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It's a wheel that doesn't cost you anything... okay...
Posted by spiv (more from spiv) on Sat, 14 Jun 2003 21:07:01
In Reply to: What is a freewheel?, K-Saab , Sat, 14 Jun 2003 19:15:53
...what it is REALLY is an overrunning-clutch mechanism found on all the two-strokes, V4 96es, Sonetts, and some early 99s.

It works like the rear hub on a bicycle. You know how on a bicycle, you can pedal and it turns the back wheel via a chain... but when you're coasting, the wheel spins freely but the pedals don't turn...? The Saab freewheel does exactly the same. When you're applying power via the engine, the freewheel hub (inside the transaxle) locks up and transmits the power to the wheels. Once you've got some momentum, you can lift off the gas -- the freewheel hub spins freely, and the car will coast along just as if you had put the transmission in neutral.

Why did SAAB install this mechanism? It originated in the era of the 2-stroke engines, in which the moving parts were lubricated by oil mixed with the gas. Without freewheel, if you were coasting down a mountain with your foot off the gas, the engine could be turning several thousand RPM with the throttle completely closed, meaning almost no oil would be getting to the moving parts. With freewheel, the engine drops off to idle as you coast, reducing engine wear.

This was no longer an issue once SAAB introduced 2-stroke engines with oil injection, as well as the conventional 4-stroke engines in subsequent models. So why did they keep the freewheel? There are a lot of speculations on this. Saab had advertised freewheel as an advantage, so maybe they didn't feel they could back away from it. They claimed it improved fuel economy a bit (which it does, slightly.) Some customers liked the smoothness and quietness it provides -- lift off the gas and there's no jerk of engine braking, and the engine noise drops off. Best of all, it allows you to downshift without using the normal clutch -- when you lift off the gas, the freewheel disengages drive, so you can just move the lever into a lower gear and then bring up the throttle again. This is really convenient in city driving, where you're always having to slow down for corners and then pick up again.

So if it was so great, why did they drop it? Well, it did add cost, without being seen by most potential buyers as a big benefit; it confused some drivers; and, well, it was one more thing to break, and occasionally it DID break -- immobilizing the car and requiring removal of the engine and transmission to fix. In fact, you find a lot of cars now on which the freewheel failed and was permanently locked.

Still, having driven SAABs with freewheel and without, I think it's nice to have at least the OPTION of using it, and it really does give a nice feeling of relaxed cruising. So if you have a choice of buying two cars in generally similar condition except that one has a working freewheel and one doesn't, buy the one that does!

posted by 68.13.13...
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