Higher 5th ratio - K8DE V6



  • Hi, I am considering changing the 5th gear ratio as:

    • I am not going on a track day
    • It would be nice to get 20-21 mph / 1000rpm in top
    • changing the 5th ratio will not affect the speedo etc.
    • 4th can go 105 mph to the redline, Ill never go faster than that anyway.
    • I dont mind 4 close ratios + 'overdrive'
    • good excuse to change the gearbox oil!
    • because, why not!
    • easy to change back…

    It seems that the end casing can be removed from the gearbox and the 5th gears removed, then replaced with something else ie MX6 or Xedos V6...?

    Has anyone done this? any tips, tools to take to the breakers? etc... can it be done in car?

    Thanks

    Trevor.



  • **I'd suggest it'd be easier to replace the differential (final gear) with a longer MX-6/Xedos one (careful - some are the same box) or just replacing the whole gearbox with an MX-6/Xedos one since it's exactly the same casing…

    Run a slightly bigger wheel/tyre combination too, to lengthen the gears further.**



  • I did much research into this a few months ago for our site www.club323f.com and here is the info for you. . . .

    Original thread is here

    Gearboxes

    With so many people asking questions about them (final drive ratios etc) I thought it would be appropriate to pop it all down in writing on our forum in one place :)

    Car / Engine MX-3 (K8 ) & Probe GT (KLDE) Gearbox G5M-R

    Gear Ratios (Input:Output)
    1st 3.307:1
    2nd 1.833:1
    3rd 1.310:1
    4th 1.030:1
    5th 0.795:1
    Final Drive 4.388:1

    Car / Engine MX-6 KL-DE & 626 KL-DE Gearbox G5M-R

    Gear Ratios (Input:Output)
    1st 3.307:1
    2nd 1.833:1
    3rd 1.310:1
    4th 1.030:1
    5th 0.795:1
    Final Drive 4.105:1

    These two gearboxes are identical except for the final drive ratio which I have highlighted, this difference should equate to around 250 - 300 rpm in the real world

    Car / Engine MX-6 FS-DE & 626 FS-DE GearboxG25M-R

    Gear Ratios (Input:Output)
    1st 3.307:1
    2nd 1.833:1
    3rd 1.233:1
    4th 0.914:1
    5th 0.717:1
    Final Drive 4.105:1

    In this gearbox you can see that 1st, 2nd and Final drive are all the same as the other boxes, the difference is in 3rd, 4th and 5th. I'm not able to work the difference in rpm by using the 5th gear in the MX-6 V6 gearbox but I would have a good guess that it would be a little lower still.

    The G15M-R gearbox is used in the BJ Diesel (RF-MDT engine) I'm sure as the other gearboxes are interchangeable then it would physically fit onto the V6 but I can't be sure, it does however benefit from a MUCH lower final drive ratio so for those of us that want a lower cruising rpm then it would be perfect to swap over the final drive ratios. . .if it fits.

    I'm pretty sure this will all apply to the BJ sport too as some of the gearboxes are the same :)

    The info in this thread is what I have collected over the past year it may not be 100% upto date and correct. Some things may not fit and as I haven't tried everything personally I won't be held responsible for people buying stuff then finding it won't fit.

    Stu



  • i did read somewhere, that its only a case of removing the black cover on the end of the gearbox and swapping in the new gear.
    There is an aftermarket 5th gear which is even taller than the probe/mx6 one.
    I know that marco knows the answer to both of these as he has done it on a couple of boxes now.



  • Thanks Everyone!

    Hi Stuz, (rember you from Club 323f :D ) I heard that 5th on the MX3 v6 was 0.84… then I got this from wiki...

    The Mazda G5M Five Speed Manual Transaxle came in three gearsets:[1][2]

    Trans # First Second Third Fourth Fifth
    G5M 3.307 1.833 1.311 1.030 0.795
    G5M 3.310 1.830 1.310 0.970 0.750 (Probe2.5L)
    G5M-R 3.666 2.059 1.310 1.030 0.837

    I would be happy with 0.795 or even 0.75 off a 2.5 probe - aparently.

    I did some calcs on a program I have (email me if you want a copy!)

    With the 0.75 5th gear i'll be pulling 21.5 mph per 1000 rpm (instead of 19.3. That would be much better. All I have to do is find a knackered probe gearbox to try it!

    Really want to know how to do it with the gearbox in the car… Id rather not take out or change a good gearbvox...



  • Think the 5th gears and selectors are held in place with staked nuts like this:-





  • i'm totally with you on this. living where i do i have an A road thats 40 miles long to get to the nearest city (60mph) and a duel carriageway thats 40 miles long to get to the other closest big town (70mph) and would love to save some fuel driving to these places as i do it on a regular basis. personally, i dont really think that the probe 5th will make much difference to the performance anyway as the little V6 is a strong little engine so i really dont think you will lose much accel in 5th by adding a taller 5th.

    and besides, most "races" are between the lights anyway (ali g style haa) so its all about acceleration. :)



  • We need to sort this out Dan…

    I just found this on ebay...

    http://www.ebay.co.uk/itm/toyota-corolla-gearbox-DOHC-1-9D-2001-2002-G5M-/360372586012?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item53e7e1461c

    Seems that Toyota use this gearbox too?

    Hope someone knows where to get replacement 5 gear sets for reasonable money?



  • well, i was going to buy this myself for a 2.5 conversion but there is a breakers near me that have a ford probe V6 in stock. i popped over there and asked about price for engine and box. they offered it to me for £100 which is a bargain in itself but i cant get the engien out and seeing as im thinking about freezing my project for a min i wont bother. i'm sure if you offered them £50 for the box you could get it for that but you would have to come to cornwall and get it out yourself. i am assuming they still have it seeing how rare probes are getting now. if you are interested let me know and i will contact them to see if they still have it



  • Thanks Dan.

    There's a probe breaking just up the road from me too - 2.5 v6… If I had the money I'd be rushing out to get one.. but to be honest I'm a bit broke for a couple of months.

    Im not in a rush, and I have other things to do such as rocker cover gaskets, exhaust, etc etc... but if a cheap solution comes up I might take it :-)



  • how about this for a corker.. i won a bid for a klde..wen i went to pick it up the guy gave me the box for £1..as the engine was £99

    :D



  • @a64c8668c8=jay1987:

    how about this for a corker.. i won a bid for a klde..wen i went to pick it up the guy gave me the box for £1..as the engine was £99

    :D

    Lucky bastard.



  • I run a .717 in both my Gearboxes. Certainly seems to help my mpg. As does megasquirt. It's very easy to swap as you can see it's in the extension housing. Much easier than a final drive swap.



  • Hi Marco, Where can I get a set of 0.717 gears.. also do I need to get just the gears or do I need to use matching synchro rings etc? PPs what does it drive like? must be a big drop from 4th to 5th! :shock:



  • @3cfcf27149=Ice:

    Hi Marco, Where can I get a set of 0.717 gears.. also do I need to get just the gears or do I need to use matching synchro rings etc? PPs what does it drive like? must be a big drop from 4th to 5th! :shock:

    Car / Engine MX-6 FS-DE & 626 FS-DE GearboxG25M-R

    Gear Ratios (Input:Output)
    1st 3.307:1
    2nd 1.833:1
    3rd 1.233:1
    4th 0.914:1
    5th 0.717:1
    Final Drive 4.105:1

    The 0.717 can be found in the G25M-R I think you will need the syncro ring too so get it just incase. . .



  • You could also try to take the 5th gear of the 2.0 Probe.

    This one would create a big gap between 4th en 5th though.



  • @1a35ae77b5=whitefinish:

    You could also try to take the 5th gear of the 2.0 Probe.

    This one would create a big gap between 4th en 5th though.

    A gap that you would not even notice, I very much doubt it would make any difference to performance etc. . .



  • Oeps.. now I see Marco posted thesame information about that gear.

    Anyways… There is a member here that has a big RPM drop when shifting from 4th to 5th...



  • Approx figures from today's driving with .717 in a k8 gearbox.

    60mph = 2700rpm
    70mph = 3250rpm

    It was never for performance for me. Boosting in 5th gear is a brilliant way destroy the gearbox! Drag racing is 1-4. So I went for the eco 5th gear, and it sets motorway cruising at the bottom of the powerband.


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