HELP: Crown wheel bolt pattern

JackF · Postby **JackF** » Wed May 13, 2015 3:24 pm

Hi all,

Can anybody categorically tell me how many bolt holes a 1.8 diff crown wheel is supposed to have?

My diff is at the shop getting a kaaz centre (which i supplied) fitted with gears I bought off the forums, and apparently the crown wheel has a different bolt pattern to the kaaz. I'm chasing up the supplier of the kaaz to make sure I've got the right one for the application, but yeah.. kinda confused on this one.

Any help would be greatly appreciated

Cheers,

Jack

hks_kansei · Postby **hks_kansei** » Wed May 13, 2015 3:26 pm

PM BartmanFTW.

I gave him a disassembled Torsen2 a while back, pretty sure he hasn't put it back together yet, so he can probably count the bolt holes.

Off the top of my head I think there were 8, but don't quote me on that.

noobee · Postby **noobee** » Wed May 13, 2015 4:52 pm

I just measured a bare torsen 2 center in the shed.10 holes of approx 10.2mm diameter on approx 129mm pcd.
Mick

JackF · Postby **JackF** » Wed May 13, 2015 4:59 pm

noobee - perfect! thanks a lot mate, exactly what I needed to know

hks_kansei - cheers, PM'd him

JackF · Postby **JackF** » Wed May 13, 2015 5:23 pm

Does anyone then know where a 12 bolt ring gear (which i was sold as from a "jdm" 3.9 diff from memory) might have come from? Were jdm diffs actually different?

hks_kansei · Postby **hks_kansei** » Wed May 13, 2015 5:33 pm

Jap diffs were the same, internal and external.

My car has an NB6 housing, a Japanese Torsen T2, and a ring and pinion from somewhere (maybe Japan?)

4wd Mazda 323s, 4wd Ford Lasers, and Mazda RX7s also used the same diff centre, and i'm 95% sure the crown and pinion were able to be swapped (I have a friend with a Laser diff in his NA)

I recall when I was speaking to the guy who built my diff that he was saying that even the NC shares the same bolt pattern as the NA/NB (granted, the crown itself has different dimensions in the NC, so you can't use an NA/NB crown)

I suspect they've sent you a diff for something non-Mazda.
The most likely culprit is that it's a Nissan unit (since they're one of the most commonly stocked LSDs)

JackF · Postby **JackF** » Thu May 14, 2015 12:44 pm

Thanks hks_kansei, lots of useful info there. You could be right with the non-mazda thing, however what I bought is a front diff housing with pinion installed and a ring gear to go with it. While i never actually took it out of the box and gave it a good look, the housing looked very similar to the one i pulled out of my car. I'm thinking it could still be a mazda diff, but just not the right one..

hks_kansei · Postby **hks_kansei** » Thu May 14, 2015 1:04 pm

Oh, so it was the Ring gear that's 12 holes?
Sorry, I thought the diff centre was the 12hole wrong one.

Are you able to post a pic of the diff you have?

A quick way to see if it's an MX5 one is to look for a pair of vertical holes on the front of the housing near the tailshaft flange.
In the MX5 these are used to attach to the PPF brace, very few cars have a PPF so if it's from something non MX5 it probably won't have those holes.
(from memory they're on the righthand side if you're looking directly at the flange)

JackF · Postby **JackF** » Thu May 14, 2015 3:24 pm

I can't post photos unfortunately, everything's at the diff shop at the moment, I'm just going off what they've told me. And yeah apparently it's the ring gear that has 12 bolt holes. My kaaz has 10, and is definitely the correct one for the application according to the kaaz site.

I double checked with the previous owner of the diff housing, its a 3.9 from an nb8 which he took the torsen centre out of.

hks_kansei · Postby **hks_kansei** » Thu May 14, 2015 3:50 pm

That's strange, all MX5s (NA to NB) should have the same crown fitment (the 1.8s anyway)

Your new Kaaz diff is for a 1.8 isn't it? it's not a 1.6 centre (no idea how many holes for the 1.6)

The only other possibility would possibly be an SE diff, I know they were slightly different, but to my knowledge it was just the driveshafts (they were a little thicker, with a different spline count)

JackF · Postby **JackF** » Thu May 14, 2015 4:55 pm

Nah the kaaz is definitely the right one, its a dbz1810 and its a 10 bolt which is apparently what 1.8 diffs are supposed to be. I've now had two people on here confirm for me that their 1.8 diffs are 10 bolt.

From the Kaaz site re: application

also theres this.

which is from http://www.miata.net/garage/diff_rr.html

So yeah, pretty sure the kaaz isn't the problem. But i'm also totally stumped as to why these gears are 12 bolt. Same as you, i thought the SE diff was just different axles, i was under the impression the gears were identical to normal 1.8 diffs.

Either way, I've found some 10 bolt 4.1 gears on ebay, and theres another set of 3.9s on here which I'm just waiting for info on, so hopefully the issue should be sorted by just getting different gears. Also if worst comes to worst I can hopefully just put the kaaz in with the stock 3.6 gears. Although i'd rather not...

Thanks for your help hks_kansei, much appreciated mate