I am finally going to get the correct speedo gears for my tranny so I will actually know how fast I am going.... ...anyway, one of the parameters in the formula/calculater I am using is: the number of revolutions it takes for the speedo to register one mile. They advise that 1000 is the present "norm". Can anyone tell me how many revolutions it takes for a '72 Skylark speedo to register one mile.?? Thanks for any help. :TU:
It depends on your transmission's final drive ratio, your rearend, your tire diameter. Here is a calculator to try. Just enter everything and start entering rpm's until you get the top gear to read 60 mph. Then take the car out and see how far off your speedo is. This should allow you to put in the right speedo gear in the trans. http://www.1bad69.com/calc.htm
what he's looking for does not involve the gear ratio, tire size, etc. All speedos register X mph for Y cable rpm. I know that there is a standard, but I don't know what it is. It has been posted here before, but probably pre-hack and lost... Hopefully someone will chime in. Or, he could just use Phil's caclulator instead...
Thanks for the responses guys. Phil, I already have a "calculator" to determine which speedo gears I need to put in the tranny. I just need to know how the Speedos in '72 registered one mile. Apparently, over the years, it has not been a constant value. It can be anywhere from 900 or so to as many as 1040 (or more) revolutions of the speedo cable. I hope that the info might be in a service manual or something, and that someone can check it out for me.
I think what you are looking for here is this. 60 mph is 1000 rpm on a speedometer. This means that if you are cruising along at say 2400 at 60 mph, you need to set up your speedo gears in the tranny to make that 2400 be 1000 rpm for the speedo to be correct. In other words , for this case, you need a 2.4 to 1 ratio on your speedo gears. To determine this ratio, simply divide the number of teeth on the driven gear ( the one the cable hooks to ) by the number of teeth on the drive gear ( the one on the output shaft) and you will have your ratio. Lets' just say your driven gear has 24 teeth and your shaft gear has 10 teeth, this will give you your 2.4 to 1 ration which will make the 2400 rpm cruise rpm lok like 1000 rpm for the speed, which will make your speedo correct. :Smarty: Jim Burek P.A.E ENTERPRISES
Yes, thank you Jim. :TU: I knew that 1000 revs./mile was the current standard, but was unsure what was used for my '72. I already made the order with the hope that 1000 was used for mine. Now I feel much better about my purchase. :bglasses: Thanks for your response Jim.! :TU:
what source can I get the speedo gears from that go into tranny? Mines is a 4 speed the gear in there is red in case that helps. Also need a 70" long speedo cable. Allen allioop108@aol.com
