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Old 09-27-2012, 11:02 AM
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Curtis did a very good write up. Thanks for that. I will add that in his example of the T10 vs the T56; the T56 has much larger gears, and it is constant mesh which as he said, means that entire big, heavy geartrain is always turning, and paddling oil around. This comparatively takes a lot of effort, not to mention these big end-loaded gearboxes often need a pump to adequately lubricate the overdrive set.
The whole double overdrive thing can be much ado about nothing in some performance cases. When Warner Gear designed the T56 for GM, it was originally a heavier duty T5, but GM wanted a double overdrive 6speed, mostly for marketing purposes. Back in the early 90s a lot of advertising was done regarding the new 6speed as a gearbox that won a lot of road races. What they didn't mention was that the gearboxes they were using had been converted to direct drive 4 speeds, the entire OD geartrain had been dummied up.
A lot of people I do business with report that they either don't use 1st gear, or that the carbed engine lugs too much in 6th and they dont use it. Especially the road race guys. 5 speeds seems to be a good compromise of a nice ratio spread and the OD.

Now for the OE side of things. A lot of development is going on with direct drive automatics with 6, 7 or 8 speeds. And direct drive 5 speeds were around in performance transmissions for years (Doug Nash). From a design standpoint, Overdrive's build heat and noise, and large overdrive ratios may have packaging concerns and strength issues. The better answer is a numerically lower rear gear, with a deeper 1st gear. Say something like a 3.08 rear and a 3:1 1st gear. You get the strength, less noise, ease of assembly and packaging of a direct drive transmission, and the economy we all desire.

WRT the original question; I think that its your imagination, although most three speed cars came from an era and an application with smaller, lower powered engines than say a modern 350 streetrod torquey motor you typically see coupled to say a 700r4 or a T5.
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