Transmission not shifting

[Bongdozer]

I just finished resurrecting an old 1975 k10. It’s pretty much ready to bring on the trails with a new lift and stuff. Big issue though. I can’t get it into gear i don’t know if this is from the np203 or the th350, I thought it was a low trans fluid issue, too which I added roughly 5 qts, it started coming out of the top of the fill accidentally. I noticed it seemed to shift but not actually go anywhere. It doesn’t link into gear, more of a very soft change, as if the vacuum understands it’s in gear and the engine mellows out, then goes nowhere. I tried to fill up the np203 a bit, with 30w. I got some in but only about 1/2 qt, because of the angle.

Seems like a faint grinding when the engine is revving a bit high. When it’s cold for example. I never let it keep making this noise, and only appears during rpm 1400 and higher.
This is a mystery trans. A family member “indicates” it was replaced with a good one, but never ran and that was over 20 years ago.

Any ideas on what to check? I looked at my cables they don’t seem stuck.

 

[Wes Harden]

1st you need to correct the Trans fld to proper level.
2nd does the front axle have manual locking hubs? Or drive slugs(full time locked)
A stock np203 will not drive if the front hubs are unlocked.
Unless you select hi loc or low loc.

 

[Bongdozer]

It feels as if the np203 isn’t in gear, the np203 has the full time slugs. No part time conversion.

The trans was never filled, left the lines undone and idk if the converter got filled. It seemed to be empty or close. So I put in roughly 4 1/2 quarts. So not near the full. I’ll check the dipstick tomorrow, is there a way to run trans in a way to fill the converter?

 

[Bongdozer]

1st you need to correct the Trans fld to proper level.
2nd does the front axle have manual locking hubs? Or drive slugs(full time locked)
A stock np203 will not drive if the front hubs are unlocked.
Unless you select hi loc or low loc

I wonder if this is the issue, the np203 feels as if it won’t drive, the center selector should be in the neutral position for normal operation… or?

 

[Wes Harden]

Normal oper is 4w hi. Snow loose dirt /sand hi lock or light light lock.
Neutral disconnects the tran from the diffs

 

[Wes Harden]

Yes the Trans needs to be full or dam near to move. Please add the correct amount.
Are You checking/filling the Trans level when the engine is on ? On level ground?

Normally when fluid comes out the top it is way over full or the engine is off.

 

[78 GMC Jimmy]

I call BS on this entire thing.