i just a got a 99 f-150 v-8. i get a drivtrain vibration from 35-45 mph, and then again starting at 70mph. but the vibration gets 5x worse when i let off the gas, but only at speeds 65 or over.

what do you think could cause this? i think ive ruled out alignment and bent driveshaft

thanks for your help

 

I suspect something in the springs, spring mounting, or pinion bearings. How many miles on this truck? Any evidence that diff. has previously been open-up?

 

Your U Joint is bad at the axle, it is probably seized up. You can't tell until you take it off.

Easy enough though...

 

the truck has 68,000 miles. could the u joints be the only thing to look at?

 

gearmanx17,

Will a bad pinion beaing actually cause the rear end to shake???

My differntial howls from 35-40mph and then again from 55-60mph and I also do have a rear end vibration. When I take my foot off the gas, the rear of truck begins to shake as I'm slowing down. It could be the tires but I'm really not sure. I had some other work done at a transmisison/rear end shop and the shop manager said that the differential was a little loud but nothing to be too concerned about.

 

AjRagno

MY experience, if diff. is vibrating, it is probably leaking oil and is about to go into major failure which would indicate that a diff. side brg. or pinion brg. is failing. Usually a noise on de-acceleration is an indicator of an outer pinion brg. failing or driveshaft or d/s angularity problem.

Many times driveshaft vibrations are transferrred and make us think the diff. is vibrating. Do you have a friend or neighbor with a late model F-150 that would let you switch wheels & tires for a test run?

I would also check rear shock mounts, rear trans. mount & d/s. Maybe d/s is bent or has a u-joint with galled needle brg's in the caps.

 

gearmanx17,

It's really been quite difficult to determine what the vibration is. It does seem to be in the tires as I can hear as well as feel it. It's just that they only have 10,000 miles and I've had them balanced and rotated repeatedly without success. The wheels themselves have also been checked.

It did seem to me, while I was towing my boat, that the vibration was lessened. Is there anything inside the differential that would be affected by the driveshaft angle, lessening the vibration???

The driveshaft and trans mounts have been checked. I replaced the u-joints as well, with OEM. No leaking and the fluid level has always been proper. I changed the fluid last summer, when I replaced the axle seals (Yes I jacked up and lower each side and then drove in a figure 8 for a few minutes and re-checked the fluid level) The differential has never been under water either. Everything looked alright when I had the cover off. There was no play in the gears or any signs of metal shavings.

As for other wheels: My neighbor just got a S-Crew.. But, I'm sure I'd just get a blank stare if I asked to borrow his wheels for a little experiment

I've actually been considering changing the 3.08 open differential to a limited-slip anyway. Maybe you could tell me if this lists all the parts I'd need, as well as your opinion of Eaton vs. Auburn???

Installation Kit
Ring & Pinion
Eaton 8.8" Ford Posi - 31 spline
Auburn Pro Posi Unit - 8.8" Ford - 31 spline

 

AjRagno,

If you are considering changing ratio & converting to a L/S; definitely install a master brg. kit (which would have new pinion brg.'s, crush sleeve, pinion nut & other goodies). Also be sure to install new axle seals (very inexpensive item).

I still believe that you have something wrong with your rear springs. You did note that vehicle did not vibrate as bad with trailer hooked-up & towing.

As for the L/S: I like the Eaton-Posi and the Auburn Pro series. The Auburn Pro is a little more expensive than the Eaton. The Eaton is rebuildable. The Auburn is not rebuildable. Once the friction cones in the Auburn wear the case out, it is a disposable item.

I have three Ford pickups with L/S. One has OEM Trac-loc (99 F-150), one has an Auburn Pro series (1979 F-150), and one has a Eaton-Posi (1994 Ranger). I like the Eaton-Posi the best and like the Trac-loc the least.

 

ok if u joints are bad, when coming to a stop will they make some sort of noise? and when stopping if you get on the gas before you stop fully will they clunk?