I changed to Amsoil sysnthetic gear oil in my 4 speed and it did not shift correctly. Honestly it's been so long ago and I left it in for a short time only, so I forgot exactly what my symptoms were. I think it was just hard shifting. I called Jamie Passom and he told me the old 833 needed regular gear oil the make the synchros work properly. He told the Amsoil was too slippery.
Synchros do not work when at a stop and shifting into any gear.
WHAT ??? The job of the synchronizer is to slow down the gear to ease engagement. The brass ring grips the cone on the gear and slows it down before the teeth engage. I would look into the shifter adjustment first, then the dis-engagement of the clutch.
Excessive bellhousing runout can also cause low speed engagement issues. You may need to change the fluid to a more syncro friendly fluid. I just use regular old dino gear oil and stay away from synthetics because they are just too slippery for the syncro rings grab the gears.
If this happened all of the sudden I would look into some mechanical issues like shifter issues or something in the clutch linkage.
Gus
