Rear End Feels Loose

[kglesq]

Just got back from an epic journey. Picked up my new 2011 Screw Raptor in Kansas City and then drove it back to Southern California. The truck has developed an issue in the rear end that has me concerned. When braking to a stop, it feels like the rear end shifts or rotates forward, and then on acceleration from the stop, it unwraps or shifts back, and makes a sound I'll describe as a groan and clunk. It did NOT do this when I picked it up.

The truck has just under 1,700 miles on it from the trip. The trip was a tough one as it snowed like crazy over the rockies and through almost all of Utah. I-70 and I-15 were commonly not plowed, with snow and ice everywhere. The truck was in 4x4 high for a good 250 miles or more (on and off; when the road was not covered in snow or ice, it was in 2H). Some of the snowy sections were rather rough due to ruts and ridges, etc., but it wasn't anything severe--minivans were handling it.

So, anyone have any thoughts on what's going on here?

 

[JP7]

Hey there,
Some of us have experienced similar issues with the rear end binding. I can't seem to find the thread links, but I remember Pirate had a really good explanation involving transmission or slip yoke lubrication.
I had Ford to a tranny reburn (computer thing) and it took away most of the issue for a while. Now my truck is doing it again periodically (usually when hot) and so I'm going to get them to look at it again. Will keep ya posted.

 

[pirate air]

I'm guessing since you're back in soCal every things thawed out by now? If not I'd first let everything dry off/de-ice and see if that helps. The leaf springs are the only components that keep the rear axle housing located under the chassis. So look over the u bolts and where the leaf springs bolt to the frame/shackles. I'd also grab a hold of the rear shocks and see if they feel loose. If you have a shock going bad or loose the suspension will cycle more possibly giving you the feeling that the rear end is moving. Might also check your lug nuts. If you don't find anything I'd get it looked at by your dealer asap.

 

[iceman302]

Mine felt that way once. Then I realized that I should never have ordered the cheeseburger at a Chinese restaurant.

Here's the other thread that JP7 mentioned...

http://www.fordraptorforum.com/f39/rear-end-binding-up-when-slowing-down-taking-off-slow-486/

 

[FSM06]

kglesq,

It sounds to me like you are experiencing what is called pinion tip-in. You described it very well in that when you are coming to a stop, the axle "winds up". Braking force forces the pinion angle down against the transmission /engine applying torque. When you accelerate from a stop, the load against the pinion releases. This is a normal condition, however, if you traveled I-70 in Colorado recently, they use a magnesium chloride component on our roads out here that gets into EVERYTHING!!!. I would not be suprised if your suspension components are coated with the stuff, and may be aggrivating a typically normal condition.


FSM06

 

[kglesq]

Thanks to all of you guys for your insight.

I tried to wash out the underbody of the truck as best I could yesterday. I sprayed between the leaves, front and rear leaf eyes, upper and lower shock eyes, etc. Admittedly this was unlikely to cure much, but I figured I'd give it a shot as I wanted to make sure I got as much of the road grime and deicing agents off the truck as possible. Not surprisingly, this did nothing.

My brother (Droid) took delivery of his Raptor the same day I did. Trucks are identical but for color. His has no miles compared to mine as he took delivery in CA, but I note that his does not do this at all.

I'll take it in and see of they can do anything to reduce or eliminate it, as it's pretty annoying--really the only blemish on an otherwise excellent truck.

 

[kglesq]

Mine felt that way once. Then I realized that I should never have ordered the cheeseburger at a Chinese restaurant.

Here's the other thread that JP7 mentioned...

http://www.fordraptorforum.com/f39/rear-end-binding-up-when-slowing-down-taking-off-slow-486/

 

[iceman302]

True story. LOL

 

[kglesq]

Oh wow. That must have been ugly . . .

 

[kglesq]

Problem Solved . . .

Lube the slip-yoke. Cured it 100%. For more info see: http://www.fordraptorforum.com/f5/25-days-later-1314/#post18231