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Jul 21st, 2025 | | | | Joined: Mar 2016 Posts: 223 'Bolter | | 'Bolter Joined: Mar 2016 Posts: 223 | 1951 3100
Need some help on this one. Supposedly, this is the transmission that came in the truck. Of course, I have no way of knowing that, but I'm assuming it's at least correct for the year. Near as I can figure, it should be a Muncie SM318. It has the 4-bolt cover plate on the side, (side shifter of course), and it is a torque tube set up. Everything inside appears to be tight and working correctly, but I have an issue inside the tail housing. The spacers, the sleeve, and the drive gear that mates to the speedometer gear, were all rattling around in the tail housing. They were not on the output shaft, as logic tells me they should be. What's the chances of anybody having a picture breakdown of this transmission? I can reassemble, but I really need to know the order they go in.
Casting number on the case.....3686382 GM
Casting number on the shifter cover..GM 591615
This number was stamped,not cast, on the face plate of the tailhousing......HO-76693.
I've searched and hunted, but these numbers don't seem to come up anywhere.
Mike
1951 3100 5 window
| | | | | Joined: Jan 2008 Posts: 4,903 'Bolter | | 'Bolter Joined: Jan 2008 Posts: 4,903 | The casting number 591615 was used from 1948 through 1954. However, they made internal changes in 1953 and 1954. The 48-52 use a 2 lug synchronizer and the 53-54 use a 4 lug synchronizer. The best way to see what you have is to pull the input shaft. If the synchro has 2 lugs, it is 48-52 and has the input and second gear to match it. If it has 4 lugs, it is a 53-54 and the matching gears. Here is a parts illustration: http://chevy.oldcarmanualproject.com/shop/1948_51truck/51ctsm0707.htmCasting numbers can be identified with the Hollander. This is the book salvage yards used to identify parts. | | | | | Joined: Mar 2016 Posts: 223 'Bolter | | 'Bolter Joined: Mar 2016 Posts: 223 | Awesome. Exact picture I was looking for. Everything inside the case appeared to be good and worked correctly. Was some wear on the 2nd and 3rd Shifter Fork, but we built (welded) that up and filed it back down. Removed the Rear Bearing Support, and that's when I found the Speedometer Drive Gear Spacer, the Speedometer Drive Gear, and the Universal Joint Spacer, just laying down in there, not ON the output shaft, but next to it. I know they go ON the output (main) shaft, I just didn't know in what order. Do now though.
Thank you, thank you.
Mike (Kade's pawpaw)
Mike
1951 3100 5 window
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