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This article was first published in September 1999.
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If you don't know of the clutch-frying abilities of the Subaru WRX, you haven't
talked to any Impreza owners! One Adelaide man, let's just call him Rex, knows all
about the on-going probs.
Owning a MY99 model fitted with a (larger) MY94 turbo, A'PEXi front-mount intercooler
and 3 inch exhaust, he was looking for some extra-strong launches. And the stock
clutch, as usual, simply wasn't up to the job. So to gain the upper hand on the
problem, his first point of call was John Keen at DAT Racing.
John's taken more than a couple of the Subaru RS/WRX gearboxes out, so it didn't
take him long to get the 'box onto the floor. There are a few tricks of the trade,
though, like how to remove the cover plug that conceals the pivot pin for the thrust
bearing - without doing that, the gearbox won't come off! The job takes about one
hour.
With the gearbox on the floor, the standard clutch is revealed. Its design and
tech specs look fine on paper, but with the immense traction of the four wheel drive
system, it's the clutch that takes a beating - not like a 2WD car, where wheelspin
tends to save the clutch (and gearbox) from the same amount of torture. It's the
filling in a power/traction sandwich.
The flywheel shows the normal amount of blackened heat spots that appear on any
WRX flywheel that's more than a few thousand kays old. However, all 'n' all, this
one wasn't too bad. One option could have been to bolt up a new clutch without machining
or replacing the original flywheel.
Interestingly, close inspection of the old clutch plate shows that it wasn't
even worn out. Again, this is pretty rare and shows that Rex just needed a more
capable clutch - he hadn't stuffed the old one by lots of abuse (like we'd all thought!).
The Exedy dual plate clutch grips solidly because it has.... dual friction plates!
Both plates have sprung centres and multiple paddles sprouting outward. John Keen
(who's more used to working on race cars than Imprezas) suggested that the clutch
looked of good quality - up to AP specs for example. It uses organic type linings,
and its compact design is very similar to that used in the 6-Pack Chargers of the
Seventies. So the general impression we got was that it's likely to be up to the
job in the Subie.
The crankshaft pilot bearing needed to be swapped from the old flywheel and into
the new one. Notice how thin and light the one-piece chrome moly Exedy flywheel
is - but remember, the dual plate clutch itself weighs a lot more than a standard
Subaru clutch. Therefore the assembly's combined mass is probably comparable to
the stock flywheel/clutch system.
Aligning the splines on the clutches is a bit of a pain - done first by eye and
then using an Impreza clutch alignment tool. The new clutch and flywheel go straight
on - it's a complete bolt-up job.
The retaining bolts were securely Loctited on - you don't want that assembly
coming loose at 7 thousand revs do you?!
The Exedy clutch in place. Pity you can't see the pretty purple when the gearbox's
bolted on!
Verdict
So what's it like in operation - more like a standard full face or a kangaroo-hopping
unsprung paddle clutch? Well, it's about half way in between. John Keen says that
he thought it drove nearly as well as the standard clutch, being able to be ridden
when making moves like reverse parks. Why reverse parks? - 'cos that's one of the
hardest maneuvers to pull with a shuddery clutch.....). The pedal weight is only
a littler bit heavier, but it's still lighter than a stock Commodore V8 for example.
It engages quicker too - Rex says that you had to be careful not to pull out the
pedal too fast, or it would bite hard and stall the engine. And on full-bore launches?
There's absolutely no slip, no matter what revs the engine's doing when the pedal's
popped. One very slight problem of the twin plate clutch though, is that it does
make a little more noise upon engagement.
And the cost for the upgrade? A$3000 will pay for the Exedy clutch, and about
another A$250 is needed to have it fitted. If it can tolerate more hard driving
kilometers than the stockie Subaru clutch, it's gotta be the better option!
But let's just hope that what's inside this thing can hold out...
Contacts:
Adelaide Clutch Service
+61 8 8234 2222
DAT Racing
+61 8 8277 4222
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