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Old 07-03-2020, 09:18 PM   #1
31Abone
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Default Rocky mountain under drive ? what is it ?

A "T" man here said it was not Model T or model A ? anyone know what it is ?
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Old 07-04-2020, 04:32 AM   #2
chrs1961815
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Default Re: Rocky mountain under drive ? what is it ?

The guy was sort of right. That actually was made for a TT truck - read this thread.
http://www.mtfca.com/discus/messages...tml?1231914641
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Old 07-04-2020, 10:21 AM   #3
31Abone
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Default Re: Rocky mountain under drive ? what is it ?

Great info..should have posted to T forum..pic that i found on search
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Old 07-04-2020, 10:49 AM   #4
rotorwrench
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Default Re: Rocky mountain under drive ? what is it ?

Most of these type units function and a two speed rear axle would. Some are under drives to allow for lower gearing ratios for pulling heavy loads. Some units like this are both an under drive and an over drive for a three way split of gears giving nine possible speeds forward and three in reverse.

Since that one is advertised as a six speed then I'd be relatively certain that it is just an under drive box with an under drive ratio and a one to one ratio only. This way a person can split shift in all three forward gears giving 6 ratios usable in forward motion and two ratios in reverse.

Units were manufactured to work with the Model AA trucks as well.
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Old 07-04-2020, 11:04 AM   #5
Bob C
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Default Re: Rocky mountain under drive ? what is it ?

Quote:
Originally Posted by rotorwrench View Post
Most of these type units function and a two speed rear axle would. Some are under drives to allow for lower gearing ratios for pulling heavy loads. Some units like this are both an under drive and an over drive for a three way split of gears giving nine possible speeds forward and three in reverse.

Since that one is advertised as a six speed then I'd be relatively certain that it is just an under drive box with an under drive ratio and a one to one ratio only. This way a person can split shift in all three forward gears giving 6 ratios usable in forward motion and two ratios in reverse.

Units were manufactured to work with the Model AA trucks as well.

The Model T only had a two speed transmission so the Rocky Mountain
would have to be a three speed to get six speeds. The ad shows
three speeds in reverse.
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Old 07-04-2020, 11:15 AM   #6
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Default Re: Rocky mountain under drive ? what is it ?

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more info picture
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Old 07-05-2020, 11:25 AM   #7
rotorwrench
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Default Re: Rocky mountain under drive ? what is it ?

Quote:
Originally Posted by Bob C View Post
The Model T only had a two speed transmission so the Rocky Mountain
would have to be a three speed to get six speeds. The ad shows
three speeds in reverse.
Your right. It's an over under then. I keep thinking about my Grandad's old IHC Six Speed Specials. He never had Model TT trucks.
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