Speedo reading almost double!!!!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mrfixit4818 · 01-27-2012, 06:59 PM

Bought a 69 in. speedo cable in my 64 c10 to replace the shorter 63 inch cable 3 on a tree cable,it now has a turbo 350 auto and when im going 40 it reads about 65!!!!???????

**Clyde65** · 01-27-2012, 07:23 PM

replace the speedo gear in the trans.

mrfixit4818 · 01-27-2012, 08:21 PM

where do you buy them?

**jocko** · 01-27-2012, 09:21 PM

Don't change a thing! That's THE most bang for the buck performance improvement I've ever heard of! AND, it will help prevent tickets to boot.

I'd agree with Clyde, probably just the wrong speedo gear in the trans. Here's a linky to someone who sells em: http://www.transmissioncenter.net/sp...___va.htm#Misc. Gears
Note some are out of stock, but I'd give them a call and explain the problem. They were helpful to me in the past.

fleetsidelarry · 01-28-2012, 10:28 AM

mrfixit. before the people that jocko suggested (they're the guys I've used):

can help, they'll need to know what you have, at least for the driven gear. and where you are (indicated mph vrs actual) exactly.

you'll need to pull the driven gear out of the side of the tranny. it'll be a certain color and have the tooth count embossed on it.

it would be helpful to the gear guys to know precisely what your indicated speed is compared to your actual. so if the actual speed you mentioned above is a rough guess you'd be better served if you found out exactly.

losthope · 01-28-2012, 05:14 PM

Quote:

Originally Posted by jocko

Don't change a thing! That's THE most bang for the buck performance improvement I've ever heard of! AND, it will help prevent tickets to boot.

HAHA sorry but that was pretty funny!!!

Fastrucken · 01-28-2012, 10:47 AM

What rear end gears does your truck have in it? probably 3:73 or 4:10

I just found two pages that will get ya fixed up...

http://www.chevymania.com/tech/speedo.htm
and
http://chevelleengineer.home.comcast...eer/speedo.htm

mrfixit4818 · 01-28-2012, 11:36 AM

410s
thanx

fleetsidelarry · 01-28-2012, 12:10 PM

it's alway nice to know the rear gear ratio, but not necessary to get the speedo sorted out.

what you're experiencing is quite common when a transmission (like the 350) is swapped in 'cause the vehicles they came from quite often had 3.08s or even 2.73and ours are often 3.73s or numerically higher.

the only problem I foresee is that you may have to also swap out the speedo drive gear. which requires removing the tranny tailshaft

mrfixit4818 · 01-28-2012, 07:42 PM

Just came back from a little ride,its about 15 to 20 mph off!!Im not worried about it now have plenty other stuff to do.Gunna try to see tomm. what size gear is in there.If I get done painting the dash early enough.

01-27-2012, 06:59 PM	#1
mrfixit4818 Registered User Join Date: Oct 2011 Location: marietta Ga. Posts: 36	Speedo reading almost double!!!!! Bought a 69 in. speedo cable in my 64 c10 to replace the shorter 63 inch cable 3 on a tree cable,it now has a turbo 350 auto and when im going 40 it reads about 65!!!!???????

01-27-2012, 07:23 PM	#2
Clyde65 1965 Chevy C10, 2005 4.8L/4l60 Join Date: Aug 2004 Location: DFW Texas Posts: 8,546	Re: Speedo reading almost double!!!!! replace the speedo gear in the trans. __________________ Clyde65 Rebuild of Clyde http://67-72chevytrucks.com/vboard/s...84#post8338184 69 Aristocrat Lo Liner build http://67-72chevytrucks.com/vboard/s...84#post7561684 *support our troops!*

01-27-2012, 08:21 PM	#3
mrfixit4818 Registered User Join Date: Oct 2011 Location: marietta Ga. Posts: 36	Re: Speedo reading almost double!!!!! where do you buy them?

01-27-2012, 09:21 PM	#4
jocko Senior Member Join Date: Oct 2009 Location: Godley, TX Posts: 17,975	Re: Speedo reading almost double!!!!! Don't change a thing! That's THE most bang for the buck performance improvement I've ever heard of! AND, it will help prevent tickets to boot. I'd agree with Clyde, probably just the wrong speedo gear in the trans. Here's a linky to someone who sells em: http://www.transmissioncenter.net/sp...___va.htm#Misc. Gears Note some are out of stock, but I'd give them a call and explain the problem. They were helpful to me in the past.

01-28-2012, 10:28 AM	#5
fleetsidelarry Senior Car Nut Join Date: Jan 2008 Location: shellman bluff, GA Posts: 1,411	Re: Speedo reading almost double!!!!! mrfixit. before the people that jocko suggested (they're the guys I've used): can help, they'll need to know what you have, at least for the driven gear. and where you are (indicated mph vrs actual) exactly. you'll need to pull the driven gear out of the side of the tranny. it'll be a certain color and have the tooth count embossed on it. it would be helpful to the gear guys to know precisely what your indicated speed is compared to your actual. so if the actual speed you mentioned above is a rough guess you'd be better served if you found out exactly. __________________ Larry

01-28-2012, 10:47 AM	#7
Fastrucken Junior Member Join Date: May 2006 Location: Peninsula, Oh Posts: 197	Re: Speedo reading almost double!!!!! What rear end gears does your truck have in it? probably 3:73 or 4:10 I just found two pages that will get ya fixed up... http://www.chevymania.com/tech/speedo.htm and http://chevelleengineer.home.comcast...eer/speedo.htm __________________ A good friend will come bail you out of jail, but a true friend will be sitting next to you saying, "That was ****ing awesome."

01-28-2012, 11:36 AM	#8
mrfixit4818 Registered User Join Date: Oct 2011 Location: marietta Ga. Posts: 36	Re: Speedo reading almost double!!!!! 410s thanx

01-28-2012, 12:10 PM	#9
fleetsidelarry Senior Car Nut Join Date: Jan 2008 Location: shellman bluff, GA Posts: 1,411	Re: Speedo reading almost double!!!!! it's alway nice to know the rear gear ratio, but not necessary to get the speedo sorted out. what you're experiencing is quite common when a transmission (like the 350) is swapped in 'cause the vehicles they came from quite often had 3.08s or even 2.73and ours are often 3.73s or numerically higher. the only problem I foresee is that you may have to also swap out the speedo drive gear. which requires removing the tranny tailshaft __________________ Larry

01-28-2012, 07:42 PM	#10
mrfixit4818 Registered User Join Date: Oct 2011 Location: marietta Ga. Posts: 36	Re: Speedo reading almost double!!!!! Just came back from a little ride,its about 15 to 20 mph off!!Im not worried about it now have plenty other stuff to do.Gunna try to see tomm. what size gear is in there.If I get done painting the dash early enough.



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