I've searched. Maybe someone has asked but I can't find it.

I'm in the middle of rebuilding my tranny and was wondering if I can change the 5th gear to a higher gear?

86 N\A Base

 

Yes, a .756 was available for an NA beginning in 89, or you can swap over to a TII driveline with a .719 (89-on) or .762 (87-88). There are also certain Miata and 626 transmission parts that will work with RX-7 transmissions, but I am not sure about the specifics. You may have better luck asking in the Race Car Tech forum.

 

Your years and specs are off a little.

The 86 and 87 used a .711 5th gear.
In 88 the coupes got a .697 while the vert got a .711 5th gear
for 89+ non turbos (including the GTUs) all got a .697 5th gear.

Perhaps your gears mentioned are non stock gearing???

 

His are likely listed from the online FSM's, of which we do not know the exact years of which they are scanned from.

I agree with your listed values, Mark, although the technical data sheets list a 0.756:1 overdrive when a viscous LSD was installed.

 

Yeah I think that is a misprint of the Turbo's .765 5th gear.

 

But the turbo was 0.719:1 for S5's, not 0.762:1. That's what I don't get.

Its lost on me.

 

No, that's stock gearing. Let me clarify: The .756 came stock in the GTUs, which uses the same transmission case as every other NA FC of the same year. The .719 (89-on) and .762 (87-88) are reference a TII transmission swap, although there may be some way to use the TII gears in the NA housing that I do not know of.

 

The 87-88 TII had the .762 gearing.

 

Ah, no:

 

My owners manual and the FSM both list .756 with the LSD installed. Also there was a formula for calculating speed in any given gear in an old RB catalog and using the.756 in it comes out to what I am doing in 5th at the RPM I plug into the formula.SO I think the GTUs did in fact have the .756 5th gear.

 

I know that, but the number 0.756:1 is listed in the 89-up technical data sheets, and MArk suggested that the 0.756 was a typo of the 0.762 number. I suggested this made no sense, since the 0.762:1 was for the S4's, so should not have been featured in the S5 data sheets.

I also don't think the GTUs got a special overdrive... I've never found any literature to prove it, but I have found literature to state its the same as all other N/A transmissions.

 

so what all is interchangable ?

 

Using my formula I get 77mph@3500rpm in 5th gear using the .756 ratio. I get 84mph@3500rpm using the .697 ratio.Whe I am at 3500rpm my speedometer is between 70 and 80mph thus I believe I have the .756 5th gear ratio. Here is the formula.I've found it useful.

(T.C)x(RPM)
_____________
(1056)x(A.R)x(T.R.)

T.C.= Tire circumference
A.R.=Rear Axle ratio
T.R.=Transmission gear ratio
RPM=Engine RPM

 

Thanks for all the replies, that formula is nice to know.
I saw it somewhere else in here.

I guess the main question is will the s5 gear fit into an s4 unmodified?

Say it works how do you get a .756 gear without tearing apart a used transmission? When using old parts who knows what you'll get. I'd like to buy it new. Who sells this gear other than the dealer?

 

Holy ****, archive please!

--Gary

 

Rather than archive, Icemark could maybe add the Mazda Comp transmission ratio list to the 2Gen FAQ page.

 

Well as long as I have the attention of the Gurus,

In the 89 engine parts list it says that the over the top gear is P/N: M512-17-611 (Non-Turbo)>(nor.susp) and P/N: M514-17-611A (Non-Turbo)>(hard.susp)

Which one is the .756 gear?

 

hard suspension would be it.




Could it be that all S5 GXL's came with a different 5th gear than the GX's? Hmm... time to do some testing.

 

If any one cares.

I called the dealer and found out that the part number for the .756 gear has changed. It's now M517-17-611. Price: $205 USD

For all the fanatics.

 

But I thought that there was no such thing as a .756 gear?