Speedometer question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Piece of Work · 09-19-2007, 05:28 PM

My speedometer is off by 33%, this I am sure of. My question is, is the mileage reading also off by 33%? Or is it separate gearing?

-Mark

cdowns · 09-19-2007, 05:31 PM

theyre driven and off or on by the same amt

**Classic Bowties** · 09-19-2007, 05:35 PM

Quote:

Originally Posted by cdowns

theyre driven and off or on by the same amt

Piece of Work · 09-19-2007, 05:43 PM

Thanks for the replies.

That's what I thought, but checking the miles against interstate mile markers, something wasn't adding up, the difference was less than 10%, and that was over several miles. I have checked the speedo with 2 different radar guns, (it's good to have local cops as friends), and it is definitely off by33% 30 MPH on the gauge, clocks at 40 MPH on the gun. 45 MPH clocks at 60 MPH. No big deal, as long as I know how fast I'm going.

mkhutch · 09-19-2007, 05:48 PM

All you have to do is change the gear in the tranny and you can correct it. I believe those little plastic gears are like $15.

68gmsee · 09-19-2007, 08:53 PM

Mine was off also. At 20 I would clock about 35 mph. Changed the driven gear and now I'm off only by 5 mph. At 20 mph I'm actually going 25 mph. I can live with that.

Here's a couple of sites you can look at.

btw: I bought the gear at the Chevy dealer for about $7.00.

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

http://www.bgsoflex.com/speedo1.html

ctouchet · 09-19-2007, 09:20 PM

How hard is it to change the driven gear, or does it need to be done by a professional.

68gmsee · 09-21-2007, 02:18 PM

Quote:

Originally Posted by ctouchet

How hard is it to change the driven gear, or does it need to be done by a professional.

The driven gear is easy. It is held in place by a small bolt and clamp. Remove the speedometer cable, the clamp and then gently pry the housing out. Should have an O ring so it may take some effort. The small plastic gear is the driven gear. It just pulls out and a new one slides in. If it's stuck, you may have to use a pair of pliars to pull it.

Now if you mean the drive gear inside the tranny, than it's a different matter. You have to remove the drive shaft and the rear of the trans (name). I've never gone that far into them.

ctouchet · 09-21-2007, 02:21 PM

Thanks for the information.

09-19-2007, 05:28 PM	#1
Piece of Work Cultural Infidel Join Date: Jan 2007 Location: Clearwater, FL Posts: 668	Speedometer question My speedometer is off by 33%, this I am sure of. My question is, is the mileage reading also off by 33%? Or is it separate gearing? -Mark __________________ posted via La-Z-Boy -Mark 1972 C-10 Fleetside 350/TH350 PS PB A/C Cab Sadly....Sold 1968 Short Fleet 350/TH400 PS PB Delivered by Fine69 Also sadly Sold! It may be that your whole purpose in life is simply to serve as a warning to others. A man is not complete until he is married -- then he is finished.

09-19-2007, 05:31 PM	#2
cdowns Senior Member Join Date: Jan 2003 Location: daytonabeach Posts: 22,956	Re: Speedometer question theyre driven and off or on by the same amt __________________ 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

09-19-2007, 05:43 PM	#4
Piece of Work Cultural Infidel Join Date: Jan 2007 Location: Clearwater, FL Posts: 668	Re: Speedometer question Thanks for the replies. That's what I thought, but checking the miles against interstate mile markers, something wasn't adding up, the difference was less than 10%, and that was over several miles. I have checked the speedo with 2 different radar guns, (it's good to have local cops as friends), and it is definitely off by33% 30 MPH on the gauge, clocks at 40 MPH on the gun. 45 MPH clocks at 60 MPH. No big deal, as long as I know how fast I'm going. __________________ posted via La-Z-Boy -Mark 1972 C-10 Fleetside 350/TH350 PS PB A/C Cab Sadly....Sold 1968 Short Fleet 350/TH400 PS PB Delivered by Fine69 Also sadly Sold! It may be that your whole purpose in life is simply to serve as a warning to others. A man is not complete until he is married -- then he is finished.

09-19-2007, 05:48 PM	#5
mkhutch Throbbing Member Join Date: Jul 2006 Location: McDonough, GA Posts: 350	Re: Speedometer question All you have to do is change the gear in the tranny and you can correct it. I believe those little plastic gears are like $15.

09-19-2007, 08:53 PM	#6
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Speedometer question Mine was off also. At 20 I would clock about 35 mph. Changed the driven gear and now I'm off only by 5 mph. At 20 mph I'm actually going 25 mph. I can live with that. Here's a couple of sites you can look at. btw: I bought the gear at the Chevy dealer for about $7.00. http://www.transmissioncenter.net/sp...n_______va.htm http://www.bgsoflex.com/speedo1.html

09-19-2007, 09:20 PM	#7
ctouchet Registered User Join Date: Nov 2005 Location: Maurice,Louisiana Posts: 169	Re: Speedometer question How hard is it to change the driven gear, or does it need to be done by a professional. __________________ 2012 F150 SuperCrew 2011 GMC 1500 (COMPANY TRUCK) 1982 Chevy Blazer 2WD (Work in Progress)

09-21-2007, 02:21 PM	#9
ctouchet Registered User Join Date: Nov 2005 Location: Maurice,Louisiana Posts: 169	Re: Speedometer question Thanks for the information. __________________ 2012 F150 SuperCrew 2011 GMC 1500 (COMPANY TRUCK) 1982 Chevy Blazer 2WD (Work in Progress)



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