speedometers

[59imp]

the speedo in my Impala packed it in, so i installed another used one and now the speed is out, at 40 MPH it reads 58 MPH (checked it against a GPS unit) can it be calibrated?
somebody told me it might be the wrong gear in the tranny, any ideas???

thanks, mo.......

 

[R Pope]

If the old one was right, the new one should be, too, unless someone was monkeying with it. Did you just change the dash unit? They all require the same cable RPM at a given road speed.

 

[Bonehead]

I have no idea.... however, there is a plastic gear where the cable goes in to some trannys that can have different tooth count, that changes the speedo speed. Usually a tire size to speedo ratio.

 

[Gastrick]

If all else fails, there's a company that makes adapters that go on the transmission that will correct a speedo that is off. I'll look it up later for you.

 

[bob w]

Are these stock speedometers? If so, I'd say the one you installed is not working correctly. You could try cleaning the dust, lint and accumulated grime from it. Or, find a speedometer repair shop.

 

[cycledog]

Are these both the same unit of measurement? IE: is one mph and the other kph?

Here is a great place if you need repair or a refurbed unit.
www.scottspeedometer.com

 

[59imp]

ok, so the bearing in the original speedo seized, so i got another stock, used unit, took it apart and cleaned it, and put it in the dash, no other changes were made. my car has a Turboglide tranny,(not a Turbo 350 or 400, a Turboglide) which is an oddball in itself, i wonder if this other speedo came from a car with a Powerglide, and if that is the problem ( i'll try to find out from the guy i bought it from).

Bonehead, i think you're on the right track, i'll call the local Trans repair shop if they can help.

Gastrick, thanks, you always seem to know where to go.

Bob W, took the unit apart before i installed it and it's spotless.

Cycledog, both are stock original speedos, i'm not sure what model car or transmission it came from, i wonder if that's part of the problem.

thanks again, mo........

 

[dmw56]

I think your on the right track. Sounds like different trannys with different speedo gears.

 

[35Mastr]

If possible.Go back and pull the plastic speedo gear from the car that you obtained the speedo from.Even if its no good.You will at least know the color and the tooth count.

 

[bob w]

You would think all speedometers from that year and model would be calibrated the same. The trans gear compensates for different rear axle ratios, not for different speedometers.

 

[59imp]

You would think all speedometers from that year and model would be calibrated the same. The trans gear compensates for different rear axle ratios, not for different speedometers.

that's a good point Bob, i'm real curious as to what's going on here. will pull the cable tomorrow after work.

 

[Gastrick]

59imp, this place has a mess of different speedo drive gears, along with adapters. Take a look

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

Here are some charts to help with the calculation.

http://www.chevelles.com/shop/speedo.html

 

[59imp]

59imp, this place has a mess of different speedo drive gears, along with adapters. Take a look

http://www.transmissioncenter.net/speedometer_calibration_______va.htm

Here are some charts to help with the calculation.

http://www.chevelles.com/shop/speedo.html

good info Gastrick, just have to get at it, at least i have a good starting point..

 

[gassersgarage]

Also, the gear ratio from the donor car might be different. For example, my buddy had a '67 Camaro that came from the factory with 4:56's. He bought the car new and wondered why his car was screaming on the freeway. He went back to the dealer and discovered it was equipted with 4:56's.

My speedo in my '31 never worked. Finally put a new speedo in it and took it to a speedo calibration shop. One gear change and it's dead nuts accurate at 60 mph. Cost was $50 bucks.

If you're a AAA member, they will check the calibration for free. In California, anyway.

 

[21tat]

You don't need no stinking speedometer!

 

[Thunder1]

You don't need no stinking speedometer!

I wish that were true! Without one I'd lose my license in a matter of weeks. They are tough on you around here!
In Davidson County (Metro Nashville) speeding 12 miles and over the posted speed limit is automatically reckless driving and speeding charges, a $500 fine and driving school! That's if the judge doesn't suspend your license for 6 months to a year, or put your butt in jail which I can't afford!

I found out the hard way in 1998. I got nabbed for doing 65 in a 45 speed zone. Luckily my boss pulled some strings and got it knocked down to just a speeding charge. I didn't have to pay the fine either. Just court costs. I did get one hell of a talking to by the judge however. He warned me to never show up on his docket again or he wouldn't be so nice next time!

Thunder1