The Stovebolt Site Forums The Shop Area Engine Shop speedometer

I decided to take old blue for a ride tonight.I had'nt checked the speedometer for accuracy since the t-5 and 12bolt 3:73 swap.At the starting point of a mile marker,to the next mile marker.My odometer is dead on,it is exact.This means my speedometer is correct,right? Could I be so lucky on this project ?

Thanks,Tim

Tim,

Interesting question. I guess if the method of measurement is a geared mechanical movement, and the odometer is correct, then the speedometer must be correct also. This subject might be too deep for me! I still have a hard time with drag racers....low E.T. but loses the race or highest top speed but finishes second?

Stuart

My odometer reads correctly also, but there are some variables with the indicated speed. The needle plugs onto a tiny shaft and the needle could be out of position. The conditon of the coiled spring could also cause faulty readings, among other factors I'm sure. To check my speedometer I use a stopwatch and drive 45 mph for 1 mile. If the speedometer is accurate, it will take 90 seconds. 92 seconds is 44 mph, etc.

I come up with 1 minute and fifteen seconds at 45mph ? 45/60 = .75

I will try the stop watch method.If I go 60 mph,it should take one minute to get from one mile marker to the next.

I believe the jimmy i took the tranny out of,had the same 3:73 rearend ratio as my rearend.

I drew myself a chart to check my speedometer last week and goes something like this:

Traveling Distance 1 mile
60 sec = 60 mph
70 sec = 55 mph
80 sec = 50 mph
90 sec = 45 mph
100 sec = 40 mph
110 sec = 35 mph
120 sec = 30 mph

Theoretically it should be right, but like Pat says there could be some variation. I still haven,t got mine right yet. I changed the gear in the trans. put on a ratio adapter & i,m still about 10% fast. The last one I did I piggybacked 2 ratio adapters before I got it right.

If the odometer didn't change during the swap, the speedometer will be as right or wrong as it was before, depending on its condition.

Thanks guys,I rebuilt the speedometer years ago.Has worked fine and right on.I kinda figured if the odometer is right,the speedometer should be the same.I am going to have one of my brothers drive beside me down the highway.I think this will be helpful also.

I don't know if you can correlate the odometer with the correct speed indication or not. The mechanism driving the odometer doesn't directly drive the needle. An accurate clocking of a measured mile would be the best way to check the accuracy.