case?
If the singles, it's easy to over-torque the u-bolts (for the u-joints that is) and crush the cup into submission. This results in a very short bearing life in the joint and, very likely, a vibration.

If you'd just changed the lift height of the suspension at the same time, I'd suspect a rear pinion angle issue. Was any other work done to the truck before this started? Maybe extra weight added to, or removed from, the rear? Springs changed? Anything at all along those lines?

There's another thing that can happen to even a new shaft. They can be assembled out of phase. For those not familiar with that, it's when the two halves are assembled with the splines out of kilter. So the two u-joints are fighting each other rather than enhancing each other.
Easy to tell if it's way out, as the caps won't align with each other when you imagine a straight line up the shaft.
If it's only one or two splines off however, you either need a good eye, or take the shaft off and lay it on the ground or other flat surface. The caps should both lay flat on the ground at the same time. No offset or rocking allowed.

Just a thought, since you said you had a new shaft.

Good luck.

Paul

 

There is only a single spline on the rear driveshaft, there was really no difference in vibration when the old drive shaft was installed. The new drive shaft is a bit longer and the booted spline was put at the differential end to lessen stress--was told shorter factory drive shafts put more stress on the splines--makes sense.

I did install an aluminum flatbed to replace the heavier 8' bed. Next time I pull a load with the goose-neck will see if the vibration lessens, which it just might. Will report observations in a couple of weeks.

Truck is otherwise stock and not lifted--it's still a work truck and belonged to my father. 400 cleveland motor replaced original 351c, 400 has about 30k on it; total vehicle miles about 130k. I've been driving it with the vibration for the last 9k miles since 2012.

 

Normally I'd say try to pin it down sooner so you don't wear it out. But if 9,000 miles hasn't done it, then the vibration either isn't bad enough to cause too much trauma, or it's not in the u-joints after all.

But you can still check it pretty quick if you have the time to take. With a decent angle finder you can check the relative angles of the front and rear u-joints in the shaft. Or put differently, the angle of the output shaft of the transfer case and the angle of the rear axle pinion. They should match, I believe to within about 3° of each other. I think?
Optimally they'd match almost exactly, but there is some leeway allowed. And the rear pinion "climbs" during acceleration and fall during deceleration anyway, so it's constantly changing.
But if in it's neutral position the two joints have too much angle differential then you will get the vibration. Especially under just certain circumstances, such as when you accelerate (as yours is doing) or decelerate.
Vibration upon acceleration would usually indicate a rear pinion pointed too high to start. Then it just gets higher as you push on the gas.

Although, being a 250 instead of a 150, those big heavy duty spring packs in the rear are not known for being too flexy and allowing much pinion climb/axle wrap.

Still, doesn't hurt to know. Interested to hear what happens when you load it up.
If you decide to measure, a digital angle-finder is the ticket. You can get pretty close with the old style dial type, but they tend to stick and might miss a couple of degrees here or there.

Good luck.

Paul

 

Update on speed specific vibration: after hauling a cultivator 200 miles with new U-joints, new rear drive shaft (in phase of course), new 80-90w in both differentials, new 80-90w in np205 and fluid replacement in the np435 transmission with 75w90, vibration really only is noticeable when I put the pedal down too fast at around 55mph. Gear shifting is normal. It's not from the front end. Will to go to another respected tire place to re-check the wheels and tires.

 

Thanks for reporting back. Glad it's almost gone at least!

Paul