H55F Shifting Problem

[Trevin]

I'm hoping someone has seen this before, this one's kicking my butt...

Newly rebuilt H55F, everything is working nicely, except it slips out of 3rd gear on deceleration.

New countershaft, bearings, 3rd gear, synchro, shift sleeve & hub and sleeve detents.

Any suggestions would be greatly appreciated.

Thanks!

 

[Eurasiaoverland]

With the vehicle stationary, does it engage positively into 3rd?

The shift shafts, interlock pins and detents in the cover are quite involved to assemble, I would imagine it's quite easy to make a mistake there or leave something out.

 

[Trevin]

With the vehicle stationary, does it engage positively into 3rd?

The shift shafts, interlock pins and detents in the cover are quite involved to assemble, I would imagine it's quite easy to make a mistake there or leave something out.

Yes, the shift into 3rd feels perfectly normal.

I didn't take the cover apart, and the detent in the cover feels very solid.

I can keep it in 3rd when decelerating by holding the shifter, but I can feel definit pressure on the shifter as it tries to disengage. It doesn't "fall" out of gear, it's as though something is forcing the 3-4 shift sleeve forward into the neutral position.