Speedometer Gear/Transmission Removal Questions

[infernosg]

I just finished the 4.30:1/Miata Torsen rear end swap. I made it all the way to the end before buggering something up. I didn't realize the GXL and GTUs speedometer driver gears were different diameters (GTUs is larger) and I smashed the speedometer driven gear in the transmission by forcing the install of the GTUs gear. The car drives just fine, but I no longer have a working speedometer.

I've done some searching/reading and it looks like the driver gear housing (the part that bolts to the transmission) is slightly different between the GXL and GTUs. It looks likw they are offset just enough to account for the difference in diameter as it appears all 2nd Gen RX-7's use the same driven gear in the transmission. When I received my GTUs driver gear I received just that, the gear, and therefore reused my GXL housing. I guess the others who've performed this swap changed over the driver gear and housing from the GTUs as I haven't read of this ever happening to anyone. Does this seem right?

So now I am in search of a GTUs driver gear housing and a new driven gear, but I have been unable to locate any part numbers whatsoever. The FSM lists them as "speedometer driver gear" and speedometer driven gear, there is no mention of the housing separately. Does anyone know these part numbers?

To replace the driven gear, it looks like, at the very least, the transmission extension housing, needs to be removed. I assume this means the entire transmission needs to come out, or is there a way to keep it bolted in while just removing the extension housing? If I do have to remove the entire transmission is there anything I should be aware of before I try?

Sorry for the long posts - I like to try to include as much information of my issues as possible.

[NoDOHC]

You could reuse the GXL gear (it will give you an idea of your speed, just read a little high)

I see two gear part numbers:
1011-17-441A (21 teeth) (hard susp non-turbo only) I read as GTUs
1669-17-441A (20 teeth) (norm susp non-turbo and turbo)

If you think about it, this makes sense, as the 20 teeth would cause the speedometer cable to rotate more per revolution than the 21 teeth would. This is a 5% increase in indicated speed (approximately the same as 4.30 to 4.10 ratio change).

Thus the 20-tooth one goes with the 4:10 ratio and the 21 tooth one goes with the 4:30 ratio.

The difference appears to be in the drive gear sleeve. (one moves the gear further away from the drive gear. Two are listed:
1011-17-442A (hard susp non-turbo only) I read as GTUs.
1669-17-442B (listed for non-turbo and turbo)

The rear housing is the same, as is the gear on the output shaft of the transmission (single part number for non-turbo: 1281-17-341)

I hope this helps!

[infernosg]

You could reuse the GXL gear (it will give you an idea of your speed, just read a little high)

I see two gear part numbers:
1011-17-441A (21 teeth) (hard susp non-turbo only) I read as GTUs
1669-17-441A (20 teeth) (norm susp non-turbo and turbo)

If you think about it, this makes sense, as the 20 teeth would cause the speedometer cable to rotate more per revolution than the 21 teeth would. This is a 5% increase in indicated speed (approximately the same as 4.30 to 4.10 ratio change).

Thus the 20-tooth one goes with the 4:10 ratio and the 21 tooth one goes with the 4:30 ratio.

The difference appears to be in the drive gear sleeve. (one moves the gear further away from the drive gear. Two are listed:
1011-17-442A (hard susp non-turbo only) I read as GTUs.
1669-17-442B (listed for non-turbo and turbo)

The rear housing is the same, as is the gear on the output shaft of the transmission (single part number for non-turbo: 1281-17-341)

I hope this helps!
The bolded part numbers were very helpful - thanks! I already have the 21-tooth drive gear - it's stuffing it in there with the GXL sleeve (what I was calling a "housing") that destroyed the driven gear. Do you have a parts catalogue or something? I wasn't able to find those P/N's anywhere.

On another note I've found 6 very small steel balls (like in ball bearings) rolling around the garage. One, I'm fairly certain fell out when I removed the speedometer gear sleeve with the broken driven gear as there should be one underneath it according to the FSM. I have no recollection of the other 5 as I found them much later, after the sleeve was reinserted. I don't imagine these things can just "fall" out of the transmission so I have no idea where they might have come from (where else on the car are these used?). I'm hoping from something completely unrelated like my creeper's castors or something because the car appears to drive and shift just fine.

[NoDOHC]

I don't know of any ball bearings in the speedo cable, It has probably been 6-8 years since I replaced a speedo cable in an RX7, so I am not the best source for that.

I found the parts in the Mazda parts catalog. This is available online.

I found it using a Google search.

RX7 Technical Data (http://www.re4life.com/Tech_Data/TechData_EN.htm#1986-88)

[infernosg]

I don't know of any ball bearings in the speedo cable, It has probably been 6-8 years since I replaced a speedo cable in an RX7, so I am not the best source for that.

I found the parts in the Mazda parts catalog. This is available online.

I found it using a Google search.

RX7 Technical Data (http://www.re4life.com/Tech_Data/TechData_EN.htm#1986-88)
Yep, I ended up searching and found that as well - downloaded!

It doesn't seem like they're the "balls" from a ball-bearing. Looking at the FSM there's a picture in the transmission section that shows a "steel ball" sitting in a tiny recess beneath the speedometer drive gear on the output shaft. I'm not really sure what purpose it serves but it would appear if the gear broken there would be nothing retaining the ball and it would fall out.

Either way, I picked up a spare transmission to play with/rebuild with Miata gears at some point so I'll be in there and know where all this crap goes.