I'm replacing the rear axle bearing/oil seals in my 83' ITA car. Car has an 85' LSD w/ small axles. I also have a spare 1981 car with a none LSD rear w/ drums. Are small axles the same on LSD vs No LSD and and disc vs drum?

 

I don't believe that there is any difference in axles between the two types of diffs.



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85 should have large bearing axles. I think all small bearing axles are the same and all large bearing 12A are the same. 13B are different.

 

It's a 1983 12a car but I'm not sure if the rear is from a 12a or a 13b 1985. If there is a difference in bearing size is it the od where the diff housing takes up the difference, or is the axle itself bigger?

 

The third members - center sections - are the same for all years. So you can install a center section from an 84-85 rearend into a 83-earlier rearend housing. To make the small bearing axles work in the 84-85 center section you have to install 79-83 side gears. Apparently someone did that before you bought the car.

79-83 rear end housings have smaller axle bearings and the axles themselves are smaller. 84-85 rearend housings (12A and 13B) use bigger axle bearings and a larger/beefier axle.

The 79-83 rear axle housing is more than strong enough for ITA/IT7 and it is little lighter.

To answer your question - yes drum brake axles will fit in your disk brake rear end.

Do you have thick bearing retainers? I have a set for sale for the small bearing rear end.

 

Still a little confused. I ordered a bearing and oil seal for an 85' w/ lsd and a 12a and they fit the axle and the od of the bearing fit the housing. How is the smaller bearing smaller, width? I made heavier retainer plates already, but thanks. So at this point, I'm not sure what I have. I was told it's and 85' rear end but is there a way I can check the housing? The axle has 24 splines and mics at just a click under 1.1".

 

Maybe I read your question wrong. If you purchased a bearing and seal for an 85 and it fit then you have a big bearing rear axle housing. All 84-85 model RX7's have big bearing rear axle housings. There is no way to interchange the small bearing axles with the big bearing axles.

If you need addtional axles in the future then you will need to source one from an 84-85 12A RX7. The cool part is the left and right axles are the same length and you can use axles from either a drum or disk brake rear end.

I show the National Bearing part number for an 85 axle as 511017

Nothing wrong with what you have - a beefy piece.

 

Thanks for being a great knowledge base, Scott. So I checked my receipt for the bearing/oil seal and I was wrong. It was for an 83'. And I know the spline count, 24, is the small axle. Bearing # is 553412 so I'm sure I have the small axle. The car is an 83' so it's probably an 83 housing. The lsd is suppose to be an 85' so if true, the side gears must have been changed.
On another issue, I've got a quick shift that came with the car but not installed. I've got 5 track hours on the car with one race and I was thinking about changing it out for faster shifts/downshifts but in reading some threads I'm a little concerned about reaching 5th with the shorter lever. Do you/have you used one for track?

 

I don’t have any experience with short throw shifters with Mazda transmissions. I did look into it several years ago but determined that they are not legal in SCCA Improved Touring . This may have changed so you need to check the latest GCR at www.scca.com.

Mazdatrix sells them and they have allot of experience racing FB’s so you might want to contact them and ask them about the 5th gear shift.

My car had a 4.88 rear end and using 5th just made the car slow down. My car was faster in 4th at every track in the Midwest Division.

 

I have the mazdatrix short shifter in my 84 GSL. Works great. No issue with 5th gear and I've never heard of anyone having problems.

 

re; axles. for the axle shafts there are 3.

79-83 small axle, they ALL have the 4x110 bolt pattern

84-85 12A. bigger diameter than the 79-83's. 4x110

84-85 13B. same as the 12A, except it has wheel studs in a 4x114.3 pattern.

alex HOUSINGS, there are 4.

79-83 drum, 81-83 disc. 84-85 drum, 84-85 disc. the drums have a square 4 bolt attachment, discs use 3.

re short shifter;

in a racing situation i think the synchro's tend to live a short life, and giving extra leverage to the driver isn't going to help that.

 

Thanks everyone.

 

this may help your axle question: https://www.rx7club.com/1st-generation-specific-1979-1985-18/gsl-rear-sb-vs-bb-822513/

 

Thanks all.