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, Sat, 9 Apr 2005 19:45:48
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Ah, welcome to the world of the C900 transmission. Sadly, Saab had a truly great car with the 900 Turbo, but only half-cooked the transmission.
As Andy says, the box is weak. The stock-standard turbo motor is more than capable of bringing the gearbox (auto or manual) to its knees even before you start increasing the power output. Much of it is down to the unconventional design/layout (though it is in fact not too dissimilar to most mid-engined, rear-wheel drive supercars out there) and smallish bearings, though I believe the amount of flex and general lack of strength in the case itself only worsens the problem.
You've probably discovered a distinct lack of gearbox upgrades available to strengthen the 'boxes. Swedish Dynamics do a pinion bearing upgrade for pre-'91 'boxes. Sweedspeed (apparently) do a reinforced shift fork and a stronger diff cover/plate for "racing use". Quaife and Phantom Grip LSDs can be made to fit with some machining. Speedparts have proper strengthening upgrade, a 4-speed, non-syncro'd gearset purely for racing that last time I checked cost Kr37,000 - ie. more than your C900. And that's about it, unless you count clutch upgrades, better CVs, solid engine mounts and short shifters, but none of these really help to strengthen the box itself.
For years the best option was considered to be a Jorgen Eriksson 4-speed rallye gearbox; a combination of a '78 99 4-speed transmission with a heap of his own custom bits. They cost US$2000-$3000 depending on spec, however Jorgen is now no longer making them (or so it appears) and is concentrating on an LSD design of his own. Scanwest also make a "stronger" 5-speed unit that I'm told costs around the US$4000; not sure what they do to it, but for that kinda cash you'd hope a fair bit ;-) !
Basically the options are to (a) baby it or (b) thrash it and fix/replace it - hope you have deep pockets for the latter.
One relatively affordable option I considered before simply giving up and deciding to keep my car's plans 'under 200HP' was to get a post-'91 box from a low-kay, non-turbo car and cryogenically treat as much metal as possible - gearsets, case, bearing surfaces, whatever I could. Cryo-treatment hardens the surface of the metal through molecular realignment - most racing teams use it extensively to increase the life of various components.
I'm interested in this .72 primary ratio you speak of, I've never heard of it before. Like most 900 Turbo pilots 1st gear irritates me greatly, especially in drags from the lights when idiots in Hyundais seem to keep up until you hook third and the APC finally decides you're worthy of some boost :-p. That said, the short 1st and 2nd gears probably exist for a reason... in a conversation with a retired Saab tech, I was told that the shorter ratios help to keep torque levels down in the gearbox when taking off and thus help to prevent the gearbox from breaking. As such, having better ratios may shorten the 'boxes life - case of better the devil you know. Still, if it was a standard fitment in Europe... I'd love to hear some more about this.
I'd love someone to spend the time designing and building a truly custom 5- or even a 6-speed (sequential perhaps?)... but I'm not holding my breath. Such a project would be very, very expensive as you'd be starting with a chunk of metal and going from there. Maybe if the market for performance C900s was anywhere near the size of the GTR/Supra/S2000/S15 market, someone might have given it a go.
That said, if you can make a 6-speed close ratio box that will happily eat 300HP+ and sell it for under US$3000, consider me in ;-)
Cheers,
Ben.
posted by 203.52.130...
, Sat, 9 Apr 2005 19:45:48
, Tue, 12 Apr 2005 08:25:21, Sat, 16 Apr 2005 18:13:45
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