Miata Turbo Forum - Boost cars, acquire cats. - 6 speed conversion

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- - 6 speed conversion - speedo drive etc (https://www.miataturbo.net/suspension-brakes-drivetrain-49/6-speed-conversion-speedo-drive-etc-69081/)

6 speed conversion - speedo drive etc

Im on the verge of installing the new race motor and 6 speed gearbox after removing the old turbo engine and 5 speed setup from the car on the weekend.

Only now I can see the differences between the two gearboxes. The speedo drive on the 6 speed appears to be electronic and the many wires coming out of the 6 speed don't appear to be the same as the 5 speed.

I would rather retain the NA's speedo if possible and the reverse lights etc are required as it is a road based track day car (at this stage...).....

Anyone provide any pointers or tips as to what is what....?

I will be going through this in a few weeks and would like to know the same..

Can you screw in the NA speedo sensor into the 6 speed box? as well as the reverse light switch?

Quote:

Originally Posted by RotorNutFD3S (Post 485514)

I used an M502-17-441 gear as I read that the M503 is good for larger wheels, such as 17". But it probably doesn't make a huge difference overall.

This is what I used to build the gear setup:

1011-17-442A - This is the sleeve/housing that will position the gear in the proper location to engage the gear within the transmission. If the sleeve that comes in a 5-speed transmission is used, the smaller 6-speed gear will be free-floating and will not engage. Thus, no readings.
M502-17-441 - This is the actual gear.
9922-20-214 - Spring Pin for holding the gear in the sleeve.
9958-60-8166 - Oil Seal for inside the sleeve.
1011-17-443 - O-Ring for the outside of the sleeve.

Hustler, I think the 1st part number listed will get you what you need to finish the project. I recommend at least getting the spring pin as well because knocking the old one out is a royal pain.

I have this in my car, it will be ~6-7 fast compared to actual speed.

Now I need to do the homework and get a 4.10 gear set.

I just unscrewed the 6 speed electronic gear and put in my 5 speed one, seems to work fine.

Oh shit, I was thinking 6/3.63. Sorry, disregard. Speed gears go wtih the R&P solely.

Quote:

Originally Posted by ssmith

I just unscrewed the 6 speed electronic gear and put in my 5 speed one, seems to work fine.

Yup, that's what you do, move the NA speed sensor over to the 6-speed if you're not changing out the R&P.

For the reverse and neutral switches you will want to use the switches already in the 6-speed as the thread pitch of the 5-speed switches make them incompatible. When I did this swap I was able to just plug the harness for the neutral switch right in. For the reverse switch, I had to cut off the NB harness end and add the bullet connectors from my NA switch. Everything operated properly.

Wrote this up when I did the swap, should clear up some questions.

I swapped my 6 speed transmission into my NA Miata yesterday and found there is surprisingly little information on how to do the swap. It turned out to be pretty straightforward, but there were a couple little issues I had to address that I could not find documented online so I figured I would share.

Benefits: The 6 speed offers significantly closer gear ratios, a considerably stronger transmission, and in my opinion smoother shifting. After the swap the car is noticibly peppier and undoubtedly a good bit quicker. I feel like this would be an excellent modification to a naturally aspirated car, even with 4.10 or 4.30 gears.

The first issue to address comes from the starter. 2 of the 3 starter bolts line up perfectly, the upper outside bolt on the transmission is lower and extended farther away from the transmission. You can see this when you line up the 6 speed starter with the 5 speed transmission.

https://www.miataturbo.net/attachmen...ine=1351022528

https://www.miataturbo.net/attachmen...ine=1351022528

You will be able to use the 5 speed starter on the 6 speed transmission using 2 of the 3 bolts. However, I feel like it's a better option to use a 6 speed starter and modify the plate between the motor and transmission. I cut the plate so the 3rd bolt would fit

https://www.miataturbo.net/attachmen...ine=1351022528

https://www.miataturbo.net/attachmen...ine=1351022528

The next issue to address is the reverse light wiring since the transmissions use different connectors. These do not have polarity and simply close a circuit when the reverse gear is engaged.

These 5 speed connectors need to be clipped off to replace the 6 speed connectors:

https://www.miataturbo.net/attachmen...ine=1351022528

This 6 speed single connector needs to be clipped off and you need to add the 5 speed connectors to each of the 2 wires:

https://www.miataturbo.net/attachmen...ine=1351022528

That's the extent of the modification you need. There are 2 white clips that are the same on both transmissions. The speedometer sensor on the 5 speed is mechanical and the 6 speed is digital, but the 5 speed sensor will swap right into place with no issues and a correct speedometer.

Wow, in my wildest dreams I couldn't have imagined a better write up!!!

After trying to figure out hustlers post and my stomach sinking (Crap, this is way more complicated than i thought)....this was a great way to finish off :)

Great thank you!

Given stock ratios on everything, when cruising at say 70mph what are the revs in top gear for both trans?

Quote:

Originally Posted by Arsenal (Post 942586)

Given stock ratios on everything, when cruising at say 70mph what are the revs in top gear for both trans?

Flyin' Miata : Technical info : Gearing calculator

--Ian

I know this thread is a little old but...

I just got my 6 speed today and the wires were torn out of the speed sensor :facepalm: Any chance one of you guys who did this swap has the 6 speed sensor still sitting in the tool box? I'll probably post a WTB thread tonight :(

Quote:

Originally Posted by EO2K (Post 998862)

You have a pm. I still have an old one.

Thanks Lars! PMd you back, please let me know if I insulted you with my offer. :party:

Quote:

Originally Posted by EO2K (Post 998862)

I've got one as well. Let me know if your other offer falls through.

I probably have a spare NB speed sensor out of a 6-speed as well...

Thanks guys :party: Lars hooked me up but I'll probably send you a PM as well (his is missing the connector, but at least it has wires!) because I kinda want to see how close I can get the speedo.

Is there something wrong with just replacing the trans and car connector with something that works together, like a weatherpack or similar?

Nothing at all wrong with that really, except that I have an NB. The 6 speed sender should be Plug and Play with my factory harness. No cutting required (from what I've read anyway.) Once I add weatherpack connectors, pins, seals and crimp tool, I'm better off just buying another used 6 speed sender. Plus it gives me the option to find the other gear to try to match my tire/rim/diff ratio.

Valid point. I have a 6spd here to swap this summer is why I asked. I already have the weather pack stuff from other little projects for the car. That connector got mangled at he yard and was just going to redo both ends of the connector. '99 NB w/ 5sp to 6sp conversion should be pretty easy considering all the drive train is out of the car.