Final drive ratios and gearboxes

[bradc]

The manual cars have a final drive of 3.684, and the auto cars a final drive of 4.111

Lets say one was to swap a manual gearbox into an auto car, would the final drive need to be changed as well? And where is the final drive ratio actually done? Is it done in the transfer box for the front wheels and in the rear diff?

I'm thinking about changing my car to an EVO 8/9 gearbox with 6 forward gears, and I'm just wondering if I would need to use the final drive of the EVO, or keep the ratio my car currently has with the auto gearbox.

[EdmundVR4]

You will need the correct rear diff ratio or your vcu will overheat & fail. I'm not sure if you need to change the transfer case output ratio to the front wheels, but I suspect so.
Very important to have front, centre & rear ratios matching & correct.

[bradc]

But if I change the gearbox only, then won't I be able to keep the rest of the drivetrain?

[Kenneth]

i would have thought so... though you total gear ratios might be different. also, depends on where the speed pickup is done as to wether you speedo goes out.

i always thought the final drive was the dif ratios... so that would be your front and rear diff. as the gearbox attaches to the transfer case, which in turn drives both the front and rear wheels, it should be ok.

but thats just my assumption

[bradc]

Thats what I thought too, but then mitsi would have needed to have made differant AYC diff's for manual and auto cars, as well as LSD diffs, and finally front diffs. Seems like a lot of work doesn't it?
If it is just in the diffs, and has nothing to do with the gearbox, then I might just install a standard 5 speed manual into my car, it will still give me a nice high cruising gear, which is the one thing I thought I would have to sacrifice to get a manual gear box, hence the EVO 8 gearbox decision.

[EdmundVR4]

On second thought you may be right if you are just changing the gearbox...your assumption does make sense. The next question is : Are the auto & manual transmission cars transfer cases the same ?
On the 7G VR4's, the transfercases are different external sizes.
I would like to change my 5 speed manual to a 6 speed from the Evo 8/9 ? Is this possible & would it be an easy swap ?
What do you think guys ?

[bradc]

Edmund, is that for your 7G or your 8G?

[EdmundVR4]

bradc, it's for my 8G (my 7G already has 6 spd from GTO). I wouldn't mind changing my 5 speed manual to a 6 speed manual on my 8G VR4, if it's easy going. Similar concern as yours, low rpm high speed cruising. I don't like to see my tachometer at 4000+rpm when I am cruising, plus my 5th gear grates when shifting at high rpms...can't be double clutching when I'm racing !
I'm going to be needing a clutch upgrade soon too...good time to do gearbox & clutch ! Is it correct that Evo7/8 clutch works on the VR4 ?
Thanks.

[bradc]

I don't know about the clutch, you could probably just buy an aftermarket one anyway. How difficult was it to install the 6 speed from a GTO onto a 6A12? If it wasn't that hard, it could probably be done for the 6A13 as well.

[EdmundVR4]

I did a conversion on my 7G VR4 a few years ago. It now has engine, gearbox & transfercase from a GTO. (no more 6A12)

[Sports GT]

I'm in a similar situation....I'm putting the Evo gearbox on my formerly automatic E84A Galant VR4/Sports GT and I need to know if I need to change the rear diff... we have the front diff from the galant which we were going to swap out but we were advised not to since it is a very difficult task... so I need to find out if the ratio on the rear diff of the Evo 1-3 is the same as the 92-96 Galant VR4... can anyone help please?

[zentac]

on a 2WD car the final drive is calculated from the number teeth on the crown wheel against the number on the output shaft, Im not sure how your rear diff comes into it. Why not look at other mitsi gearboxes and see if you can take the gears out of them, thats what Im currently doing with a Galant V6 as it has better ratios than my FTO. Im also going to try different crown wheels to give me different final drives and hopfully longer gears.