4-Speeds are so cool...aren't they?
There's lots of talk on the intarweb about how cool it'd be to have a 4-speed transmission from a 99 or early 900. Well I got one and there's some things to know about them before dashing out to Walmart to pick one up.
- There aren't many around, so you'll have to go hunting for one.
- Most of the gear clusters, I'm told, are split at the gear roots. So just because you find a 'box doesn't mean the cluster is usable for power. Good luck.
- The only ones to have are the later, chain-driven versions (77+?? 78+??). The gear-driven 'boxes aren't worth crap on a 900.
- The best ones are said to be "chill cast," whatever the hell that means. To me, it doesn't mean much because this info is on the intarweb only, so until someone produces some Saab documentation, it's just a rumor. That said, mine happens to be the same p/n as the purported "chill cast" boxes. I feel special. Really. Actually, not really.
- You're going to lose your oil filler: the 4-speed has a narrow dipstick tube because the oil was added through the valve cover back then. You'll either have to suffer through adding oil through this tube, welding on a newer, 5-speed dipstick tube fitting, or fit a filler cap to your valve cover. I used a customized filler made of plastic from a Subaru. You can also get a generic filler cap from Summit Racing, etc. and weld it on. Or cut one off of some other car's valve cover.
- Your turbo bracket won't fit -- you'll need to notch it a little to clear a rib on the 'box. Nothing major, though.
- Your 900 downpipe bracket won't fit, either. You'll either need to fab a new one or get one from a 4-speed Turbo.
- Your gearing is going to suck on the highway: these 'boxes are geared short, and you'll be turning around 3 grand at 60 mph. If you live where the speed limit is 70, then you'll be closing in on 4k RPM when keeping up with fast (75+) highway traffic. For a daily driver with a highway commute, a 4-speed is, frankly, silly.
- The pinion bearing problem is still a problem. It's just the gears that are stronger.
- The 4-speed cases are heavier than 5-speed cases, in part, due to a different alloy. There is less magnesium in them. (I am told that the newer, 5-speed cases are more brittle, in part, because of a higher magnesium content in the alloy).
posted by saabhippo at 6:51 PM
4 Comments:
The FOUR speed boxes are awesome on the highway, IF, you replace the primary drive gears, chains, and chain tensioner with one from a 5 speed, THEN 1st will be a bit luggish-not much, and 4th will be just like 5th in a 5speed (ie 3k rpms = 75 to 80 mph in 4th gear)
Also, I had an spg for years, with all the upgrades, brakes, bilsteins, 2.1 head and intake, 9000 clutch, 8 valve fuel pump, rrfpr, 25 psi of boost, and on an on, and it had 6 trans in its life, 2 5speeds and 4 4speeds, and the best 4 speed I had was a 1974 geardriven one that had the primary drive swapped with one from a 1978 4 speed, lasted 2 years, and 30k miles without breaking, it met it's demise when I scrapped the car.
My '88 has a '91 transmission (well the casing is still from the '88), and I'm keeping the 5-speed. The pinion bearing issue bit me HARD. I'm all about the bigger pinion, baby!
Great blog. This is my first read.
Additionally, yes, the additional magnesium makes the casing a little more brittle, but the newer casings are weaker primarily becuase the additional strength of the magnesium allows for thinner castings. The thinner castings are in turn more brittle...
More brittle, but stronger? Yes, this is seemingly a paradox, but it's really a language thing. Strength is measured by strain and compression. However, toughness (brittleness is the opposite) can only be measured by repeating stress. Glass, for instance, can be a very strong material, but it is exceedingly brittle.
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