i have this issue with two speedo's cables. one that is a vinyal and the other one is a steel cable both came from jim carter. what i found is when i chuck up the drill with my spare speedo mounted in the vice i found i cant have the nut on the back of speedo tight because if it is the drill cant spin it over. when i loosen the nut a little it sometimes work and sometimes it jumps around. it does that with both cables. the vinyal one that is hooked up in the dump truck is the same way and i have to find a sweet spot in the tightness of the nut in order to get it to respond properly too tight its herky jerky too loose it binds it fast somewhere on the dial.

i hooked up a gmc speedo adapter (thier two speed rears) to the speedo in the vise and had excellant results with the steel cable and no herky jerky out of the needle because the key from the adapter is held true with the back of the speedo i dont know but i think what was happening on the back of the speedo is now happening on the back of the adapter but because of its configuration it didnt affect the speedo response it was nice and smooth. i went to put the adapter on the dump speedo and there isnt enough clearence to spin it on with out a conflict.

while i was experimenting on both cables and the speedo in the truck and at the vise with the same results i started looking at the cables. what i found is that i could not tighten the nuts completely without binding the cable fast. when i loosened the nuts the cable drops due to the weight of the cable and when i spin it it's enough to bind the cable which makes the needle herky jerky and can and does bind the needle in a fixed position until i straighten out the cable on the back of the speedo.

i had to look deeper as to why this was happening because i paid for two cables that dont work and the steel one is 3" too short which the speedo adapter is 3" long which makes that up. i had a messed up original cable that is no good but it has the right end on it. i laid all the cables next to each other and pulled all the cables out far enough to see how the connections were made. the old cable has a key and a collar with a washer between the collar and the inside of the nut. both new cables are the same except there is no back up washer between the collar and the nut. both were made on the other side of the pond and I think it is in the manufacturing of the cable ends themselves.

i contacted bob's speedometer and was going to get one from them he said it was $110 and i said that was a bit much but he said but we make them up special and they are made in the USA not overseas. i told him thanks but i couldnt see laying that kind of money out that only see occasional use. so im back to square 1

40 GMC 250 STAKE/FLAT BED
1951 Chevy 6100 Dump
51 GMC 350 ENGINE 500/500
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