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Track rebuilding with conveyor belts


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Well, after many months have gone by and my primary plan of having new bands made here in the USA have fallen apart, I have decided to just rebuild my own tracks with conveyor belting as that was my very first option anyways.  

In making up a template I have discovered some questions.  In looking at original Studebaker prints on the 56 grouser tracks I have based my template on that pattern. The spacing/pitch is 4.5" center to center and 56 pitches per track. That works out to a length of 252".  I have been told on Facebook that the 55 grouser tracks use a spacing/pitch of 4.613" and 55 pitches for a length of 253.715".  Now doing the calculations on the radius that works out to 40.37999639" on the 55 count and 40.10704566" on the 56 count. 

In order for those tracks to be interchangeable, which I'm sure they were, then the inner bands that the road wheels ride on would have to be different thicknesses so that the timing of the sprocket is correct.  With that in mind, its common knowledge that the 55 count tracks have 1" thick inner bands.  So doing the math on that using the 4.613" pitch, as given on Facebook, and subtracting the 1" thickness for the inner band, you would have a new radius of 39.37999639" and new circumference of 247.4318" for the top of the inner bands. 

If you then take that circumference of 247.4318" and reverse the calculations to determine the band thickness of the 56 count tracks, I come up with a inner band thickness of 0.72705".

This would make sense being that the sprockets don't change and the further away from the center of the sprocket you are, the further apart that the grousers would need to be spaced in order to still be in correct timing. And the closer to the center of the sprocket that you are, the closer together that the grouser would need to be in order to still be in correct timing.


Does anyone have more knowledge on this subject that can confirm or deny my assessments here?  


The 4.613" pitch came from a drawing the someone had that showed the spacing between the grousers was 2.363" from bolt hole to bolt hole, then adding the 2.25" spacing of the distance between the bolt holes on grousers.  

On the earlier 56 count tracks all of the hole spacings are 2.25" on both the grousers and between the grousers. 

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Thank you both for the feed back and confirmation of some of this data @nwarcade@OZM29C.

Based on what I've got so far I've drawn up what these difference look like in CAD.

The track sprocket image is just a simple sketch using measurements from a NOS sprocket that I have. I am assuming that all of the drive sprockets are the same in terms of the number of teeth and layout and diameter. I realize that there may be some differences in actual design due to production changes through the years, but that the functional parts of the sprockets remained the same.  

On the track sprocket sketch you can see the comparisons of the 55 and 56 grouser layouts.  The red circle is the 55 type track using the 4.613 pitch. The green circle is the 56 type track using the 4.5 pitch. The yellow circle is the actual diameter of the sprocket where the outer rubber wheels would ride. The blue lines are the length and locations of the drive sprocket teeth. As you can see, both track types will ride in the middle of the sprocket teeth.


On the track band diameter sketch you can see the comparisons of the 55 and 56 grouser layouts and the different bands when it comes to the diameter of the entire track.  The red line is the 55 type track with a 4.613" pitch and diameter of 80.75999277".  The green line is that same 55 type track and 4.613" pitch, but removing 2" from the diameter to account for the 1" thick rubber inner bands.  The blue line is for the 56 type track using 4.5" pitch and a diameter of 80.21409132".  The yellow line is the same 56 type track and 4.5" pitch but removing 1.4541" from the diameter to account for the calculated o.72705" inner track bands.  The purple line is using the same 56 type track with 4.5" pitch but removing 1.5" from the diameter instead of 1.4541", this allows for a more commercially available size of 3/4" inner track bands. The difference in the diameter is almost negligible.


  Where I think people in the past have gone wrong is rebuilding the 56 type track using the 1" inner bands. Doing this will result in a 1.715" shorter circumference from the 55 type track and will causing timing issues.  Even using the 3/4" inner bands on the 56 type track instead of the calculated 0.72705" will cause a circumference difference of 0.144203695" when compared to the factory 55 type track and 1" inner bands. 

I plan to make a test run of this and verify what I'm getting on the computer before too long.

Thank you,




Edited by 04mustang
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A little further into this discussion, 

What I drew above is based on 1" inner bands. We have the drawings that show it is actually 15/16".  So I did another drawing to show the differences on that and a few options for using the 56 type track and 55 type track to achieve the same diameter. 

The 55 type track with a 15/16" inner band comes out to a diameter of 78.88499277". Translating this over to the 56 type track, in order to achieve the same diameter we need an inner band thickness of 0.66455" which will give us 78.88499132" diameter.  Using an actual number of 21/32" we have a diameter of 78.90159132".  

I already have conveyor belting that is 3/4" for use on the inner bands. So that calculation works out to 78.71409132" diameter. 


This comes out to the following overall distances/circumferences:

55 type track with 15/16" inner bands: 247.8245138"

55 type track with 1" inner bands: 247.4318147"

56 type track with 21/32" inner bands: 247.8766596"

56 type track with 3/4" inner bands: 247.287611"

56 type track with 1" inner bands: 245.7168147"

track band diameter 2.png

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So my head is starting to spin a little bit in looking over the plans from Studebaker and comparing 55 to 56 type track and digging through the ORD manual (thank you @Patrick Tipton for the manuals). 

Here are some comparisons that I have put together. 

  Studebaker Part No. Ordnance No. Notes
Sprocket SD-905654 C128337 Part of Drive Wheel C128336
  SD-908991   Part of Drive Wheel 7324249
Drive Wheel Assembly SD-905653 C128336 Used Through Serial No. 2101 (M29)
  SD-908167 C128459 Used Through Serial No. 2101 - 14229
  SD-908990 7324249 Used After Serial No. 14229 (Supersedes 128459)
20" Tracks SD-908172 D73029 Outer Cable Type, Used Through Serial No. 2102 - 14108 (Except 13584, 13585, 13660)
  SD-908646 7016555 Outer Cable Type, Used Through Serial No. 14108-14158 (&13584, 13545, 13660)
  SD-908657 7016556

Outer Band Type, Used After Serial No. 14159 (Supersedes D73029 & 7016555)


For your viewing pleasure I have attached the actual drawings from Studebaker.  These were prints that I purchased from the archives to compare the differences But i hope they can be useful to everyone.  I firmly believe that getting information like this out to the general public is the only way that we can save these machines for future use/learning/generations. 

One thing ill note is that The assembly drawing of the 55 type track shows an inner band thickness of 60/64 (15/16), but the band drawing shows a thickness of 0.960. 

I also now believe that the critical distance isn't the thickness of the band relative to the grouser face. I think its more so important to look at the measurement from the top of the band to where it will be bending as the track turns (i.e. the internal cable locations). 


55 Type Inner Bands.jpg

55 Type Track Assembley.jpg

55 Type Track Grouser.jpg

56 Type Grouser.jpg

56 Type Inner Bands.jpg

56 Type Track Assembley.jpg


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