Imprezer

iTrader: (9)

We have covered the differences between the US 5-speed and JDM 6-speed transmissions. There are much more drivetrain related parts that make that 6-speed equipped STi WRX’s so much better in every aspect. In this article, I will cover these differences.

Rear Differential

Newer STi WRXs in Japan come with a larger R180 rear differential. That unit is significantly larger than the USDM R160 units. The diff housing of the R180 diff is also larger proportionally to the diff, meaning that the R180’s get more fluid to “swim” in that the R160’s. More fluid means better cooling and better differential performance. The bearings inside of the housing are also larger and stronger. Finally, the New Age STi’s WRX come with an intelligent SureTrack LSD which transfers torque from the slipping wheel to the gripping wheel, evidently making more sense of the famous SOA add campaign that applied the same “from the wheels that slip to the wheels that grip” theory to all Subaru’s. (note: Some Subaru’s did not have LSD’s installed). All these goodies come at a price of added weight. Stock R160 diff in housing weights 52 lbs, while R180 weights 64lbs.

Installation of the R180 rear diff is a simple procedure. It will bolt right in place of the stock R160. However, USDM rear axles cannot be used with the R180, hence, you need to get some STi axles, which I will talk about later. And, if you get the axles, you have to get the STi hubs and the rear brakes. So, swapping a rear diff, will cost you much more than just a price for the diff itself.



(Pic: On the left, R180. On the right, R160)

Axles

Once again, the STi axles are bigger and stronger. The CV joints are massive as are the shafts themselves. Of course, that comes with a price of added weight, but these shafts won’t break, unless you are doing something really wild. The rear axles are slightly shorter, since the R180 and its housing are wider. The front ones are the same length, which means that STi axles can be used with the 5MT and the regular axles can be used with the 6MT. The front axles is a nice “option” and recommended for high power cars, while the rears are a must for those wishing to use the R180 rear diff. Each axle is about 2lbs heavier than the regular one.





(Pics: front and rear 5MT vs. 6MT shafts. The top 2 on each pic are 5MT)

Driveshaft

There are only 3 differences between the 6MT and 5MT driveshafts. First of all, since the 6MT is about 4 inches longer, the 6MT shaft is shorter. That makes it mandatory to use 6MT driveshaft with the 6MT. Then there is a slight weight difference. The last difference is the flex joint. As you know, the Subaru drivershaft is a 2-piece unit. The 5MT unit has a ball joint that connects the two halves while the 6MT has a universal joint. No doubt that the universal joint is stronger. Most high power cars that have 2-piece driveshaft, have a universal joint.





(Pics: Right is the 6MT driveshaft)

Hubs & Brakes

You do not need front hubs. Your stock front hubs will work just fine. I am still checking to see if the STi hubs have bigger bearings and will update this document accordingly later on. The rear hubs is must for those who choose to use the R180 diff. As an added bonus, you will be able to use the sweet 2-pot BREMBO calipers with massive 316x20mm vented rear rotors. The pads have larger surface area and are taller than the short stock pad. All that will produce greater stopping power under any conditions.





Shifter

The shifter is obviously different and features a “pull-up” locking mechanism for the R gear. The shift patter is same as the 5MT, but the 6th gear is located with the R gear on the 5MT, plus the R gear in the “full-left-pull-up-down” position.

(Pic coming soon)

Please stay tuned for the next installment of the 6MT conversion project and as usual, the questions are welcomed.

areg

iTrader: (6)

great info..



areg

BADWRX

iTrader: (5)

No, but you have to swap the ring and pinion to make it a 3.90. I am running the R160 in my setup with the 6MT.

Andy

andyscoob

i thought the stock wrx came with a 3.90 rear already?, i remember reading it in a magazine when the car first hit the market..

Imprezer

iTrader: (9)

US WRX final drive ratio is 3.9, but there is a reduction 1 : 1.1 gear in the transfer case.

go go go

iTrader: (2)

which drive shaft did you use?
6MT drive shaft bolts onto R160 ok?

NegativeC

Can the 5MT Driveshaft be shortened and used instead of buying the shorter 6MT driveshaft?
Thanks

BADWRX

iTrader: (5)

Yes, and yes.

I am running the GDB driveshaft, but, you could run a shortened 5 speed driveshaft, or the OEM auto driveshaft.

All that you need to do the swap is:

1. 6 Speed Tranny
2. Shortened/GDB driveshaft
3. R160 3.90 ring and pinion
4. Shifter

I am running a legacy differential housingwith the wrx guts with the 3.90 ring gear on the stock wrx lsd swapped with the stocker.

Very simple swap.

andyscoob

you just completely confused me...
u used a legacy rear diff? i thought the wrx came with the r160?
and the whole 3.90 gear thing im still confused on.. i thought the wrx already came w/ the 3.90 ring and pinion?
all i can see you needing, is the 6mt, and the shortened drive shaft, and the new shifter...
please clear things up for me. im only going by stuff i read.

BADWRX

iTrader: (5)

But the legacy already has the pinion gear installed. If you have to change the pinion gear on the WRX it is $$$ as it has to be pressed out and bearings and all. A real PIA.

The Legacy, and the WRX differentials have different internals, so you have to use all of the parts out of the WRX diff (Diffs, and spline thingys) a basic bolt in swap...you just have to change the ring gear on the LSD to the one that correllates to the 3.90 out of the legacy diff.

I am confusing myself trying to explain! Lol! It is actually quite simple.

BADWRX

iTrader: (5)

No, your assumption is incorrect. The WRX front open differential is a 3.90, and the rear LSD is a 3.54. That is why the center differential is a funky 1.1:1 ratio, to balance the torque load. On the 6mt, the center diff is 1:1, so the front sure-track LSD is a 3.90, and the rear must be a 3.90 too.

Do you get it now? I hope that I assisted you in getting your mind right! :P

Keep the questions comming.

Andy

1fastGC

iTrader: (3)

Andy, I am thinking about getting the 6MT myself. Just wondering if it will be straight bolt on?

BADWRX

iTrader: (5)

Pretty much Cal, as long as you have a 3.90 rear diff. If not, I have one that I may sell soon for $600 (Includes hubs, disks, calipers, axles, and the assembled pumpkin.

You GC8 guys must also convert your clutch from a pull to a push...(I think)...

No biggie!

Andy

bamfwrx

what is different about the rear hubs that you can't use the WRX brakes?


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Robert
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