Crit

iTrader: (6)

A buddy of mine jammed his SA in gear at Road Atlanta, and I've always heard they're weaker than the FB tranny. I've been told that the shifter block inside the shifter tower is pinned to the selector rod in the SA, whereas the FB has a drilled, tapped, and counterbored hole at the end of the rod. This means that a bigger shoulder screw can be used to carry that shear, as it'll slip through the side of the shifter block and pilot into the counterbore on the rod.

That's what I THOUGHT, anyway. I just pulled the SA tranny out of my REPU because it's just got to go. No 5th, 4th grinds, and pops out of 1st. When I pulled the tailshaft so I could move it to my FB gearbox, I found a counterbored and tapped selector rod. The P.O. knew a lot of rotary stuff, so I figured he made the same mod by doing the extra machining. Out of curiosity, I cracked open a spare SA box that was due to go in the RX-2, and it's got a hex head on the side of the shifter box, which tells me it has a screw in there rather than a pin.

Can someone tell me what the shortcoming is with the SA, and basically tell me if there's more machining I need to do in order to fit an SA tailshaft onto my FB gearbox without asking for trouble?

BTW, I'm not looking to shorten an FB tailshaft (I've already got one of those) because the tall REPU shifter will only mate with an SA tailshaft, so I'm tied to the SA shifter. As long as I'm in here, though, I'd like to avoid any obvious problems.

Thanks guys,
Crit


--- UPDATE ---

I just got off the phone with the previous owner, and didn't learn anything new about the shifter end and the elusive pin I've heard about. I DID, however, discover what his mod to the gearbox was.

In the SA gearbox, the heads of the 3 shift rails are screwed onto the shifter fork rods. They had a bad habit, back in the day, of backing out and leaving you in neutral. Worse yet, they could get jammed a little bit forward or rearward on the rod, which could jam you in gear, but with all the heads lined up as if you're in neutral. You could then select another gear and engage that at the same time. As soon as you clutch out, KABOOM - you've returned all your gear oil to mother earth.

His fix for this was to add longer screws and jam nuts to the heads on the selector fork rods, and make sure that they're damn good and tight before closing up the gearbox. What I don't know, though, is if these heads are still attached the same way on the FB, or if they're maybe cast onto the selector fork rods the same way the rod running back to the shifter is.

Crit

iTrader: (6)

****. I'm not gonna be able to do what I want. For those that aren't intimately familiar with SA vs. FB trannies, check the following link.

http://www.geocities.com/izzmus/trans/trans.html

And the speedo gear chart that's referenced has now moved to HERE.

Basically, the selector rod has a different offset and elevation on SA vs. FB. If you want to just swap tailshafts, you have to replace the heads on all three selector forks (I was wondering why mine wouldn't fit). Peejay has stated that there are later SA boxes that will work, but I've got the old one.

The REPU is just gonna have to get an SA tranny, and the FB gearboxes I have will continue to rot in the garage.

speedturn

iTrader: (1)

Instead of putting in longer screws and nuts, one of my road race boxes had the heads of the screws drilled, and then safety wire installed to ensure that a screw would not loosen.

Last year, I tried putting an FB tailshaft housing on a good SA box I had. (My street car is an FB chassis.) It was not a simple, straightforward swap. The 3 shift heads on the FB trannys use roll pins to secure them. The 3 shift heads on the FB tranny are orientated slightly different than the SA tranny; they are clocked slightly different on the shift rods. I did this last year, so my memory is not perfect, but I had to do some match drilling of one of the little shift heads to the shift rod. It was hard to get the little shift head to hold still on the shaft while I was drilling on it. It did work out, but it was not perfect. I may have even had to change out one of the shift rods to make things work out; can't remember for sure.

I would not try to do that again. A year ago, I would have traded you my good SA box for a good FB box.

I have been inside several of both boxes, and the basic gears and shafts seem equally strong to me. There were several small improvments in the shift linkage and the synchros over the years in the gear boxes.

For many years, I was running $100 or $200 junk yard trannys in my street FB. They would last about a year or so, then the bearings would start to whine and the synchs would get worse. After several tranny changes, I finally got tired of changing them and built a very nice, 100% new bearings and new synchs, new shift forks, transmission in my car now.

If your chassis needs an SA box, then I would have an SA box properly built for the car. A decent shop like ISC Racing charged $450 labor + parts for a rebuild. A nicely rebuilt tranny, which will take several hundred dollars worth of parts plus several hours worth of labor, will go for around $900. Rebuilt Miata gear boxes for Spec Miata road racers are also going for around $900. The Miata boxes are very similar to an FB gear box.

Crit

iTrader: (6)

Hey Speedturn, dd you ever consider changing the shift fork rods out between the two trannies? I may have a line on a good SA box, but I still may need to do the tailshaft swap as a backup. I'm not sure if I'd have to swap shift forks out or not - hopefully just the rods and heads, which would work with an SA tailshaft.

j9fd3s

iTrader: (3)

i think peejay made a thread, but basically there are TWO SA boxes.

the late production SA boxes switched over the FB roll pin/shift finger setup, so you can easily swap the FB/SA tail housing.

the early SA box, like speedturn says is different.

other than that there are not a lot of differences between SA/FB, the bearings were updated, but in 1987/89, etc etc

i also agree with mr turn, these use junkyard boxes are pretty crap, and its not too bad to rebuild em. kinda like the engines, if everything is good and in spec, it lasts for quite a long time*

*synchro life depends on the driver(s), especially racing

Crit

iTrader: (6)

So where does one get a set of bearings and synchros with which to rebuild a gearbox?

t_g_farrell

iTrader: (1)

All the bearings and seals look to be available from rockauto. The synchros and gears would probably be mazda items.

j9fd3s

iTrader: (3)

i haven't ordered any aftermarket stuff in this century... you use to be able to get a full bearing set aftermarket, but by the time you replace 2 of the bearings with updated mazda ones, its more work for no money savings...

in 87, mazda changed the center counter shaft bearing from a dual row ball to a roller. not sure what the other update is/was i'd have to look

Rx Seven

iTrader: (12)

I believe I have an example of an early 79' SA Transmission and a late 80' SA Transmission. But I am only going off of the exterior and the fact that my SA is a late 80's model and the 79 SA I pulled the trans from was a pretty early vin. I have not opened these up.

My question is on my 80's trans (dirty trans in back of picture) there are a couple extra electrical connections that are not on the 79' trans (in front of picture with blue numbers)? If i use the 79 Trans will I experience any problems?

80's old school

iTrader: (7)

Circle on left is the top switch...opens contact when shifting into 4th gear. Circle on the right is the overdrive switch.... opens contact when shifting into 5th gear.

Used for emissions...I think it retards the timing of the trailing plugs when shifting into either 4th or 5th...

In other words..yes you can do without them.

80's old school

iTrader: (7)

BTW your 79 is prolly a non California emission tranny.

Crit

iTrader: (6)

If you notice, the late 80 trans also has 4 short screws that hold the shift tower onto the tailshaft. Most SA trannies have two long and two short screws, with two raised bosses on the tower for the long screws. If you want an SA tailshaft that'll bolt to an FB tranny, that tailshaft with 4 short screws is the one to look for.

rxtasy3

iTrader: (2)

the tranny with the blue writing is missing the far rearward switch(backup lights). don't really know what the other two switches do. never hooked them up.

Rx Seven

iTrader: (12)

Thank you everyone for all your the help, I just finished putting this in. I hope its a descent tranny but ill find out tomorrow. If not ill have to steal the tranny from my fb.

80's old school

iTrader: (7)

I am in the same shoes...I am about to drop an unknown 5 speed into my 4 speed car...

Jeff20B

iTrader: (13)

I put an unknown 5 speed SA trans into the GLC. It seemed to work out ok.

Crit

iTrader: (6)

Sorry to dig up an old thread, but it's on a related note. I've put a 4.63 rear end behind this 80 SA tranny and need to change the speedo gears. This is in the REPU, so the wheels are significantly taller, as well.

I searched quite a bit and found some good speedo gear info. The best reference seems to be HERE at the bottom of solomiata's page. Unfotunately, they make it very clear that FBs used a coarse drive gear and is therefore unsuitable for interchanging with all the other gears listed.

1.) Is there a similar reference somewhere regarding interchanging coarse-drive speedo gears?

2.) Can you swap a fine speedo drive gear onto an SA output shaft and make use of all these miata parts that are out there?

3.) If coarse drive gear assortments exist, does anyone have a list of coarse-drive cars and their speedo gear tooth-counts, or better yet, Mazda part numbers?

I'd love to swap just the speedo gear, but it looks like Mazda didn't make it quite that easy.

j9fd3s

iTrader: (3)

if there is another place they would be listed its here http://fm.no-ip.com/

having both miata and rx7 transmission parts in the garage, i don't see why you couldn't swap the gear on the output shaft...

Crit

iTrader: (6)

I'm just not sure it would interchange. I suspect it may, but was hoping someone would know. Can you slide a coarse drive gear off and slide a fine one on? Does anyone know what the tooth count on an 80 transmission is?