[lharmon1202]

After rebuilding my 2003 4r100 (7.3) my transmission will not shift out of first gear and when I let off the accelerator it brakes and barks the tires. I just removed the transmission thinking I possibly installed the one way clutch sprag upside down. But this is not the case it spins freely counter-clockwise and locks clockwise. I was sure the braking effect was a dead give away that this was the issue. Any thoughts or ideas of what is causing the issue is much appreciated.
(I'll add to this that the reason for the rebuild planetary gear failure within the coast clutch assembly Also installed transgo tugger kit)

 

[rc4man]

There's a member here, Maryland Diesel Nick you might send a PM to, he's very experienced with these, recently did an extensive series here on rebuilding these tranny's

 

[Mark Kovalsky]

The OP got the answer on another website. Here is what was written, and he replied that it fixed his problem.

Check the low reverse modulator valves, make sure they are installed correctly and are free to move in the bore. They are the same size and fit in the same bore, it is possible that they are backwards.

This can cause the tires to lockup on the 1-2 shift and can give you the impression of a backwards sprag.

 

[lharmon1202]

Yes, I was meaning to come over and share on this topic. Problem is solved, Intermittent reverse modulator valve was sticking, After testing the valve a few times it finally stuck, confirming the issue. Thanks for your help