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Some additional notes Posted by Ari [Email] ![]() ![]() In Reply to: How to Double Clutch and Extend your Manual Tranny Life, KevinOD, Fri, 14 Dec 2001 13:04:59 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Double clutching helps extend the life of synchros, because the purpose of synchros (synchonizers) is to match the gear speeds, just like double-clutching does. If you double-clutch properly, the synchos work is easier, and they live longer. And yes,you crunch gears less.
A couple of points-
The weak spots in the 900 transmission is reverse, 5th, and the pinion gear. Double clutching won't help reverse, and because the torque is low, will have minimal help with 5th. The pinion gear is helped a little by double-clutching mostly because it tends to slow your shifts down, so the shifts aren't as hard.
It's important to remember that the purpose of double clutching is to match the speed of the gears. Just pumping the clutch, once with the shifter in neutral, doesn't do this. It requires your right foot, too.
When you have the clutch out in neutral, you want to have the engine running at the same speed as it will be when you shift into your new gear. The purpose is to spin up the gear to the right speed.
For example on an upshift (all speeds are examples - I don't remember what road speed is what engine speed in a 900 tranny) - you're in second gear at 35 mph, which is 3000 rpm, and you want to shift into 3rd, which would be 2000 rpm at 35 mph. You push in the clutch, and shift to neutral. Release the clutch, and let the engine revs DROP down to 2000 rpm. This spins the gears up to the proper speed to match. Now, holding the engine at 2000 rpm, push in the clutch and shift into 3rd. Since all the gears are running at the same speed, it should be nice and smooth.
It's even more important when downshifting - that's where double-clutching does the most good, in my opinion. Say you're approaching a corner and want to shift down. You're going 45 mph in 3rd gear, which is about 2500 rpm. You push in the clutch, shift into neutral, and let the clutch out. At the same time, you bring the engine revs up to a hair over 3800 rpm. Still holding the revs up there, you push in the clutch and shift into 2nd. 3800 rpm is where you'd be at 45 mph in 2nd gear.
If you kept the engine revs the same and just pumped the clutch twice, once when you were in neutral, it would do no good other than wear the throwout bearing a little and exercise your left leg.
Matching engine speed sounds hard (quick - what's the engine rpm in 3rd gear at 47.3 mph?), but pretty soon you learn your shift points in various gears. But it's also obvious why for the great majority of the population, the general use of synchonizers in manual transmissions was a godsend.
So don't forget that the critical part of double-clutching is speed matching.
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