Vibration (probably my fault),please help!

Well, I've had myself a busy weekend. I installed Rough Country add-a-leaf springs, extended shocks, brake pads, and changed the differential fluid in the rear. Ford keys on the torsion bars, extended shocks and changed the differential fluid in the front. Also changed the transfer case fluid, oil, and fuel filter. Raised the vehicle 2.5" overall, looks great....BUT. Being pround of my mechanical triumphs, I took my "new" ride out for a spin. I noticed a vibration coming from the rear. It's weird. I first noticed it after I had accerelated to about 45 mph, as soon as I let off the gas, the vibration started. If I roll on the throttle, it goes away. If I coast from 45 mph, it vibrates untill i get to under 10 mph.

I pulled it back into the garage and checked my work. Everything is good and tight. Anybody have any ideas? I would have to think it's something I've done. Everything I've read on here about vibration points at the wheels being out of balance, but they were OK on friday. I know that after I put the new torsion bar keys in that I would need an alignment, but i figure that if that was the case, my vibration would be comming from the front end.

For what's it's worth. I used Lucas oils 80/90 gear oil in the differentials, and Dexron/mercron in my manual transfer case.


Any ideas? I'd love to hear 'em!!

check your drive shaft

Crawled under there today, the driveshaft seems good. There is no play typical of bad U-joints. I'll most likely just replace them anyway. I had a guy tell me today that I should check to see that the pumpkin is level. He explained that if the coupling coming out of the differential was off level that it would have an adverse effect. Does this hold any merit? I've checked all over this forum and have found nobody else to be having these problems after installing the add-a-leafs.

Thanks

The amount the angle would have changed by installing an add-a-leaf would not cause a vibration unless the u-joint was already bad. Some places that sell add-a-leaf kits actually provide a tapered shim so it tilts the rear differential upwards at the front to keep the pinion and the drive shaft at the same angle. First thing i would check is the u-joints and if the vibration is still there after replacing them i would look into installing one of those shims on each side.

If all else fails lift the rear end and lossen the bolts and retighten by hand. Then set the truck on the ground and go back and tighten the bolts.

I would think the leafs had a set pinion angle built in, and even that small of a lift shouldn't matter.