Transmission Trouble

[karsis]

I have 2 old transmissions, one that grinds because the synchros are shot, and the other pops out of fourth. Why do these transmissions pop out of fourth like that? Which would be the more likely candidate for a rebuild? I was going to try rebuilding one to replace the one in my driver, which is getting sloppy. I would like to use the one that needs fewer parts.

[So Cal Mark]

usually when the jump out of gear you've got worn forks, sliders, hubs and maybe gears. The worn synchro unit is probably a better choice, but the grinding may have damaged some gears. It may take a combo of the two to make a good one

[bradartigue]

I have pictures of why the car jumps out of gear at http://www.artigue.com/fiat/1970 , scroll around until you find the transmission fork pictures.

It is easy to replace forks. Synchros require additional disassembly.