Author Topic: Muncie speedo gear part numbers  (Read 9044 times)

L78 steve

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Muncie speedo gear part numbers
« on: September 25, 2007, 06:34:35 PM »
Does anyone know the part numbers for the range of drive and driven gears on the Muncie trans?Or where I can find a list?
69 Z/28 Dover White. SOLD
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C. SOLD
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B

1968RSZ28

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Re: Muncie speedo gear part numbers
« Reply #1 on: September 25, 2007, 07:38:42 PM »
Steve -

No part numbers, but hope this help:  http://www.chevelles.com/shop/speedo.html

Paul


JohnZ

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Re: Muncie speedo gear part numbers
« Reply #2 on: September 26, 2007, 03:28:28 PM »
Steve -

No part numbers, but hope this help:  http://www.chevelles.com/shop/speedo.html

Paul


That chart is for THM350/400 automatics. I put together the summary below last year for Muncies in Corvettes - the combinations assume midyear Corvette tire diameter (27.1"), but it details the DRIVE and DRIVEN gear families that go together:

CORVETTE SPEEDO GEAR TECH



   ’63-’67 4-speed and ’63-’67 Powerglide used pressed-on steel DRIVE
       gears on the mainshaft:

      GM #3708144 (8-tooth), 1.85” O.D., designed for use with nylon
                       gears from 18 to 22 teeth (silver); these “small” DRIVEN gears
                       are 0.8” O.D. and were used as follows:

      3.08 = 18-tooth, #3987918 (brown)
      3.36 = 20-tooth, #3987920 (blue)
      3.55 = 21-tooth, #3987921 (red)
      3.70 = 22-tooth, #3987922 (silver)

      GM #3708145 (8-tooth), 1.77” O.D., designed for use with nylon
      gears from 22 teeth (green) to 25 teeth; these “large” DRIVEN
      gears are 0.87” O.D. and were used as follows:

      3.70 = 22-tooth, #3860345 (green)
                   23-tooth, #3860346 (black)
      4.11 = 24-tooth, #3860347 (yellow)
      4.56 = 20-tooth, #3860329 (steel – used with special
                                 transmission with 1.77” diameter 6-tooth DRIVE gear)

   ’68-’70 Muncie 4-speeds used two different 8-tooth NYLON DRIVE
       gears, retained on the mainshaft with a spring steel clip:

      1.85” O.D. – GM #3924098 (later, #6261794); same “large” O.D. 
          as #3708144, used the same range of 18-22-tooth “small”
                          DRIVEN gears, and was light green in color.

      1.77” O.D. – GM #3924097 (later, #6261795); same “small” O.D.
          as #3708145, used the same range of 22-25-tooth “large”
          DRIVEN gears, and was medium blue in color.

   ’71-up 4-speeds had a larger mainshaft, and used only one DRIVE
       gear; 8-tooth, GM #3978758, the “large” size, 1.85” O.D., and used
       the 18-22-tooth range of “small” DRIVEN gears. There was no
       range of 22-tooth (green) to 25-tooth DRIVEN gears that would
       work with this DRIVE gear for 3.70 and higher numerical axle
       ratios, so an adapter gearbox was used for those axles along with
       the 18-22-tooth family of DRIVEN gears.


NOTE: The above assumes use of stock tire sizes. To calculate the correct
    speedo DRIVEN gear for other tire size/axle ratio combinations, use the
    following formula:

1)   Tire revs per mile – get from the tire manufacturer, or calculate:
Revs/Mile = 20168/tire diameter in inches.

2)   DRIVE gear teeth x axle ratio x revs per mile/1001 = DRIVEN gear
tooth count.

(GM speedos turn 1001 rpm @ 60 mph, or 1001 revs per mile)

(1-tooth driven gear change results in a 5% speedo change)
'69 Z/28
Fathom Green
CRG

1968RSZ28

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Re: Muncie speedo gear part numbers
« Reply #3 on: September 26, 2007, 04:13:27 PM »
Thanks John!    :)

Paul

L78 steve

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Re: Muncie speedo gear part numbers
« Reply #4 on: September 26, 2007, 04:57:11 PM »
Thank you John,exactly what I am looking for.Would you happen to have the part # for the 19 tooth white gear that would place between the 3.08 and 3.36 ratios?
69 Z/28 Dover White. SOLD
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C. SOLD
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B

JohnZ

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Re: Muncie speedo gear part numbers
« Reply #5 on: September 27, 2007, 04:20:31 PM »
Thank you John,exactly what I am looking for.Would you happen to have the part # for the 19 tooth white gear that would place between the 3.08 and 3.36 ratios?

The 19-tooth "natural" gear is #3987919.
'69 Z/28
Fathom Green
CRG

L78 steve

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Re: Muncie speedo gear part numbers
« Reply #6 on: September 27, 2007, 05:40:56 PM »
That makes sense,Thanks,John.
69 Z/28 Dover White. SOLD
67 SS/RS Mt. Green 1W,2LGSR,3SL,4K,5BY,07C. SOLD
70 Nova L78 Blk. Cherry,Sandalwood,M21,02B