1950-1966 [Subscribe to Daily Digest] |
When freewheeling is active, it allows car speed to exceed engine speed. With most cars, if you take your foot off the accelerator while going down a hill, engine braking will hold down car speed. In a vintage Saab with the freewheel active, the engine speed will drop off to idle, while the car coasts along freely.
If that's not clear, think about riding a bicycle. When you're going up a hill, you turn the pedals and the drive wheel turns in step with them. But when you go downhill, you can hold the pedals still and the drive wheel can still turn without moving the pedals. This is because there's a freewheel mechanism in the wheel hub, and it does basically the same as the freewheel hub in your Saab's transaxle.
What are the advantages? Well, freewheel originated when Saabs were powered by two-stroke engines that were lubricated by oil mixed with the gasoline. Without freewheel, descending a steep hill with your foot off the accelerator could cause the engine to turn at fairly high speed with the throttle closed. No throttle = no fuel = no lubricating oil = seized engine. So, Saab incorporated the freewheel mechanism, allowing the engine to slow down to idle while the car rolled freely.
Freewheel wasn't really necessary on the later V4-powered cars, but Saab kept it anyway (it was even on the first 99 models, in fact.) Why? Well, it does have a few other advantages:
-- Fuel economy is improved a bit because you can coast whenever you want, simply by lifting your foot off the accelerator.
-- The interior is quieter because the engine drops off to idle whenever it isn't actually working.
-- You can downshift without using the clutch: Just lift your foot off the accelerator and, as the car's speed drops, move the lever into the next lower gear. This is a big convenience in around-town driving, and can be a real plus in competition driving as well -- no fancy heel-and-toeing required to match revs on downshifts!
So if freewheel had these advantages, why did Saab drop it? Several possible reasons:
-- It could be damaged if the driver didn't understand how to use it. You have to bring the car to a complete stop before engaging or disengaging it; if you fail to do so, the teeth in the locking sleeve can be sheared off.
-- It's a bit fragile if abused: the older 6-roller hub is supposedly pretty robust, but the later 10-roller hub can break if the driver brings up engine speed too abruptly and slams it into engagement.
-- It could create a scary situation for a driver unfamiliar with it, because there's no engine braking as with a normal car. This doesn't affect just timid novice drivers, either! I belong to a track-driving club, and when I was passing the exam for membership, my instructor offered to take a few laps in my Sonett with me riding along, so he could "show me how to drive better." There was one corner where, in his race-prepared VW Rabbit, he liked to lift off at the apex and let engine braking take the car onto the proper line to exit the turn. When he tried the same thing in my Sonett, of course there was no engine braking, and he found himself barely able to escape going off! I was impressed that he didn't scream, although his eyes got really big...
posted by 68.13.13...
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