basic diff choice question

I'm pretty sure my front open stock diff is starting to go.

I KNOW i'll need to replace my stock rear diff after an event (maybe 2).

So I'm starting to search now for what my options are. won't actually buy anything for a while.


I'm looking at a barely used cusco rear dif 1-way for the rear...should be a decent choice, yes?


For the front, I assume some brand of 1.5way would be sufficient?



I know a lot of this is 'preference' or 'driving style', but since I think these parts will have to be replaced before I figure that out, lets just start with the basics.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

bump, still doing research, but wanted opinions on 2-way vs 1-way for a rear and front diff.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

So it seems like you'd want a 1 way or MAYBE a 1.5 way for the front, because a 2 way will just induce a bunch of understeer unless you are on the throttle. I know in FWD cars, a welded front or 2-way is a big learning curve. You can't turn the car without throttle. I did a 1.5 way on the golf.

for the rear however the 2 way would add lockup under braking making the car more prone to oversteer, which if you can deal with it (it gets exciting I'd imagine) the car would turn in nice, though a 1.5 way would be a lot more "user friendly". less lockup (oversteer) on braking/entry and full lockup (traction) on throttle/exit

I think the drift kiddies all like 2 way rear diffs on RWD cars because they make the car pretty silly sideways without much effort at corner entry (hard braking to throttle transitions immediately to oversteer)

This is theorycrafting btw, I don't own any 4wd's, and really the center diff is not taken into account in the above -- but I think that's how the diffs work.

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http://www.ckrally.com

thx..makes sense. I have a 20kg center diff (still needs to be installed), and I guess with a 2-way rear diff that's pretty close to RWD!?



RIGHT NOW, with open diffs and rear LSD and crappy center diff, my car actually turns in pretty nicely, and I've gotten used to it....so a 1.5 in the front sounds about right.

for the rear.....2 way is too much, methinks...but I can get a good deal on a used 1-way, so if that's similar to my current LSD...that would be perfect.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

In general, or at least what I've overheard, usually involves a 0.5 difference between front and rear. So if you have a 1.5 in rear, you want a 1.0 in front. 2.0 in rear, 1.5 in front.
I'd call a reputable rally shop that also sells differentials and talk to them and if you end up buying stuff also make sure to buy it from them. I think the one in Canada that's had probably the best results in NA in a AWD Subaru would probably be a good place to start.

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Grant Hughes

If you don't have an upgraded center diff already then you are going about this all out of order. In a Subaru (not talking STi, but regular WRX) the priority is to upgrade the center diff first. Usually to the 20kg/100rpm viscous STi unit. The stock 5-speed uses a 4kg/100rpm viscous so it's barely better than an open diff. Upgrading the center diff will give you the best improvement in handling out of the three (front/center/rear.) Next, you should upgrade the rear diff. KAZZ makes a good unit here. Or upgrade to the R180 rear (which also requires the R180 knuckles and axles so can be $$ but a worthwile upgrade. The R160 stuff is puny and weak and will be your weak link if you have any power.) Usually you go 2-way in the rear, both the KAAZ and the stock Subaru R180 are 2-way. The stock STi R180 LSD is actually a really nice strong clutch unit and you can get more aggressive pressure plates that provide more lock up for rally use.
After you have the center and rear the front is pretty optional, really. Usually you go 1.5-way in the front. STi has a nice one but expensive. All the front diffs are expensive $1000-$1500 range. Cusco has an interesting one with preload springs and the option to set it up 1.5 way and 1 way or 2 way, I think. I forget.
Don't do any of the others without doing the center diff first or you are just wasting your time and money.

^^thx Dave, that's what I was looking for...basic, precise...good info.

sti centder diff--check, just need to install.

I also have a line on a good 2-way rear (barely used), little out of my price range though, but we'll see.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/

a little off topic -- but what exactly is different between the R180 and R160 diffs regarding axles?

I have an STI 3.90 R180 (from a 2004 japanese STI) and an STI 4.11 R160 (from a 1995 japanese STI) sitting next to eachother. The R160 axles seem like they fit just fine in the R180.

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http://www.ckrally.com

cblakely Wrote:
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> a little off topic -- but what exactly is
> different between the R180 and R160 diffs
> regarding axles?
>
> I have an STI 3.90 R180 (from a 2004 japanese STI)
> and an STI 4.11 R160 (from a 1995 japanese STI)
> sitting next to eachother. The R160 axles seem
> like they fit just fine in the R180.
>
>
>
Hitachi R160 is the ring gear diameter, and R180 is 180mm ring gear diameter.
Expressed in INCHEs like American axles you can see why those cars are rightfully held in contempt as underdimesioned junk. The 160mm is 6.3" and that's tiny for a car supposedly making some ft/lbs and being pounded.
180mm is 7" and thats just OK.
To give you an idea, the OEM Ford 4x4 front is 6.5" and rear is 7.0" and the 2wd cars get 7.5" diffs.

EARLY GpA got 7.5" front and 9" rear.
Late 4wd GpA Ford got 8.5 or 8.8" front and 9" rear.

In Sub-a-rat defense, unlike any fwd cars, at least you can upgrade the diffs.

Then there's the question of the driveshaft and spline sizes, CV size---again marginal compared to other similar cars.
> ------------------------------------
>
>

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

cblakely Wrote:
-------------------------------------------------------
> a little off topic -- but what exactly is
> different between the R180 and R160 diffs
> regarding axles?
>
> I have an STI 3.90 R180 (from a 2004 japanese STI)
> and an STI 4.11 R160 (from a 1995 japanese STI)
> sitting next to eachother. The R160 axles seem
> like they fit just fine in the R180.


They may seem like it but they don't. The R180 splines are bigger, though not by much. The outers are bigger, too. The shafts are bigger, too. The R180 knuckles are bigger as they have bigger wheel bearings. Some people try to take the cheap route and use the R180 diff with cobbled together axles to adapt them to the R160 knuckles. What is the point od that? Now you are just going to break the outers as that is still the weak link.
As JV mentioned the ring gear size is dramatically bigger on the R180. The R160 ring gear is considerably smaller than the front 5-speed ring gear. The R180 ring gear is slightly larger than the front 5-speed ring gear.

good to know... I guess I need to find some STI axles to use with the R180 though. Since I'm using it in a Datsun 510 I really don't care about hubs and stuff, nor do I care about the outer CV since I have to adapt it to a 4-bolt U joint plate thing that is the stub axle.

Frankendriveline!

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http://www.ckrally.com

john vanlandingham Wrote:
-------------------------------------------------------
>
> In Sub-a-rat defense, unlike any fwd cars, at
> least you can upgrade the diffs.
>

Bah. You can upgrade the diffs in fwd. It's just a royal pain in the ass and requires several hours of mining, and possibly (at least in the case of golves)
a grinder and buncha shims.

BUT YOU CAN DO IT!


Er...not to be sidetracked from the topic at hand. Clearly I need another beer.

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Self-righteous douche canoe

hoche Wrote:
-------------------------------------------------------
> john vanlandingham Wrote:
> --------------------------------------------------
> -----
> >
> > In Sub-a-rat defense, unlike any fwd cars,
> at
> > least you can upgrade the diffs.
> >
>
> Bah. You can upgrade the diffs in fwd. It's just a
> royal pain in the ass and requires several hours
> of mining, and possibly (at least in the case of
> golves)
> a grinder and buncha shims.
>
> BUT YOU CAN DO IT!


UPgrade as in INSTALL A BIGGER unit, BIGGER, STRONGER

>
>
> Er...not to be sidetracked from the topic at hand.
> Clearly I need another beer.

Yeah, have another even if it is 0745.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Remember that Subaru front diff i asked all the questions about??

Yeah....it's likely forsale!

best i can tell it's probably a Cusco. I love it in my car. However the rest of the 5 spd took a holiday. So i'm upgrading everything to 6 spd!


I've also got a rear "mechanical" center section from a diff i could have up forsale as well. It was fantastic, and gets rid of the spider gears and makes the R160 alot stronger.

Also got an STI 20KG center diff....but you'll have to use the "old" rear transfer case section to use this.

Let me know if you have interest in anything.

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Chris

approx price and mileage on the front diff? this is down the road too....probably not until end of the year.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/