well i usally re-use the spacer, but i always purchase a new crush sleeve... thats how you set the backlash...once you torque it down, you can't re-use it.....
to set the depth you raise or lower and move in/out the ring gear via the adjusters on the ring gear side bearings...

The shim stays with the diff case. According to Mazda they mfg'd the pinions so well that they are virtually identical, but the cases were not as precision made so the shim is needed to make the gear case fit the pinion. I used this method on my racecar and its perfect. The gear marking compound is used to check the gear contact area just to be sure. After you have set the backlash of course. 680, how do you set the crush collar? Do you use the ultra low torque wrench called out for in the FSM to measure pinion drag? I had a hell of a time finding that wrench. Found it in a aerospace surplus store. What a gold mine that place is. :D

yah, i use an ultra low torque wrench, it works great!!

Ultra low torgue wrench ? As in inch ounces instead of foot pounds ?

I will be there this weekend.

Yes. Look in the FSM and read the procedure.

no problem, you buy lunch!!

Will any of the junkyard options mentioned on the first page work with the earlier '81-'83 diffs?

I'd totally dig a set of 4.44's for my '79, that'd give me the extra kick I need to totally annihilate my buddies Supra. :devil:

Interesting stuff. I am putting 3.73's in mine. I want to be able to highway cruise the car below 3000 RPM.

They should fit no problem since the pinion flange from an early diff fits an FB one.

Dude !!! Going shorter r&p gear ( from 3.909 to 3.73 ) is pretty minimal. Don't expect alot. Just like going taller to 4.11 ain't much at all either. Each to his own, but I would only MAYBE make that small a change if I was trying to correct final gear ratio to get back to stock so the speedo wouldn't lie. Probably wouldn't do it, though. :(

Hell, if you're wanting to go that way, just go to a slightly taller tire on the back and call it a day. ;)

Damn shame you can't put a SUPER DUTY STEERING QUICKENER in-line ( reversiblefor more or less turns per rev ) between the propellor shaft and the third member !!! :rlaugh:

Hmmm... ( wheels in head whirring thinking about wheels on car whirring )

i'm not sure, but is the automatic rear end/differential actually lower than the GSL-SE 3.90? like when your cruising @ 60mph the rpm's will be @ 2500 rather than the SE's 2800-2850 or the GSL's 3000 rpm cruising?? someone correct me if i'm wrong here. also will the automatic diffenretial work/fit in the gsl-se differential housing?

I'm not the authority n SE's, but I believe the 3.909 was shared between man and auto on the other models. The effective difference is the tranny gears... automatic 2.458, 1.458, and 1.000... manual 3.674, 2.217, 1.432, 1.000, and .825.

The manual tranny's fifth gear should yield the lowest cruising rpm's if the tire/wheel height is the same on the comparison cars.

i have a feeling it's the auto diff. that will actually yield the lowest rpm cruise rate say 60mph

Could I put 4.88 gears in my 79 diff? What all would I need for the swap?

Sorry, kind of noobie questions but I really want to do this. Thanks

Actually, I have a 4.076 (SE Rear End) in my car right now, so a 3.73 gear is enough of a difference to bring my cruising speed at 2500 RPM from
62 MPH to 67 MPH with the same size tire.

Since I WILL be putting on taller tires to boot, it will make an even larger difference to gearing.

Check out the Attached RPM/Tranny/Gearing calculator I have attached.
It is currently setup for my car with the 87-88 Turbo II tranny.

It will help everyone here figure out how high in MPH each gear can get too.

EDIT: It's too large to attach, can anybody host it? It's a 427KB Excel file.

I can Send it to me on MSN messenger.

I like to use this gear calculator. Works good and is easy to use.
http://www.race-technology.com/WebPa...lculation.html

Over the years, I developed a pretty slick Excel spreadsheet for comparring up to four setups simultaneously. There is also reference data (common RX-7 transmission ratios) and a Ring and Pinion chart, showing all combos. Check it out:

RPMSpeed.XLS.zip

https://www.rx7club.com/forum/attach...id=82370&stc=1

Very nice, Blake. :)

My only gripe is that most of these calculators do not allow you to put in ALL the variables to determine EXACTLY what results are possible or likely.

Somebody could get the impression that with super tall tires and gearing changes on a stock 12A that 200 mph is possible. You would need to factor in the hp and torque curves at different RPM levels, coefficient of drag, parasitic loss of accessories or gain from removing them, and on and on.

They are great for comparison to move the user at least in the direction they are trying to go.

IMO too many people don't have a clear idea of what they are trying to achieve. What is the purpose of the car. Are you going for an 1/8 mile car ? 1/4 mile ? redlight to redlight beast ? rally ? drifting ? land speed record ? or just drive daily with a little extra so civics don't embarrass you ?

All require very different and critical setups to be able to do the desired thing really well. But for sure, no one car can do it all !

Hey that's the same one I have!

Nice Job Blake, - On the copy I had I went ahead and put the Turbo II
gearing to help get an idea of the rear ends gearing that I was leaning to.

Now I know I can hit almost 70 mph by redlining 2nd gear. :)

Here Guys, Use this to enter YOUR setup into the Calculator:


US SPEC MAZDA DRIVELINE RATIOS

*** FIRST GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
RX-7. 79-83 3.674 2.218 1.433 1.000 0.825 3.909 3.227 185/70-13 892...2878
RX-7. 83-83 3.674 2.218 1.433 1.000 0.825 3.909 3.227 195/60-14 891...2875
AUTO. 84-84 2.458 1.458 1.000 0.720 N/A...3.909 3.909 185/70-13 892...3487
GSLSE 84-84 3.622 2.186 1.419 1.000 0.758 4.083 3.097 205/60-14 878...2719
RX-7. 84-84 3.622 2.186 1.419 1.000 0.807 3.933 3.175 185/70-13 892...2832
RX-7. 85-85 3.622 2.186 1.419 1.000 0.807 3.909 3.156 185/70-13 892...2815
GSLSE 85-85 3.622 2.186 1.419 1.000 0.715 4.077 2.914 205/60-14 851...2480
RX-7. 85-85 3.622 2.186 1.419 1.000 0.697 4.444 3.099 205/55-14 910...2820

*** SECOND GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
Base. 86-91 3.476 2.002 1.366 1.000 0.711 4.100 2.917 185/70-14 855...2494
GXL.. 87-91 3.476 2.002 1.366 1.000 0.697 4.100 2.859 205/60-15 841...2404
Turbo 87-91 3.483 2.015 1.391 1.000 0.719 4.100 2.948 205/55-16 828...2441
Conv. 88-91
GTUs. 89-91 3.476 2.002 1.366 1.000 0.758 4.300 3.261 205/55-16 828...2700

*** THIRD GENERATION ***
……………………………………………………………….…….………………………………..AXLE..FINAL.TIRE......TIRE..ENGINE
VEH.. YEAR. 1ST.. 2ND...3RD.. 4TH...5TH...RATIO RATIO SIZE……....RPM...RPM @ 60 MPH
(FD). 93-95 3.483 2.015 1.391 1.000 0.719 4.100 2.948 225/50-16 829...2444

You forgot to mention AutoX and Road Racing. You may need a different gear every weekend to match the a certain course or track you are on.

With autocrossing you can't even really know what gear you need until you are there walking the course. Then a lot times you can carry more speed or you need to go slower than you thought when walking the course. So you don't know which gear you need until you have made a run or two. I love it. Not that I have ever changed a rear end to suit a certain course but you can at least theorize about it.

What is that? I've never seen that as a stock config.

Top speed is only limited by horsepower. The aerodynamic drag (biggest factor), rolling resistance, etc. determines how much horsepower is required to do the job. Torque curve has nothing to do with it, and gearing only matters in the sense that you have to keep RPM limited to less than redline in the highest gear for the targeted speed. Regardless, estimating the top speed is completely outside the purpose of my spreadsheet! All it tells you is what speed you would be at for various RPM/gear combinations. Whether you can manage to get there is your own problem. :P

But, you missed the biggest fault of the calculator: it only accounts for nominal values. Tires, in particular, are never the nominal size in reality, and they wear over time. The actual (starting) size can be determined by the manufacturer's specification of "revs per mile". For example, a Bridgestone SO2 in 205/55R16 has a revs per mile specification of 833, while a Yokohama AVS Sport in the same size is 836. Regardless -- and again -- such matters are outside the scope of my calculator. I'm just going for "good enough" to decide "do want a 4.88 rear end gear?", or "if I get the 4.88, should I swap over to a GSL-SE transmission with a taller 5th gear?", or "what will happen if I go from a 185/70R13 to a 205/55R16?". These kind of questions inspired me to create the spreadsheet and continue to refine it to test multiple cases. I have no interest in delving into matters that would require a physics degree and still not give you an accurate number (too many variables!). I might as well create a drivetrain loss calculator to figure out BHP from WHP...I'd be rich!

Thanks. A lot of people use it and probably forgot the origin (though my name is right at the top of the worksheet). I did the first version back in 1997 and have been refining it a little bit at a time ever since. Not sure if you have it, but the latest version (a couple years old, at this point) has reference data included. You have to use the tabs at the bottom of the page to get to the other worksheets (Reference Data, Tire & Wheel Calc, and Ring & Pinion). Just copy and paste!