DonaldSmith Posted June 14, 2009 Report Share Posted June 14, 2009 I installed my rebuilt speedometer. The needle was jumping and sticking. I returned to the speedo shop last Friday, since I promised to bring the car around anyway. The proprietor loved my 47 DeSoto Suburban. They just don't make them like that any more ... But back to the speedometer story. The needle hub appeared to be rubbing the shield at the glass. Gentle taps would help the needle return to zero. I had hand-made the gasket at one point. Mr Speedo suggested I add another gasket. As far as the needle jumping, they had just trimmed off the end of the old cable rather than replace it. The old cable may be whipping. They will make up a new cable Monday, when the proprietor's son is back. Back home, I took the speedometer out, and found that the needle was rubbing the inner lens, the one with the numbers and hash marks. There were two tabs to hold the lens assembly in place that were not bent back. Easy fix. I added an extra gasket anyway. Checking the odometer against the our statute mile road system, I noted 7.6 miles for a 7.0 mile distance out, the same coming back. That's 8-1/2% high. I have a twenty-tooth speedometer gear at the transmission. A ninteen-tooth gear would reduce it by about five percent. 19/20 times 7.6 equals 7.22, versus 7.0, about 3 percent high, probably as good as you can get, without a ratio changer. The big problem is, comparing the Garmin speed for various needle speeds, I get a speedometer reading that's 15 to 18 percent high. It should have been 8-1/2% high, the same percentage as the odometer. I shall speak to the proprietor about this. But first: For a steady speed, the Garmin is right on, right? Could the fluctuating cable itself produce a high reading? Does anyone have a nineteen-tooth speedometer gear that fits the M-5 Tiptoe-Shift (Klunk-O-matic) transmission? Quote Link to comment Share on other sites More sharing options...
Jim Yergin Posted June 14, 2009 Report Share Posted June 14, 2009 Don, I have a 19 tooth speedo grear that causes my speedometer to be 8.5% too fast. I would like to have one with more teeth but I thought 19 was as high as it went. Maybe we could trade. My speedo gear looks just like this 18 tooth one except it is metal and, of course, has one more tooth. Jim Yergin Quote Link to comment Share on other sites More sharing options...
DonaldSmith Posted June 14, 2009 Author Report Share Posted June 14, 2009 My speedometer gear (pinion) looks different. They are probably not interchangeable. My DeSoto manual lists 6-tooth gears with 16- to 19-tooth pinions for the manual transmission, and 7-tooth gears with 19- to 20-tooth pinions for the Tip-Toe trans. It seems the numerically higher the differential, the more teeth in the pinion. That makes sense; the transmission is turning more per road speed, so the speedometer cable should turn more, too. Tire size is included in the chart, but with no consistent pattern. Quote Link to comment Share on other sites More sharing options...
P-12 Tommy Posted June 15, 2009 Report Share Posted June 15, 2009 Wanna hear a good one? My speedometer reads 15 MPH too slow. But my odometer is right on the money. Tom Quote Link to comment Share on other sites More sharing options...
james curl Posted June 15, 2009 Report Share Posted June 15, 2009 I bought a new speedometer for my 55 chevy pick up and had the same problem. The vendor told me it needed to be calibrated. I opened it up and found that the hair spring has an adajustable anchor that moves on a notched surface and each notch was about 5 mph adjustment. I used my adajustable speed drill with the end of an old cable to turn the speedometer to adjust the speed. ran the drill to see what speed was showing and then loosened the spring tension by clicks until it read 15 mph faster at the same rpm. Hopes this helps. Quote Link to comment Share on other sites More sharing options...
P-12 Tommy Posted June 15, 2009 Report Share Posted June 15, 2009 Thanks James, I'll have to check that. Tom Quote Link to comment Share on other sites More sharing options...
DonaldSmith Posted June 15, 2009 Author Report Share Posted June 15, 2009 Today I took the car back to the speedometer shop to get a new cable, since the existing one was making the needle jerky. I tried to save ten bucks by putting the new cable in by myself, but it got more difficult toward the end, and I couldn't get the last quarter inch in. I needed professional help. The owner's son couldn't do any better. Finally he replaced the ferrule at the speedometer end, which was keeping the new cable from seating. Father and son cursed the cheapjap cable and sheath that I had bought a few years ago. So if you want the good stuff, go to a speedo shop. Ok, that cost me $50. I had clocked the odometer at 8-1/2% high, and the speedo at about 11% high. Understood, the speedo shop has no control over the odometer reading, since it depends on tire size and speedo gearing at the trans. I guess I can't argue over the remaining 2-1/2%. I was considering switching from a 20-tooth pinion to a 19-tooth pinion, but that is not the way to go. I measured my tires and figured tire and driveshaft revolutions per mile, divided by cable revolutions per mile, and got 3.16. Dividing the seven teeth of the speedo gear by the 20 teeth of the pinion, I get 2.86. 3.16 is about 10 percent more than 2.86. 19 teeth would make the number 16 percent off. (The 25" diameter times pi (3.1416) gives a 78.54 circumference. Dividing 63360 inches in a mile by the circumference, times a 3.91 diff, gives 3,155 revs per mile. Divide that by 1,000 cable revs per mile and get 3.16.) (For the tire diameter, I measured from the ground to the center of the hubcap and multiplied by two, which was an inch or so less than the diameter measured horizontally. If I was supposed to measure horizontally, the number would be closer to the 8-1/2% that I clocked.) Ratio adaptors are available custom assembled for almost any ratio, for $85 and up, but I think I'll buy a ready-made adaptor on line, for $62 plus about $9 for shipping, to reduce the speedometer reading by 10%. Tha tshould be close enough. Quote Link to comment Share on other sites More sharing options...
BobT-47P15 Posted June 16, 2009 Report Share Posted June 16, 2009 My odometer is off as well as my speedometer. Am thinking of getting a new cable, too......may need a ratio adapter. I've discovered there's a place in Independence, MO (Kansas City) called Metro Speedometer L L C. Their business card says "we repair GM, Ford and Chrysler speedometers". They custom build cables and ratio adapters. Their phone is (816) 478-0116. email is metrospeedo@sbcglobl.net. The man named on the card is a Mr Bill Tingley. So, the next question is -- do they work on OLD speedometers???? Quote Link to comment Share on other sites More sharing options...
BobT-47P15 Posted June 16, 2009 Report Share Posted June 16, 2009 The speedo shop in Nashville says they can make a new cable based on an example. But they send the antique speedos to one of two different places.....do not now work on them in house. Those places are in other states......per a conversation with the business. Quote Link to comment Share on other sites More sharing options...
james curl Posted June 16, 2009 Report Share Posted June 16, 2009 In the Austin Texas area the only speedometer repair shop only works on electronic speedometers. I tried to get my new speedometer for my 55 chevy pick up calibrated but no one local would work on it. So I took it apart and found that the anchor for the hair spring moved on a notched strip and you can tighten or loosen the hair spring to change the speed that it reads, 60 mph at 1,000 rpm input. Quote Link to comment Share on other sites More sharing options...
DonaldSmith Posted June 16, 2009 Author Report Share Posted June 16, 2009 The old guy fixed my 47 DeSoto speedo, and has several old speedos in his collection, like a 35 Plymouth, a 57 Oldsmobile, and a 61 DeSoto. He showed me brochures for the 57 and 60 DeSotos, among his collection. The old guy would rather work on the old speedos, with the metal shells, not that plastic sh..tuff. The son does the grunt work and I suppose he's the one to manage the website, scottspeedometer.com. Their phone is 248.338.4148. Maybe this is the shop the other shops send the old speedometers to. Quote Link to comment Share on other sites More sharing options...
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