First off I have a 94 Auto that comes stock with the tall 3.90 gears. I want to change them over to the Jdm rx7 4.30 gears that way I can actually get up to speeds over 140 quickly. What I want to know is if I do this will this effect my spedometer? and if it does how can I fix it. also what do I need to do to install the gears iam not very well aquainted with doing this. Any info would be great. thanks.

 

You should have the gears professionally done. The tolerances and setup are beyond the skill of most people, even if they turn a wrench reasonably well.

 

Yes, the speedo will be off a bit.

 

take jimlab's advice and have someone install the gears who is familiar with differentials ( I was going to say rear ends- but- whatever). If you do it yourself, it is unlikely you will get the parts shimmed out properly to get the proper wear pattern, so you will get to do it over again in about 10-15 k miles. It cost me $265 labor plus the parts at a local transmission shop. Do not take it to the Mazda dealer, unless you want to learn something about your own rear end.
Ron A.

 

is there anyway I can correct the spedo when I put the gears in?

 

Man you will be changing gears at weird times too.

Speedo corection= New sensor

 

I would be more concerned with what Jt-imports is saying.

Is there a new shift sensor or something that you will need to put in with the new gears?

 

Who was selling the 4.77 or 4.88 ring and pinion set in japan for about $450? Are they still avalible?

 

Yeah you can change the sensors. Im not sure how it would work with an AUTO though, but MAN you can no problem, up to a point till you need to get aftermarket parts.

4.77 yes its available here.

 

you know what I never thought of that! would the shifting be all fucked up?

 

The shifting will be fine.
The speedo will read about 5-10 mph higher, not a big deal. If you don't like it take apart the dash and fix the needle.
Actually this is a very good mod for auto's, you won't regret it.

 

I have a 4.777 final gear. To fix it, I left the stock sensor in and installed an apexi rev/speed meter. It has a correction value you put in that fixes the problem. I tested it vs. a military police speed gun...he told me my speed over the one way radio and it showed the same value over the meter every time.

 

Dakota Digital makes a signal conversion box (SGI-5) for about $85 that you wire inline with the signal from the transmission to the dash. It has a number of dip switches for setting the ratio and can double (x2) or halve (x0.5) the signal, with many settings in between.

http://www.dakotadigital.com/Detail....rtNumber=SGI-5

 

You sure about that huh?

 

Good call...

4.777 requires a sensor change or the speed meter (hehe).

A 4.300 or 4.33 really doesnt require one, just a stock one. Well at least when your coming up from a 3.900

 

JT-imports,
can you get stock 99 rear gears used? (4.30) I believe for the RZ's etc. (ring and pinion) and if so, what's the cost?
art

 

sure about what?

 

Here goes:

From: Rick Zehr (rzehr@pacbell.net)
Date: October 25, 2000

I just had a 4.30 gear set installed in my `93 Touring Automatic, and thought I'd report on the results. Sorry for the long post, but I thought I'd cover the topic once and for all...

Warning - Personal Opinion Follows:

Opinion ON

IMHO, this should be the first mod for any Automatic FD, for reasons I'll describe below. Opinion OFF

OK, now the facts - compare the gear ratios and rear-end ratio in the 5-speed, vs. the automatic.

Higher numbers are 'lower' gears, smaller numbers are 'higher' gears.

5-speed Stock
Manual Auto
Diff. Ratio 4.09 3.91

Trans. 1 3.48 3.03
Gear 2 2.02 1.62
3 1.39 1.00
4 1.00 0.69
5 0.72

So to get the overall gear ratio (ratio of engine revolutions to rear-wheel revolutions), we multiply the ratio of the gear times the ratio of the differential, and get the following table.

4.09 3.91 4.30
Manual Auto Auto

Gear 1 14.2 11.8 13.0
Ratio 2 8.2 6.3 7.0
3 5.7 3.9 4.3
4 4.1 2.71 2.98
5 2.94

If you graph this in a spreadsheet (See below), it is very obvious that the stock automatic suffers compared to a 5-speed in several ways:

Its lowest gear (first) is much higher than the manual - almost 20% higher a ratio. This makes for a slow start, because the engine is fighting too high a gear for first.


Its highest gear (4) is almost 7% longer than the highest gear on a manual. While this makes for relaxed and quiet cruising, it also makes for mediocre acceleration on the highway.


Second and third gears are each much higher than the corresponding manual gear at any given speed. This means the car is sluggish in traffic.
The alternative for an automatic (or for a manual, just less change) is to replace the ring and pinion gears in the differential with a different 'lower' ratio set. Mazda supplies a 4.30 gear set (43 teeth on the ring, and 10 on the pinion), and all the usual vendors carry this gear.

This lowers the ratio of all four gears by 10% (4.30/3.91 = 110%), and has the following effects:

First gear becomes much closer to that of a 5-speed, giving better acceleration from a stop.


Second gear becomes excellent in traffic - it fits just between 2nd and 3rd on a 5-speed. It only goes to 65 mph at 6000rpm instead of to 72, but it is much more useful (second was too high), and, being lower, works well to allow third gear to be useful, instead of just another sluggish gear that goes to 120mph. Third now fits in the middle of 3rd and 4th on a 5-speed, and is more useful than it was for suburban driving.


Fourth gear is 10% lower, and this gives better acceleration on the highway, at the expense of more rpms at any given speed. With the stock diff, my car ran 2800 at 80mph. With the 4.30, it runs 3100rpm at 80, compared to a 5-peed, which is closer to 3050.
The top speed of the car is probably not affected, since fourth gear still gives 26mph per 1000rpm, and so it should still be able to reach the same speed, since wind resistance is the major retarding force, and it would be running 6000rpm at 156mph - still right in the peak power band.



Overall, the car feels much 'lighter' - the stock automatic just isn't very peppy, and most performance improvements are only effective at high rpms, which you can't use because of the high gears - you can't often go fast enough to hit 6000rpm in third...


Compared to other performance options, this is effective even at low rpm - you get 10% more torque even at 1500 rpm. Compare this to 'breathing' performance enhancements, which often reduce power at the low rpm you really use in 99% of real-life driving.


And then there is the single negative: my speedometer now reads 10% high - at indicated 80, I am really only going 72. But hey, this makes you feel like you are even faster, and when you drive down the road at 80 all the time, your girlfriend will be impressed 6^)
Installation requires that the diff be removed, because you have to re-shim and adjust the bearings, even if you don't replace them. This requires special Mazda shims, of course.

Prices for the gearset range from $474 (Racing Beat) to $563 (Mazdatrix). I believe that these are all the same Mazda part, which will work in either manual or auto cars of any year.

This would be a really good opportunity to replace the bearings and the seals, at a cost of just under $200 at Mazda prices. You could also replace the diff bushings at this time, if there is any slop in them (I didn't).

I had the work done by C2 Automotive in Oakland, CA, and am pleased with the results and the service. William drives a CYM R1, tells me that he has done alignment on M2's racing cars, and he obviously works on a lot of FDs (two in the lot when I was there). (510-272-9869) He charged me for 7 hours at $70, located the needed bits and pieces and istalled it all in one day (aside from the ring and pinion which I supplied).

So, for me, the bottom line is that for comparable money I could have got a couple of other performance pieces - say an intake and catback, but probably would not have got 10% more peak hp and torque, and certainly not 10% at all rpm ranges, and no way 10% more on top of any future performance improvements I make later.

Further, this is the only available performance tweak that makes NO additional noise. Even a downpipe adds to the noise level, and an intake unleashes a whole barnyard of new noises under the hood.

So, for all automatic FD owners, I suggest making this your first performance tweak. For 5-speeds, it's harder to justify - only a 5% difference, but it is 5% times your total torque, however high that might someday be...

 

Good info

The reason I mentioned messing with gear changes.

If you step on the gas in "D" is that that badboy peg to 8000rpms? Or where does it switch now?

Thats what I was saying. Im pretty sure if you always had your auto swtiching at say 5000rpms, that it wont be swtiching gears there anymore.

Understand what I mean?

This looks like you got it off a webpage, any info in RPMs?

 

DOUBLE POST

Server went busy.

 

Don't be intimidated by this project, swapping a ring a pinion isn't really that hard. Just find some info (spicer has some good stuff) on what correct tooth contact patterns should be, this will help you shim it right and set the right backlash.

It may take a while of trial and error to get it right, but eventually you will get it and will have learned alot in the process.

 

Well sometime here in the future I plan on installing a turbo II diff from the 2nd gen. From what I understand they are much stronger than the 3rd gen diffs plus I don't want to change the ratio. Usually I will try to do most things myself but, transmission and diff work are something I would normally leave to the experts. Now having said that, when I take the turbo II diff to the mechanic, what exactly is he going to do to swap out the internal parts? I hate being clueless when it comes to stuff like this.

 

All he's going to do is take out all the bolts around the edge of the diff that hold the ring gear to it, then take the turbo II limited slip bolt it up to the ring gear then put it back together (again, having to check shim thickness and backlash).

The last few pages of section M (front and rear axles) expalins pretty much everything you need to know. Go to the 3rd gen section and look at the mazda service manual.

http://www.iluvmyrx7.com

 

Just curious as to why it would change shifting pattern. Doesnt the auto shift at engine speed? I wouldnt think it would have anything to do with diff speed, only engine rpm.

Not disagreeing just curious.

 

SJS--Me too. Im asking for the most part/curious. I dont deal with autos, just 5-6 speeds