that is correct, no LSD in 98-99. there are lots of possiblities for rear diffs, anything from an OEM on 00-01/WRX, Quaife, Kaaz, Cusco, STi, you name it. lots to choose from. however, you will also need to upgrade the rear half-shafts to ones off of a 00-01.
So since I have a 98 and it doesn't have a LSD does that mean I am putting excessive wear on my rear differential? I'd imagine that since it's this way stock that it can't be too bad but I thought the LSD was rather important in an AWD system. Technically if I understand it right, without a LSD you'd face the same problems as a person with 4wd who left it on all the time.
I might just be confused and worrying about nothing but I am curious about it.
in the manual subaru AWD system, there are 3 differentials. Only the center one needs to be a LSD. In all current US market Subarus, the center diff is a viscous coupling unit. this means that as one drive shaft spins faster then the other (indicating slip) a fluid in the diff gets heated up and becomes thicker, creating more resistance against the spinning driveshaft and thus encouraging torque to go to the other driveshaft (from the wheels that slip to the wheels that grip). In some cars, such as the MY98-99, the front and rear diffs are open. this won't cause any type of accessive wear, it will just produce less traction because you then have to have both fronts or both rears maintain traction if one end looses it. with LSDs at the ends, then you can still pull yourself out with only one wheel still having traction. in the MY00-01 RS and the US-spec WRX, the fronts are open and the rear is another Viscous Coupling LSD. In cool places where they get things like the STi and 22b, they have all kinds of crazy mechanical diffs which are far better, and in some cases for the center diff, you can manually adjust the torque split. very trick shit. and then there are WRC cars which use electronically controlled diffs to constantly vary the torque distribution to maintain maximum traction.
Excellent explanation, thank you. I didn't realize that the center diff was a LSD, that's where the confusion came in. While I live in Michigan and traction can be hard to come by in the winter I don't think I will bother with adding a rear LSD to my car. For one it sounds like a much more complicated affair than I am ready to tackle and for two I don't want to have to buy shorter axle's and those $81 a piece bearings you guys have been complaining about.
I'm so torn on what to do with my car at this point. I'm still paying it off due to making the mistake of leasing it first and when I'm done I'm not sure if I want to mod it or trade it in. I don't really like the round headlight look of the newer model RS's and WRX's but at the same time I'd love to get a model with a tougher engine and SOHC as I've heard the block on the 98's is weak and can't handle much over 200hp.
If the thread in the General forum about the upcoming STi in the US is true then maybe I'll just shoot for that. I guess I rambled a little bit there and got off topic, who knew a LSD discussion could get me to tell you my life story.
On a related note, what would a front Quaiffe ATB vs a rear Quaiffe ATB do in regards to handling (assuming the other diff remains open)? Would both be more beneficial than just the front or rear would (I imagine it would)?
well, an LSD gives you more traction by sending the torque to both wheels, rather then whichever one has the least traction (which is obviously bad). I haven't personally driven in or riden in a car equiped with any Quaiffe product, so this is all conjecture. the rear LSD is going to give you more grip to the rear wheels. this should help it behave more RWDish, especially on a tight hairpin deal (power-on oversteer). the front LSD should give you good front end grip coming out of a corner. however, i imagine that its going to take a bit more effort to get the initial turn in done since that requires the wheels traveling at different speeds which is what the LSD is trying to keep from happening. How much more effort will depend on the amount of lock in the diff. obviously, suspension tuning goes hand in hand with this. you won't want a real tight diff in the front unless you plan on having the car sliding alot at the entry of a turn (i.e. rally).
like i said, i have no actual experience with this, so take it with a grain of salt.
oh, also, i agree, there probably is a cumulative effect with the front and rear diffs.
I'm definately having fun with the car so far and it's totally stock except for a set of Michelin tires (I work for them so I had to ditch the crapball Firestone/Bridgestone ones). The car has amazed me many times in the four and a half years I've had it, I'm very happy that I bought it.
While I'd like to mod it I'll probably have to wait until it's paid off. I have a large amount of debt from stupid mistakes I've made in the past and I'm literally paying for them now. With a wedding coming up in June I don't have anything to spare yet.
At the moment though my plans are to start simple, hopefully with new rear droplinks and a rear sway bar followed by a front sway bar and at least a rear strut tower brace. From there hopefully some new headers, maybe a high flow cat and a new muffler too. I don't want to do too much to this car as I will probably sell it eventually for a newer Subaru.
00-01 RS LSDs are fairly easy to get from junkyards but you must get the axles too. Another option (similar price though) is Phantom Grip LSD conversions. Pahtom Grip has both front and rear LSD units for us, both for less than any aftermarket rear. Check out their website http://www.phantomgrip.com/ .