Speedometer reads WAAAAYYYYY Fast - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**chev-obsession** · 12-15-2020, 06:18 PM

I put a 700R4 into my 65 c10, I used the speedometer gear calculators found on various websites to determine the drive gear and the driven gear. Installed the gears the calculator said to use and now the speedometer reads about twice what it should.

My question is, do I need the speedometer gear reducer box found on the SM465 or does the automatic trans not use those?
Posted via Mobile Device

**PGSigns** · 12-15-2020, 07:02 PM

I just did a 700r4 conversion in a 72. Gray drive gear and blue driven gear. 373 gear and 28" tall tires.
Jimmy

**chev-obsession** · 12-15-2020, 08:15 PM

Quote:

Originally Posted by PGSigns

I just did a 700r4 conversion in a 72. Gray drive gear and blue driven gear. 373 gear and 28" tall tires.
Jimmy

Did you connect the speedo cable directly to the transmission speedo drive gear housing?
Posted via Mobile Device

Rick Bollinger · 12-16-2020, 12:26 AM

Mine had electric and converted it to mechanical using one of these. Nothing else needed but don't remember which color gears. 700r4 3:73 and 29" tires.
https://www.classictransmissionsolut...20%7C%20%24118

vince1 · 12-19-2020, 04:37 PM

Mine reads too slow as a result of changing from a 3.73 to a 3.07. It seems to work great up here though by doubling the MPH to get KPH. It hurt to drive at 15 through a 30 school zone but I didn't get stopped and on the return trip from the lumber yard he had someone else pulled over.

**PGSigns** · 12-19-2020, 08:24 PM

Yes screwed it right to the transmission. You can easily change one to mechanical.
Jimmy

[QUOTE=chev-obsession;8850417]Did you connect the speedo cable directly to the transmission speedo drive gear housing?
Posted via Mobile Device[/QUOTE

**chev-obsession** · 12-20-2020, 02:05 AM

Sounds good, I was just making sure I didn’t need a gear reducer like I had on the sm465

12-15-2020, 06:18 PM	#1
chev-obsession Senior Member Join Date: Jul 2008 Location: kennewick, WA Posts: 1,464	Speedometer reads WAAAAYYYYY Fast I put a 700R4 into my 65 c10, I used the speedometer gear calculators found on various websites to determine the drive gear and the driven gear. Installed the gears the calculator said to use and now the speedometer reads about twice what it should. My question is, do I need the speedometer gear reducer box found on the SM465 or does the automatic trans not use those? Posted via Mobile Device

12-15-2020, 07:02 PM	#2
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	Re: Speedometer reads WAAAAYYYYY Fast I just did a 700r4 conversion in a 72. Gray drive gear and blue driven gear. 373 gear and 28" tall tires. Jimmy __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

12-16-2020, 12:26 AM	#4
Rick Bollinger Registered User Join Date: Mar 2018 Location: Colchester IL Posts: 284	Re: Speedometer reads WAAAAYYYYY Fast Mine had electric and converted it to mechanical using one of these. Nothing else needed but don't remember which color gears. 700r4 3:73 and 29" tires. https://www.classictransmissionsolut...20%7C%20%24118

12-19-2020, 04:37 PM	#5
vince1 Registered User Join Date: Jan 2013 Location: Calgary Alberta Posts: 1,164	Re: Speedometer reads WAAAAYYYYY Fast Mine reads too slow as a result of changing from a 3.73 to a 3.07. It seems to work great up here though by doubling the MPH to get KPH. It hurt to drive at 15 through a 30 school zone but I didn't get stopped and on the return trip from the lumber yard he had someone else pulled over.

12-19-2020, 08:24 PM	#6
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	Re: Speedometer reads WAAAAYYYYY Fast Yes screwed it right to the transmission. You can easily change one to mechanical. Jimmy [QUOTE=chev-obsession;8850417]Did you connect the speedo cable directly to the transmission speedo drive gear housing? Posted via Mobile Device[/QUOTE __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

12-20-2020, 02:05 AM	#7
chev-obsession Senior Member Join Date: Jul 2008 Location: kennewick, WA Posts: 1,464	Re: Speedometer reads WAAAAYYYYY Fast Sounds good, I was just making sure I didn’t need a gear reducer like I had on the sm465 __________________ 1965 c/10 swb 1969 c/10 lwb



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.