So I've been under the impression that the 90w in the transmission and diff was used on cars till about the mid '80s then manufactures found that they could spec. a lighter weight oil and benefit from easier shifting, better gas mileage and less parasitic hp loss.

I'm changing my trans oil ('85 GSL, 5spd, road/race pressure plate road/race clutch). I am switching to Amsoil and want the best product for my car. Also changing the oil in the diff.

I wanted to know what others were using, why they were using it and the results they got.

Thanks

 

ive been using atf in the trans for quite a while, shifting is improved like synthetic, but its cheap

keep the 75-90 in the diff

 

50/50 ATF/80w-90 made a huge difference for me.

 

Shifting ease?

 

I'm glad to see that the 50/50 mix is working well for so many people. The ATF lubes fine, and is loaded with detergents that really gets the crud out of the synchros. Definitely allows faster and smoother shifting. Also, you end up with a thinner mixture, so a reduction in parasitic loss just like you were hoping for.

The old Datsun race teams used this mixture for years and swore by it. I've been using it for about 20 years, on probably over a dozen vehicles, and always see great improvement...

 

This thread deserves a bump.

 

i've only heard a good atf/80-90w ratio is 30/70, but hey i'll give 50/50 a try, it's getting about that time anyways lol

 

Does it help the shifter not be jerky into gear? 1,2,3, & R have a stiffness it changes but theres no common reason (temp, etc)

The shifters just jerky like when I shift into R theres a metal sound like DING if the clutch was slightly not all the way down, but sometimes you'll move the shifter and it wont go further and you have to re do it. It's odd, like somethings not lubed the tranny fluid was fresh when changed few days ago

now it got harder to shift, if I push the clutch fully down and use some ***** it's okay I guess but just relaxing it's difficult everything appears to be redone with the tranny and well taken care of...

 

I just changed out with Royal Purple which is already mixed in the bottle 50/50. Works great, shifts a little smoother and all of the gears are easier to find, especially reverse.

 

So when you mix ATF with gear oil can you use a synthetic gear oil? Say mix Amsoil Super Shift Racing Transmission Fluid (ART) and Amsoil 75W-90 Long Life Synthetic Gear Lube.

Thinking of using Amsoil Severe Gear 75W-90 in the diff.

 

I switched my diff to Royal Purple about 300 miles ago, and was sufficiently impressed that I switched the trans over as well. I've only driven the trans about 40 miles thus far, but it does seem a little lighter on the shift. I haven't noticed any real change in trans noise, one way or the other.

Another nice feature of Royal Purple is that it doesn't reek like traditional hypoid lube does... It still has an odor, but it is faint. If your shift lever boots are aging, you might find that a nice side benefit.

When I swap my steering gear out, I plan on using it there as well.

 

Mixed with what?

 

Cmans, clunking or grinding when going into reverse is normal (if you are not doing it right, that is). Try this:

Clutch in
Move lever into 1st gear
Move lever into reverse
Release clutch

This is due to the lack of synchros for reverse. Shifting into 1st gear sets everything up for a smooth shift into reverse. Do not release the clutch between 1st/reverse.

 

I started with 50/50, had to drain some later and replaced it with straight gear oil, so it's probably more like 30/70 now. Anyway, second gear was nearly unusable before. Didn't matter what you tried, it would always grind really badly. Now it still grinds a bit if you try to shift too fast, but it's perfectly drivable. It's sufficiently better that I have no plans to swap trannies until I get a TII unit.

 

I must do this.

 

I race my car and I have found that 75-140W Amsoil or Royal Purple in the transmission provides the best performance during a race. The viscosity range allows for good shifting when the car is cold (I have raced in 40 degree weather) and later when the car is red hot. I have also used Mobil One 80-90w in the past but by the end of a race I had shifting issues.

It is true that thinner lubes don't consume as much HP as the thicker ones do. But I really need my gear box to last so I am going to stay away from an ATF mix.

By the way, while ATF is used in allot of manual transmissions it isn't necessarily because of fuel mileage concerns. For example, the T-5 used in Mustangs and GM F Bodies used ATF because the syncros have clutch material bonded to them. Standard gear lube disolves the glue that holds the clutch material in place and ruins the syncro's.

 

On the subject of reverse: Are the reverse gears in the SA trans straight-cut?

 

i like to shift to fifth, but i think its the same picture

 

Fifth here to.

 

If I can't get it into reverse the first try I usually stick it in 5th and edge up a few inches then shift to reverse. Only thing I'm sick of is that when I want to downshift to 2nd at 40MPH it won't let me... Same with 3rd at 60MPH. The FC would let me do it all day long, but the SA won't! I may have to try this 50/50 deal.

 

Double clutch for you my friend! It will go right in when down shifting.

 

I filled her up with the 50-50 mix and it feels slightly easier. It seems to be a bit quieter too. Why would I need to double clutch a street car? It's not a semi truck.

 

Ohh thanks man, that'd make sense

btw I found that the shifter is very very smooth till driven hard it seems or driven alot, then it just stiffens a bit randomly (Im guessing the syncros)

no grinding or anything though

 

yes, they are. in 86 they put a synchro on reverse, so its not straight cut after that

 

double clutching will help the synchros work better