Freds new (rwd FE3 related) toy :-) [Gearbox]

[fredio54]

i'm lead footed, but shift smoothly and quickly, a delay in shifting for the revs to rise again/throttle to go back down, and some sticky rears in a highish gear, and something has to give(usually the clutch, but when thats bullet proof...).

[carcenomy]

Funny you should mention that. There's always going to be a weakpoint, and if it's not the box, clutch or diff... I've heard of a heavily worked 2T-G Corolla twisting its driveshaft in two...

[fredio54]

mmm, thats gotta hurt, i've seen boats with V drives sink like that (or with uni joint failures.

finished cleanin it today, and ripped into it to inspect the gears, clean the inards a bit, and count the teeth.

it doesnt work quite how i thought it would on the inside. instead of fourth having dogs on the end of the in and out shafts that are engaged together, it seems that fourth gets a gear. fourth is still 1:1, so if i counted the teeth accurately, the layshaft to output shaft gears must be the inverse of the fourth gear pair.

pairs are as follows :
in the main forward part of the casing :
1st : in 34 lay 14 width 22mm
2nd : in 29 lay 20 width 22mm
3rd : in 29 lay 33 width 21mm
4th : in 22 lay 40 width 22mm + 2mm spring loaded silencer part gear.
in the rear part :
5th : in 27 lay 54 (this has the best chance of being wrong, counted through the filler hole with a torch!) width looked to be 20 odd mm too, but couldnt get a vivid in let alone a rule.

the input shaft is a bit odd, i measured it at 25.4mm and counted 23 splines, the only listings like this are 26.2mm, i assume it is just supposed to be a slightly loose fit to aid sliding of the disk.

the output shaft is a 22mm 25 spline job, this seems to be different from the van box from my previous measurements of the similar van box. this could mean finding a yoke could be difficult.

i was only able to count the teeth on the idler reverse gear, that is 17 of them. that doesnt give a ratio, because the other two gears teeth counts are missing.

the way i see it is this : if 4th is 1:1 and has an input ratio of 1:1.81, then its output ratio must be 1.81:1.

34/14 * 40/22 = 4.4156:1
29/20 * 40/22 = 2.6364:1
29/33 * 40/22 = 1.5978:1
22/40 * 40/22 = 1:1 fourth
27/54 * 40/22 = 0.9090:1 recurring fifth

my diffs are all 4.444444 in ratio, which should see my quater by relatively quick, and each gear not last long.

if anyone can see any issues with my logic or calculations, please post. also if the ratios seem strange. they seem right to me considering the fact that it is a ute box.

fred.

[sry_not4sale]

A couple of things:

- The box in the background of the first pic is also found in 1984 - 1986 8-valve FE powered 929's

- The bellhousing off that box will mate up to 1st gen RX-7 boxes, including the very strong 12aT boxes

[fredio54]

thanks not-for-sale, i knew that the came in older stuff too, the older (pre 87?) ones with no ribs have weaker guts. as for the 12aT box, is that four speed? does it look like the one in the foreground, but without the extra section between the main ribbed part, and the tail shaft part? if so, its what the one in the foreground is derived from. do the early housings really fit on? it seems unlikely because the early ones "bell housing" is also the main casing front half. whereas the R type boxs have a proper bell housing. got any photos? if the 12aT box is similar in appearance to the box in the background, then i cant see how it would be any stronger. all the na rotas, utes, vans, mx5s etc used the same box with different bell/front halves, different rear extensions, and different ratios. only the late model 6 speed mx5 box is different to the rest(excluding those early R type 4 speeds.) cheers for commenting.

fred.

[carcenomy]

Mmm, six speed MX5 box... how different is it?

[fredio54]

completely, its not mazda, its one of those trans manufacturers. dont know how strong it is either.

[sry_not4sale]

- The 12aT box is 5-speed
- It definately looks very similar to the box at the rear (with different bell housing of course)
- Yup, bell housing for HB 929's, RWD 626's, 1st gen RX-7's, and i think even Non-turbo S4 RX-7s are all interchangable
- None of the boxes are extremely strong, and alot of people use the MA boxes (626/929) behind a rotary bellhousing for the ratios, but the 12at boxes are definately stronger than the other derivations (not sure what how they were strengthened)
- And yes, the bellhousing's are also the casing for the front half.

Here's a pic of a 12aT box: http://images.trademe.co.nz/photoser...96174_full.jpg

Here's a really good resource on early mazda boxes (mainly rx and piston derivatives): http://ausrotary.dntinternet.com/for...pic.php?t=2735

Originally Posted by fredio54

thanks not-for-sale, i knew that the came in older stuff too, the older (pre 87?) ones with no ribs have weaker guts. as for the 12aT box, is that four speed? does it look like the one in the foreground, but without the extra section between the main ribbed part, and the tail shaft part? if so, its what the one in the foreground is derived from. do the early housings really fit on? it seems unlikely because the early ones "bell housing" is also the main casing front half. whereas the R type boxs have a proper bell housing. got any photos? if the 12aT box is similar in appearance to the box in the background, then i cant see how it would be any stronger. all the na rotas, utes, vans, mx5s etc used the same box with different bell/front halves, different rear extensions, and different ratios. only the late model 6 speed mx5 box is different to the rest(excluding those early R type 4 speeds.) cheers for commenting.

fred.

[fredio54]

great link, so i guess we are talking about the smooth case, and rx-4 box, only its not an rx4 box because those have 4 gears, no extra middle bit and different bolt pattern on the tail shaft ext to their descendents. i like the bit where it says "only give trouble on extreme hp cars" :-) suits me!!

[sry_not4sale]

Originally Posted by fredio54

great link, so i guess we are talking about the smooth case, and rx-4 box, only its not an rx4 box because those have 4 gears, no extra middle bit and different bolt pattern on the tail shaft ext to their descendents. i like the bit where it says "only give trouble on extreme hp cars" :-) suits me!!

Yes the box at the rear is a "smooth case" type box, no idea about the front box - do you think its a rx-4 based box like most modern rx boxes?

I have a RWD 929/Cosmo MA 5-speed, FE 5-speed and 12a-T 5-speed at my lockup. When I get a chance I will try get some pictures of them for ya. I have a workshop manual too so can give exact ratios on an 929 FE box if anyone needs them.

[fredio54]

isnt that 929 from the "weak" generation pre '87? (probably how the 12aT box got dubbed strong)

i believe it is derived from that early rx4 box, however if the rx4 box has 5speeds, then it isnt the first in the line. there is one with 4 speeds that has a missing section, but still has the removable sump that was first. my (good) box is pretty much the same as the late boosted rx7 boxs, upto 6, and maybe 7. the bell housing, rear end, and ratios are different.

from your link i learned about the "twisted type" boxs, the one pictured is twisted!! the other bellhousing i have is from a van, and is different, it is a straight type!! glad i got a set!! i think my spare bellhousing does suit the rx7 late boxs, i think they are mostly straight, but i could be wrong.

i'll post a pic when i borrow a cam.

fred.

[sry_not4sale]

Originally Posted by fredio54

isnt that 929 from the "weak" generation pre '87? (probably how the 12aT box got dubbed strong)

it is, I plan to run a 12a-T box when I convert my 929 to FE3 power. We will see how it fares, otherwise I may go the same route as you - especially if there are FE bellhousing that fit late model Rx-7 boxes!

[carcenomy]

Isn't the 929 a reasonably bigger shell than a 626? A 929 might almost be nicer with something like a KLZE in it.

[sry_not4sale]

Originally Posted by carcenomy

Isn't the 929 a reasonably bigger shell than a 626? A 929 might almost be nicer with something like a KLZE in it.

Check the pic of the cosmo in my sig, a 929 is not much different (only cosmetic changes). They are not too beefy, only 1250kgs with petrol/spares. I think you might be thinking of a HC 929 (the model after with the v6)

[fredio54]

there are, there are, regularly visit your pickapart down there, and look under the larger mazda vans. might pay to research shifter locations vs flat or twisted. theres also the b2600 box, dont know if thats flat or twisted, but i suspect twisted.