What was the Model TT rear diff advantage?

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TorontoMD
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What was the Model TT rear diff advantage?

Post by TorontoMD » Sat Nov 07, 2020 3:35 pm

What was the reason for the worm gear drive in the TT?
Weren’t the actual axle shafts the weak part?
Is there an advantage to putting a TT rear on a speedster?
Curious if it was a locking diff for bad roads/farm fields or slipped like the standard t diff?


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Re: What was the Model TT rear diff advantage?

Post by Adam » Sat Nov 07, 2020 4:07 pm

TorontoMD wrote:
Sat Nov 07, 2020 3:35 pm
Is there an advantage to putting a TT rear on a speedster?
YES, so you can win First Place at the Slow Races!


But kidding aside, it was a much heavier built axle with a lower gear ratio. The lower ratio meant the vehicle moved quite a bit slower but could carry much more weight. The axle shafts are much thicker. I think one Ford brochure had the TT listed as having a speed of 18 mph.

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Re: What was the Model TT rear diff advantage?

Post by Humblej » Sat Nov 07, 2020 4:43 pm

Like Adam wrote, The TT rear axle mechanically reduces the speed of the wheels for the same engine rpm providing more "power" to the rear wheels. This is necessary to allow a model T engine and transmission to run and stop a truck loaded with one ton of payload. Top end with the early TT rear axles is about 17 mph, with the later TT rear axles about 25 mph. Not the setup for a speedster.


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TorontoMD
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Re: What was the Model TT rear diff advantage?

Post by TorontoMD » Sat Nov 07, 2020 4:55 pm

What about the Ruckstell TT rear ends?


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Re: What was the Model TT rear diff advantage?

Post by Andy Loso » Sat Nov 07, 2020 5:05 pm

Ruckstells are an under drive, so you'll go even slower.


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Re: What was the Model TT rear diff advantage?

Post by kmatt2 » Sat Nov 07, 2020 5:53 pm

The stock TT axle is quite strong for it's intended use, TT's have been known to carry loads well over one ton back in the day. The fact that modified to fit TT axles are used in Chevy 490's today to avoid the famious Chevy cone clutch broken axle should say something about the TT axle strength.


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Re: What was the Model TT rear diff advantage?

Post by HPetrino » Sat Nov 07, 2020 6:00 pm

In a stock set-up you're not likely to win any races, but you can't hardly destroy the thing either. It was used for a specific purpose and fulfilled that purpose quit well. Putting a TT rear end in a speedster strikes me as oxymoronic.

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Re: What was the Model TT rear diff advantage?

Post by A Whiteman » Wed Nov 11, 2020 12:38 am

I believe the worm was used due to two main considerations. Firstly, one of metallurgy of the time. Worm drives are a lot stronger and easier to make than a heavy duty crown wheel and pinion, and weigh much less than a whacking big solid crown wheel.

Given the low power of engines then, the worm also gives a mechanical advantage compared with the crown wheel. Any help when moving heavy loads with low power was welcome.

High speeds were not an issue given the road surfaces of the time but also compared to what everyone was used to - the horse. Practically anything was 'high speed' compared to a tired on 'dobbin'.

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