1.8 diff conversion

BRM · Post by **BRM** » Fri May 03, 2013 7:17 pm

Hi guys
Im doing a diff swap so i can run my new lsd.
So far, from what ive researched i need...
1.8 axles
1.8 drive shaft
1.8 rear cover (the alloy bit)

Is there anything else i'll need
(ive already a diff housing(metal bit)

Also.
Im having a really hard time finding a either a 3.9 or preferably 4.1 ratio....
And really the other parts listed.
If anyone could help, thatll be great

Thanks

SLYDIT · Post by **SLYDIT** » Fri May 03, 2013 8:38 pm

http://miataturbo.wikidot.com/differential

http://www.solomiata.com/Drivetrain.html

chris · Post by **chris** » Mon May 06, 2013 10:59 am

BRM wrote:Hi guys
Im doing a diff swap so i can run my new lsd.
So far, from what ive researched i need...
1.8 axles
1.8 drive shaft
1.8 rear cover (the alloy bit)

Is there anything else i'll need
(ive already a diff housing(metal bit)

Also.
Im having a really hard time finding a either a 3.9 or preferably 4.1 ratio....
And really the other parts listed.
If anyone could help, thatll be great

Thanks

Sup - Chris from Club Roadster.

Okay what on earth do you mean the rear cover? Are you building a diff? Replacing the internals of a 1.6? What are you doing? You would normally buy the 1.8 diff that comes with the cover..

marcellarius · Post by **marcellarius** » Mon May 06, 2013 12:05 pm

You'll need the entire diff carrier assembly from a 1.8, as well as the rear alloy housing.

If you just have the differential (#22 in the diagram), then you'll need to get the rest of that stuff from somewhere, as the 1.6 rear isn't compatible. Setting up the diff is going to require some specialised tools... my shop manual advises to 'take it to an engineering shop because you'll wreck it'.

If you have an assembled Torsen diff and carrier already, then it should be a matter of attaching and sealing the rear housing, and installing the driveshafts. It's worth checking the condition of the bushes on the housing (where it bolts to the chassis); if you get rubber replacements, you will need to get these pressed in, not sure about polyurethane replacements.

The Mazda factory manual has some useful details: http://www.mellens.net/mazda/Mazda-Miat ... ential.pdf

There is some doubt/misinformation online whether the two-piece half shafts used on early 1.8 models can be used: yes, they can. I'm using '94 two-piece shafts with a 4.3 ratio Torsen out of an NB. I already had a Torsen diff before the swap (-_-) but I'm pretty sure that open diff 1.8s use the same sized shafts.

Other bits you might need, especially if you're pedantic:

* Axle oil seals. I bought these through Mazda but I had to wait a couple of weeks for them to ship them in from Japan. They cost about $14 each. You need two.

* Axle retaining clip. About $7 from Mazda. There is a C shaped clip that retains each half-shaft in the diff. Manual says to replace them, but in my experience unless they are way out of spec or damaged, or missing from the new axles, keep the existing ones. I insisted on replacing them and it was one of the most frustrating exercises I've ever undertaken... I couldn't get them onto the shafts and still get the size within spec (a couple of mm over the specs in the Mazda manuals). I gave in and used them slightly out of spec.

* Exhaust gasket for the catalytic converter. $22 from Mazda. You'll have to split the exhaust to get stuff out and may end up with a leak if you don't replace the gasket.

* Diff oil.

I didn't have to replace my shafts so I'm not sure if there's anything you'll need for the hubs. Cotter pins?

BRM · Post by **BRM** » Mon May 06, 2013 7:40 pm

Thank you SLYDIT!
The second one was most helpful I think.

chris wrote: Okay what on earth do you mean the rear cover? Are you building a diff? Replacing the internals of a 1.6? What are you doing? You would normally buy the 1.8 diff that comes with the cover..

Hai!
Yup, I'm building an 1.8 diff.
I would just buy the diff with the cover, but atm everything is..
for me anyway..
a bit hard to get a hold of.

Also.. the rear cover.. is literally that.
The alloy cover with the subframe mounts in it.

That's what I have at the moment.
I'm using the rear LSD and scraping the open.
That ratio is a 3.6.
I'm after a 4.1 - 3.9

marcellarius - Thanks for the info =)

What i've got there is a 1.8 diff housing with what you see.
For gaskets and seals and all of that, we have suppliers, so it's all over night stuff.
Yes I'm building it and setting it up myself.

Thanks.

REDBEN · Post by **REDBEN** » Mon May 06, 2013 8:43 pm

BRM,

I have the Same diff as you but a Cusco Version I would advise setting it up for 1.5 way use if you plan on using it on the road I have mine set at 2 way and it is too aggressive for street driving.

You will also need to order a new crush collar from Mazda when you reassemble it, I have all the diff rebuild DIY info too if you would like it?

In saying it is aggressive it is alot of fun to drive but you lose the comfort factor...

Let me know if you need any more info.

Ben

REDBEN · Post by **REDBEN** » Mon May 06, 2013 8:46 pm

By Crush collar I mean the "Collapsible Spacer" in the above Diagram #11

BRM · Post by **BRM** » Mon May 06, 2013 9:05 pm

REDBEN wrote:BRM,

I have the Same diff as you but a Cusco Version I would advise setting it up for 1.5 way use if you plan on using it on the road I have mine set at 2 way and it is too aggressive for street driving.

You will also need to order a new crush collar from Mazda when you reassemble it, I have all the diff rebuild DIY info too if you would like it?

In saying it is aggressive it is alot of fun to drive but you lose the comfort factor...

Let me know if you need any more info.

Ben

Hey Ben.

Its only one setting unfortunatly, so ill have to deal with it =)
Im kinda hoping to be a little lazy and just check to see if pinion height is in spec before i go pulling stuff apart, unless it needs new bearings.
How ive got it set at the moment should be quite tight in the preload,
But need some 1.8 axles to check it properly.
Its pretty easy to 'loosen it up' i guess.

If you could sort me out with a diy that would be cool,
Just to see if its any different to how i do

Thanks!

REDBEN · Post by **REDBEN** » Mon May 06, 2013 9:10 pm

Sweet I only have it in Paperform where about on the Shore are you? I work just off constellation Drive if you want to collect in...

PM me for further details

BRM · Post by **BRM** » Mon May 06, 2013 9:23 pm

Done!

last_resort14 · Post by **last_resort14** » Mon May 06, 2013 10:14 pm

I'm keen on that open centre if you want to get rid of it

BRM · Post by **BRM** » Mon May 06, 2013 10:17 pm

Yours.

Im heading south on thursday / friday for targa rotorua.
Can meet up / drop off then or sunday if you wAnt

chris · Post by **chris** » Tue May 07, 2013 9:10 am

Ahh okay. Good luck with it man

Do a full write up ;D

BRM · Post by **BRM** » Tue May 07, 2013 9:10 pm

chris wrote:Ahh okay. Good luck with it man

Do a full write up ;D

Ahuh
Thanks

Ill try when i get rest of the bits i need...

1.8 diff conversion

1.8 diff conversion

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