calibrating speedo - The 1947 - Present Chevrolet & GMC Truck Message Board Network

BoeJaker1976 · 08-06-2010, 11:31 AM

Ok, i went down in tire size, and now my speedo is reading 10 MPH faster than i am going. I pulled the driven gear and its has 19 teeth (yellow) and moved the output shaft on the tranny so i can see the drive gear, its green. by the way its a th350 tranny
i have 2.73 rear
with 275/50 r17's

Which driven gear should i go with? do i need to go up in gear teeth? or down? im confused.

Since im here, whats the oil capacity needed for the 350 (might as well change the tranny oil filter and fluid since im there)

joe231 · 08-06-2010, 05:46 PM

According to TCI, yellow driven gear is 41 teeth, the 19 tooth is natural colored
I inputed your data and it says you need a brown 18 tooth driven gear with a green 9 tooth drive gear...doesn't really jive with what you are saying...

http://www.tciauto.com/Products/Tech...eedo_gears.asp

http://chevelleengineer.home.comcast...eer/speedo.htm

CheyenneC20 · 08-06-2010, 07:34 PM

I had the same issue with my C20 with turbo 400. I found a 4 teeth change at the driven gear made a 10mph change at the speedo.

CheyenneC20 · 08-06-2010, 07:36 PM

more teeth on the driven gear will slow it down

S10Fan · 08-06-2010, 09:39 PM

Contact these folks........................

http://www.transmissioncenter.net/

08-06-2010, 11:31 AM	#1
BoeJaker1976 Registered User Join Date: May 2005 Location: copperas Cove, TX Posts: 85	calibrating speedo Ok, i went down in tire size, and now my speedo is reading 10 MPH faster than i am going. I pulled the driven gear and its has 19 teeth (yellow) and moved the output shaft on the tranny so i can see the drive gear, its green. by the way its a th350 tranny i have 2.73 rear with 275/50 r17's Which driven gear should i go with? do i need to go up in gear teeth? or down? im confused. Since im here, whats the oil capacity needed for the 350 (might as well change the tranny oil filter and fluid since im there) __________________ 1976 Red chevy steppy, Proud service member, US ARMY 15Y, AH-64D Apache Longbow Armament, Avionics, Electronics technician

08-06-2010, 05:46 PM	#2
joe231 Registered User Join Date: Dec 2007 Location: Palmer, Alaska Posts: 13,821	Re: calibrating speedo According to TCI, yellow driven gear is 41 teeth, the 19 tooth is natural colored I inputed your data and it says you need a brown 18 tooth driven gear with a green 9 tooth drive gear...doesn't really jive with what you are saying... http://www.tciauto.com/Products/Tech...eedo_gears.asp http://chevelleengineer.home.comcast...eer/speedo.htm __________________ *CHEVY ONLY* Last edited by joe231; 08-06-2010 at 07:59 PM.

08-06-2010, 07:34 PM	#3
CheyenneC20 Registered User Join Date: Jul 2010 Location: Auckland New Zealand Posts: 5	Re: calibrating speedo I had the same issue with my C20 with turbo 400. I found a 4 teeth change at the driven gear made a 10mph change at the speedo.

08-06-2010, 07:36 PM	#4
CheyenneC20 Registered User Join Date: Jul 2010 Location: Auckland New Zealand Posts: 5	Re: calibrating speedo more teeth on the driven gear will slow it down

08-06-2010, 09:39 PM	#5
S10Fan Old Heap Driver Join Date: Mar 2008 Location: Newport News, Va Posts: 2,640	Re: calibrating speedo Contact these folks........................ http://www.transmissioncenter.net/ __________________ _____________________________ Bryan '99 Silverado 1500, 4.3, 5-speed, reg cab, short bed '50 Chevy 2DR Hard Top, 350/350, M2 Front End, 3:08 gear, cruiser. '40 F**d Sedan, all Chevy power, Heidt's front end, TCI rear, nice driver.



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