I have a 4r100 that I recently converted from 2wd to 4wd for my E350 van. I changed the rear output shaft, rear housing and pan and replaced all of the lip seals, clutches, steels, and such in the process.

It drove and shifted just fine for the first 250 miles. It still shifts just fine but it squeaks when I let off of the gas and coast. It does it in all forward gears, and in manual 3rd, 2nd, and 1st. I can recreate the sound with the rear wheels off of the ground by manually rotating the drive shaft with the transmission in neutral. It squeaks when I turn the shaft counter-clockwise (looking toward the front). It does not squeak when I turn the shaft clockwise.

I thought it might be coming from a driveshaft or the transfer case, so I removed all of that and it still only squeaks when I turn the transmission output shaft.

I'm hoping to get an idea of what to look for when I pull the transmission out and tear it down again. Damaged sprag, did I miss a thrust washer/bearing somewhere?

 

Since you pulled the driveshaft and it still squeaks, that eliminates the easy one--a u-joint.

Based on my experience with squeaks, you will see it real quick when you do the tear down.

Any metal in the oil?

 

I drained about 3 quarts of oil from the pan and it still looks new, no metal. I also strained about half-a-cup through my beard when I separated the t-case from the trans... no metal there either.

 

A perfectly good working sprag can squeak when rotating the drive shaft one way and not the other, that transmission has three of them.

Noticing it while driving is unusual.