FD Diff in a FC TII Rear End Questions

[Christopher W.]

Does anyone know of a write up on putting a FD diff into a FC TII rear?

[TehMonkay]

You'll need S4 T2 Axle stubs

It's just a bolt in process, pretty easy, except you need to set the backlash, which i'd reccomend having someone else do.

[Phoenix7]

Originally Posted by TehMonkay

You'll need S4 T2 Axle stubs

It's just a bolt in process, pretty easy, except you need to set the backlash, which i'd reccomend having someone else do.

Now lets go into the reasons/questions:

S4 instead of S5 because the shafts are equal length in the S4 vs. unequal length in the S5. Got it.

What's the BACKLASH?

[Christopher W.]

I have a 1990 TII rear. So are you saying I still need to get S4 stub axles? Would that mean S4 haft shafts or S5? Or are they the same?

I bought a 4.3 R&P for a S5 TII rear. Should I order pinion bearing for S5 TII?

I am not doing the work. A guy who builds American racing engines and rear ends is. He isn't exactly familiar with Mazda rear but can accomplish what has to be done. I am just trying to get the correct parts to him.

I don't really know what backlash is but I do know it has to be set by someone with the right tools and knowledge. Macon Motorsports is handling all of that.

[Phoenix7]

He says S4 is the way to go (I've heard this from Higgi before too) because they are equal length. The S5's are not:
MAZDATRIX

[hIGGI]

Originally Posted by TehMonkay

the halfshafts are the same.

Use all FC ring and pinion stuff, since it's the FC casing.

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 lenght. Lenght 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....

[Christopher W.]

After talking to Mazdatrix they don't have real experience with this swap. They did say I need the S4 stub axles. They said there are two different length haftshafts available but didn't have anymore information on that subject.

I am not sure about which stub axles, the short or long. I don't know if that depends on which haftshafts I get.

Should I first buy the haftshafts then determine which stub axles?

Does anyone know off hand if there are two different part numbers for S4 TII haftshafts. Or what the length measurements are for the short and long haftshafts.

In reference to hIGGI's statements above that means if I buy shorter haftshafts then I should get the longer stub axles or longer haftshafts and get shorter stub axles.

[hIGGI]

by looking at mazdatrix picture, u can simply assume that

S4 after VIN 608385 and ALL S5 TII halfshafts are longer :

Get these S5 TII longer halfshafts and then shorter S4 TII stub shafts (S4 after VIN 608385, part number shown in picture.

That should be ok.

We run FD torsen in about 10 FC's so far, its most affordable LSD for us...

Swap is pretty straightforward, set backslash and DONT forget to glue bolts to the ring gear (on one of our diffs they did break loose and it did not ended up good )

Here are some pics from swap :

http://rx7cz.net/photos/workshop56/

[Phoenix7]

^^^ great pics in his workshop links.

So, get the LONG S5 shaft (7 1/16th") with the S4 (5 7/8th") short shaft in order for the FD LSD to work?

[hIGGI]

Originally Posted by phoenix7

^^^ great pics in his workshop links.

So, get the LONG S5 shaft (7 1/16th") with the S4 (5 7/8th") short shaft in order for the FD LSD to work?

NO! Read again what i wrote

[Christopher W.]

Originally Posted by hIGGI

by looking at mazdatrix picture, u can simply assume that

S4 after VIN 608385 and ALL S5 TII halfshafts are longer :

Get these S5 TII longer halfshafts and then shorter S4 TII stub shafts (S4 after VIN 608385, part number shown in picture.

That should be ok.

We run FD torsen in about 10 FC's so far, its most affordable LSD for us...

Swap is pretty straightforward, set backslash and DONT forget to glue bolts to the ring gear (on one of our diffs they did break loose and it did not ended up good )

Here are some pics from swap :

http://rx7cz.net/photos/workshop56/

So, by looking at the different lengths of the stub axles on the S5 and then looking at the length of the short S4 stub axle you can see that the S4 is sort of a compromise in length between the short and long S5 stubs. You are saying that that compromise is acceptable, huh?

Then of course I would get two S5 haftshafts.

[Phoenix7]

I don't think so. If my reading isn't failing me still, He wants you to get the S4 (5 7/8") stub shafts with S5 axles/half shafts.

Get these S5 TII longer halfshafts and then shorter S4 TII stub shafts (S4 after VIN 608385, part number shown in picture.)

[Christopher W.]

Originally Posted by phoenix7

I don't think so. If my reading isn't failing me still, He wants you to get the S4 (5 7/8") stub shafts with S5 axles/half shafts.

If my reading isn't falling me I think that is what I said...

Short S4 stub with S5 axle/haftshafts. I think I might have been confused a bit because I was thinking the S5 had two different length axles but I now understand they don't. But in general I got it.

Thanks for all of the help. I will update later when I get it all together.

This has been a bit confusing....

[djmtsu]

Thread cleaned up a bit per phoenix7's request!

[josh18_2k]

whats with all this mixing of shafts and stubs?
i have an FD torsen and just reused my S4 stubs/shafts.
maybe all the confusion is if you piece together the rear end?