On my new-to-me (3500 miles of my own, 101k total) 2000 excursion, I have encountered a weird behavior which seems to be coming from the rear end.

After more than a few minutes cruising at speed, if I come to a complete stop, the rear end will bind up on launch. The torque converter spins up and stalls, and then the truck will crawl forward until it unbinds, at which point it will lurch forward and drive completely normally. If I'm driving stoplight-to-stoplight, or even at speed for just a minute or two, it doesn't happen; I'll come to the stop, and just launch normally.

I do have a leak from somewhere around the front pinion seal, but it's just weeping. I had the fluid in the diff topped off before my highway run yesterday (~600 miles), and the tech said it only took a pint. Unfortunately I didn't think to ask whether that was to the hole, or just to whatever the "full" level should be.

Following the advice in this post:

I checked the play in the pinion bearing. There is perhaps 4 or 5 degrees of play; I can definitely feel it rock from one side to the other, but it doesn't feel excessive at all.

Anybody run into this before? Thoughts?

 

That play of 4 degrees isn't a big deal IMO (shaft turns 4 deg before engaging the ring gear). Are your drive shaft U-joints ok? No excessive play there? The seal is a relatively easy fix, but focus on solving the binding issue before diving into the leaky seal. If U-joints are OK, crack open the differencial, drain the oil and see what's binding in there.

 

Is it possible for the pinion bearing to be off its axis and binding that way? I'll check the u-joints, but what should I look for? I don't see how they could cause binding.

Thanks for the suggestions!

 

Could it be low transmission fluid? Seems like the TC may be winding up to get enough pressure to apply power, then dumping the force of the higher RPM motor straight into the rear end. Could be a sign of low transmission fluid.

Is yours the diesel or the V-10 gasser?

 

Transmission fluid is full; checked that last week. It's a 5.4 4x2.

 

Pinion would have to be super loose. When you take off the rear driveshaft to check that U-joint, can you pull the pinion flange in and out (forward and backward)? U-joint will be sloppy and might have rusty residue where the cap meets the joint caused by no lube on the needle bearings. They can get squeeky too.

Some pics at the end of this thread.
https://www.ford-trucks.com/forums/1...nion-seal.html

How about a dry driveshaft slip joint?

 

Here are some pictures of the u-joints; they're rusty and have a dirt build-up at the joints, but look like I'd expect them to.

Rear with picture of the pinion seal

https://picasaweb.google.com/lh/phot...SfhiIpISOmSEmQ

Some detail of the rear

https://picasaweb.google.com/lh/phot...S2M2J-fAJinCfw

Some detail of the front

https://picasaweb.google.com/lh/phot...gvV476jfz_1hqg

In the third picture, the black stuff appeared at first to be metallic. However, upon physical inspection it is just essentially baked-on grease. The same basic condition on the rear joint. Are the U-joints serviceable at all, or are they sealed?

Where is the driveshaft slip joint? My driveshaft is solid - one piece from the front u-joint to the back.

 

Apparently your 2wd has a little different set up than my 4wd. I'm thinking the 3rd picture grease came from that u-joint- worth checking further off the truck. Looks like that's the u-joint near the tranny? It's connected with a slip joint into the tranny rather than on the shaft like mine (you saw my pics right?). Before you pop off the drive shaft, jack up a rear wheel (safely) and turn the driveshaft by hand (Tranny in N, blocked tires so she won't roll over ya) both directions. See if you can duplicate that binding by hand. Turn a wheel by hand also see if it binds. Hang in there, we'll get 'cha sorted out.

 

I finally got the truck in to the transmission shop (a different branch) a couple of weeks ago, and they went completely through the tranny - pulled it apart, found nothing physically wrong with it, added a line pressure increase kit, and put it all back together.

The guy at this branch had told me when I brought it in to get it diagnosed that it could be something as simple as an incorrect torque spec on one of the valve body bolts - I assume this would cause leaking between the valve body channels and therefore incomplete engagement. Since it was put back together, I have not experienced the slipping (which is what I'm now convinced it was).

Thanks for all the help and ideas - I've now got a better running truck and a better understanding of the driveline.