CAn I change only the final drive gears?

[fowljesse]

Let me know if this is right:
If I changed only the final drive gears, It would change the 1st gear slightly, making it taller, and would affect the others the same way, but exponentially slightly more.
Even if it would change all of the gears at the same rate, I want to do this. I have plenty of power down low to get a good launch in a gear somewhere between 1st, and second, and would love to get better gas mileage, but don't want to jump from the original 4th to a taller 5th. My 1st gear is kind of useless, anyway.
So, is there a slightly bigger ratio final drive available?

[Ryan]

exponentially slightly more.

Yes, you've got your theory right.

My car, at highway speeds (100kph)

revs ~3000 RPM
5th gear ratio 0.731:1
output on tranny will be ~2200 RPM
final drive is 4.105:1
Wheels will be doing ~530 RPM

Tires are 185/65/14's

65% of 185 is 120.25mm plus 14" (355.6mm) = 475.85mm radius

circumference formula... C = 2pi(r) = 2989.8mm

530 RPM @ 2990 per rev = 1 584 622 mm/minute

conversion aside, It comes to 95kph

Say I change my FD to... 3:1

731 rev @ 2990

2 185 690 mm/min
(x60/1 000 000)
= 131 kph

To go 95 kph with that FD, my engine speed would be...

1 583 333mm/min / 2990mm

plus tranny ratios = 2173 RPM



Yes, I like math, yes, I am a dork

where can you get one? Not sure. You'd need to change the entire FD. Spider gears and the main one. Find one that bolts onto G series with the same size/spline axles and you're golden. Try probetalk, 626.com....

Take a peek here

http://www.mx-3.com/phpBB3/viewtopic.php?f=30&t=65792" onclick="window.open(this.href);return false;

If you discover anything, be sure to post!

[wytbishop]

I wonder if you could put a MX-3 bell housing on a 626 tranny??? I think they have the taller final drive and generally better gear ratios. I'm sure you could. I've been doing some reading and I read about one dude who mixed and matched bellhousings and shafts.

I'll get back to you.

[fowljesse]

I'm glad you said "Yes" before all that math. I started hearing buzzes, and pops, and then felt like A giant Indian, and had the urge to throw a water fountain through a window, and run away.
Thanks for doing the research, Wytbishop. It would definitely drive me over the Cuckoo's nest.
Please let me know what you find!
By the way, I was hoping (and had a feeling) that someone who knows what "exponentially" means would answer! About 90% of the time I hear it used, the person doesn't know what it means. "You're slow. I'm exponentially faster."

[marcdh]

exponentially slightly more.

wasn't sure if you slipped that oxymoron in as a trick

In a simple life I would just like a 6th gear, but more realistically a much taller 5th gear would be nice.

[Mooneggs]

In a simple life I would just like a 6th gear, but more realistically a much taller 5th gear would be nice.

sigh a 6th gear would be amazing with a klze

I have the taller gear and I'm not happy LOL

[fowljesse]

I was trying to say that it would increase on an exponential curve, but on the lower end of the curve, because the rising rate doesn't have to be extreme. For instace, the final drive change could make the 1st gear 1% taller, 2nd 2.5%, 3rd 3.5%, 4th 6%, and 5th 9%.
That's nowhere near accurate, but I hope I'm illustrating it.. I'd have to draw a picture to explain, since that sems yo be the only side of my brain that works properly. The math side must have taken all the abuse.

[Nd4SpdSe]

I wonder if you could put a MX-3 bell housing on a 626 tranny??? I think they have the taller final drive and generally better gear ratios. I'm sure you could. I've been doing some reading and I read about one dude who mixed and matched bellhousings and shafts.

I'll get back to you.

Why would you need to change the bellhousings? The gearboxes themselves are swappable as well as the gearing inside.

Yes, the final drive changes the ratios of all the gear...if you know RWD cars, it would give you exactly the same results if you changed the "rear end" gear. Because of the FWD setup, that whole system is together in a "transaxle unit".

To swap the final drive, you need to change the pinion gear and the differential. The diff is easy, but I've been told that to take a gear of a shaft is a huge pain.

Probably what I would suggest which would be the easiest, get an Mx-6/626 tranny and swap the 5th gear from that of your Mx-3, that would give you the exact combo you're looking for and the 5th gear would be a super easy swap...Gears 1-4 themselves as far as I know are totally identical between Probe/Mx-3/626/Mx-6.

[fowljesse]

Good idea. Thanks
To the junkyard!

[wytbishop]

I wonder if you could put a MX-3 bell housing on a 626 tranny??? I think they have the taller final drive and generally better gear ratios. I'm sure you could. I've been doing some reading and I read about one dude who mixed and matched bellhousings and shafts.

I'll get back to you.

Why would you need to change the bellhousings? The gearboxes themselves are swappable as well as the gearing inside.

Yes, the final drive changes the ratios of all the gear...if you know RWD cars, it would give you exactly the same results if you changed the "rear end" gear. Because of the FWD setup, that whole system is together in a "transaxle unit".

To swap the final drive, you need to change the pinion gear and the differential. The diff is easy, but I've been told that to take a gear of a shaft is a huge pain.

Probably what I would suggest which would be the easiest, get an Mx-6/626 tranny and swap the 5th gear from that of your Mx-3, that would give you the exact combo you're looking for and the 5th gear would be a super easy swap...Gears 1-4 themselves as far as I know are totally identical between Probe/Mx-3/626/Mx-6.

That exact thing occurred to me as I was making dinner. Ahhh...der.

I don't think that they all have the same ratios 1 - 4 though...although I cannot confirm that.

I do think it would be relatively easy to change the final drive. I will be able to tell you exactly that...with pictures in a week or so. My Synchro and Bearing kit arrived today and I hope to do the rebuild this weekend at which point I will have the final drive gear in my hand.

[Nd4SpdSe]

http://homepage.ntlworld.com/mx6-uk/mai ... #transspec" onclick="window.open(this.href);return false;

I've looked in the past at MANY different sites when i was looking for proof that the 626 had a longer gear then the Mx-6 (in which they both have it) and none stated any different, even for 5th gear, which we know IS different, some just round the numbers up, but i couldn't find any evidence of difference in gear ratios

[wytbishop]

This thread shows a complete diff replacement in a G series tranny.



This is the gear that drives the differential. It would be very easy to change this gear and the diff to get the taller final drive ratio. It is a very simple transmission to work on based on my reading so far.

[wytbishop]

You'll also see int that link at iMazda that they have quoted Gro-Harlem regarding G tranny applications. The 4 cyl cars are supposed to have the taller gear ratios. Mike, the thread you posted also suggests that. All the internals interchange from the 4cyl G tranny to the 6cyl G tranny. So you should be able to put the gears and diff from a MX-6 LS into your MX-3 GS tranny case and achive some taller gear ratios.

It wouldn't even be that hard...I think.

[wytbishop]

I spent yesterday disassembling my spare tranny. The kit I was supplied had all the wrong bearings in it, but I learned a lot anyway. It took me about an hour to the point at which that the picture I posted above was taken. The worst part was unstaking the lock nuts. From there it was quite straightforward.

The answer to Jesse's question when he created this topic, is yes, you could easily change only the final drive ratio. The final drive gear is the first gear on the diff end of the secondary shaft. In a rebuild, you would be pressing that bearing off to replace it so it would be quite simple to remove the gear as well and replace it with one from a MX-6, 626 or even any of the 4cyl cars. OF all the vehicles that were given a G tranny only the PGT and MX-3 GS had the shorter 4.39 final drive gear ratio, so you could take the 4.11 diff and final drive gear out of any of the other G series trannies and put them into your MX-3 tranny and you would make each gear taller by approximately 6.8%. However, in terms of strength and durability, this would leave you exactly where you are with the stock unit.

The Mazdaspeed LSD has the same spline count (28) as our open diff but is somewhat stronger. The Quaiffe differential is a helical diff and is much stronger still. The MFactory diff is also a helical diff and about $800 - 1000 less than the Quaiffe. A group buy is currently in progress on ProbeTalk.com for the Mfactory. Both the Quaiffe and MFactory diffs are supplied without a ring gear so you can source one from whatever diff you want by simply grinding off the rivets and bolting it to the new diff (ARP bolts are available for this and MFactory is throwing a set in with this first run of diffs they are selling in the PT group buy).

There is some conjecture regarding the final drive ratio of the Mazdaspeed diff (in my mind anyway). The iMazda how to thread says they are installing it in a 95PGT tranny which has 4.39 final drive same as us and they make no mention of changing the final drive gear on the secondary shaft, but Gro Harlem in his transmission thread HERE says that the MSP LSD has a 4.11 final drive ratio and you must change the final drive gear. They may be talking about different diffs. I can't be sure.

If you're going to upgrade your diff, make sure you are clear what ratio ring gear it has if it has one. If you're going Quaiffe or MFactory you will have to source the ring gear (and the final drive gear if you're not going to stick with the 4.39 of the MX-3).

You can also upgrade the gears and synchros from a number of more modern vehicles which also use G25M-R trannies but apparently had better internal components. Gro Harlem did so and his post discusses the different cars that you can source internal components from.

[Nd4SpdSe]

Hmm, I remember that article, and i think your right about it using Probe gears...but I did talk to Gro when he first did his gearset swap and he said to me it has to be the 4.11:1. I've even got my gearset and LSD from him. All the info I searched for listed the MSP using a final drive of 4.11:1. Someone said that the final drive was almost impossible to remove, maybe without the proper tools, could be my mistake on that one.