So after the tranny is warm, it grinds a bit going into first or reverse. Those gears are not synchronized (second and third are) and after the gear oil is heated up by driving, it gets thinner and gears are still spinning as you attempt the shift. I would consider that normal. All my 4 speed trannys do that (none are synchronized in first and reverse).

I cannot explain the difference due to your change in oil. Perhaps it is because it is summer in Michigan now and the oil is thinner?

Kent


1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix