Speedo calibration question...need help! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

silvereagle07 · 01-31-2009, 12:56 PM

I'm posting this to help a co-worker. He has a mid 80's s-10 he has put a v8 in. He is trying to get the speedo to work correctly. It has a th350, 3.23 gears , 26 in tall tires, drive gear has 7 teeth and the new driven gear has 22 teeth (gray). The speedo is still 10-12 mph fast. What does he need to do to correct the problem?

Arad68 · 01-31-2009, 01:32 PM

Try this link. I used it to fix my problems.

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

silvereagle07 · 01-31-2009, 02:45 PM

I used this link before I posted and came up with 17.12 # of driven teeth. used this equation # Drive Teeth X Axle Ratio X Tire Rev. per Mile = # Driven Teeth
1001

silvereagle07 · 01-31-2009, 02:47 PM

He changed the driven gear from a 19 tooth to a 22 tooth gear. That's what a local trans shop said to do. It was orignally was about 30 to 40 mph fast and now its only 12-15 fast.

gchemist · 01-31-2009, 07:58 PM

He needs 8 driven and 20 driven gears. Driven ratio = 20.023. The speed will be almost dead accurate if he has a locking torque converter.

10 driven and 25 driven = 25.029

The top combo works the best.

Myself · 02-06-2009, 05:39 PM

I agree with the above. Change the drive gear. It's really easy, only takes about 30 mins.

silvereagle07 · 02-06-2009, 11:31 PM

Thanks guys!

silvereagle07 · 02-09-2009, 10:57 AM

He has a 7 drive and 21 driven non locking torque convetor th 350. Does he need anything different w nonlocking?

gchemist · 02-09-2009, 11:56 PM

No, he'll run ~200-300 RPMs higher to keep the speed indicated. Maybe more depending on the converter slippage.

01-31-2009, 12:56 PM	#1
silvereagle07 Registered User Join Date: Sep 2008 Location: Bailey, NC Posts: 2,462	Speedo calibration question...need help! I'm posting this to help a co-worker. He has a mid 80's s-10 he has put a v8 in. He is trying to get the speedo to work correctly. It has a th350, 3.23 gears , 26 in tall tires, drive gear has 7 teeth and the new driven gear has 22 teeth (gray). The speedo is still 10-12 mph fast. What does he need to do to correct the problem? __________________ Jeramy '84 GMC project truck '85 Chevy 4X4 SOLD '07 Chevy Trailblazer SS 5th Annual SHPHC Car/Truck Show Pics http://67-72chevytrucks.com/vboard/s...d.php?t=543605 UPDATED PICS! CHECK 'EM OUT

01-31-2009, 01:32 PM	#2
Arad68 Trucks N Tranzams Join Date: Dec 2002 Location: North Las Vegas, Nevada Posts: 816	Re: Speedo calibration question...need help! Try this link. I used it to fix my problems. http://www.tciauto.com/Products/Tech...eedo_gears.asp __________________ Don '68 Chevy LB 383 TH400/GV/373 posi '56 Chevy 4WD SWB '64 Chevy short stepside '79 Trans Am 455/TH2004R/12blt/4whldisc 95 Kia (Wifes car) 2002 S-10 extended cab pickup "God punishes small sins immediately"

01-31-2009, 02:45 PM	#3
silvereagle07 Registered User Join Date: Sep 2008 Location: Bailey, NC Posts: 2,462	Re: Speedo calibration question...need help! I used this link before I posted and came up with 17.12 # of driven teeth. used this equation # Drive Teeth X Axle Ratio X Tire Rev. per Mile = # Driven Teeth 1001 __________________ Jeramy '84 GMC project truck '85 Chevy 4X4 SOLD '07 Chevy Trailblazer SS 5th Annual SHPHC Car/Truck Show Pics http://67-72chevytrucks.com/vboard/s...d.php?t=543605 UPDATED PICS! CHECK 'EM OUT

01-31-2009, 02:47 PM	#4
silvereagle07 Registered User Join Date: Sep 2008 Location: Bailey, NC Posts: 2,462	Re: Speedo calibration question...need help! He changed the driven gear from a 19 tooth to a 22 tooth gear. That's what a local trans shop said to do. It was orignally was about 30 to 40 mph fast and now its only 12-15 fast. __________________ Jeramy '84 GMC project truck '85 Chevy 4X4 SOLD '07 Chevy Trailblazer SS 5th Annual SHPHC Car/Truck Show Pics http://67-72chevytrucks.com/vboard/s...d.php?t=543605 UPDATED PICS! CHECK 'EM OUT Last edited by silvereagle07; 01-31-2009 at 02:55 PM. Reason: don't know

01-31-2009, 07:58 PM	#5
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Re: Speedo calibration question...need help! He needs 8 driven and 20 driven gears. Driven ratio = 20.023. The speed will be almost dead accurate if he has a locking torque converter. 10 driven and 25 driven = 25.029 The top combo works the best. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos

02-06-2009, 05:39 PM	#6
Myself Registered User Join Date: Oct 2005 Location: Northern Arkansas Posts: 1,128	Re: Speedo calibration question...need help! I agree with the above. Change the drive gear. It's really easy, only takes about 30 mins.

02-06-2009, 11:31 PM	#7
silvereagle07 Registered User Join Date: Sep 2008 Location: Bailey, NC Posts: 2,462	Re: Speedo calibration question...need help! Thanks guys! __________________ Jeramy '84 GMC project truck '85 Chevy 4X4 SOLD '07 Chevy Trailblazer SS 5th Annual SHPHC Car/Truck Show Pics http://67-72chevytrucks.com/vboard/s...d.php?t=543605 UPDATED PICS! CHECK 'EM OUT

02-09-2009, 10:57 AM	#8
silvereagle07 Registered User Join Date: Sep 2008 Location: Bailey, NC Posts: 2,462	Re: Speedo calibration question...need help! He has a 7 drive and 21 driven non locking torque convetor th 350. Does he need anything different w nonlocking? __________________ Jeramy '84 GMC project truck '85 Chevy 4X4 SOLD '07 Chevy Trailblazer SS 5th Annual SHPHC Car/Truck Show Pics http://67-72chevytrucks.com/vboard/s...d.php?t=543605 UPDATED PICS! CHECK 'EM OUT

02-09-2009, 11:56 PM	#9
gchemist BAD BOW-Silverado XST Join Date: May 2000 Location: Senior Member from Austin, TX Posts: 6,431	Re: Speedo calibration question...need help! No, he'll run ~200-300 RPMs higher to keep the speed indicated. Maybe more depending on the converter slippage. __________________ Gerardo a.k.a. Mad Chemist Silverado XST videos Last edited by gchemist; 02-09-2009 at 11:56 PM.



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