TT worm drive ratio

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
Posts: 85
Joined: Mon Apr 22, 2019 4:57 pm
First Name: Preston
Last Name: Wells
Location: Central Florida
Board Member Since: 2008

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.

"There is more to life than what we see"

1923 T Roadster
1926 TT Truck
1948 Willys Pickup
1937 Harley WL45
1919 IHC Titan 10-20

Posts: 439
Joined: Sun Jan 06, 2019 12:23 pm
First Name: Jeff
Last Name: Humble
Location: Charlevoix, Mi
Board Member Since: 2006

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.

Posts: 337
Joined: Sun Jan 06, 2019 11:14 am
First Name: Henry
Last Name: Petrino
Location: Modesto, CA

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
Posts: 194
Joined: Mon Jan 07, 2019 12:32 am
First Name: Erik
Last Name: Barrett
Location: Auburn, Ca.

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
Posts: 761
Joined: Sun Jan 06, 2019 12:07 pm
First Name: Thomas
Last Name: Hicks
Location: Chesterfield, VA
MTFCA Number: 32518

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.
Technology, the solution to all of our problems... and the cause of most of them.

User avatar

Posts: 20
Joined: Mon Jan 07, 2019 10:02 am
First Name: Tim
Last Name: Smith
Location: Oviedo

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.....

Post Reply Previous topicNext topic