4th.gear sync.

[henry]

I changed the 4th gear sync. two weeks ago and I'm having problems with it again, any suggestions?

[pope]

There are several things that account for this.
The fork that moves the sleeve could be worn (common), the fork is what actually hold the individual gear in position until you change it and check that the teeth on the sleeve are not rounding off. These are the usual wear items.

What gear oil are you putting in the trans.
When you drained the old oil out, was there flicks of gold in the oil, meaning brass filings.

[henry]

What about the spring between the gear and the synchronizer? Bent or worn main shaft? I never had so many problems with the transmission until I decided to rebuilt it.

[pope]

Possible spring, but not likely, especially since you replaced the syncro and thought it had enough spring to reassemble it. Also not likely a bent main shaft, would affect more gears.
Truer word could not be spoken about you taking it apart. That is where the problem probably lies, have you ever taken one apart before? There are so many washers and gears that have to be put back in a certain direction that it is very possible to screw it up easily.