I need exact information on this swap. I have searched and not found what I need.
Forgive me if I seem ignorant on this....I am.
I am not doing the swap anyway. I am just trying to order the right parts.

Does anyone know of a write up for this swap?

Here is what I have:

1990 TII rear end

4.3 R&P for 1990 TII rear end

1993 FD Torsen Diff

I need to know what pinion bearing is needed. FC or FD?

Do I need to get different stub axles?

Are there any other parts that should be replaced while it is all apart?

Here is where I am really ignorant in terminology...

Does the backlash setting and maybe tooth contact need to be to FCspecs or FD Specs?

All the information I can get will be appreciated!

 

Aren't FD rear ends weaker than FCs?

 

The actual differential between the two is interchangeable. So what you'll do is Put the TII ring on the FD differential carrier (the actual torsen unit) and put that into the TII housing. You'll then need S4 TII axle stubs to get everything to work. You can get them at mazdatrix. I've used both kinds of S4 tII stubs with no ill effects. There is enough play in axle cv joints to compensate for the difference in length between both types.



All your settings and measurement need to be FC settings. You are after all putting it into an FC. If you don't have good bearings, go ahead and replace them. Other than that, have fun!

 

I am going 20b n/a. I will be in the 350+ rwhp range. Fd diff should be good to 400rwhp I have been told. I am after the Torsen diff characteristics.

 

Great information man!

Do I need to source S4 or S5 TII axles? You know haft shafts or whatever the proper term is?

 

IIRC, i thought the S5 Tll rear was a viscous type, S4 is clutch type.

I know for an S4 Tll rear with FD Torsen unit, you use everything FC, swap the R&P over to the FD unit and reinstall as per FSM.


Search in 3rd Gen section, its been covered alot there; but FD rear using S4 tll clutch type LSD.


Edit: https://www.rx7club.com/automotive-news-lounge-22/s4-clutch-typle-lsd-vs-s5-viscous-lsd-460891/ good info there. Just skimmed it, you need S4 diff.

 

I see you edited your post... So I edited mine

 

S5 is viscous. S4 is clutch type. S6 is torsen.

The torsen diff never really locks. It just transfers the torque. Much like the viscous but, doesn't where out like the viscous does. The clutch type uses friction to "lock" the wheels so it's more aggresive.

 

ive got this rear in mine. i thought id post to say im not compleatly happy with it. power out of a bend and wait for the end to gradually step out but with this set up its nothing then a sudden snap out. its not predicable like a clutch type. if i had the money id change it.

 

First off hIGGI has got me the correct information about this swap. There is a lot of misunderstanding because with my S5 TII housing I need S4 stub axle to put the S6 diff in. The question arises which stub axle, short or long. All Mazda material I have reference does not say there are two different length axles for the S4 but obviously there must of been because there are two stub lengths.

I even spoke to Ray at Malloy and he was a bit stumped by it.

Anyway, hIGGI sorted me out. I am to get later vin# 87-88 short stub axles. Then get two of the longer haftshafts from a S5 TII rear end. I think that is the drivers side....?

He says they have run this setup in about 10 FC's so I am going to take his word.

 

That is interesting because I am under the impression that it should be opposite from that.

Here is a table from the FC3S Pro website on the different lock-up characteristics of the different types of LSDs available...

The whole page is available here - http://fc3spro.com/TECH/MODS/DT/lsd.htm

I am not dismissing what you are experiencing it just seems a bit counter to what I have heard. Are you road racing or drifting?

 

S5 TII haftshafts are all the same length, correct?

 

I've had the understanding that all TII axles are the same length. Even if they were slightly different in length, the built in play in the CV joint makes up for the 3/8 of an inch difference in the two types of Stub shafts available for the S4 TII.

Looking at part numbers for the axles, I find the part number of the S5 turbo to be:M040-25-500E and the S4 to be M040-25-500D.

Again, i've done 3 torsen conversions and never had to worry about any of this. I just made sure the s4 TII stubs were in place.

Good luck with your swap!

In terms of response... I road race the car and have fairly sticky tires as a result I haven't really experienced the rear severely breaking out on me. However on the occasions when I'm playing in a parking lot, the rear is really easy to swing out, but transitioning from left to right does take a moment where a clutch type just stays locked. I enjoy the torsen because I don't ever have to rebuild it!!

 

This statement was posted on another forum. It was also spoken to me by Mazdatrix. They were not really confident in their own experience to advise me but said to be aware of the issue.

hIGGI;

Beware!

Halfshafts are not same. I have came across to two different lenghts of TII halfshafts. As you can see in mazdatrix pictures, first two stub shafts are from S4 TII and they differ in length. Length does not change inside of differential, but outside. And thats where you need to be carefull about choosing right halfshaft. Longer halfshaft has to match 5 7/8" stub shaft, shorter halfshaft has to match 6 1/4" stub shaft.

Using wrongly matched stub + halfshafts will cause you problems. We once used short + short and stub shafts were pulled out of diff during driving......long + long will cause unwanted pressure on the diff from side and/or could damage/break halfshaft assembly....

Something to definitely watch out for....

 

When they switched stub-axles, were the halfshafts also different lengths? Are there two different part numbers for those?

You cant use the S5 TII halfshafts because, although they will fit, the longer one will extend into the shorter one's side, effectively locking the differential until something breaks.

 

Hell if I know... I have been told repeatedly that S5 haftshafts are the same length. I don't quite understand about the S5 stubs being different length. The difference might be inside the case. I am not able to speak with any real knowledge...

I am going with short S4 stubs and S5 haftshafts. When we install we will check and if something isn't right we will adjust. I need parts in hand to talk anymore about it. That will be in a couple of weeks.

Going on a week long Florida vacation.

 

I did this swap very recently. You will NEED the S4 TII axle stubs. I bought two of the shorter ones, and they work perfectly.

The S5 stubs are unusable because the longer stub pushes out the shorter one. The car then becomes one-wheel drive, with a dangerous tendency to pull to the left every single time you get on the gas. I had to drive the car for 150 miles in this state. :p

 

you got me wanting to go out and check my rear end now with all this talk of driveshaft length. i used the stock 1990 tII stubs and shafts. nothing visually wrong and its done about 8000 miles like this.

the torson diff is a free diff untill it sences torque bias. then it does its funky thing. when deliberately kicking the rear out it is nice and predictable because it is loaded up straight away.

i feel that when it changes from unloaded to loaded there is a jump. this jump translates to , i dont know but about 15 degree's. i expect it but i dont know when its coming.

this is when accelerating and turning at the same time.

a permenantly locked (just an example) diff will be predictable because the wheels are doing the same thing. the change of rear end angle is controled by your throttle. the torsen is changing from one thing to another as well as the input from your throttle. im not saying its crap im just saying i would change it.

 

oh, just want to clear a couple of things up. the english tII has an open diff to start with. this might be why there are the differences in shafts you are talking about.

also my jump isnt all the time it is specificly under acceleration on a tight'ish corner. wanting it to step out into a power slide. its nothing like as predictable as my bmw's

 

The shorter S4 ones should work fine, since the distance between the bearing surface and the mounting flange for the short ones are the same as the S5 ones, so the S5 halfshafts are sure to work and not cause length problems.

I dont see how you could really drive and not notice it if you accidentally used the S5 stub axles, since the diff would be either locked or perminantly one-wheel drive. Are you sure it was an S5 or limited slip (IIRC there were some JDM turbo cars with open diffs)?

 

It is only the unequal length viscous limited slip axle stubs that do not work. They make the car one wheel drive with dangerous handling characteristics.

 

ok im sort of confused here, i just broke my stub axle, i have the 88 tii one, and they are selling me an 87 stub axle. can that one fit in my car, basically the one that broke is the second one on the graph, can the first one work for me? or are the lengths of the half shafts going to be a problem.

 

it'll probably work... it just sticks out of the LSD a little bit more, but the half shafts should have some slack.

Why wouldn't you just get one for an 88?