What LSD will fit my car???

poison · Post by **poison** » Thu Aug 02, 2007 11:29 pm

I've read so much stuff on the net about diff's but am still confused.

I have a 98 N8BC, which (if any) of the sreies 5,6,7 RX7 diffs will fit into my housing?

When I bought my car I was told it had a torsen but out of an intersection the inside wheel will spin up easily if I give the throttle a bit of a blip. although on an uphill both wheels will spin (in the wet). So I am fairly sure it' not an LSD.

Help please JIF, SLYDIT etc.......

Ian · Post by **Ian** » Fri Aug 03, 2007 8:04 am

There is an article on LSDs onMiata Net..garage section...should take you to Randy Stockers Solo Miata site etc. I think you have to pull an axle to beabsolutely sure if you have a torsen, though Keith Tanner's book Performance Projects suggests you can inspect your diff via the oil filler hole....if you see wom gears its a torsen, if you can see spider gears its an open diff. (A large cylinder would indicate a clutch type lsd - unlikely in your model, or a type 2 torsen from a 2001+ mx5, again unlikely, I would have thought).
A torsen (type 1) is the one to go for...should be a straight bolt in for your car.
I fitted one from a 98 into my 94, though I had to change to the later 1 piece axles to do so.

Post by **jif** » Fri Aug 03, 2007 2:10 pm

doesn't sound like you have a LSD then

you'll either want a series4 rx7 clutch type:
http://members.aol.com/solomiata2/RX7LSD.pdf

... or a torsen diff. The latter is relatively inexpensive here (no spec-miata racers driving prices up!).

Either way you want some kind of 7" Mazda diff , apparently the RWD 626 and b2200 diffs also fit, albeit with very different ratios. FD rx7's are 8" ... NA6's are 6", and kinda fragile.

Euen · Post by **Euen** » Fri Aug 03, 2007 3:55 pm

Gary, if you go over to Nth Harbour Mazda, they can tell you what diff the car had when it left the factory. All they need is the chassis no. (There is no guarantee that it is still the same diff though) They will probably be more agreeable if you are buying something though. (They can even print it out for you after I told them how to use ctrl-P)

Gordon Tucker · Post by **Gordon Tucker** » Fri Aug 03, 2007 4:48 pm

An easy way to tell if it has a LSD or not is to jack up the rear with both back wheels off the ground. With the car out of gear and handbrake off, turn one of the rear wheels by hand. If the other wheel turns the same direction you have a LSD, if it turns the opposite direction you don't.

badcf4 · Post by **badcf4** » Fri Aug 03, 2007 4:58 pm

if the diff from a rwd 626 fits then also will the series 1/2/3 rx7......series two and three were optioned with an lsd (or maybe just series three??)

anyway they are pretty pricey if you can find one......I didnt think the b series ute diff heads worked unless its the really old ones.....in which case they wouldnt have been lsd.

however the internals would have been bulletproof and are probably adaptable in some way as most mazda stuff is like lego.

Id suggest having a search here if you can put up with the txt speak and profanitys and plain stupidity as im sure lsd's and diffs would have been discussed many a time

www.rotahavik.co.nz

Gort · Post by **Gort** » Fri Aug 03, 2007 5:12 pm

Gordon Tucker wrote:

An easy way to tell if it has a LSD or not is to jack up the rear with
both back wheels off the ground. With the car out of gear and handbrake
off, turn one of the rear wheels by hand. If the other wheel turns the
same direction you have a LSD, if it turns the opposite direction you don't.

Not true for a "torsen" diff. My MX definitely has a torsen LSD, and
the wheels turn in the opposite direction. My 300zx has a normal LSD,
and they turn in the same direction.

Cheers, G

poison · Post by **poison** » Fri Aug 03, 2007 5:34 pm

Thanks for the tips, maybe I left out one important piece of information... My car came into NZ with a clutch type LSD but the new owner didn't know and put in the wrong oil and ruined the plates. It was replaced with one out of a 2002 Miata and he was told by the wrecker that it was an LSD. But I think he was told pork pies.

One of the great mysteries of Torsens seems to be that you can't just jack up the back of the car. No idea why that is but almost everything I have read mentions this. Another thing being that if one wheel is fully unloaded then the diff can act like an open diff.... again I don't know why, just read it a few places.

Ignoring the type 1- type 2 Torsen choice, I'd be happy at this point just to find a Torsen that will fit my car. Also given that most of our cars are imports anything could have be fitted in Japan and most owners wouldn't have a clue. So that's why I am looking at RX7's as their LSD's are often much cheaper than the MX5 ones.

I've found a few RX7 LSD's for sale, but the sellers never know what size they are (6",7",8") they just know what it came out of. Can someone please tell me where is this 7" measured from (no rude comments

) I would assume that it's the outer diameter of the case where the ring gear bolts on, or maybe the inner or outer diameter of the ring gear????? I think if I knew this I would be well on my way…. Thanks again.

MN · Post by MN » Fri Aug 03, 2007 8:25 pm

Gordon Tucker wrote:An easy way to tell if it has a LSD or not is to jack up the rear with both back wheels off the ground. With the car out of gear and handbrake off, turn one of the rear wheels by hand. If the other wheel turns the same direction you have a LSD, if it turns the opposite direction you don't.

And this doesn't mean it actually works under load when you want it to. My car has an LSD but pushed on the track or on a rally and you can hear the inside wheel spin.

poison · Post by **poison** » Fri Aug 03, 2007 9:13 pm

OK, I just jacked the back and pulled the oil filler and it's pretty hard to see anything

there seems to be some sort of revolving case like on an LSD but hard to see past that (yes I used a torch

)

Can anyone post me a link of what a normal diff would look like inside? I seem to be looking directly in on the ring gear but it seems to be inside the revolving housing which wouldn't work so I'm a bit confused. Deep inside I could see some gears which don't look like spider gears so I'm none the wiser.

LSD or Not LSD... That is the question....

Ian · Post by **Ian** » Fri Aug 03, 2007 10:42 pm

Try going to Miata net site....
go to Garage
go to Engine and Drivetrain
scroll to Diff Spotters Guide

There is more info on interchangeability elsewhere also

Good luck
The torsen's advantage over a viscous or clutch type are that they don't break, wear out or need adjustment.
Cheer, Ian

SLYDIT · Post by **SLYDIT** » Sat Aug 04, 2007 2:00 pm

all of the mazda 7" diffs share the same gears that attatch to the centers.The differences are in the splines and pinion "nose" shaft.When people say that type"x" diff will fit..what they really mean is that the gears fit or that the center"pumpkin " will fit, but may need appropriate axles to match..Either way i think the best option is to get a series four RX7 clutch unit and have it rebuilt into your 99 housing. The clutch pack ones can be preloaded to adjust how much lock up they have. Thay can also be adjusted for wear.Torsens while good will also wear out and cant be rebuilt, so its a one shot solution. Torsens WILL wear out on a turbo application.

So to sum up...get a clutch pack LSD from a S4 RX7 and have your gears from your NB fitted to it. then have it installed into your NB housing.

Post by **jif** » Sat Aug 04, 2007 2:21 pm

duuude... that pdf I linked to before has pics, instructions, etc for id'ing a torsen

poison · Post by **poison** » Sat Aug 04, 2007 3:28 pm

Thanks Guys, and yes Jif the PDF was great thanks

and I saved a copy, but looking through the tiny oil hole, it's damn hard to see anything let alone identify what I was actually looking at.

Thanks Ian that link http://www.miata.net/garage/diffguide/index.html
really brilliant, cheers.

And from this I am ceratin I have an open diff.

So now the hunt begins for a 7" LSD, I have read that the clutch type rebuild packs are pretty pricy though....

Anyone with one for sale...??

SLYDIT · Post by **SLYDIT** » Sun Aug 05, 2007 6:39 pm

well a rebuild kit for a clutch pack is cheaper than a new torsen...because a torsen WILL wear out on a turbo....you could also look at getting a new KAAZ LSD diff from australia...i think theyre about $1800 AU and then youll have to get it fitted into your diff housing.......

OR YOU COULD JUST BUY SOME REALLY REALLY STICKY TYRES AND FORGET THE LSD ALL TOGETHER! HEHE. Such as the Yokohama (AO48??) that was standard fitment on the Mitsi EVO 8

Ian · Post by **Ian** » Sun Aug 05, 2007 10:10 pm

Forgive me for believing that torsens were fitted to series 6 RX7 twin turbos from 1993...

I was under the impression that they are trouble free and recognised as being smoother in operation than any clutch type, useful in a road going car.

2001 and later cars may have come with a Toshiki-Fuji unit which is a torsen principle and a stronger carrier.

I am using a type 2 torsen which has more bias than the type 1.

Post by **jif** » Sat Aug 11, 2007 10:21 am

gazz, buy this before I do

http://202.21.128.2/Trade-Me-Motors/Car ... 16.htm?p=1

Ian - s6+ rx7's do have a torsen LSD... but it's an 8" version and isn't a drop in deal for us

Ian · Post by **Ian** » Sat Aug 11, 2007 12:10 pm

jif...

Yes, I was aware that the RX7 torsen was a not a fit...was just using the example to make the point that a torsen is a robust unit.
Keith Tanner has an interesting ongoing build site for his intended Newfoundland Targa car. Admittedly naturally aspirated, but with some nice gear - Ohlins, 2 litre stroker etc etc and target of 200HP at the wheels. He has the same diff as me - 4.3 NB torsen.

Just had 3 days cruising the Banks Peninsular roads - MX5 utopia!
Cheers from an (almost) sunny Mainland.

Ian