3.7 / 3.54 rear diff

[Filip]

Is it straight swap, or i have to change rear axles as well ? Just out of curiosity, what would happen, if transmission and rear differntial would have different final drive ratios ?

With regards,
Filip

[Trevor]

Originally Posted by Filip

Is it straight swap, or i have to change rear axles as well ? Just out of curiosity, what would happen, if transmission and rear differntial would have different final drive ratios ?

With regards,
Filip

Both ratios must match, be the same, otherwise the transmission will become damaged. Front and rear would be fighting each other through the transmission.

[Filip]

Good explaining Trevor. What about rear axles, are they same across markets, so i can just swap rear diff for 3.54 one, without buying 3.54 axles too ?

Filip

[oab_au]

The rear has to be the same ratio as the front diff, auto or manual.

Depending on which box you are putting in the car. If you use a box with a different front ratio, you will have to get the rear diff from the same car as the box so that you have the same ratios.

To use the 4.44, 4.1, or the 3.5, ratio you will have to swap the ring and pinion gears, from the low ratio diff and fit them into the SVX housing, using the SVX Limited slip centre, so that the SVX axles will fit the diff, they won’t fit the low ratio diff from another model.

If you use a 6 speed that box has a front ratio 3.7 the same as the rear diff in your VTD and you can still use the R160, changing to the R180 is not necessary.

[Trevor]

Originally Posted by Filip

Good explaining Trevor. What about rear axles, are they same across markets, so i can just swap rear diff for 3.54 one, without buying 3.54 axles too ?

Filip

Kia ora Filip,

Your questions appear to indicate that you may have decided to replace your transmission, rather than at first find out if your problem can be fixed without great expense.

The cost involved in replacing the transmission, when considered against the value of the car, requires careful thought. As also does the fact that the car will no longer be an original collectable example and therefore will lose market value.

Regards, Trevor.

[Filip]

Originally Posted by oab_au

The rear has to be the same ratio as the front diff, auto or manual.

Depending on which box you are putting in the car. If you use a box with a different front ratio, you will have to get the rear diff from the same car as the box so that you have the same ratios.

To use the 4.44, 4.1, or the 3.5, ratio you will have to swap the ring and pinion gears, from the low ratio diff and fit them into the SVX housing, using the SVX Limited slip centre, so that the SVX axles will fit the diff, they won’t fit the low ratio diff from another model.

If you use a 6 speed that box has a front ratio 3.7 the same as the rear diff in your VTD and you can still use the R160, changing to the R180 is not necessary.

Harvey,

that would be great news, but are you sure ? Because from reading other topics here, i got feeling that 6 speeds are 3.9 and thus can be used only with US model 3.54 due to centre diff conversion.

Can you please confirm me, that i really can use 6 speed, either from 06,07 or 08+ Imprezza STI models ?

With regards,
Filip

[Filip]

Originally Posted by Trevor

Kia ora Filip,

Your questions appear to indicate that you may have decided to replace your transmission, rather than at first find out if your problem can be fixed without great expense.

The cost involved in replacing the transmission, when considered against the value of the car, requires careful thought. As also does the fact that the car will no longer be an original collectable example and therefore will lose market value.

Regards, Trevor.

Ahoj Trevore ,

Those are all important things to consider, indeed. I was thinking about them intensively past two months.

I could write whole letter about my thoughts, but i won't. I only ask you two questions, whose answers would help me:

...1) How many actions would remain, if solenoid C were to be OK, before you would recommend me an "expensive" solution?

...2) I suppose you have the same gearbox as me, so i would be curious, how are your experiences with it? Could you describe it as reliable?

By reliable, I also mean, you don't have that unpleasant inner feeling, that the tranny will let you down in most inconvenient times and that you don't worry about depressing the gas pedal strongly from time to time.

But please, don't imagine me as a guy, who is redlining a cold car, etc. I am trying to do my best to be gentle. But even gentlemen wanna have some fun sometimes!

Filip

[Trevor]

Hoooooray Filip,

(1) Please refer my posts within your previous lengthy thread “3rd and 4th gear not engaging + weird smell”.

(2) I had no qualms in respect of my SVX as I had fitted a pressure gauge which constantly displayed the transmission line pressure so tat it was clearly visible in front of the steering wheel.

But please, don't imagine me as a guy, who is redlining a cold car, etc. I am trying to do my best to be gentle. But even gentleman wanna have some fun sometimes!

My sport has been motor racing and on two occasions I came very close to death! As long as you always drive the car correctly rather than specifically gently, you can have lots of fun.

In all of this, fitting a manual transmission in order to have fun, involves an entirely different set of circumstances and therefore it could be worthwhile.

Cheers, Trevor.

[Tireiron]

The front diff of all 6MT transmissions is a 3.9 ratio. The older ones use a 1:1 center ratio requiring a 3.9 rear diff. The newer ones use a 1.1:1 center ratio requiring a 3.54 rear diff.

The USDM (I'm not sure if the overseas WRX got the transmission change) 06-07 NON STi WRX 5mt uses a 3.7 front diff with a 1:1 center ratio requiring a 3.7 rear diff.

Also, the SVX axleshafts in the rear are unique, however that being said you could technically swap from a 3.7 SVX rear diff to a 3.54 SVX rear diff without requiring any diff work. However the better option is to swap to a STi rear r180 and the STi rear axleshafts. The r180 is available in either 3.54 or 3.9 depending on the transmission you use. And with the r180 the 05-07 USDM 5x114 STi rear axleshafts will bolt in.

*I specify USDM because the years change between JDM and USDM markets because if the USDM auto maker release schedule.

[oab_au]

Sorry Filip the 6 speed does have a 3.9:1 diff ratio, I though it was the same as the 5 speed auto of the same years that has the 3.7:1 ratio, Tireiron is right.

For the cost and time the change to a Manual box would take, I really think you would be better to spend the money to have your VTD box and torque converter overhauled by a good Auto trans rebuilder, they will use all the updated parts including the modified high clutch, all new solenoids, seals and lathe cut rings, and the lockup clutch in the converter, to have a box that is the same as the 95 model box that is virtually “bulletproof”.
My 95 VTD has lead a hard life for 180,000 km, I developed the ”Quick Change” on it with many hard changes, and it is as new.

[Stevebsy]

This is very useful for potential trans. swaps:

http://rallispec.com/downloads/Trans...art_Public.pdf

[oab_au]

Thanks Steve, that is pretty comprehensive.

[Trevor]

Originally Posted by oab_au

Sorry Filip the 6 speed does have a 3.9:1 diff ratio, I though it was the same as the 5 speed auto of the same years that has the 3.7:1 ratio, Tireiron is right.

For the cost and time the change to a Manual box would take, I really think you would be better to spend the money to have your VTD box and torque converter overhauled by a good Auto trans rebuilder, they will use all the updated parts including the modified high clutch, all new solenoids, seals and lathe cut rings, and the lockup clutch in the converter, to have a box that is the same as the 95 model box that is virtually “bulletproof”.
My 95 VTD has lead a hard life for 180,000 km, I developed the ”Quick Change” on it with many hard changes, and it is as new.

I would say that the six speed was in the main introduced as a means of meeting a market trend and not be outdone by the opposition. The SVX has a relatively wide torque range and five speeds would be a better choice on several counts and therefore Filip has no need to be concerned in this regard.

If I was spending the sort of money and time involved, I would certainly fit a manual transmission as this would transform the car from a drivers point of view. Filip has indicated that he drives for the fun of it.

[Filip]

Trevor : "My sport has been motor racing and on two occasions I came very close to death! As long as you always drive the car correctly rather than specifically gently, you can have lots of fun. "

-From that short time, i had pleasure to drive SVX on all 4spd., i can probably feel, where this coming from - i had impression EG33 really like to be above 3000rpm, similary like VTEC engines.

Tireiron: Hello, exactly, what i was asking about, thank you for informations.
Stevebsy: I saw this chart somewhere, but could not find it, thanks for posting.

Filip

[Filip]

oab_au : "I really think you would be better to spend the money to have your VTD box and torque converter overhauled by a good Auto trans rebuilder, they will use all the updated parts including the modified high clutch, all new solenoids, seals and lathe cut rings, and the lockup clutch in the converter, to have a box that is the same as the 95 model box that is virtually “bulletproof”

This is interesting information and definitely worth to think about. Let me ask few questions:

1) How much would cost all parts needed for this overhaul?

2) How many hours, it should take for mechanic to do the whole job ? I need to "be in the picture" as I agree with Trevor, that they will try to rob me for money. I already had this feeling from one specialized auto rebuilder shop I was in contact with when my problem started.

3) Regarding 95+ parts, how can I be sure, that they would use really these parts and not the older ones? Are 95+ parts the only ones available on the market? Are 95+ part numbers same as pre-95 ?

I have heard stories of people paying sums around $1500USD, only to find out, that weeks later, they had nothing fixed and the tranny can be rebuilt again. This I am trying to overcome. But if you are saying you have 180,000km since rebuild, that is definitely vital information. But J need to be vigilant.

Best regards,
Filip