Miata gear swap

[infernosg]

I've read several threads on the evil forum and everything Mazdatrix has to say on the matter and I'm still a little confused how to proceed. I've gotten this far with both transmissions:





Everything I've read just says "swap the guts and modify the input shaft," which isn't overly helpful. Has anyone here done this swap/modification? What I'm trying to figure out:

1. Do I need to swap output shafts to keep the harmonic balancer?
2. Do I need to swap the 5th/reverse housing and/or bearing plate?
3. Is there an easier way to remove the input shaft than what's outlined in the FSM?

[infernosg]

I guess no one on these forums has done this swap?

I spoke with Mazdatrix about this and they basically answered all my questions:

1. They don't swap the mainshaft to retain the harmonic balancer and they haven't noticed any negative effects.

2. They swap the 5th/reverse housings (called the intermediate housing by Mazda). The exterior designs are similar but there are quite a few differences internally. To remove this housing from the RX-7 assembly you have to remove the harmonic balancer, which requires removing a ~2.5" nut with a special tool. I forgot to ask about the bearing plate but I assume that's kept from the Miata. They should be essentially the same anyway.

3. The only way to remove the input shaft is to disassembly the gear set down to the mainshaft. This involves disassembling the 5th/reverse gear set and separating the main and counter shafts from the bearing plate. There are several bearings/large nuts that need to be removed that require special tools from Mazda.

I'm going to attempt to tackle this myself and turn this into a "how-to" thread as I wasn't able to find any others out there. The hardest parts are going to be removing the bearings and large nuts without SST's.

[RETed]

Is there a reason why you need to swap out the input and output shafts?
Just eyeballing the pics, it looks like the both are close - the output shafts look pretty damn close to me.
Is it the spline count?
Might be cheaper to go with a custom driveshaft?
If it's input spline count, then go with a "custom" clutch set-up?

As for special tools...
For the nuts, you can cut a socket in half and weld them back up on a length of pipe.
For a super long puller, someone had the ingenius idea of using a regular puller but using special cut long length "arms" to extend the pullers reach - kinda hard to explain, but if you seen the pics, you'd understand...

EDIT: Courtesy of FC Zach...
http://www.rotarycarclub.com/rotary_...ghlight=puller


-Ted

[infernosg]

Originally Posted by RETed

Is there a reason why you need to swap out the input and output shafts?
Just eyeballing the pics, it looks like the both are close - the output shafts look pretty damn close to me.
Is it the spline count?
Might be cheaper to go with a custom driveshaft?
If it's input spline count, then go with a "custom" clutch set-up?

As for special tools...
For the nuts, you can cut a socket in half and weld them back up on a length of pipe.
For a super long puller, someone had the ingenius idea of using a regular puller but using special cut long length "arms" to extend the pullers reach - kinda hard to explain, but if you seen the pics, you'd understand...

EDIT: Courtesy of FC Zach...
http://www.rotarycarclub.com/rotary_...ghlight=puller


-Ted

The "output" shaft (Mazda calls it the "main" shaft) doesn't need to be swapped as I've confirmed with Mazdatrix. I was asking because the RX-7 main shaft has the provisions for the large harmonic balancer and the Miata one does not. Apparently it's not needed. The input shaft, which is a separate piece on the front of the main shaft doesn't need to be swapped but the Miata one needs to be removed and modified. It's hard to tell from the photographs above but it's actually about 0.5" longer than the RX-7 one so it needs to be cut down to avoid binding the splines with the pilot bearing. It's unfortunate you have to disassemble the entire 5th/reverse gear assembly to remove the input shaft.

The make-shift tools are a neat idea. I'm pretty sure I could make up some super-long sockets and a bearing puller like FC Zach. I'm curious how he removed the even bigger nut on the output shaft behind the harmonic balancer though. I measured it with some calipers last night and it's something like ~2.46" or ~62.5 mm.

[targarx7]

Transmission updates?

[infernosg]

Originally Posted by targarx7

Transmission updates?

I've got the Miata transmission completely torn down and the input shaft removed. I now need to find a machinist willing to modify it for me.

I ended up borrowing the tools FC Zach created but I needed to make longer arms for the modified puller. I now plan on completely diassembling everything so I can inspect each part individually. My build thread has all the current information. I plan on taking better pictures during reassembly that I'll use in reverse order for the "how-to." Overall the process isn't too difficult if you have the correct tools and patience.