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| | | | Joined: Mar 2018 Posts: 140 'Bolter | | 'Bolter Joined: Mar 2018 Posts: 140 | So I have been searching for a driven gear for the 3 speed i have in my 1951 truck that is not original. it is a GM 3 speed. Case number GM15, 3354726, E245. The tailpiece is GM8, 8866722, E226. The P.O. converted it to a floor shift. The hole for the speedometer gear housing does not have threads. The housing has an O ring and is missing the driven gear. I looked into the hole and the drive gear looks good. What is the correct driven gear for this mystery? I understand to have the speedometer read correctly, you calculate the tooth number of the driven gear based on tire size ( 235/75 x 15), rear end gearing (3.90) and revolutions/mile. The formula I was given was driven gear=drive gear x rear end ratio x rev/mile divided by 1000. With my tires and rear endangering drive gear tooth number ( estimated by looking into the hole), I came up with either 14 or 16 tooth driven gear. I don’t know if this is correct but it is a start. My first concern is to locat a correct driven gear. Thanks for this site- it has helped immensly in my gentle restoration of my 1951 5 window 1/2 ton. Hopefully it will be rolling before the snow flies. | | | | | Joined: Jul 2000 Posts: 2,200 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,200 | Maybe this will help you to identify your transmission: Trans IDI think I would prowl around a wrecking yard to find a gear that fits. Don't worry about the ratio at this point; just find something that will fill the hole. Next, drive the truck with a GPS to compare speedo reading with true speed. Then figure out the correction required. Probably will need an adapter. Just an idea. I will be doing something like I suggested in the future. Or I might just permanently install a GPS.
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | One can also count the green roadside markers which in CO have miles on them, other states might have Morse code or something else! It is real easy to remember that one's speedo is something fast or slow in percentage, gives one something to do while traveling along.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
| | | | | Joined: Mar 2018 Posts: 140 'Bolter | | 'Bolter Joined: Mar 2018 Posts: 140 | Gord,
It looks like a Muncie 3 speed manual but I need to find out the year in order to find a driven gear. Casting number on the case is 3354726. | | | | | Joined: Apr 2005 Posts: 2,101 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,101 | I have found the same rear housings on both trucks and cars. The speedometer drive gear determines which type driven gear to use.
An example would be: 55-59 truck with a 3:90 rear end would use a 19 tooth metal gear. It has a corresponding drive gear which is larger than used in a passenger car. If the same truck had a car transmission, it would probably use a 22 tooth plastic gear. The corresponding drive gear would be smaller than the truck drive gear to accommodate the larger plastic gear. Subsequently, if it has a car drive gear it won't turn a truck driven gear. Pick up a plastic gear - many on ebay for about $12 and see if it fits.
Fred
1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine
| | | | | Joined: Jan 2013 Posts: 1,518 'Bolter | | 'Bolter Joined: Jan 2013 Posts: 1,518 | Make sure the pitch of the drive gear matches the driven gear or they will eat each other up.
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
| | | | | Joined: Mar 2018 Posts: 140 'Bolter | | 'Bolter Joined: Mar 2018 Posts: 140 | Ordered some plastic gears and will try one. Thanks for the advice. Hopefully it will work! | | | | | Joined: Mar 2018 Posts: 140 'Bolter | | 'Bolter Joined: Mar 2018 Posts: 140 | I think from all the clues i have a car 3 speed. Driven gear bullet has an o ring, not screwed in like the truck version. Got the 22 tooth plastic driven gear in and still no speedo. Then i put my finger in the hole and found the drive gear moves freely so i need another one. How is it attached? How do you take off the old one and put on a new one? As Rosanna Dana says, “It’s always something”! | | |
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