Hi All
I have been debugging my recent failure of my speedometer ( 1955 first series, C3100, 235-6, 3spd manual on tree) and am now looking at the transmission itself, or what appears to be a speedometer ratio adapter on my truck. My speedometer and odometer stopped working last week and I tested the cable itself and the speedometer in place in the dash and they both test OK - here is what I have done so far ( Speedometer and odometer have been working since I have owned the truck starting about 4 years ago)
1) Using a drill, I spun the cable (unplugged both ends) from tranny end and speedo end spins with it - indicating cable OK
2) Screwing cable connector back into speedo back, I spun the tranny end of the cable again with drill and speedo needle works - holds steady reading and follows drill speed as well

So I noticed that the speedometer cable plugs directly into what appears to me to be a ratio adapter at the tranny and the adapter then connects to the tranny housing. I am now focusing on this adapter and how it hooks into my tranny

Q1 - I notice that I can rotate the adapter about 20 degrees around the attachment axis even though everything is tight connection wise - It has same type of attachment as speedo cable to tranny, since it goes inline, but it also rotates in place - is this normal?
Q2 - I am hoping to take it off for testing and was going to try to rotate the input to see if the output rotates on the adapter - If the output rotates, I am then guessing that the problem is in the speedo gear in the tranny housing - is this reasonable?
Q3 - If I can, I was going to remove the adapter and then plug the speedo cable directly to the housing and see if things work correctly - any reason not to do this or other test suggested?
Q4 - Any other tests I should try?

Interestingly, the speedo ( which was working for last 4 years) is off by about 7-9 mph (low) - which I attributed to the speedo itself - I did not measure if the odometer is accurate (my understanding is that the odometer is actually what is driven by the speedometer cable - speedometer needle is driven from odometer movement in the speedo itself) - so even if the adapter is functioning, I am not sure I should replace it anyways

Any suggestions would be appreciated

Joe

Joe Finkelstine
Born and bred in Motown