Severe chatter turning and under load. Diff ? Transmission ? Driveshaft ?

My truck is a 08 F350 6.4 5R110 4x4 LB CC.

I bought it with 82K on it last fall. Its now got 110ish on it.

Its a very clean truck. The previous owner never towed with it as far as I can tell.
Its given me zero problems other than engine issues covered under warranty.

A month ago I pulled our 13K 5er about 450 miles in some hills.

When I got to the campground I noticed that the rear diff chattered going around corners, especially with the 5er hooked up. My '99 F250 does the same thing, but not nearly as hard.

I also noticed a bad vibration from the rear axle area under hard acceleration in the lower gears with the 5er hooked up, like when you are accelerating away from a stoplight. This happens when driving in a straight line.

I put a couple thousand miles on the truck and then we went camping again. This time I pulled the trailer about 600 miles. A couple times I noticed some vibration in the rear when accelerating. Once it was after an OD to 4th downshift.

One day I was driving up a 5% grade, slowly accelerating. I was going around a bit of a curve. The transmission tried to upshift into OD, but there was a horrible chatter and it wouldn't complete the shift until I backed off the throttle.

Our house is at the top of a hill. There is a steep section about 3 blocks long to get to it. It has a slight curve. When I pulled our trailer up it at about 15 MPH, the rear axle chattered hard the whole way up. It was shaking the entire truck. The transmission was not trying to shift.

The truck also has a slight vibration at highway speeds on smooth roads. It shakes/vibrates an empty child seat sitting on the back seat.

Tonight I dropped the driveshaft on the differential end. My truck has a steady bearing. The steady bearing seems OK. The slip joint works, but its a bit stiff. The differential U joints seem to move fine in all directions.

I opened the diff and drained the oil. It appeared to me to be the first time it was opened. The oil is a bit dark but does not smell burnt. There was about 1/8" of debris on the diff drain plug. The ring gear pattern looks good. The volume of oil drained out seems about right.

Prior to pulling the 5er the chatter going around corners was slight. Now it is much more pronounced.

Other than the mentioned transmission incidents, it seems to work great.

What is causing my truck to chatter ?

Try adding more friction modifier, my guess is that it is your limited slip clutches chattering.

I was thinking the same thing, but would that happen when going in a straight line ?

I've had limit slip chatter on my '99 pretty much since it was new. Through several diff oil changes and friction modifier additions. Any tips to fix this problem on both my trucks ?

:whs:
My buddies obs did this bad added some friction modifier and it cleared up, Its worth a try change oil and add the mf, hope that is all it is!

I just had the same problems and my pinion bearings were shot.. so try jerking on your rear end yoke and see if your bearing have any play.

Jeremysmith9902 said:

I just had the same problems and my pinion bearings were shot.. so try jerking on your rear end yoke and see if your bearing have any play.

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You had the exact same symptoms ?

How much is "any" play ? There is a bit of rotational play, but its hard to tell if its too much or not.

I forgot that I have the 08 shop manual in my garage... I guess I should look this stuff up and share it.

Thanks for the replies.

me2 said:

I was thinking the same thing, but would that happen when going in a straight line ?

I've had limit slip chatter on my '99 pretty much since it was new. Through several diff oil changes and friction modifier additions. Any tips to fix this problem on both my trucks ?

Click to expand...

Mine will have some(very slight) chatter in a straight line when towing the 5th wheel camper from takeoff. Unloaded I have no chatter in turning or straight.

There was a TSB for updated clutches, cannot remember what years though.

Thanks for the replies.

Reading between the lines in the shop manual diagnosis charts, I think the diff would be whining if the pinion bearings were loose. Mine is quiet.

I definitely think its a locker clutch issue now that other people tell me they had chatter during mostly straight acceleration, like I do.

I'm changing oil in the diff and adding 8 ounces ( 2 x 4 ounce bottles) of friction modifier. That 85W140 is sure expensive !

If I continue to have locker issues, I am going to swap my diff for a 2011 10.5 with an electric locker from a gasser Superduty. A local wrecker has one and wants $1500. I wonder what I would get for my used one ?

I'd spend $500 to swap for an electric locker versus pulling my current diff apart to rebuild the locker. Looking at the shop manual, its not trivial to rebuild the locker and shop time at a Ford dealer is $$$$.

As far as the vibration during straight line acceleration, id say the pinion on the rear axle is raising and putting the u joint at a bad enough angle to cause the problem.

What have you had balanced to try to cure the high speed vibration?

Aaron

Aaron S said:

As far as the vibration during straight line acceleration, id say the pinion on the rear axle is raising and putting the u joint at a bad enough angle to cause the problem.

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I don't doubt there is some axle wrap going on. I need to mount a video camera under the truck to watch what is actually happening.

What have you had balanced to try to cure the high speed vibration ?

Click to expand...

Absolutely nothing. Its pretty mild. I'm going to install an air ride rear suspension system this fall. I'll tackle it this winter if its still a problem. It might be related to this other stuff, so I'll sort that out first.

I put the cover back on the diff and added a quart of new oil and 8 oz of friction modifier.

I reused the old oil because I suspect I have to take the cover off the diff when I build my air suspension later this fall.

I also reconnected the drive shaft. I'll probably take it for a test drive tomorrow.

I drove it around town running errands. The chatter is much, much better. Its better than my '99 in this regard, but there is still a bit of chatter.

I think its the nature of the beast that after towing heavy these limit slips get a bit aggressive.

I just shot a video of the rear suspension while driving around the block and climbing a steep hill with the trailer behind.

When climbing the front of the leaf spring is totally flattened out, to slightly bowed up and the nose of the differential is climbing up about 3 inches. I am climbing in 1st gear, but no where near full throttle. The trailer weighs about 13K.

There are a few clunks from the diff during the climb. I can hear them in the cab too.

The diff in my '99 makes noises and some clunks climbing this same hill.

I also probably found the source of the vibration at high speed. One of my back wheels is wobbling. Its a wheel from my '99 that I swapped on this truck.