The Stovebolt Site Forums The Shop Area Driveline 55 C3100 3 speed manual driven speedo gear problems

HI All
I asked for help a month or so ago for my still non-working speedometer in my 55 series 1 C3100 with 3 speed manual on the tree, and now believe I have found a significant cause. I pulled the driven speedometer gear out of the tranny through the access hole and found 3-4 threads pretty sheared/smashed and obviously not engaging. The original gear was white and plastic ( white color seems to indicate 25 teeth according to what I can see so far). I have looked at my 55 shop manual which just points out the exploded view and does not give me a part number - I also found the speedo cable quite dry and the ratio adapter also had high friction - I re-lubed the cable and also cleaned/re-greased the ratio adapter and the cable and adapter are now much more free to spin. I am guessing the binding in the cable and adapter lead to my driven gear problem. Now my task is to identify the correct plastic driven gear to buy for my truck - I have looked for a while and the closest I can find so far are references for 55-57 chevy cars with manual 3 speeds, which look quite similar, but I would appreciate any help finding a supply for this - I am hoping it is the last link in getting my speedo back and working ( have verified speedo itself is good). I have also found a similar looking gear on Eckler's for a 57 manual 3 speed, but I cant find any cross reference.

Any suggestions or URL's along with part number or other way to find it would be appreciated - Also, if you think I might also want to check something else, please let me know

Thanks,

Joe

Trucks normally had a steel gear so it is likely your truck has a passenger car transmission or at least the rear housing and the gear.
Cars and trucks with OD used the plastic gear. The long shaft white gear is available on ebay for about $10 from Muttonhollow Chevy's in Utah. If you found it at ecklers that would be fine also.
Fred

Hi Fred
Thanks for the insight - Interesting points you raise. I do have plastic gear and I definitely do not have an OD transmission - It was all working before however, so I will purchase another white gear. I have cleaned up the speedo cable and ratio box, in hopes that they were the cause of the gear failure ( speedo cable was dry, ratio adapter was also quite difficult to spin ) - they are now cleaned up and lubricated and much easier to spin - I also notice there are different colored gears (differing tooth count) available, so I might have another path to correct the speedo if it is still showing about 5-10 mph low - my first thoughts is all the friction in the cable/adapter was causing the low speed reading. I am hoping it will all work now after getting the new gear and then I can determine if I need a driven gear with a different tooth count - got to get it working first

Thanks for your help

Joe

Joe,
The ratio adapter was could have been installed because the 25 tooth gear wasn't correct and that was their attempt to fix it.
I seems to me that the ratio adapter would have cost more than trying several cheaper plastic gears to get it right.
It may have been that there wasn't anything else available at the time.
If it has a 3:90 rear end the original (steel) gear had 19 teeth. The drive gear was larger to fit that configuration.
The car transmission used a smaller drive gear and there are more options available with the plastic driven gears.
55-57 cars had a wide variety of rear end options from 4:10 through 3:36 and speedometer gears to match.
1/2 ton trucks had a 3:90 standard or a 4:10 if it came with OD.
Fred

Hi Fred
I was thinking along the same lines about the white gear in place here. I was told by the previous owner that the ratio was 3.90 on the rear end. My first approach was to put a new white gear in place and hopefully get it working with the adapter in place and drive some measured (GPS) miles to see if the odometer is correct or off as well. From my memory, the odometer is directly driven form the cable, whereas the speedo needle is coupled to odometer. It appears I have some options if the white gear is not correct, including removing the adapter - First things first though - Gotta get her working again. Perhaps the ultimate solution is to remove the adapter and find a colored gear that is as close to 19 teeth as possible - I have the adapter apart (clean and re-grease) and will try to figure out its ratio as well

I am hoping that the drive gear is not plastic and the weak link in this system is the plastic driven gear - If the drive gear is damaged, I am in for a much more painful fix I believe and that is out of my scope of talent/experience

Joe,
I didn't mean to mislead you. The 19 tooth metal gear is driven by a larger drive gear. They are not inter-changeable. All the drive gears are metal and usually don't get damaged with a plastic gear. You could probably use the yellow - 24 tooth gear without the adapter and be pretty close. Another possibility is the green gear with 22 teeth. Other factors could be in play here also such as tire size and actual speedometer calibration.
Fred