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post #39 of (permalink) Old 03-13-2012, 10:12 PM
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Join Date: May 2005
Posts: 5,288
Originally Posted by larry View Post
In neutral input shaft spins counter shaft which turns 1st and all other gears, only the mainshaft is stationary (driveshaft not turning thus you are slowing 1st to match speed of mainshaft That is an Downshift.... In no case are you ever trying to speed up 1st for a shift.
What? Rethink that, it's exactly backward. SLOWING the clutch-inputshaft-countershaft is an UPSHIFT.

Driving down the road, the output shaft is directly connected to the differential, and is turning at road speed (wheel rpm times DIff ratio). If you're in third and UPSHIFT to fourth, you press the clutch in and pull on the shift lever. The third syncro disengages and the fourth starts to engage. You are moving from a high engine speed to a lower engine speed at the same road speed. It has to SLOW down the clutch-inputshaft-countershaft to match the output shaft. Then you release the clutch and the engine slows (it at least partially did with your foot off the gas) to match the road speed.

As you UPSHIFT, the clutch-inputshaft-countershaft - all firmly meshed together - SLOWS DOWN.

Similarly, as you DOWNSHIFT, the clutch-inputshaft-countershaft SPEEDS UP.

Sitting at a stop with the clutch engaged and the TX in neutral, the output shaft is stationary. The clutch, input shaft, and countershaft are rotating at the engine idle speed. Press the clutch in, and push the shift lever to first gear. The counter shaft, input shaft, and clutch SLOW DOWN, so that when engaged it matches the STATIONARY speed of the output shaft. You still are not moving after all.

SLOWING the countershaft is an UPSHIFT. But the Alfa TX does not have an UPSHIFT syncro, so it goes GRRUNCH. Brand new. The only time it doesn't is if the synchs are new and tight, so the small cone engagement before the dog teeth engage is enough friction to stop the countershaft. New bearings from the Throw-Out-Bearing in the clutch to the back of the TX can also add a bit of drag to help slow the countershaft. If you try to shift quickly into first from idling neutral at a stop, you will hit the dog teeth before all that rotating Clutch-input shaft-countershaft-mass can stop. GRRUNCH!!


Last edited by 60sRacer; 03-13-2012 at 10:20 PM. Reason: auto spell keeps trying to make GRRUNCH into Grinch.
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