TT worm drive ratio

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70shovelhead
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TT worm drive ratio

Post by 70shovelhead » Thu Oct 24, 2019 3:36 pm

Can the TT ratio be determined in a sealed housing and the axles stuck. In otherwords are there any outside markings? I am at a swap meet and a fella has a rear end he says is 5:1 but no physical way to check it. Thought about pulling the worm but the bolt heads are about to the point of needing a cuttin torch.
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Humblej
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Re: TT worm drive ratio

Post by Humblej » Thu Oct 24, 2019 4:32 pm

The early tt axles have a bead on the outer part of the pumpkin casting where the axle tube attaches. The early axles are the slow speed gearing. If the axle assy you are looking at does not have the bead it will likely be the high speed gearing. Thats the best you can do wothout turning the driveshaft or pulling the gears out.


hpetrino
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Re: TT worm drive ratio

Post by hpetrino » Thu Oct 24, 2019 6:14 pm

What Jeff says about the bead on the clam shell at the axle tube indicating an early rear end is true. However, from my experience most TT rear ends have the low speed gears, regardless of the date of manufacture. I can't give you a percentage, but certainly less than 50% of TT rear ends have high speed gears.

There are no markings to indicate low or high. Some guys say there was a painted marking (I don't remember what they said it looked like), but given the age of these things it's pretty unlikely you'll find a painted marking and even if you do you can't be sure what you're looking at. Also, even if what Jeff says about early being low and later being high when manufactured, there has been 100 years for folks to change things.

The only reliable means to know for sure is to either take it apart and count teeth or turn the driveshaft and count turns. Of course, depending on how much is being asked for it, you could always just take your chances and buy it then get it apart when you get it home.


Erik Barrett
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Re: TT worm drive ratio

Post by Erik Barrett » Thu Oct 24, 2019 6:16 pm

Remove the four bolt cover behind the worm gear. Take the big nut off and remove the thrust bearing and worm gear roller bearing. Look in with a pen light and count the teeth on the worm gear. Four teeth, low speed. Six teeth, high speed.


Tom Hicks
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Re: TT worm drive ratio

Post by Tom Hicks » Thu Oct 24, 2019 6:31 pm

Even if the axle was marked as to ratio when made, the gears could have been changed.

If you can turn the driveshaft you can determine the ratio by counting the number of turns of the wheel.

But the value is determined by the condition of the gears, and you have to remove the gears to determine their wear and longevity.

So I feel it is best to actually get your hands on the gears so you can determine their value.

These gears are getting rare and the value of good sets is going up. Their is a guy who makes limited numbers of new sets every few years. His last batch was $2,400/set.
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One390
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Re: TT worm drive ratio

Post by One390 » Thu Oct 24, 2019 10:10 pm

I will double check as I have 2 in the garage, but I think if the bearing will come out of input side you can count teeth as well. Assumption is rear doesn’t have torque tube on it. Just a thought. No outside markings that are a sure thing from my experience. Like a box of chocolates.....

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