Model TT rear end gears

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Model T Ford Forum: Forum 2015: Model TT rear end gears
Top of pagePrevious messageNext messageBottom of page Link to this message  By Justin H. - Western PA on Wednesday, February 18, 2015 - 10:02 pm:

There has been a lot of discussion about the different rear end ratios originally supplied in the TT trucks. Also, the question frequently pops up on how to tell the difference and if there is an easy way to check what gear is in a rear end. While there is a lot of good information to be found there are few pictures so here are a few for those who search in the future.

The left gear is high speed (5.17:1, 31 teeth) and the right is standard (7.25:1, 29 teeth)


Comparison of "toes" on the teeth. The top gear is standard and is very close to being a NOS gear with very little wear (Traded to me by John Danuser R.I.P.). The bottom gear is high speed with some wear but no knife edges. Because the high speed gear has two more teeth than the standard gear in the same circumference, un-worn toes will be a different width with the high speed being more narrow. A heavily worn gear will tend to be very sharp at the outer edges and sometimes in the center in severe cases. When the edges become sharp they tend to chip. Depending on the usage of the truck, which will typically be minimal, even a mildly chipped gear would most likely be usable if nothing better can be found.


The top worm is high speed with 6 teeth and the bottom is low speed with 4 teeth.


Low speed worm gear as viewed on the end.


High speed worm gear as viewed on the end.


To check the ratio in a rear end, pull the rear thrust bearing cap, thrust bearing nut and thrust assembly, and rear Hyatt bearing. The end of the worm gear will be visible. Counting the teeth on the worm will tell what ratio is in the rear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Wednesday, February 18, 2015 - 11:51 pm:

I do believe another quick clue is the axle shift lever that identifies the two speed or high speed rear axle with the 31 tooth ring gear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By bob middleton on Wednesday, February 18, 2015 - 11:54 pm:

Not sure i rebiult many t rear ends and couple tt never heard of this axke shift lever please exsplain thanks


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Schreiber- Santa Isabel Ecuador on Thursday, February 19, 2015 - 07:15 am:

I believe James thinks these photos belong to a two speed TT rear end.


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