Who is an NP205 expert?

[SilverMiner]

I'm stumped and I hope somebody here can help. I just finished rebuilding the NP205 in my 1980 K20 Suburban attached to a TH400. The rebuild went extremely well with the help of Off Road Design, some knowledgeable friends and of course YouTube videos. The reason for the rebuild was to replace a stripped 32-spline input shaft. A twin-stick conversion was done a few years back when I first installed the TH400.

The problem today is once everything was back together (on the bench), placing the Rear Axle rail into HIGH locks everything up. The input shaft will not turn and feels bound tight. Both shift rails move smoothly, and if the rear is placed in LOW everything turns fine. With the rear axle in LOW, the front can be engaged in LOW and everything is still fine. If the rear is in NEUTRAL, the front can be placed in either HIGH or LOW and everything turns. Upon sliding the rear into HIGH the input shaft is bound.

HOWEVER - messing around with it last night, I discovered I could make everything work perfectly by removing the poppet, spring, and ball from the rear axle shift rail. WHY? I don't understand how simply adding the slight compression of the poppet spring could bind up the input shaft via the shift rail at all.

I welcome any and all theories you may have. I'm confused enough at this point I may just have to blame it on the Russians.

[SunSoaked]

I've been thru that process with my 205, th400, twin-stick conversion.
Did you modify the shift rails or use modified (ORD) rails?

[SilverMiner]

Originally Posted by SunSoaked

I've been thru that process with my 205, th400, twin-stick conversion.
Did you modify the shift rails or use modified (ORD) rails?

I used the whole twin-stick kit from ORD - those guys are fantastic. I pulled the offending shift rail and inspected it in comparison to the original which I kept, and I can't see anything wrong. I even ran it over a sheet of glass to confirm it didn't somehow get bent.

I'm utterly stumped, and if the good folks here can't help me solve this I intend to give ORD a call and see what they suggest. I won't be able to make the call until later in the week, though.

[sweetk30]

you happen to flip the shift fork by accident ?

otherwise i got no real clue and i have done a few 205's .

[SilverMiner]

Originally Posted by sweetk30

you happen to flip the shift fork by accident ?

otherwise i got no real clue and i have done a few 205's .

I can see the detents in the rail through the poppet hole, so I don't think the rail is rotated at all. The roll pin for the shift fork will only allow two positions 180 degrees opposite each other, and if it were rotated the detents would disappear.

I've also tried swapping between the indicator light poppet and the standard bolt poppet - same binding result. How the heck can the shift rail even bind the input shaft? I can't even seem to visualize the interference.

[SunSoaked]

Are the rails interchangeable? I can't recall if they can be swapped? Just wondering if so the slots may be in different locations.
Is the ball & spring bound up or not seating correctly?

[sweetk30]

rails will slide in but not line up correctly .


i asked if the shift FORK got flipped around . this can set the fork webbing the wrong way and pull in to the gear maybe ?

do you have the pto cover off and looking up inside ? this will tell you a lot on how things play inside as you shift .

[SilverMiner]

Originally Posted by sweetk30

rails will slide in but not line up correctly .


i asked if the shift FORK got flipped around . this can set the fork webbing the wrong way and pull in to the gear maybe ?

do you have the pto cover off and looking up inside ? this will tell you a lot on how things play inside as you shift .

Yes, the PTO cover is off, and I can confirm the fork is positioned correctly with the "long end" facing to the front.

Also, not mentioned earlier is that both forks and the sliding clutches are new parts from ORD. The old ones appeared fine, but buying new seemed like cheap insurance.