speedometer gear size for 3:43 rear end - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Red68 · 05-28-2011, 04:39 PM

My speedometer is off about 10 mph, I have an original 3 speed manual transmission. Several years ago i switched out the 4:11 rear end gears for 3:43's so I think that is why my speedometer is off. I found where I can purchase a different transmission speedometer gear but I dont know which one to use for the 3:43 gears. Any ideas on how to figure this out?

The link below is an example of what I am looking for.

http://www.classicparts.com/1963-78-...ctinfo/91-930/

**john** · 05-28-2011, 05:08 PM

Heres a site to calculate gear ratio, tire size, etc for speedo gear size.

http://www.transmissioncenter.net/sp...FQE0xgodER69XQ

.

Red68 · 05-28-2011, 05:49 PM

Thanks John, this should help me figure it out.

eightbanger · 05-28-2011, 07:35 PM

I'm running a 4.11 rear end, i'm registering about 5-10 mph over depending on overall speed, the gear I have in there has a 39 tooth count and using the calculator I need 44 tooth....but something I didn't realise is....if you need a speedo gear in the 40-45 tooth range as I do then I have to also buy a new housing which is $56 well they can poke it, i'll stick with my 39 tooth and put up with the incorrect reading.
If your reading was correct before the swap Red, that means you may need to change your housing to be able to run the lower tooth count gear.

Red68 · 05-28-2011, 09:24 PM

I am running 10 mph under, I suppose it does not matter if it is over or under. I have not taken out the gear in my transmission, is it right where the speedometer connects? How do you change the housing?

eightbanger · 05-29-2011, 08:19 AM

It's a very easy job Red, the housing is the aluminum doohickey that the plastic gear sits in...(see pic) and yes it is where the speedo connects.
Plenty on Ebay..http://shop.ebay.com/i.html?_kw=Spee...ts_Accessories

05-28-2011, 04:39 PM	#1
Red68 Registered User Join Date: Jan 2002 Location: Rhome, TX Posts: 209	speedometer gear size for 3:43 rear end My speedometer is off about 10 mph, I have an original 3 speed manual transmission. Several years ago i switched out the 4:11 rear end gears for 3:43's so I think that is why my speedometer is off. I found where I can purchase a different transmission speedometer gear but I dont know which one to use for the 3:43 gears. Any ideas on how to figure this out? The link below is an example of what I am looking for. http://www.classicparts.com/1963-78-...ctinfo/91-930/ __________________ 1968 C10 LWB 327 bored 40 over, RHS heads, KB pistons, Eagle rods, Edlebrock carb & intake 1968 C10 flatbed 307 w/ 4 spd manual (dads old ride) 1936 1/2 tn pickup, 400sb 350 turbo (partially restored) 1949 1/2 tn, needs complete restore (future project) 1969 Chevy impala 4 dr no post (wifes future car) 2010 GMC Serria 4x4 crew, leveling kit

05-28-2011, 05:08 PM	#2
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Re: speedometer gear size for 3:43 rear end Heres a site to calculate gear ratio, tire size, etc for speedo gear size. http://www.transmissioncenter.net/sp...FQE0xgodER69XQ . __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/

05-28-2011, 05:49 PM	#3
Red68 Registered User Join Date: Jan 2002 Location: Rhome, TX Posts: 209	Re: speedometer gear size for 3:43 rear end Thanks John, this should help me figure it out. __________________ 1968 C10 LWB 327 bored 40 over, RHS heads, KB pistons, Eagle rods, Edlebrock carb & intake 1968 C10 flatbed 307 w/ 4 spd manual (dads old ride) 1936 1/2 tn pickup, 400sb 350 turbo (partially restored) 1949 1/2 tn, needs complete restore (future project) 1969 Chevy impala 4 dr no post (wifes future car) 2010 GMC Serria 4x4 crew, leveling kit

05-28-2011, 07:35 PM	#4
eightbanger 454 MAKES IT ROAR Join Date: Jan 2008 Location: Essex, U.K Posts: 2,701	Re: speedometer gear size for 3:43 rear end I'm running a 4.11 rear end, i'm registering about 5-10 mph over depending on overall speed, the gear I have in there has a 39 tooth count and using the calculator I need 44 tooth....but something I didn't realise is....if you need a speedo gear in the 40-45 tooth range as I do then I have to also buy a new housing which is $56 well they can poke it, i'll stick with my 39 tooth and put up with the incorrect reading. If your reading was correct before the swap Red, that means you may need to change your housing to be able to run the lower tooth count gear. __________________ Nigel. An American living in a British body. 1971 Chevy Cheyenne 10 454 "In a time of universal deceit, telling the truth becomes a revolutionary act." - George Orwell "When injustice becomes law, resistance becomes duty" - Thomas Jefferson No more pain. 03.12.60 -- 12.28.10 http://www.youtube.com/Eightbanger Last edited by eightbanger; 05-28-2011 at 07:37 PM.

05-28-2011, 09:24 PM	#5
Red68 Registered User Join Date: Jan 2002 Location: Rhome, TX Posts: 209	Re: speedometer gear size for 3:43 rear end I am running 10 mph under, I suppose it does not matter if it is over or under. I have not taken out the gear in my transmission, is it right where the speedometer connects? How do you change the housing? __________________ 1968 C10 LWB 327 bored 40 over, RHS heads, KB pistons, Eagle rods, Edlebrock carb & intake 1968 C10 flatbed 307 w/ 4 spd manual (dads old ride) 1936 1/2 tn pickup, 400sb 350 turbo (partially restored) 1949 1/2 tn, needs complete restore (future project) 1969 Chevy impala 4 dr no post (wifes future car) 2010 GMC Serria 4x4 crew, leveling kit

05-29-2011, 08:19 AM	#6
eightbanger 454 MAKES IT ROAR Join Date: Jan 2008 Location: Essex, U.K Posts: 2,701	Re: speedometer gear size for 3:43 rear end It's a very easy job Red, the housing is the aluminum doohickey that the plastic gear sits in...(see pic) and yes it is where the speedo connects. Plenty on Ebay..http://shop.ebay.com/i.html?_kw=Spee...ts_Accessories Attached Images __________________ Nigel. An American living in a British body. 1971 Chevy Cheyenne 10 454 "In a time of universal deceit, telling the truth becomes a revolutionary act." - George Orwell "When injustice becomes law, resistance becomes duty" - Thomas Jefferson No more pain. 03.12.60 -- 12.28.10 http://www.youtube.com/Eightbanger Last edited by eightbanger; 05-29-2011 at 08:23 AM.



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