synthetic lubricant and top loader

[427 S/O]

Rebuilt my top loader with all new parts, including new 'wide ratio' gears from southern gear, I had a little 'bump' when shifting from 1 to 2, re-adjusted linkage a couple of times and checked position of shifter arms. Finally called 'Dan Williams Top Loader Transmissions' and explained my problem, the first thing
he ask, did you fill it with synthetic dope?, yes I did, he said drain it and replace with good old regular 90 weight, after about 500 miles drain it and replace with good old 90 weight again.
Problem solved, shifts great........he said the synthetic slowed up the meshing of synchronizers, I didn't ask but, this may be a problem only on 30+ year old low tech transmissions?.

[blykins]

Of course it is....but I think most of the members on here run dyno gear oil in their Toploaders.

If you rebuilt your tranny, you can see how the blocking rings fit on the gear cones. All this works off of friction.....so if you take the friction away, it won't shift smoothly. It won't let the blocking rings and gears spin up to the correct rpm to match the synchronizer hubs.....