What's the Diff?
 

I have studied many results of searching here and elsewhere for info on when Mazda went to the larger axles, and I'm confused. Some say the '83-'85 open diffs are all the same, some indicate there was a midyear change, some say axles are small. :scratch:
It's an '83 GS, mfg 7/83, drum brakes, open diff (AFAIK). It's all original/stock. We have to replace the diff (goes chuk, chuk, chuk...). I just want to replace the pumpkin without "upgrading" anything; does my car have the larger axles?
TIA

Some will argue, but I've personally seen 83s with big axles and with small axles, with beehives and with standalones. Anyway....

A 7/83 car is nearly guaranteed to be a big-axle car. The easiest way to check is to look at the pinion flange which the driveshaft bolts to. If you have thru-holes with bolts that pass through the holes, then uses nuts to tighten then it's a big-bearing. If the pinion flange is threaded and you just have bolts that thread into the holes (no nuts on the back side of the flange) then it's a small-bearing.

but to add to that... you can still have a small spline differential as i discovered. My 3rd member i had was from an 83, never checked the bearings, but the flange was not threaded. But the differential was a small spline.

you can also swap out third member from some different vehicles for some gearing selection as well. i through it in a video vlog i have, but i did a side by side of the b2600, kia sportage and the stock mazda

http://www.youtube.com/watch?v=2ypp6UPxKFk

oh actually 83's got the nut and bolt flange, but kept the small axle axles. its in the parts fische if you want details...

i think they did it for the 12at cars, that way big or small axle everything 83-85 can use the same driveshaft.

to the OP, 83 has the big driveshaft flange and small diff side gears to make it a small axle. you can use an earlier diff, and swap the driveshaft or driveshaft flange. or use a later diff and swap in the diff side gears from yours

The diff flange, where the driveshaft bolts up, is not a good reference to see if you have a small or large bearing diff. The best thing to do is take the pumpkin out and count the splines. I bought an 83 parts car last year that had the driveshaft bolted to the flange with seperate bolts and nuts thinking it would be a large axle diff, since that`s what I needed. It turned out to be a small axle diff. I didn`t think to check the manufacturing date of the car though.

edit: j9fd3s and I posted almost at the same time. His explanation makes alot of sense in my case. It`s exactly what I had in my 83 parts car.

Got it apart today, that sukka is toast. The pinion gear shaved the ring big time; the pic shows about half of the large fragments of ring gear on the ground. We got the housing all cleaned up, all we now need is a big axle pumpkin.

So If have an 83 gsl rear end, it's small axle?
And an 85 open diff is big axle?

If we are referring to the size of the axles then it is clear that the 84-85 are the larger axles with a different spline count and bigger bearings. There are no 83 models with the big bearings.

The only difference that you may be referring to is the flange on the pumpkin unit which generally as a whole is the larger one on the 83 models but has nothing to do with the axles.

As posted many times-

http://mazdatrix.com/g5.htm

Brake line threads changed in '81, shoes drums, and adjusters are much better 81-85. Driveshaft flange changed in '83.

3rd Member Interchangeable except must match drive shaft and flange (larger in '83)

What did you do to that diff?

By the looks of it he has a 900 hp engine and solid transmission mounds, and he dropped the clutch

When it came time to replace the diff in my '85 GS, I chose to replace the entire rear end with a unit from a '84 GSL (84 or 85 would have worked). This gave me a couple of other upgrades, like rear disc brakes and a LSD, both of which are awesome. I think it was also a lot easier doing it this way than tearing it all apart to just replace the innards.




.

The PO told me he attempted a burnout in his driveway and - BOOM - there went the rearend. If I could find a complete disc brake rearend, I'd jump on it; but we're out in the middle of the state and there's nothing near here for parts sources.
Yeah - I'm confused - so I have a big flange/small axle rearend? What would I measure to be sure? I mean, I could easily bring the old pumpkin and an axle with me when I get the replacement, I suppose...

well first, the big driveshaft flange and small axle is correct for 83.

the big driveshaft flange is the nut and bolt one, AFIK they will interchange, so if you found a small axle small flange rear, i think it just swaps over. they didn't change the case, bearings, ring and pinion, just the driveshaft flange and axle size.

big axle vs small axle? the difference is the diff side gears, the spot where the axle actually goes, and the rear end housing is changed to hold larger axle bearings. easy way is to just measure the axle, or hole and make sure that doesn't change.

sometimes there is a stamp on the ring gear, and you can look it up in the parts fische

Yup, the low-miles '82 pumpkin we got at the wrecking yard is a near-perfect fit. Colin's '83 does indeed have the smaller driveshafts. The only difference is the (front) pinion shaft seal - the seal shield on the '83 flange does not lap over the edge of the housing to protect the seal like the '82 does. We're not worried; I'm sure that someday, we'll replace that seal and it will be updated then.
Everything cleaned up nicely, black RTV to seal, overnight set, lubed & popped that puppy in next day and drove it around that afternoon!
BTW, we found a great use for that limited-service spare roller skate wheel - we mounted it, gently, patiently pounded it to pop out the axles - worked like a charm. When we reassembled the thing, we applied a little anti-seize to help everything go together.
I am a little concerned to see that the brake plates are all that keep the axles in; all that force...
I love rescuing cool things! :icon_tup:

So if I was to want to put a Rx7 LSD in my Rx2 a 83 would not work correct? I thought it was all about the small vs large bearings but now it looks like its the driveshaft mount right?

It dosent take that much to destroy a diff with a shock load.
Stock 82 GSL(Clutch drop at 6k):
http://i88.photobucket.com/albums/k1...234d42f9bd.jpg
64 Mustang about 500hp(9 inch, again clutch drop):
http://i88.photobucket.com/albums/k1...3bb2b4eb83.jpg
If you know 9 inches they are some beefy rear ends.

So is there any hard numbers to compare if you have a large axle or small axle. How many splines on each or how large are the axle shafts in diameter?

Measuring the spline end of the shaft for diameter with a micrometer:

Small = <1.0"
Large = >1.0"

For clarification, i have an '82 small axle GSL, and an '84 large axle GS. I took the axles out and took measurements and pictures.

Here's both side by side, the large axle on the bottom and the small on the top in the picture

http://i358.photobucket.com/albums/o...s/DSCN0510.jpg

And side by side, large axle on the left, small on the rights

http://i358.photobucket.com/albums/o...s/DSCN0511.jpg

A measurment of the end nearest the splines on the large axle

http://i358.photobucket.com/albums/o...s/DSCN0515.jpg

A measurement of the end nearest the splines on the small axle

http://i358.photobucket.com/albums/o...s/DSCN0517.jpg

The large axle bearing.

http://i358.photobucket.com/albums/o...s/DSCN0521.jpg

And the small axle bearing

http://i358.photobucket.com/albums/o...s/DSCN0523.jpg

So one can infer that axle housings are different because the outer diameter of the axle bearings is different.

thanks for doing that!

this is very helpful. thanks for the measurments