9" Ford with a spool , wt and syn or not ? been some time since I have changed a gear setup for drag car.

I have run Lucas 75/90 gear oil in everything from a 7 second dragster to my 11 second street car.

Not saying its the best, but its never gave me any problems and I can get it locally when needed.

I'd say it doesn't matter with a spool unless you're NHRA class racing. Any rated gear oil should work just fine.

Amsoil Severe Gear. 75w90.

With a spool and non-syncro transmissions I like the RedLine shockproof blue stuff. It really hangs on the gears.

Gus

My preference is a full synthetic.

When using non-synthetic the first run of the day was always slower even when warming up the rear end on jack stands.

With the full synthetic not a problem. I have used Valvoline and Lucas without issue.

I seen the same results in my car

I use the Redline brand Lightweight Shockproof blue/green colored synthetic gear lube in the blue labeled bottles, not the Super Lightweight red colored in the yellow labeled bottles, in my S/P car with a Mark Williams Dana 60 with 40 spline spool and axles using a set of stock 4.56 Dana pickup used gears, that lube flat works great, 1.24 60 Ft. so far launching off the trans brake at 5800 RPM

I've been running 75w140 synthetic, Haw much of a difference would it make switching to 75w90?

its funny i use the Lucas 85/140 mineral . That is what Strange supplied and recommended for my S60 with detroit locker . When i went transbrake i checked with them they said use the same . Daily driver / bracket racer

Tex

Maybe some change, maybe not
I would try it to find out
My car came with that green/blue lube in it, the former owner had ran a blown aluminum B1 on alcohol with 5.86 Pro gears in it and he told me he never had a gear problem wit that lube
I order what I thought was the same gear lube but I didn't know the correct part number and ended up ordering both the lightweight and super lightweight gear lube to have it when I swap the 4:56 for the 5:86 gears in the rear end.
That gear lube pours out of the bottle cold like ATF does It is really good stuff, get you some of that
I'm a little scared to try the super lightweight do to the old adage of not fixing what isn't broke