Sorry, I know this is the wrong section, but I couldnt find a transmission section.

Mods. Move it if you think im a tool.



A few years back when I bought my racecar, it came with a spare gearbox.

Its been sitting in my basement since then, then the other day i ripped it apart to determine what the hell it is.



SA style shifter model

Gear teeth:

28/13

26/20

21/25

17/29

31/15



At first I was like "Cool, another racebox" based on the 28/13 gears which in my simple mind gives a ratio of 2.153:1 Pretty long even for a racebox. But somehow, based on the other gears, I think I've got something wrong, did I miss an extra conversion ratio or what ?



I would upload pictures, but my internets' broke and the work pc wont accept bluetooth transfer Either way, it looks like any other gearbox inside, nothing fancy.



Kim

 

dont you need to go off of the imput shaft to get the ratio, ie 4th gear over 1-5 to get proper ratios. maybe im wrong too i never could keep them straight i just used the mazdatrix web site as a chart and logged each box that way for stock boxes anyways. now we are having barrington hillbillies build ower dog boxes with differnt ratios out of na trannies.



randy

 

shoot heretic a pm, theres a conversion you do.



if its a sa style box, its prolly just stock

 

It has been a while since I played with an early gearbox, but 28/13 sounds about right.



Don't forget that there is a drop ratio from the input shaft to the countershaft (layshaft?). It's something like 1.4:1 or thereabouts. I know the info is on Felix Miata's website, filename "tranchrt.txt". Sounds like a generic standard box. If the sides of the middle housing look like an FB or FC unit, then you have a rare-ish late '80 model that is genetically compatible with the later units. If the sides look malnourished, all sunken in around the bolts, then it's an early unit. It looks like the geartrains can be swapped into later cases and vice-versa but the shifting mechanism is case-specific. I haven't had need to try.



I can remember an obscure filename on a website I haven't visited in years, but I can't remember where I put my other set of keys.

 

Could you dig out a link for that site, please. ?

 

haha, well at least you got the important stuff!

 

Google-fu lesson:



Google search for "Felix Miata" nets his site as first hit. http://www.google.com/search?hl=en&q=f...G=Google+Search



Or, the filename is known. Searching for that filename nets links to the exact page. http://www.google.com/search?hl=en&q=t...amp;btnG=Search



Now, here's what is funny. This very thread is, at this time, the fifth discrete hit, and the third site hit. It's like a hall of mirrors in here.

 

Back to on topic, the link to the page is http://mrmazda.no-ip.com/tranchrt.txt and according to that page, 13/28 is standard teeth count for all transmissions 1979-1983. The input and countershaft's corresponding input gears are somewhat erroneously listed as "4th gear", but the tooth counts for those are 17 on the input and 29 on the countershaft.



So that means there is a 17/29 reduction followed by a 13/28 reduction. Since we work in ratios that are written the other way around (we care about multiplying the torque, not multiplying the speed) we divide the driven gear by the drive gear. 29/17 is 1.70, 28/13 is 2.15, multiply the two and we get 3.66, which sounds about right as a 1st gear for a bog standard gearbox.

 

Heretic to the win.

Thanks man - that chart is friggin nice.



I'm starting to understand gearbox's