1975 F100- Long bed. We've got a drive-line vibration that starts about 45mph and continues to get worse as mph increases. It isn't as bad under acceleration but holding a steady speed and coasting it is. I forgot to add; IT IS MPH DEPENDENT not RPM dependent.

Drive-shafts have new u-joints, new swing bearing and have been balanced. Rear housing is a new Currie 9in with all new stuff in it. Transmission is 3 speed. The motor has been balanced.

Thanks.

 

You sure it's not the wheels out of balance?

 

Thanks. That's one thing I forgot to add. They were mounted and balanced by a shop. Aluminum wheels.

 

"Where" are you feeling the vibration?

 

New and balanced everything? How's the driveline angles? If you hit the pinion angle too steep, it could cause a vibration. Also, "new" doesn't mean "good". Your rear could have too much back lash in the gears. You could STILL have a bad u-joint. The output shaft of the transmission could have a bad bearing. The center bearing could have torn rubber or not fit the shaft correctly. You need to go through every part and systematically check off each one. I bet when you go through everything, you'll find something you missed. What about tires? You didn't say they were new, just that they were mounted and balanced. Could one of them have a belt separating?

I'm just giving you ideas since I'm not standing there, looking at the truck.

Let us know what you find.

 

I had my new tires mounted and balanced by a shop. They still balanced them incorrectly, and caused a vibration.

 

Gents, thanks for responding; great ideas. So, yes the tires were new and still don't have many miles on them. We bought them brand new. It feels like the vibration is coming from the center of the truck if that makes sense. We had the diff set up by a drive-shaft shop that specialized in rear ends and drive-shafts.

The rear is an all new Currie housing ordered directly from Currie with their Trac-loc diff. Original 3.25 gears used. New 31 spline axles. The rear drive-shaft was custom made by the same shop. The original front was reused.

So later, after we still had the vibration, we re-balanced all four wheels and tires. I took the whole front and rear drive-shaft out and had all new u-joints replaced, swing bearing replaced and the whole thing balanced.

Now I haven't changed the pinion angle from stock. I haven't checked internally in the trans. I haven't changed the trans mount. I haven't looked at the flywheel, clutch kit or pilot bearing since we replaced it all.

 

Could the u-joints be out of phase?

 

What is "u joints out of phase"?

 

U-joints being out of phase is when the u-joints on a drive shaft are not lined up, or not clocked the same.

 

How many u-joints are in your rear drive shaft?

 

I just checked mine and the front is definitely out of phase with the rear two, as I was completely unaware of this "phase" thing upon installation. How serious of a problem is it?

 

Sorry guys, A LOT of yard work yesterday. I'll have the check the phasing. The truck is at my dad's house. I do know when they balanced the ENTIRE shaft at the driveshaft shop, they aligned the slip yoke together with 2 arrows.

It's a long bed. So if I'm remembering right, there is one joint right behind the output shaft and 2 in the the rear shaft; one right behind the slip yoke and of course another at the pinion flange. Right?

 

Thanks - good to know

 

As far as I can tell, everything is lined up. The rear shaft are definitely in phase. It's hard to tell looking past the swing bearing from the front to see if the front is out.