I'm looking @ changing out the fluid on my 5-speed tranny and rear differential. Looking to do a basic drain and fill but I'd like to get your guys opinions if you think flushing these prior to refill is a smart or dumb move.

 

Certainly not a dumb move.
Definatly wont hurt.
I dont see why you wouldnt.

 

I've read that the high pressure forcing of cleaning solvents back through the engine and transmission can jam the debris it's cleaning back into the small passages and galleries that have one-way valves that keep the fluids from backtracking.

"By using an aggressive cleaning procedure like flushing, large chunks of accumulated sludge are broken off and forced backwards through these galleries and valves and, more often than not, lodge tightly and block them. This cuts off the normal flow of the fluid and causes lack of lubrication in an engine and abnormal or no shifting in a transmission. The results are expensive repairs, or more often, engine or transmission replacement."

 

How many quarts of Mobile 1 Synthetic 75W-90 would I need to fill my 5-speed tranny and the rear diff???

 

i think mine took 5 or 6

 

I would get 6 for everything. We have gear fluids here

http://www.raimotorsport.com/category-s/3060.htm