871/971 Selectospeed transmissions

ErnieD · Dec 9, 2015

Are the gear ratios the same for 871 and 971 transmissions?

Dean · Dec 9, 2015

Yes.

Dean

ErnieD · Dec 9, 2015

Thank you.

Larry NCKS · Dec 9, 2015

Transmission ratios are identical, but the 9 is still a slower machine because of the drop box planetaries on the rear axle.

Dean · Dec 9, 2015

I think you'll find that the 7/9** drop boxes are spur gears, Larry.

Dean

Ultradog MN · Dec 10, 2015

Yes they are spur gears.
And I always thought they were a 1:1 ratio meaning no reduction.

Larry NCKS · Dec 10, 2015

(quoted from post at 07:15:56 12/10/15) Yes they are spur gears.
And I always thought they were a 1:1 ratio meaning no reduction.

You and Dean are both correct in one respect: It is a spur gear system! Just was typing absent mindedly on that part.

However, take a good look at a parts schematic or a service manual. You'll quickly see that the drive gear is much smaller than the driven gear, making it a reduction drive.

Dean · Dec 10, 2015

Agreed. The final drives do provide gear reduction.

They also reverse direction, which is why the pinion gear is on the opposite side of the ring gear in the differential on the 7/9** tractors.

Dean

871/971 Selectospeed transmissions

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