915 odd 1st gear lock up after reverse
 

I have an 80 SC with 160k on the clock and an original refurbished 915 that's been gone thru recently by a respectable P-shop. It seems to shift and operate well overall - but I've experienced something odd happening that I can't figure out.

When parking in tight spaces and going back and forth between reverse and 1st gear, on 2 or 3 occasions the transmission has locked up when put back in 1st gear. In other word the shifter goes from reverse into 1st no problem, but when I let out the clutch and apply gas I feel the engine rev and push against the clutch, but the wheels don't move… they're locked up. It's like the emergency brake is on. If I shift back to reverse and roll back a few inches, and then re-engage 1st the lock lets up. Anyone know what's causing this?

take it back to the rebuilder and have them put the detents in the proper place. disassembly required.

I've never dealt with that particular issue, or heard of it, but it's very possible that John W. is correct. If all is well with the linkage, and your technique is correct (coming to a full stop in reverse before removing the shift lever from that selection), and this problem only began since the trans was apart, there is a good chance that the problem is internal.

This might be an interesting detail to pay attention to - it's possible I'm unconsciously sliding it out of reverse before coming to a full stop...

It seems as though it is not fully releasing reverse. Could be a detent or bad adjustment of the 5th/reverse shift fork.

there are 2 steel, T head plugs on the outside of the trans. one on top of the diff and one on top of the center housing. the detents load there. the plugs can be pried/tapped out. if you see the rounded end of a detent in there, (mirror and flashlight) then it's in the wrong place. they go under the shift shaft, so you should only see the curved side of the shaft. have your shop check that, as it will be easier up on a rack. usually it's the one in the center housing.