| fsacht | -- 05-02-2013 @ 7:38 PM |
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My 49 Ford speedometer wasn't working right. Lubed it as suggessted on the forum. Didn't fix. Sent it to Iowa for repair and calibration. Got it back recently and it works but speedo reads slower than actual speed,like reads 30 when going 40. Counted teeth on gear at trans. It is correct spec 21 teeth for Overdrive with 4.10 axle. Tires are P215 75R 15 radials so C/Line axle to floor is less than 6.70 15 bias ply by 3/4". So - will a 22 tooth gear get actual speed and speedo closer or a 20 tooth gear?
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| CharlieStephens | -- 05-02-2013 @ 9:05 PM |
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Check the odometer before you change anything on the speedometer gear. If it is correct then the problem is not with having the wrong gear. Charlie Stephens
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| Old Henry | -- 05-02-2013 @ 10:13 PM |
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You can check the odometer on any highway that has mile markers. Check it over a 5 mile stretch rather than just one to see how accurate the odometer really is. As Charlie said,if the odometer's right there's no need to suspect wrong gears. You might just have to remember its off so you don't get caught speeding. Old Henry (The older I get, the better old looks.)
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| fsacht | -- 05-03-2013 @ 7:38 PM |
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Here is my question: If the speedometer reads slower than actual speed; for example - speedometer says 30 MPH and actual speed is 40 MPH, were one to choose to bring the two figures closer together would one increase or decrease the number of teeth on the gear that drives the speedometer cable?
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| ford38v8 | -- 05-03-2013 @ 8:05 PM |
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In any gear drive, changing the number of teeth on the driven gear will slow down that drive if the tooth count is increased, and speeding the drive if the number is decreased. Alan
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| 39 Ken | -- 05-04-2013 @ 4:36 AM |
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Fred, You said at the beginning that you sent this unit to Iowa for repair and calibration. I think the problem is that they didn't calibrate it properly. I had the same problem with a speedo shop and I sent it back to them. They got it right and no problem since. If you're sure that the 4.10 rear ratio is correct, and the speedometer gear at the trans is correct, then the calibration is off. I'd send it back and have the shop do it correctly. Ken
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| supereal | -- 05-04-2013 @ 7:20 AM |
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I agree with Ken. Even though I am in Iowa, we have Bob's Speedometer in Michigan do our speedo work. If the drive gear does match the rear end ratio, it is likely the magnetic discs are either weak or improperly adjusted. This can also be caused by a worn speedo body. Most rely on the die cast body to carry the input shaft, instead of an actual bushing. As wear accumulates, the discs drags, affecting the needle, while the odometer continues to be accurate.
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| fsacht | -- 05-04-2013 @ 5:38 PM |
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Bob, I removed the speedo gear and counted the teeth - 21. Am assuming the axle to be standard for 49 with overdive @ 4.10:1 Ran a 6 mile measured mile and picked up 1/10 of a mile. The repair was done by a service advertiser in the Jan/Feb V8 Times at a hefty price. The invoice says Recondition Speedometer, replace Magnet Assy. Replace Speed Cup and Spindle. Can't imagine they failed to calibrate. That's why all my speed gear option questions should all else fail. I'll be calling the comapny again this week and hope the call is returned. Kind of discouraged.
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| supereal | -- 05-04-2013 @ 6:40 PM |
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Keep after them, Fred. Just because someone claims to be an expert, doesn't mean they can't screw something up. I'd confirm the rear end ratio. Mark the tire and the driveshaft for an idea of what is back there. With these old cars, nothing is surprising.
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| fsacht | -- 05-04-2013 @ 8:07 PM |
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I'll verify ratio tomorrow. The service company will want to know all the details about my car. Their shop is along the big river maybe their still cleaning up after the flooding. Thanks to all for the help.
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