A speedometer Mystery - The 1947 - Present Chevrolet & GMC Truck Message Board Network

TobyArnot · 03-11-2013, 08:15 PM

O.K. , I spent all weekend making some repairs and updates to my stepper. New heater controls and cables, new dash panel and some minor wiring snafu's. Found the connector for the heater blower switch was half melted and was approaching meltdown. Managed to cobble up a new connector amd got the heater working again, even the light, which I didn't have. My question: Installed a "new" built-up dash with a used speedometer, Camaro (ala Gringloco) tach and all LED lights. The new sppedometer works great and is very smooth, but it appears to be reading faster than the old one. Do some of these speedos use a different "turn ratio"? Old speedo was about 10% slow, which I attributed to the larger diameter rear tires, but the "new" one appears to be reading faster. Same cable, etc., but ~5% fast.
What gives?

**LockDoc** · 03-11-2013, 10:53 PM

-
Could very well have a different ratio in the head. I don't know if this site will help you at all but there is a lot of information on it.

http://www.transmissioncenter.net/sp...n_______va.htm

LockDoc

TobyArnot · 03-12-2013, 09:22 AM

Thanks Leon,
.
That's a great site, but it looks like most of the differences are on the tranny end. I didn't change anything but the speedo head itself. The linked page for "speedometer calibration" addresses the "turns per mile" issue and there may well be a difference there. The old speedo was (I assume [?] - original '70 model) had a round high beam light opening and a white on black field. The replacement speedo (year unknown) has a rectangular high beam opening and a pale green on black field. I'm too sore from crawling around under the dash to pull it and look for any small numbers referenced on the calibration page.
.

To top it all off, this morning as I was leaving the house for work in a light misting rain, the wipers aren't working, but that's another whole issue.
.
I think I will call the number on the website later today and pick the guy's brain.
.
Again, thanks for the assistance.

cdowns · 03-12-2013, 09:46 AM

sounds to me like you were guessin b4 and guessin now with not a real true fact of what is what or how fast u r really goin

me? i'd drop the truck off at a place that has speedo certification and i'd pay to have it calibrated accuratly

Sammy · 03-12-2013, 10:38 AM

Borrow a GPS from someone. It will then give you accurate info on what your truck is saying versus the speedo.

71swb4x4 · 03-12-2013, 11:15 AM

The wipers aren't a whole different issue. The motor is behind the instrument cluster it's possible you inadvertently unplugged it.

As far as I know there aren't different speedo heads. As Cliff says you really need to check it rather thn assume.
Posted via Mobile Device

**LockDoc** · 03-12-2013, 11:31 AM

Quote:

Originally Posted by TobyArnot

Thanks Leon,

wwaah:To top it all off, this morning as I was leaving the house for work in a light misting rain, the wipers aren't working, but that's another whole issue.

Again, thanks for the assistance.

Not a problem Toby.

As far as the wipers check this thread out when you start digging into that problem.

http://67-72chevytrucks.com/vboard/s...d.php?t=413551

LockDoc

03-11-2013, 08:15 PM	#1
TobyArnot Quit if it's not FUN!!! Join Date: Jul 2010 Location: Indian Trail, N.C, Posts: 864	A speedometer Mystery O.K. , I spent all weekend making some repairs and updates to my stepper. New heater controls and cables, new dash panel and some minor wiring snafu's. Found the connector for the heater blower switch was half melted and was approaching meltdown. Managed to cobble up a new connector amd got the heater working again, even the light, which I didn't have. My question: Installed a "new" built-up dash with a used speedometer, Camaro (ala Gringloco) tach and all LED lights. The new sppedometer works great and is very smooth, but it appears to be reading faster than the old one. Do some of these speedos use a different "turn ratio"? Old speedo was about 10% slow, which I attributed to the larger diameter rear tires, but the "new" one appears to be reading faster. Same cable, etc., but ~5% fast. What gives?

03-11-2013, 10:53 PM	#2
LockDoc The Older Generation Join Date: Aug 2006 Location: Montezuma, Iowa Posts: 25,633	Re: A speedometer Mystery - Could very well have a different ratio in the head. I don't know if this site will help you at all but there is a lot of information on it. http://www.transmissioncenter.net/sp...n_______va.htm LockDoc __________________ Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 -

03-12-2013, 09:22 AM	#3
TobyArnot Quit if it's not FUN!!! Join Date: Jul 2010 Location: Indian Trail, N.C, Posts: 864	Re: A speedometer Mystery Thanks Leon, . That's a great site, but it looks like most of the differences are on the tranny end. I didn't change anything but the speedo head itself. The linked page for "speedometer calibration" addresses the "turns per mile" issue and there may well be a difference there. The old speedo was (I assume [?] - original '70 model) had a round high beam light opening and a white on black field. The replacement speedo (year unknown) has a rectangular high beam opening and a pale green on black field. I'm too sore from crawling around under the dash to pull it and look for any small numbers referenced on the calibration page. . To top it all off, this morning as I was leaving the house for work in a light misting rain, the wipers aren't working, but that's another whole issue. . I think I will call the number on the website later today and pick the guy's brain. . Again, thanks for the assistance. __________________ MY MOTTO: Eat it all up, Wear it out, Use the last few drops, Spend all you've got, Late in life, you'll think of the things you didn't do, not the things you did. - Get out and experience life ! . Robbie Robinson a.k.a. TobyArnot (Toe Bee or not toe bee)

03-12-2013, 09:46 AM	#4
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: A speedometer Mystery sounds to me like you were guessin b4 and guessin now with not a real true fact of what is what or how fast u r really goin me? i'd drop the truck off at a place that has speedo certification and i'd pay to have it calibrated accuratly __________________ 71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY

03-12-2013, 10:38 AM	#5
Sammy Registered User Join Date: Apr 2000 Location: Bonne Terre, Mo Posts: 3,005	Re: A speedometer Mystery Borrow a GPS from someone. It will then give you accurate info on what your truck is saying versus the speedo. __________________ '69 Chevy Long Fleet & '71 GMC Short Step & Project "ODD BALL" "You can wash a pig, soak it in most expensive perfume. In the end it is still just a pig." ODD BALL build thread http://67-72chevytrucks.com/vboard/s...d.php?t=478629"

03-12-2013, 11:15 AM	#6
71swb4x4 Senior Member Join Date: Nov 2003 Location: Brookings, SD Posts: 10,497	Re: A speedometer Mystery The wipers aren't a whole different issue. The motor is behind the instrument cluster it's possible you inadvertently unplugged it. As far as I know there aren't different speedo heads. As Cliff says you really need to check it rather thn assume. Posted via Mobile Device __________________ Some people are like slinkies, they aren't good for anything, but you can't help but smile when you see one tumble down the stairs.



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