Triple gear dimensions

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Model T Ford Forum: Forum 2013: Triple gear dimensions
Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave DeYoung on Monday, June 03, 2013 - 06:19 pm:

Does anyone know what the pitch diameter is of each gear on the triple gear setup and what size pin you would use to check that dimension? I have several triple gears and I would like to know which ones have the least wear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Tuesday, June 04, 2013 - 02:21 pm:

Dave,

If you know the number of teeth, (n), and the outside diameter, (O.D.), of each gear, you can then calculate the pitch, (P).

P = n+2/O.D.

The pitch diameter, (PD), is then;

PD = n/P

This is theoretical. If Ford tweeked the gear math then there may be some variation.

According to Van Keuren, the pin sizes you would use, depending on what pitch you've got, are as follows;

5p - .346
6p - .288
8P - .216
9p - .1728
11p - .158
12p - .144
14p - .123

If you can tell me the pitch & number of teeth for each gear, I can tell you what the theoretical measurement over wires, (pins), would be for each gear. Again, Ford may have varied some from the theoretical gear math, that's not uncommon. I am assuming a 14.5 degree pressure angle, which was common in the days of the T.


Top of pagePrevious messageNext messageBottom of page Link to this message  By George_Cherry Hill NJ on Tuesday, June 04, 2013 - 07:10 pm:

Dave,

A straight out of the box easy answer based on the original drawings with the implied 14-1/2 degree system taken to a MoW pin way is…

For the 24 tooth side, the wire should be 0.1728” and the MoW = 2.6425”

For the 33 tooth center, the wire should be 0.1728” and the MoW = 3.5412”

For the 27 tooth center, the wire should be 0.1728”, and the MoW = 2.9388”

The Ford tolerance on PD was +/- 0.001”

HOWEVER…I must warn, there is a HUGE red herring taking such a simplistic approach! Something that 'passes' this way may still be totally wrong!

I'd bet my teeth and then some that Ford manufacturing did NOT produce to what you see on the drawings! Just not the way it was done 'in the era' before AGMA by ANY shop. Model T folks think I speak heresy on some of these things and am the village idiot sounding off, but also fail to comprehend my own background...so I won't bore with the details of 'why' here, but if anyone wants to hear them privately send me a PM.

Your best recourse is to find someone with new-in-box original stamped logo Ford triple gear (reportedly there are a few out there), and have them have it measured with 0.1728” pins and come up with a number. THAT will be the real as produced number. You won't know where in the tolerance zone you are...but it will be much more closer than trying to use todays ways with MoW and what was in the era only an engineering reference PD to begin with.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Tuesday, June 04, 2013 - 07:34 pm:

You could measure the tooth width on the gears you have with a vernier and evaluate the surface visually and pick the best you have. If you have a complete original transmission, use the original gears and bushings as they have worn together in harmony and will give you the most quiet transmission. If you rebush and change gears, your transmission will be a real screamer.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John W. Oder - Houston, Texas on Tuesday, June 04, 2013 - 07:39 pm:

I'll add some to this discussion :-)

We can see in Jerry's post the .1728" wire discussed in George's post.

We can also see it was for 9 DP (Diametral Pitch)

Borrowing George's tooth counts, we can come up with standard Pitch Diameters (also sometimes referred to as Pitch Circle)

24 T is 2.6666" PD
33 T is 3.6666" PD
27 T is 3.0000" PD

It is important to realize they may not have been made to any one's standard but Henry's. :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Dave DeYoung on Tuesday, June 04, 2013 - 10:06 pm:

Thanks for the input guys. I remember reading that the person who did the gear cutting for the T-100 project used a modern tooth profile rather than the original design to make them as quiet as possible. That is why I came here first rather than pull out my Machinist Handbook.

I think what I will do is use your dimensions and pin size to establish a comparison baseline. Logic would say that the highest reading would have the least amount of wear.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Wednesday, June 05, 2013 - 11:23 am:

John,

George is correct with 10P being .1728, (9P is .192). I made a mistake in my chart above.

Ted,

The proper tool to measure gear tooth thickness is much more than just a vernier caliper.

They are very expensive as well.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Wednesday, June 05, 2013 - 11:31 am:

Dave,

The stub teeth that Ford used on the T-100's were indeed VERY quiet, while they lasted...

As I understand it, the clearances in the triple gear and drum bushings opened up with use and the amount of engagement between the gears decreased to the point that they began to wear very fast. There are no T-100 gears in any of the T-100 transmissions still in use.


Top of pagePrevious messageNext messageBottom of page Link to this message  By John W. Oder - Houston, Texas on Wednesday, June 05, 2013 - 11:41 am:

Okay, and thanks Jerry. :-)

New P.D.s for 10 DP:

24T = 2.4000
33T = 3.3000
27T = 2.7000


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