Just Wondering
 

I have a 79 rx7, I'm getting a s4 tII trani for it in a couple of days. I think the s4 tII trani has a shorter 5th gear than the s5 trani's and the s4 trani is stronger than the stock 79 trani. I'm gettin a later 1st gen rear axle assembly too, since they have rear disc and a LSD. I'm just wondering what is involved in this. Like custom trani cross member? custom drive shaft. putting a tII trani in a 79 with a later 1st gen axle I dont know if this combo is gonna work. Maybe its possible but im a rx7 n00b, so tell me how it is boys.

John Paul Caruana

First off what is a trani?

the s4 tranny will not bolt right in. you will need to cut up the tunnel and remove the sa center console. i have a similar problem. i think the concensus is to keep the 79 tranny.
for rear axle, find a 81-82 gsl axle and it will be a pretty much strait swap. ( lsd)

The S4 wont fit eh? Why do you need to remove the center console?

Shift is located in a different position, further back in the later models.

That goes for any 81-up trans.The 79-80 were the only years where the shifter was up front with a long stick.
The 81-85 trannies were some 4-5" furthur back,and the 86-92 trannies were another 1" more.

The rearend is an easy swap since its a 1st gen part.The driveline will need to be custom made.The TII tranny can be made to work,the mounting is actually not hard at all.But the position of the shifter will require a bit of sheetmetal hacking and youll have to come up with a plan for the interior consol and trim.

Any particular reason for choosing the TII tranny?
Yes,it is strong....they regularly hold upwards of 400HP with no complaints.If your still running an N/A engine,even a 13B,the TII box seems like overkill and an un-needed headache when you could just source a good condition or rebuilt 79-80 box.

Switching to an 81+ rear end will require some brake line work also. The SA's, 79/80, have a different thread pitch on the brake lines.

I want the s4 TII trany for the gear ratio's plus the strength

No doubt the strength is what TII trannies are all about.I didnt notice the difference in gear ratios so much,if at all....but Im running a ported S5 TII engine.
1st and 2nd are slightly taller (about 0.20) compared to the 79-80 5 speed.
The S4 5th gear is 0.762......0.006 shorter than the 89',and 0.043 shorter than the 91'.
Thats a bit taller than the 79's 5th gear ratio of 0.825.If you experience any lugging in 5th,you can always swap in some 4.07 GSL-SE rearend gears to compensate.Thats also give you back a little more pep in the lower gears since the TII box is taller than the 79',from 1st to 3rd.

You can just modify the S4 tranny to fit in the 79 chassis. You have to customize the shifter extenions/rod/rod tube/ bracket. I shortened the sfifter location on the tranny by about 4 inches, so now I dont need to cut the console on the 79.