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This week I want to mention a Company that sells Speedometer Reducers and Speedometer Cables for our vintage vehicles. Instrument Sales and Service out of Kent, WA (800) 444-7976 makes a reducer for our old transmissions Part Number TA-2525. Now the hard part is not calling them up and ordering, it is figuring out the ratio you need. Tom, one of the staff there gave me two ways to do this. One is using your cell phone GPS feature, the other is driving an exacting distance of 5 miles recording Odometer reading at the start and end of the run.
GPS is laggy and not very reliable on cloudy days. It is important to sample low, medium and high speeds. I chose 30mph, 45mph and 60mph so we could compare the ratios to ensure there wasn't any other problems. The problem as I said, it was a cloudy day and I noticed you have to hold that desired speed for at least 30 seconds to test anywhere near reliably.
Distance Measurement is better but you have to find a known 5 mile exact stretch to drive on. We have an Interstate Highway going through our town so I just used the Mile Markers to do this. Simply write down the Odometer reading at the beginning and end of the 5 mile run. When you tell them the numbers, they will calculate which reduction gear they need to include. The charge is about $50 for the Reducer. Tom also mentioned they make speedo cables as well.
Maybe my brain is fried, but if someone out there has the mathematical formula for figuring out the reduction yourself, please share. That would be good information to include here. After doing the 3:55 Torque Tube rear end swap, my speedometer was way off. The reduction I needed was 1.3235. Thanks to Dave Folsom for recommending these guys!
GPS is laggy and not very reliable on cloudy days. It is important to sample low, medium and high speeds. I chose 30mph, 45mph and 60mph so we could compare the ratios to ensure there wasn't any other problems. The problem as I said, it was a cloudy day and I noticed you have to hold that desired speed for at least 30 seconds to test anywhere near reliably.
Distance Measurement is better but you have to find a known 5 mile exact stretch to drive on. We have an Interstate Highway going through our town so I just used the Mile Markers to do this. Simply write down the Odometer reading at the beginning and end of the 5 mile run. When you tell them the numbers, they will calculate which reduction gear they need to include. The charge is about $50 for the Reducer. Tom also mentioned they make speedo cables as well.
Maybe my brain is fried, but if someone out there has the mathematical formula for figuring out the reduction yourself, please share. That would be good information to include here. After doing the 3:55 Torque Tube rear end swap, my speedometer was way off. The reduction I needed was 1.3235. Thanks to Dave Folsom for recommending these guys!
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