Gear ratio in transmission. Explain please. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Smokintire70 · 08-13-2016, 01:22 PM

I don't know how the gear ratio works in a transmission. Can some one explain it to me like I'm im kindergarten? That would be great. Thanks.

Alex V. · 08-13-2016, 01:55 PM

The changing of ratios, or how each ratio relates to engine RPM, ground speed, etc.? More specifically, automatic or manual?

davepl · 08-13-2016, 02:21 PM

Its like your old ten speed bike, but instead of big gears and little gears connected by a chain, it's big gears and little gears meshed together directly. In lower gears the engine can produce more axle torque but at lower speeds, good for climbing hills and pulling boats. At higher speeds that gear reduction goes away until in high gear it's 1:1 (in our trucks) and the rear end is the only gear reduction between piston and tire.

Since you can't stop the wheels while the engine is running, the torque converter allows some slip between the engine and the trans when they two are turning slowly, and then less and less slip as they turn faster, up to about 1500 rpm when there's almost no slip.

Old Powerglides only have 2 gears. Most of our automatics in these trucks are 3 speeds. Later models have 4 or 6 or even 10 speeds these days.

Basic enough? Need more detail?

Smokintire70 · 08-13-2016, 03:43 PM

It's a 700R4. So the first gear is 3.06. Does this mean the output of the transmission is basically 1/3 of the engine speed? And 3rd gear is 1.00, meaning the engine speed is equal to output speed of tranny? Also the 700R4's overdrive is .70 so the tranny output spins faster than the engine speed. Is this all correct?

davepl · 08-13-2016, 05:20 PM

Quote:

Originally Posted by Smokintire70

It's a 700R4. So the first gear is 3.06. Does this mean the output of the transmission is basically 1/3 of the engine speed? And 3rd gear is 1.00, meaning the engine speed is equal to output speed of tranny? Also the 700R4's overdrive is .70 so the tranny output spins faster than the engine speed. Is this all correct?

It is. Also on these later model units there is a clutch that can lock up so that the torque converter doesn't slip -at all- once rolling along at a good speed in top gear, for example.

Bigdav160 · 08-13-2016, 04:40 PM

Yes!

Smokintire70 · 08-13-2016, 05:20 PM

Cool thank you guys! It was kinda confusing to me. Glad I got it.

08-13-2016, 01:22 PM	#1
Smokintire70 Registered User Join Date: Jul 2016 Location: Santa Rosa California Posts: 52	Gear ratio in transmission. Explain please. I don't know how the gear ratio works in a transmission. Can some one explain it to me like I'm im kindergarten? That would be great. Thanks.

08-13-2016, 01:55 PM	#2
Alex V. Registered User Join Date: Mar 2013 Location: Campbellsville, KY Posts: 888	Re: Gear ratio in transmission. Explain please. The changing of ratios, or how each ratio relates to engine RPM, ground speed, etc.? More specifically, automatic or manual? __________________ Alex V. ------ 1967 C10 Suburban, 350/NP435, Green/Green, PS, PB, HD cooling, charging, shocks, and springs. 1985 GMC C3500 SRW, Sierra Classic, 454/TH400, white/blue.

08-13-2016, 02:21 PM	#3
davepl Registered User Join Date: Aug 2006 Location: Redmond, WA Posts: 6,332	Re: Gear ratio in transmission. Explain please. Its like your old ten speed bike, but instead of big gears and little gears connected by a chain, it's big gears and little gears meshed together directly. In lower gears the engine can produce more axle torque but at lower speeds, good for climbing hills and pulling boats. At higher speeds that gear reduction goes away until in high gear it's 1:1 (in our trucks) and the rear end is the only gear reduction between piston and tire. Since you can't stop the wheels while the engine is running, the torque converter allows some slip between the engine and the trans when they two are turning slowly, and then less and less slip as they turn faster, up to about 1500 rpm when there's almost no slip. Old Powerglides only have 2 gears. Most of our automatics in these trucks are 3 speeds. Later models have 4 or 6 or even 10 speeds these days. Basic enough? Need more detail? __________________ 1970 GMC Sierra Grande Custom Camper - Built, not Bought 1969 Pontiac 2+2 427/390 4-speed Coupe 1969 Pontiac 2+2 427/390 4-speed Convertible

08-13-2016, 03:43 PM	#4
Smokintire70 Registered User Join Date: Jul 2016 Location: Santa Rosa California Posts: 52	Re: Gear ratio in transmission. Explain please. It's a 700R4. So the first gear is 3.06. Does this mean the output of the transmission is basically 1/3 of the engine speed? And 3rd gear is 1.00, meaning the engine speed is equal to output speed of tranny? Also the 700R4's overdrive is .70 so the tranny output spins faster than the engine speed. Is this all correct?

08-13-2016, 04:40 PM	#6
Bigdav160 Registered User Join Date: Apr 2011 Location: Klein Texas Posts: 3,852	Re: Gear ratio in transmission. Explain please. Yes! __________________ My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe

08-13-2016, 05:20 PM	#7
Smokintire70 Registered User Join Date: Jul 2016 Location: Santa Rosa California Posts: 52	Re: Gear ratio in transmission. Explain please. Cool thank you guys! It was kinda confusing to me. Glad I got it.



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