Diff

[Ricco_04]

Hi, was wondering if there was any advice I could tap into....

I have an open diff in the TII and while its sat on the garage floor I thought it would be a good idea to investigate the options..... oh and im not an intentional drifter.

Was reading from the 2nd gen section and I can see some options are

MX-5 diff (either 1.6 or 1. (strength?)
FD diff
Others??
RX-8 diff?? (is it different to the FD? Better or worse or even possable?)

I\'m not looking at kaaz etc cause I have a tight budjet, so is it even worth the swap? Use would be normal road use + the odd blast..

Last question, what kind of cost is invoved in this, if any one has any experience of this? (diff is on floor & I would be bolting it all back up)  Or is the swap something I could undertake myself?

Cheers

[Brett]

IIRC the FD diff will fit... I think McPie on here has done the conversion... and kind of LSD will be worth the upgrade IMO.

[dthebuk]

im under the impression that the MX5 diffs are for the egi\'s.

I think the FD diff will be you\'re best bet. It will be more than fine for getting you round a track quickly. Cheaper option is to weld but i assume you wont want to do that, what a shame!!

Anyway, hows the FC coming along? I remeber the old project thread which i havnt see in ages!

[Prof]

Am I right in assuming that once you\'ve drained the oil, taken the back plate off, and remove the output drive shafts, the diff gear mechanism should just be removable?
 
So provided the FC drive shafts fit in the FD\'s torsen unit, you could just bolt this unit to the ring gear in the diff?
 
BTW - I don\'t know the answer - I\'m looking for the info as well

[Ricco_04]

Thanks for the reply\'s folks....

Project??  Oh yeah, I almost forgot :o:o:o lol

It\'s coming along got a lot of things done (well for me anyway!)  Last weekend I made up some new brake lines (amongst others) for the rear and fitted them which look rather good and lined up perfectly which was a bit of a shocker!  I stopped doing updates because lets face it - I was raving about fitting a bolt in the end!

I was thinking of welding it but the only thing stopping me was how the thing reacts on tight turns.  I dont know anything aside from that about welded diff\'s (I wouldnt even know where you weld it or how much etc)

Ok so the MX-5 diffs are out, which is fine.  Anyone know if the RX-8 diff is different / better / stronger than the FD one (is the FD torsen?)

From what you say Prof, it\'s tempting to fit one myself, I have heard of people doing it.  So really its just sockets to open the thing (maybe a rubber mallet to crack the case off) and general tools to swap over plus some liquid gasket & new oil....hmm have to do some more digging........ I\'m sure i saw some pictures of someone doing one on here.

[dthebuk]

Im pretty sure the half shafts wont fit. I think they just slide on from memory, been a while since i was under an fd though. Maybe you can use the FC half shaft joins on the fd diff.

Couldn\'t tell you about the 8 diff. Might have a different ratio etc. No idea about the strength.

Changing a diff on an FC is a pain in the arse IMO. Entire subframe has to come out, i also had to half take off my rear hubs too. Youll need someone to give you a hand putting it back together i reckon. If you can leave it on the car that would be the best option.

As for the welded diff, I\'d find someone whos done a lot of them if you plan on getting that done. Its not a big hassle to drive with IMO. Harsh coil overs are much worse. Basically on tight turns (as in full lock at 3 mph) it acts as a brake and theres a bit of tire hop.Other than that there dont seem to be any drawbacks. Very predicable in comparison to an LSD

[bumpstart]

FC t2 diff is long-nose and 30 spline
FD diff is short nose and 30 spline

NA FC diff is long-nose and 26 spline
mx5 is  long-nose and 26 spline

halfshafts are different on all of them,, and even unique between years of FC
-- VLSD ( s5 ) versions have unequal length inner shafts that are unique
and there is also revision part way through the standard FC t2 series shafts


the only thing that is going to swap is if you find a LSD pumpkin from an FD and refit your crown gears to it and stick it back into the FC nose
  ( using the already lapped to pinion FC crown is much preferred to using the same ratio crown from an FD )

if you wish to alter the ratio,,for 30 splines
 3.9 is from FC/FD autos, 4.1 is in the manuals
and occasionally in some special models you will find a 4.30
( methinks the only FC 4.30 is US NA GTUs and so is a 26 spline smaller crown, not so sure about infini/efini t2 models  )

else the 4.4 and 4.875 and 5.1 options will amount to fabbing a new tailshaft and diff nose cradle onto a commercial van/ute short nose diff
or by being tricky and welding a fabbed extension onto a short pinion gear for the T2 nose
- none of this easy or cheap,, and are not really good ratios for turbo cars anyhows


methinks there is a post somewhere on miata net and also on mazdatrix that shows the differences between the half shafts

[bumpstart]

if you wish to do the locker you must do it by just welding the spider gears to one another and to the case
and also a spot,, ( ground back so it clears when the pumpkin rotates )
to the ends of the pin that holds the spider gears

using the other drop in plate method is usually much stronger
 but for FC you must remember that the half shafts are C clipped into place
- and any plate will negate you getting the clips back in

PS
 penetrene/ CRC is you friend to limit spatter on oily parts
( even the mig will spit )
when doing so,, place the half shaft back in so as to protect the splines from spatter

[bumpstart]

http://www.mazdatrix.com/G8LSD.HTM

note the differences in half shafts
S4 post VIN 608385 and ALL S5 TII halfshafts are longer, stub shaft shorter

post VIN 608385 Longer halfshaft has to match 5 7/8" stub shaft
pre VIN 608385 shorter halfshaft has to match 6 1/4" stub shaft

http://www.mazdatrix.com/g7.htm
note on this page,, they advertise exchange pinion swaps ( and bill ) to make 4.875 and 5.1 long pinions up for you
and that P092-27-110B should come up as an FC t2 4.30 gear set

[no_boingers]

I was thinking of welding it but the only thing stopping me was how the thing reacts on tight turns.

It\'s not just tight turns, it\'s any turns - think about why diffs do what they do in the first place!

I would advise against a locked diff in a tarmac car.  We used to lock the Escort diffs but they were rally cars on the loose where the inner wheel could spin rather than drag.

The stress induced in the inner wheel when cornering fast in a medium turn will be phenomenal (it will try to twist your half-shafts... where\'s that force going to go?), and the induced understeer will be unwelcome.

[Ricco_04]

Wow, thanks for the info - Think im going to have to read that a few times before I understand it! :2Confused :Laugh

The more I read up on it the more confused I seem to get.  I was just reading that the UK TII\'s would be fine with it\'s standard stubby shafts & halfshafts and I just find conflicting info everywhere!

Back to more reading then.... (and youtube videos - video helps me lots lol)

Right, for me the welded diff is out and torsen is on the cards, if I can work it out :spank

[Prof]

Wow, thanks for the info - Think im going to have to read that a few times before I understand it! :2Confused :Laugh
 
The more I read up on it the more confused I seem to get. I was just reading that the UK TII\'s would be fine with it\'s standard stubby shafts & halfshafts and I just find conflicting info everywhere!
 
Back to more reading then.... (and youtube videos - video helps me lots lol)
 
Right, for me the welded diff is out and torsen is on the cards, if I can work it out :spank

If you figure out how to do it, post it up - I think a few of us may be interested

[Ricco_04]

Ha ha, yes no worries - its a big learning curve for me but I will be happy to post something up when my poor brain can get over it!

[Ricco_04]

Oh I feel kinda stupid asking but what is the \'pumpkin\' thats been mentioned above

[Prof]

That\'s the big round part of the diff - it looks like the front cone shape bit can be detached from that part - at least on some diffs.  So the pumpkin actually houses the differential gears themselves.  The actual working part is I think called the \'gear case\' and that has the ring gear attached to it - that\'s where the power comes in from the pinion driven by the prop shaft.
 
The two drive shafts come out of the \'Gear Case\' - which is where all the magic is done
 
I still think I have a viscous diff - if I rotate one back wheel slowly, the other goes the opposite way, bit if I rotate one wheel back and forth quickly, then just in one direction, the other wheel comes the same way.