Diff possibly failing

[HammaMan]

Started noticing some unusual backlash while cruising with neutral speed like going downhill where the cruise and gravity velocity are the same, almost felt like a bucking as it'd go back and forth between regen/cruising where the speeds are perfectly aligned. With the ebrake and footbrake on, going between D and R results in about 35-40 degrees of rotation of the pinion flange and sometimes a clunk (with ICE off, e-motor only).

It showed up on a road trip a few weeks back when I noticed the baby bucking as described above. Not even 8k miles on it.

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[SilverPigeon]

Well, I don't know PBs, but it's got to be at one end or the other; if not the diff, could the electric motor (or the software driving it) be grabbing at the wrong time? I guess taking the rear u-joint on the tailshaft apart would isolate it to one end?

 

[HammaMan]

With the ebrake / foot brake on there's not much play capable in the rear end as the axles are fixed in place. The backlash on the ring and pinion should 1 degree at most. The axle shafts to spiders shouldn't have any play so the play is either in the spiders/intermediates or the ring and pinion. 35+ degrees is way excessive. It's got nothing to do with the trans side of thing. The actual rotation is ~45 degrees, I'm taking off 7 for axle windup of +/- 1 degree. This is parked / idle, not underway. There's no noise from the ring and pinion so sounds like it's the diff.

 

[Ford Motor Company]

Started noticing some unusual backlash while cruising with neutral speed like going downhill where the cruise and gravity velocity are the same, almost felt like a bucking as it'd go back and forth between regen/cruising where the speeds are perfectly aligned. With the ebrake and footbrake on, going between D and R results in about 35-40 degrees of rotation of the pinion flange and sometimes a clunk (with ICE off, e-motor only).

It showed up on a road trip a few weeks back when I noticed the baby bucking as described above. Not even 8k miles on it.

Hello! Could you privately message us with your VIN and the name and location of your Ford dealer so I can look into this concern? Thank you!

 

[powerboatr]

Did you engage locker for rear then try to twist drive shaft to see if it was same

Really only way to know the truth ....is pop the cover and get a look inside
And...it's under warranty
Let em put it up on lift and do a good inspection

 

[Porpoise Hork]

Mine started out doing this very same thing. Took about 3-4 months before it ended up getting so bad that it would make a loud clack/pop when shifting into Drive or Reverse. Then it started doing when driving and pressing the brake. Took it in and after a lengthy diagnosis they determined both axles and differential were faulty and needed to be replaced. I have the Max tow so there's an open recall on it but they rebuilt the rear end anyway replacing the diff, axles, bearings, and all associated parts resolving the issue.

The recall is still open on it since Ford has not released a fix yet. So I'll get that done when they do finally figure out what they are going to do.

 

[HammaMan]

I don't have a max tow so its issues aren't on the table. What failed in your diff?

 

[Porpoise Hork]

I don't have a max tow so its issues aren't on the table. What failed in your diff?

They said that there was a significant loss of torque to the driver's rear tire even when in 4wd and determined there was a fault with the rear diff. I didn't ask for more details once they said they were replacing pretty much everything except the housing.

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