Gearbox final drive mods...

[EvoMayhem]

Hey folks.

I know some of you guys on here have some gearbox and diff modifications done, namely the changing of the final drive from the stock ratio to 3.545:1, so I would like to ask some questions about this.

Am I right in the understanding its the CC Lancer GSR's ratio?

I have been also told that this ratio swap requires a bit of the gearbox housing to be machined? If so, is it a large amount?

What I would also like to know is other than the ring gear on the front diff, what exactly on the actual gearkit needs to be changed out? (ie; what drives the front diff itself?)

Would anyone be able to point me in the right direction for the parts themselves, including the bits for the rear diff? (If Mitsi are the only option, could someone please tell me the part numbers that I could use to order them up?

And lastly, on a slightly different, but related note. There is nowhere in the UK (To my knowledge) that I can buy an uprated '4 spider' centre diff. Anyone got any clues as to where I might get one of these?

Any help from you guys would be gratefully recieved!

 

[bazeng]

How are you?

To convert your 3.9 ratio box to a 3.5 ratio, I believe you don't need to machine anything. Simply change the crown wheel and pinion in the gearbox. You will need to also find a a crown wheel etc to suit the rear also.

They can be obtained from
1989 - 1992 GALANT VR4
Lancer GSR's

I did this recently and it is better for drag racing but not so much on the street / track. Unless you need the legs for more top end speed.
The 3.9's do a really good job of making an underpowered car feel very fast and an over powered car feel insanely fast! All I remember doing when I had 3.9's was shifting like a mad man!!!

 

[EVO-00X]

Just so I dont have to type a lot contingencies to account for all possible scenarios, can you tell me what drivetrain you currently have now? lol EVO I, II or III?
Does your existing gearbox and rear differential have LSD's fitted? If yes, mechanical or viscous?

 

[EvoMayhem]

Just so I dont have to type a lot contingencies to account for all possible scenarios, can you tell me what drivetrain you currently have now? lol EVO I, II or III?
Does your existing gearbox and rear differential have LSD's fitted? If yes, mechanical or viscous?

Whoops! :lol: :lol:

Thats not like me to leave important bits of info out like that!

Right, I'm running an Evo III, with full III running gear. Standard rear mechanical LSD, standard viscous centre with '2 spider' diff, and open front diff. I'm going to be changing out the front diff, to probably something like the Quaife ATB.

Got a forged, 500bhp+ capable engine fitted now, that I'm just getting dialled in with a 20G TD05H and ECMLink V3 lite, and I'm looking for the best way to get some more top end out of the gearbox, along with a better cruising rpm for 70mph. Currently, thats around 3,250/3500rpm at 70mph.

 

[EvoMayhem]

How are you?

To convert your 3.9 ratio box to a 3.5 ratio, I believe you don't need to machine anything. Simply change the crown wheel and pinion in the gearbox. You will need to also find a a crown wheel etc to suit the rear also.

They can be obtained from
1989 - 1992 GALANT VR4
Lancer GSR's

I did this recently and it is better for drag racing but not so much on the street / track. Unless you need the legs for more top end speed.
The 3.9's do a really good job of making an underpowered car feel very fast and an over powered car feel insanely fast! All I remember doing when I had 3.9's was shifting like a mad man!!!

Not bad, you?

The rear diff swap wouldn't be a prob, but as per my previous post, I just can't get my head round what exactly in the gearkit constitutes as the pinion in the gearbox? Is it a gear on the output shaft? I ask as after looking here....

Magnus Motorsports gearkits

...they talk about changing '...3rd gear and spool gear...' What exactly is the spool gear?

Don't worry, I'm not about to undertake the swap and build myself, as I clearly don't have a clue about the gearbox! :lol: :lol:

 

[GVR40]

talk to jetgsr. he did this swap when he put evo 3 rear diff and whatnot into his gsr lancer, he wanted to keep with 3.545. i think he had to get the crown wheel machined from his gsr to match the evo diff

 

[EVO-00X]

hmmm you're a bit confusing when you wrote standard viscous centre with 2 spider, and open front diff? Might be better if you tell me the gearbox code on your Evo gearbox lol :lol:
Regardless whether you have viscous front LSD or not, you're going to get rid of the existing Evo front diff anyway and replace it with a Quaife. Just ensure that you use a normal open diff cv cup on the driver's side when you fit the Quaife in it.

Anyhow, changing from EVO 3 drivetrain to GSR 3.545 setup is the most involving because you cant keep the EVO 3 transfer case.

You will need to open your gearbox, remove the EVO 3 front diff with 63 tooth crownwheel and 15 tooth output pinion out of the box. Then fit a GSR 58 tooth front diff crownwheel to your Quaife ATB front diff and use a matching GSR 15 tooth output pinion. Evo 15 tooth output pinions are different to GSR 15 tooth output pinions. The teeth sizes are different and they stick out further on the GSR pinion. Dont let anybody else try to tell you any different. You cannot use an Evo ouput pinion with a GSR crownwheel or vice-vera... it wont work. Once you have the GSR parts fitted close your gearbox back up. In summary 58/15 = 3.867 front diff ratio.

Now, your EVO 3 transfer case is no good to you anymore as the EVO 3 transfer ratio is made to only suit the EVO 3 front diff ratio. ie. EVO 3 transfer ratio is 1.074. Now that you have a GSR front diff ratio in your gearbox, you will need a transfer case from a GSR, EVO 1 or EVO 2 which run 1.09 ratios. Out your way you should find an Evo 1 or 2 transfer case easy so use one of them. In summary 24/22 = 1.090 transfer ratio.

Rear diff is currently Evo 3.909 mech LSD. You will need to open the rear diff housing, remove the Evo crownwheel and pinion and replace it with a GSR 3.545 crownwheel and pinion, set the tooth alignment and backlash. Yes, the GSR crownwheel and pinion will fit inside the Evo housing using the Evo rear mech LSD. In summary 39/11 = 3.545

When doing the math now, you need to ensure the front diff ratio of 3.867 matches the ratio of the transfer case x the rear diff.
Threrefore transfer 1.090 x rear diff 3.545 = 3.864. That's the GSR front and rear diff ratios sorted.
You dont need to machine anything to make any of these items fit.

The centre diff is a completely different story. It will need to be opened and the housing machined. The cross-shaft in the centre diff will need to have the other 2 ends machined to suit another 2 spider gears, hence making a 4-spider centre. The extra 2 spider gears can be taken from another spare centre diff. Dont forget to use a total of 8 brass shims for the spider gears. The housing machining to accept the 2 additional spider gears will have to be done by a professional. Once done, you should end up with a cross-shaft that fits 4 spider gears which should fit nice and flush inside a newly machined housing.

There are a few companies out there than can supply additional parts for the centre diff like a hardened chromoly 4-spider cross-shaft and a machined top hat with a torrington bearing upgrade for the centre diff pinion to add even more strength and reliability to the centre diff. That's the way I went when building my own custom gearbox

A GSR gearbox when cruising at 100kmh in 5th gear according to the GPS, registers only 2850rpm on my AVCR There's other combinations that can make 5th gear cruising even better with lower rpms, but 2850 is a nice sweet spot IMO when running a bigger turbo thats not producing positive pressure that low in the rev range.

 

[EvoMayhem]

hmmm you're a bit confusing when you wrote standard viscous centre with 2 spider, and open front diff?

As I'm currently floating about in the North Sea on an oil rig, getting specific numbers will be a bit difficult! Lol!

However, W5M33-2-UPGE. That is to say, it has the standard centre diff assembly (I only say that to let you know its not been modified with a Kaaz, Cusco, or other diff...), evo 3 GSR, and non-LSD (open) front diff.

Anyhow, changing from EVO 3 drivetrain to GSR 3.545 setup is the most involving because you cant keep the EVO 3 transfer case.

You will need to open your gearbox, remove the EVO 3 front diff with 63 tooth crownwheel and 15 tooth output pinion out of the box. Then fit a GSR 58 tooth front diff crownwheel to your Quaife ATB front diff and use a matching GSR 15 tooth output pinion. Evo 15 tooth output pinions are different to GSR 15 tooth output pinions. The teeth sizes are different and they stick out further on the GSR pinion. Dont let anybody else try to tell you any different. You cannot use an Evo ouput pinion with a GSR crownwheel or vice-vera... it wont work. Once you have the GSR parts fitted close your gearbox back up. In summary 58/15 = 3.867 front diff ratio.

Now, your EVO 3 transfer case is no good to you anymore as the EVO 3 transfer ratio is made to only suit the EVO 3 front diff ratio. ie. EVO 3 transfer ratio is 1.074. Now that you have a GSR front diff ratio in your gearbox, you will need a transfer case from a GSR, EVO 1 or EVO 2 which run 1.09 ratios. Out your way you should find an Evo 1 or 2 transfer case easy so use one of them. In summary 24/22 = 1.090 transfer ratio.

Rear diff is currently Evo 3.909 mech LSD. You will need to open the rear diff housing, remove the Evo crownwheel and pinion and replace it with a GSR 3.545 crownwheel and pinion, set the tooth alignment and backlash. Yes, the GSR crownwheel and pinion will fit inside the Evo housing using the Evo rear mech LSD. In summary 39/11 = 3.545

When doing the math now, you need to ensure the front diff ratio of 3.867 matches the ratio of the transfer case x the rear diff.
Threrefore transfer 1.090 x rear diff 3.545 = 3.864. That's the GSR front and rear diff ratios sorted.
You dont need to machine anything to make any of these items fit.

The centre diff is a completely different story. It will need to be opened and the housing machined. The cross-shaft in the centre diff will need to have the other 2 ends machined to suit another 2 spider gears, hence making a 4-spider centre. The extra 2 spider gears can be taken from another spare centre diff. Dont forget to use a total of 8 brass shims for the spider gears. The housing machining to accept the 2 additional spider gears will have to be done by a professional. Once done, you should end up with a cross-shaft that fits 4 spider gears which should fit nice and flush inside a newly machined housing.

There are a few companies out there than can supply additional parts for the centre diff like a hardened chromoly 4-spider cross-shaft and a machined top hat with a torrington bearing upgrade for the centre diff pinion to add even more strength and reliability to the centre diff. That's the way I went when building my own custom gearbox

Man, that has to be the single most complete answer I have had on this subject yet! B) No-one had said anything about the need for the transfer box swap, but then again, I hadn't came across anyone with a III that had done this either. Nice one!

Thanks for all that info, I now have some shopping to do! :lol: :lol:

 

[EVO-00X]

You're welcome.
Now you owe me a Rep point you buggar because as I was typing all that out for you, my Mrs got pissed off that I didnt go to bed with her :lol:

 

[EvoMayhem]

You're welcome.
Now you owe me a Rep point you buggar because as I was typing all that out for you, my Mrs got pissed off that I didnt go to bed with her :lol:

:lol:

Done.

I'm now one happy Scotsman. Cheers to all who replied.