i agree viscosity is very important to correct functioning of synchros. they depend on the viscosity to speed up the gears for a smooth shift. to heavy or too light are both problems. i would start with what is recommended for your tranny and adjust from there.

depending on the year there are different oils recommended. check your owners manual. if you dont have one post year and model here.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.