gears

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john2189
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gears

Postby john2189 » Sat Sep 24, 2016 3:39 pm

Is the gear ratio different in a 1949 and a 1972 cub transmission? The 49 has a much faster ground speed mowing in second gear with a woods 59 than the 72 same gear and mower. They both are at 2100 rpms at the pto. the ag tires on the 49 may be 1" or so taller than the turf tires on the 72.
thanks, john
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Re: gears

Postby ScottyD'sdad » Sat Sep 24, 2016 5:11 pm

Second gear was changed, between the time that those cubs were made.
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Re: gears

Postby john2189 » Sat Sep 24, 2016 6:25 pm

Ok so they slowed the 72 down.
Thanks
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Re: gears

Postby Glen » Sat Sep 24, 2016 7:34 pm

Hi,
Here is a page from the Cub parts book showing the transmission gears. The 2nd gear was changed at serial number 192113, which was late 1955. The newer Cubs are slightly slower in 2nd gear, than before 192113, evidently. I don't have one of each to compare the speeds.
The gears are numbers 8 and 22 in the pic. :)

http://www.farmallcub.info/manuals/cub_ ... 007-08.jpg

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Re: gears

Postby Crimson Tim » Sat Sep 24, 2016 7:52 pm

Curious about the gear change. I did not know that.

A larger diameter tire will also result in a faster road speed, all else being equal.



Side note: what did they do with the high crops? Did they just slap larger wheels on, and let the speed increase accordingly, or did they also have special high crop final drives, geared to negate the speed increase from the larger wheels?

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Re: gears

Postby john2189 » Sat Sep 24, 2016 9:29 pm

Wouldn't the taller tires on the high crop cause a power loss also?
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Re: gears

Postby Crimson Tim » Sat Sep 24, 2016 11:08 pm

john2189 wrote:Wouldn't the taller tires on the high crop cause a power loss also?


Yes, unless the final drive gears were redone on the high crop to negate the speed increase.

The torque from the engine will be multiplied by a series of gear ratios (transmission, differential, final drive) and then divided by the wheel radius to get the motive force applied to the ground. The larger the radius, the smaller the force. What I don't know is whether they tweaked one of the other gear ratios (probably final drive) to compensate.

On one hand, a high crop is not a very good candidate for heavy grunt work due to increased instability from the height, so maybe they just didn't worry about the power loss. Then again, you don't really want increased speed along with your increased instability, either.

Edit: looking at the diagram Glen referred to, they changed each gear one tooth for second. It should have reduced the forward speed in that gear by 8.5%. What's the forward speed in second? Something close to 4 mph if I recall, so a little under 1/2 mph difference from the gear change.

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Re: gears

Postby Glen » Sun Sep 25, 2016 8:25 pm

Hi Crimson Tim,

Here are pages from the Cub parts book, there's no mention of the final drive gears being different on a High Clearance Cub.

http://www.farmallcub.info/manuals/cub_ ... 007-12.jpg

http://www.farmallcub.info/manuals/cub_ ... 007-13.jpg

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Re: gears

Postby Crimson Tim » Mon Sep 26, 2016 8:24 am

Thanks, Glen. I figured you would be able to find the documents to answer that question, if they were out there.

I figured that since the final drives were mostly unchanged between the standard Cubs and the lo boys, and that there seem to be a lot more lo boys than hi crops, that the weren't likely to have gone so far as to make special hi crop final drive castings to get more height and take different gears. The only hi crop changes I saw on there were spacers to set the wheels out from the hubs.

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Re: gears

Postby Matt Kirsch » Tue Sep 27, 2016 2:33 pm

Far as I know, there were no gearing changes with the high-wide option. It was all external bolt-on stuff.

Since the tractor was only intended to perform cultivating duties with the high-wide package installed, the faster ground speed could be regulated by lowering the throttle, since not much power was needed to cultivate.

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Re: gears

Postby Glen » Wed Sep 28, 2016 9:30 pm

Hi,
Here is info from the 1955 Cub brochure about the High Clearance Cubs.
When they changed the number of 2nd gear teeth at serial number 192113, they also raised the engine RPM from 1600 to 1800. :)
Attachments
Cub 3.jpg


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