A different Speedometer gear question?
 

I’m fiddling with rear end ratios and it would be nice to keep a speedometer that would be reasonably accurate if possible.

Using a Quaife wide ration transmission and will be swapping between 4.778 and 3.909 rear end ratios for different disciplines of competition.

Typical speedo gears I know can be found with tooth counts between 17 and 23 teeth. A 21 tooth works ok with a 3.909 but I think it would take a 25 tooth that doesn’t exist to work with the 4.778.

Wondering if there is different drive gears inside the transmission that would fit to make it work. Stock Miata drive gear inside the transmission is M503-17-341A, it has 6 teeth. I have a 1984 B2000 transmission apart and the drive gear in it fits the Miata and it has 7 teeth and basically the same dimensions but the helix angle on the teeth goes the opposite direction.

By my calculations if I could find a part number for a 7 tooth drive gear with the correct helix direction I could get reasonable speed readout with either a 4.778 or a 3.909 rear end on the stock speedometer by swapping between an 18tooth speedo gear for the 3.909 and a 22 tooth with the 4.778.

It may be a stretch but does anybody know a part number for a 7 tooth speedo drive gear that would fit in a Miata transmission and have the helix direction correct? Late 80’s RX7’s use some different part numbers even have a different one between turbo and non-turbo for that part while but the parts books don’t list tooth count or helix direction so I have no Idea if they would work without buying a bunch of different ones.

Use a gear for 3.9 and slow it down electronically when using the 4.77, bluntly assuming NB stuff :D

NA mechanical speedo.

Use math or GPS to figure out your actual speeds.

Email RevLimiter

Get a custom gauge, instead of MPH/kph, get one that's for 3.909/4.778

Id like the convenience of the nice analog needle gage in my stock gage cluster.

If I'm not mistaken, what Curly is suggesting is instead of calibrating the needle to point to the correct number on the existing gauge face, just get a new face for the existing gauge that is calibrated to the needle. You'd still have an analog gauge.
Have it made with two sets of markings, and instead of those markings being MPH/KPM it's for your two different rear end gear setups.

This was going to be my route when if i ever get my 3.3 gear.

I'm sure it won't be SPOT on, but it will get me pretty dang close.

I'd just use GPS to calculate and note that when the speedo is in the X'o-clock position i'm doing Y speed. Do that for as many different speeds as possible. Then have him print the speeds in those locations.

30 minutes to swap out gauge faces. Even quicker than changing a speedo gear and less messy.

I was going to suggest the same thing, you could probably change an instrument cluster faster than the speedo gear. Just have two, with one being an offset speedo.

The mileage and trip counter would be wrong, though.

If he's going through the trouble of changing the rear end for different applications, a cluster should be easy.

Maybe make some type of quick connect plug ends for it and a snap in style system made out of something a little more robust than the OEM plastic.

the speedo gear swaps real easy way easer than the gage cluster like less than a minute to change. It takes about an hour to change the rear diff carrier assembly.

Interesting it looks like all the rx7 stuff has left hand helix as well and the Miata is right hand. speedo would go backwards. I dont know how to determine which models can interchange parts.

86-92 RX7 convertable vs. 4:30 miata. note the teath slant the opposite direction.

Doesn't some kind of electronic box exist where you can just tell it to input one signal, modify it, and output another? I swear I've seen someone reference one somewhere. That would make things easy.

That doesn't work with mechanical speedometers.

That gear is just pressed on and plastic. Try and find some hobby gear or something that will press on that shaft that works for you.

I think I have it figured out if in fact the M501-17-341 is a 7t drive gear Im looking for. Its a good part number on Mazdamotorsports.

driven gears sleve housing
17T M501-17-441 1669-17-442B 89 B2000
18T M508-17-441 1011-17-442A 86 929
19T M502-17-441 1011-17-442A 86 929
20T M503-17-441 1011-17-442A 929
21T M504-17-441 1011-17-442A E2000
22T M510-17-441 1669-17-442B NA miata with 4:10
23T 1472-17-441A 1669-17-442B 90-92 NA miata with 4:30


Drive Gears
6T M503-17-341A NA-NB Miata 5 or 6 speed
7T? M501-17-341A 1988 Mazda E2000 with 4.778

swapping to a 7T drive gear in the transmission would make it so I could get what I need with a quick dreven gear swap.

I have always admired intelligent people who are able to offer practical solutions.
Props.

The following post is theory, but its something I've considered:

1. Convert to NB electronic sender
2. Buy YellowBox
3. ???
4. Profit

The yellow box should allow you to correct for the ratio changes. I believe the NA still has an electric pulse generator thing on the end of the cable in the back of the cluster so its possible you could use the yellow box to hijack that signal and do the correction rather than moving to the NB sender. Food for thought anyway.

Profit?

Seems way more expensive and time consuming than a $13 gear that takes less than a minute to swap out with one tiny bolt while the rear carrier gets swaped.

Sorry, Its from a cartoon and I watch too much TV.
True. I figured it might be another avenue to explore, depending on how things turn out. Its something I stumbled across while trying to not buy the $120 sender for my 3.63 diff.

Does the NA mechanical spedometer read positive speed in reverse?

Wondering if I can go to gears that spin it the opposite direction and have it work. It seems to be easyer to find those parts.

Just did a test for you since I'm sitting in a 94 na8. They do not register speed in reverse.

Thanks. I wasn't sure and my car is apart right now. that narrows the potential parts list.

I wonder if this is something that could be created and 3d printed. Not sure how well the plastic from 3d printing would hold up, but could be a possible option.

I have several 3d plastic printers at work. I've considered it.

My research seems to indicate that M501-17-341A is the 7 tooth version of the M503-17-341A 6tooth drive gear that is use in the Miata. It is pared on an automatic 929 that also uses the same 20T drive gear M503-17-441 driven gear that I have been using with my 3.636 rear end so I think it will mesh with Miata compatible speedo gears and I’m hoping it is in fact 7 tooth. It is also used on a Mazda E2000 which is sort of a small delivery truck/van only sold in Asia where it gets pared with the 4.778 ring and pinion.

7 tooth drive gear. M501-17-341A
22 tooth driven gear M510-17-441A when using 4.778
18 tooth driven gear 3902-17-441A when using 3.909

I hope that’s what works. The M501-17-341A is on backorder however might take a while to get from Japan and of the three 18 tooth driven gear part numbers I found that is the only one that worked with Mazda motorsports parts list I hope it has the correct direction it is found on some b series trucks that use M part number drive gears. I’m hoping the M in the part number means the Miata direction but I am not sure of that even. its not too terribly expensive to find out the parts run between $13-$15. Way cheaper than gage faces or added electronics.

I like my indiglow gage faces with shiny polished button covers and orange painted needle backs.

Because its still a $129 "solution" (unless you bought just the speedo)
Because you would need 2 clusters and 2 sets of gauge faces, one to match each diff you plan to run
Because it can't be changed as easily as a sender...

No, you do not have to change anything.
See how it says Km/h and MPH on the dial?
It will say 3.909 and 4.778 instead.
Simple. Clean. Elegant. Clever.

NO ONE (but godless commie) IS LISTENING TO ME

Holiday party and I'm drunkposting on my phone. :dealwithit:

THANK YOU FOR EXPLAINING IT IN A WAY US THICK HEADED CAVEMEN CAN UNDERSTAND

I'm guessing Rev already has the scaling for the various popular gear ratios? Its not something I've ever looked into as I'm happy with the stock gauge faces. It IS a simple and elegant solution.

Sorry Bob, I'll get the fuck out of your thread now. Thanks again for loaning Gesso the bolt so he could limp the Exocet home. :bowdown:

I read your o.g. post and thought to myself "damn. that is an elegant solution"

Then lol'd at everyone still stumbling over senders and swapping things.

Well played Curly! :rofl:

Dakota Digital I believe makes boxes that can do exactly what you want. Not exactly cheap solution.

ECD-100

Pretty sure Rev keeps completely stock locations for MPH and kph, so you would have to tell him what indicated speeds equals what actual speeds using one of many free GPS apps.

Cheap NB speed sensor, electronically-controlled motor hooked to speedo cable, Ardunio and some custom software that reads the NB speed and drives the speedo cable at the right speed?

--Ian

Cause that's easier than a gauge face.

But nowhere close to Rube Goldberg-y enough!

--Ian

Did some research because this is interesting and found this document if it helps at all.

http://fm.no-ip.com/Car/sgpartno.txt

A bit helpful thanks.

I discovered an error in my calculation. I laid out my xl spread sheet then typed in the formula wrong and got multiply and divide swapped doh. Actually need a 5 tooth drive gear not a 7. But I think the 929/E2000 one M501-17-341A may in fact be the 5 tooth I need anyway that can swap with the Miata M503-17-341A 6 tooth and still will give me what I need I’m hoping.

Unfortunately that listing doesn't give the tooth counts for everything. Another piece of information that is always missing is whether the helix angle is to the right or left on any of them. Everything I have found is incomplete so it's still a crap shoot, order parts and see if they will work together or if they are what you think they are.

Has anyone used one of the NB speed sensors? I assume it just outputs a square wave? If so it looks like a way better solution than a hall effect sensor/magnet for my data system.

Nope, the speed sensor outputs a nasty sawtooth signal.
See more in this thread.

Wow, that's quite the signal. Thanks for the information (and the lead on a pretty nice looking little 'scope). Looks like a place to start at least, just a little conditioning to do.

Just ran across this thread.

For the record, doing a rescaled speedo is pretty easy. I get a table of values from the customer that they generated, either by math or with a GPS. Then I re-scale the speedo. Since there's so many different tire/diff combos out there, I don't really have a pre-made selection of different speed scales saved. I always ask for a speed table.

I've done this for tachs as well. Ford V8 guys like to tweak the dashpot on the tach to give it a 7000 rpm end point. I've done a half dozen or so sets of this order.

And I don't do indiglo gauges. sorry. heh

And the thing that curly posted Lonnnnnng ago in the thread, would work pretty well. I could do a dual-scale gauge face. That would be pretty sweet actually. You can swap diffs as often as you like and leave the stock gear inside the transmission. When you swapped, one scale would become accurate and the other would no longer be used.

It better have Hello Kitty on it or Im not going to use it.

As long as there is something immasculating and colorful I'm in.

update. Nothing I found was working from the OEM mazda parts catalogs. but look what I found. looks like they have aftermarket mechanical speedo drive gears for 3.909 21T which mazda currently lists as no longer available and a 24 or 25 tooth for a 4.778

Maruha Driven Gear Set for NA | Chikara Motorsports Ltd.Chikara Motorsports Ltd.

A question from the less than perfectly informed, could it be possible to merge a NB sensor with their NA stuff to make the 4.778 work in a NB senor?
4.778 is much closer to my 4.875 fg than my current 4.1 sensor gear :)

I wounder if it would be possible to machine out the center shaft on a mechanical gear and somehow get just the plastic part to fit on the NB sensor shaft somehow.

I think the Chikara one is 24t based on trying to count teeth in fuzzy pictures. Its probably closer for a 4.6 than a 4.8. but better than a 22t or a 23t. a 25t would be better.

Found this on a related google image search.

https://www.miataturbo.net/attachmen...ine=1422387964

Needs to be a Hello Kitty napkin.

Here. I had some free time and did a mockup of the dual scale gauge.

https://www.miataturbo.net/attachmen...ine=1422419709

You would LITERALLY not need anything else. Just pop a gauge in the cluster and let the stock speedo gear live a happy life in the transmission housing. Swap diffs at your leisure and just pay attention to the correct side of the gauge.

Seriously, I have 5$ for a fund for that.

tears. lol lol lol

I don't actually want to take it live yet. Need to see if people are serious about it lol. And I need a better title and description

Dang, that's an awesome gauge. But I'll stick with the plan at hand.

Absolutely take it live. I will contribute. Hell I will even take one of the production run for my beer fridge.

Alright, I need to get some stuff together. Rev, would it be the full 289 for custom gauges?

For just the speedo, I'd be happy to do it for $30. That's my rate for singles. The design already exists (and was posted) and that dual speed scale SHOULD be accurate. It's just a mathematic scale though and not based on any GPS readings.

To do a whole set, I'd ask $169. I'd need to expand the design to the other four gauges. A set is $129 and I charge $40 per hour for design work. I don't see it taking more than an hour.

Custom gauges are always charged based on the time it takes to do. The $289 price on my site is just an estimate at 4 hours of labor and the base gauge fee.

Sorry that this post is so price and marketing heavy. If any of the staff is unhappy, please edit. Don't mean to anger anyone. I'm just answering questions.

Scratch that, kickstarter takes too long. This is live now:

Pony Gauges For Bundy by Aidan Daly-Jensen - GoFundMe