Odometer Not Even Close - The 1947 - Present Chevrolet & GMC Truck Message Board Network

48richard · 03-01-2012, 11:47 AM

I chased around a similar problem. Found that 2 teeth on the speedo driven gear in the transmission were worn down to almost nothing. My speedo was also reading 10% low because I have 31" tires, so I replaced both gears in the transmission and solved all my issues - rock steady needle, accurate to 1 mph at 60, and correct odometer reading.

justagoodolboy · 03-01-2012, 12:42 PM

Quote:

Originally Posted by 48richard

I chased around a similar problem. Found that 2 teeth on the speedo driven gear in the transmission were worn down to almost nothing. My speedo was also reading 10% low because I have 31" tires, so I replaced both gears in the transmission and solved all my issues - rock steady needle, accurate to 1 mph at 60, and correct odometer reading.

If that worked for you hopefully it'll fix my problem. I'll have to check the teeth first chance I get. the speedo being off doesn't bother me that much but the odometer drives me nuts.

**425HP409** · 03-01-2012, 06:20 PM

The odometer is a direct mechanical drive off of the speedometer cable. You can change the gears in your transmission, or get a reducer adapter to correct this, but any change you make with the odometer will also change what the speedometer reads by the same proportional amount. The problem you have is twofold. 1. The speedometer gears are wrong for your truck with the gearing you have. 2. The speedometer is way off of calibration. If you change your odometer to read correct, the speedo will be really way off. You will not be able to make both of them read correctly with the existing speedometer that you have unless you take the speedometer out and have it calibrated magnetically at a speedo repair shop.

**FL71C10** · 03-01-2012, 07:02 PM

The good news is that once you fix it your gas mileage will go up significantly!

justagoodolboy · 03-01-2012, 07:20 PM

Quote:

Originally Posted by FL71C10

The good news is that once you fix it your gas mileage will go up significantly!

Good point. If I ever start driving it daily I'll have to fix it cause I write my miles down for tax purposes. But I'll prolly try to fix it anyway. I'd rather it didn't work at all than to have it not working right. Stuff like this bugs me like crazy.

03-01-2012, 11:47 AM	#1
48richard Registered User Join Date: Oct 2009 Location: Phoenix, AZ Posts: 475	Re: Odometer Not Even Close I chased around a similar problem. Found that 2 teeth on the speedo driven gear in the transmission were worn down to almost nothing. My speedo was also reading 10% low because I have 31" tires, so I replaced both gears in the transmission and solved all my issues - rock steady needle, accurate to 1 mph at 60, and correct odometer reading. __________________ 1971 C10 Longbed, 350/TH350

03-01-2012, 06:20 PM	#3
425HP409 425hp409 Join Date: Oct 2008 Location: Prosper Texas Posts: 841	Re: Odometer Not Even Close The odometer is a direct mechanical drive off of the speedometer cable. You can change the gears in your transmission, or get a reducer adapter to correct this, but any change you make with the odometer will also change what the speedometer reads by the same proportional amount. The problem you have is twofold. 1. The speedometer gears are wrong for your truck with the gearing you have. 2. The speedometer is way off of calibration. If you change your odometer to read correct, the speedo will be really way off. You will not be able to make both of them read correctly with the existing speedometer that you have unless you take the speedometer out and have it calibrated magnetically at a speedo repair shop. __________________ Charles 68 SWB, Dad bought new, now 396 & factory ac 64 Impala SS, 409 425HP, 4 speed AC 64 Bel Air Wagon, 400 Small Block 57 Bel Air all original 283 w/Factory Air 77 GMC Sprint, 454/425HP 67 Olds 442, all original 90 ZR1 Corvette

03-01-2012, 07:02 PM	#4
FL71C10 Senior Member Join Date: Jun 2010 Location: Orlando, Florida Posts: 2,514	Re: Odometer Not Even Close The good news is that once you fix it your gas mileage will go up significantly! __________________ 71 Chevy C10 Shortbed Stepside. LT1 with 4l60E. Just got back from painter, in assembly now.



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