In my '81 S model, someone installed a LARGE FLANGE rear end from a GSL. What are the visible clues to let me know whether it's an '83 or the large axle '84-'85? What should I look for? Thanks.

 

I installed an 84-85 rear end in my 82, and the differences I noticed are that
the 84-85 has a large square shaped flange, where the earlier one is more of a rectangle, and also the 84-85 uses bolts w/ nuts that secure on the back, where as the earlier one just has bolts that thread into the flange

Hope this helps

 

Small axle chunks had threaded holes on the pinion flange. If they're thru-holes, then it's a large axle.

 

You can't conclusively tell by the flange. The '83 is an oddball. It has the same flange, driveshaft, and thu-holes as the 84/85 cars, but they have the small axle.

Perhaps you can locate a casting mark/number. The housings are different between small axle and large. You could also pull and axle and measure the size/look at the spline count. These are the only ways that I can think of to separate an '83 from the '84/'85 models. The dust shields show as different part #s, but not sure if there is a clear/easy way to tell them apart (bolt spacing, number stamped?, etc.).

 

In that case, no, there's nothing else to check. The next-easiest thing to do would be to incline the housing to one side, pop the axle out of the high side (no oil) and just count the splines.

 

I don't know anything about rearends (that's why I'm asking here) so I'm not going to pop out an axle. I'm hoping there are visible clues on the outside.

I have easy access to an '84-'85 GSL so that will be my guide as I compare features on the S.

The main reason I need to know which rearend I have is because I'd like to order a set of braided stainless brake lines. There's a different part number for '84-'85. Then if it turns out I have an '84-'85, I can get some Moser axels at some later point.

 

Measure the OD of the casting around the bearing. The S3 should be larger due to the larger bearing.

 

+1, the housings are different part numbers...

also maybe you can take a wheel off and measure the axle that sticks thru the hub flange?

 

Good ideas. Thanks.

 

+2

Since you have access to a known 84/85 - measure the outside of the housing tube with a machinist caliper. Measure as close as you can to the backside of the caliper bracket flange.

Large spline axles are over 1" in diameter at the spline and Small spline are under 1" diameter at the spline.


81-83 will be smaller than the 84-85.

If you do pull an axle, 1979-1983 splines will measure under 1" diameter and 84-85 splines will measure over 1" diameter.

Someone has already measured a few rear end housings and posted the dimensions. I could not find it with a quick search but you might be luckier.

-billy

 

Oh...... it was me 14th post in this link

https://www.rx7club.com/showthread.p...hlight=housing


-billy

 

lol, forgotten more than most will ever know?

 

I forgot to mention the reason for needing to know my rearend year is so I can order a set of braided SS hoses. There is a different part number for '84-'85.

The weather here has been stupid the past few days but maybe I can get out there and compare today.

 

I finally had a chance to take a look. I had three 1st gens jacks up with wheels removed: '83 GSL, '84 GSL and my S model with the unknown GSL rearend. A visual inpection rendered nothing. Measured the axel housing with a digital caliper showed the same size. I didn't want to pop out an axel because I've never done it before and was unsure what it would do to the seal or anything else.

Ten I noticed the front brake lines are different. The front! It appears Mazda went to a shorter flex line on '84-'85 cars for some reason. That must be the difference. Looks like I'm ordering the '81-'83 set.

 

You don't really need to worry about the seal when pulling an axle. If nothing else, a light coat of silicone will take care of that. I would go ahead and pull it to make sure. I'm not sure if there's a difference between the S2 and S3 rear brake hoses.