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#1 |
Registered User
Join Date: Jul 2013
Location: Uvalde, Texas
Posts: 1
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Gear Ratio
I have a 72 C10 long bed with a 350 and auto transmission. I need to rebuild or replace my rear end and want to match existing gear ratio.
Is there any identifying marks on the rear housing or codes on the vehicle somewhere that could tell me what the gear ratio is without having to remove cover and count teeth? Thanks for any help. |
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#2 |
The Older Generation
![]() ![]() ![]() Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,483
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Re: Gear Ratio
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Check out this thread I posted on the subject: http://67-72chevytrucks.com/vboard/s...d.php?t=578793 Look at posts #8 & #19 for possible code locations. LockDoc
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Leon Locksmith, Specializing In Antique Trucks, Automobiles, & Motorcycles (My Dually Pickup Project Thread) http://67-72chevytrucks.com/vboard/s...d.php?t=829820 - |
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#3 | |
Registered User
Join Date: May 2012
Location: Faith,NC
Posts: 1,626
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Re: Gear Ratio
Quote:
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#4 |
20' Daredevil (Ret)
![]() Join Date: May 2003
Location: Jefferson State
Posts: 13,623
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Re: Gear Ratio
Stamped numbers (as well as the SPID) will tell you what gear ratio was in the truck when new. Over the years, many trucks have had their gearsets changed out. If you want to be sure what's in there now, you'll still need to verify by counting teeth -- or at least counting driveshaft rotations.
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- Mike - 1972 K20 LWB 350/350/205 RIP El Jay |
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#5 |
Registered User
Join Date: Jan 2014
Location: Wasilla Alaska
Posts: 537
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Re: Gear Ratio
Seems like it takes me way longer to find and wire brush the stamped numbers and then find a chart that is 100% accurate then it does to just pull the cover.
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#6 |
Registered User
Join Date: Jul 2008
Location: Bowie, MD
Posts: 313
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Re: Gear Ratio
Using a tach should get you close, or jack up the rear and spin the tires one full revolution, count the number of driveshaft rotations. But you cannot be certain without pulling the rear cover. Probably easiest to use marking compound so you can keep track of which teeth you've counted.
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#7 | |
Senior Member
![]() Join Date: Feb 2010
Location: Falls City, Nebraska "100 Miles From Nowhere"
Posts: 2,219
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Re: Gear Ratio
Quote:
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Michael of the clan Hill, "Two Seventy Two's" 71 1-ton Dually 350 4-Speed 71 C/50 Grain Truck, 350 Split-Axle 4-Speed 02 3/4 ton Express 14 Indian Chief Vintage 1952 Ford 8N, "Only Ford Allowed On The Property" ![]() "Be American, Buy American" ![]() |
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#8 |
Senior Member
Join Date: Jan 2003
Location: daytonabeach
Posts: 22,956
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Re: Gear Ratio
you say you need to rebuild is needed? I honestly don't know how you'd do that without removing the coner.. why don't you dive in and get it done?
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71c-10 350/2004r/4:11 lowered3/4 longbed/dead by hurricane MEANING OF DEATH::::: SOMEBODY ELSE GETS YOUR STUFF DONT BELIEVE EVERYTHING YOU THINK TAKE MY ADVISE;I DON'T USE IT ANYWAY |
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#9 |
Senior Member
![]() Join Date: Oct 2009
Location: Godley, TX
Posts: 17,963
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Re: Gear Ratio
just guessin here, but op must want new gears - thus the "want to match my existing gear ratio" comment - and would perhaps like to order them before rippin it all apart so as to do it in one ssession. i.e. a driver.
Having said that - why do you (tx72c10) suspect you need a rebuild (if you haven't inspected it yet)? Odds are that you won't actually need new r&p gears, but you never know. People usually only replace the r&p gears if they want to change the ratio or if they know what they currently have has grenaded (it would be obvious) after a 16 year old's burnout (don't ask). Lockdoc's charts are great - but if you have no reason to believe the rear has never apart - then you can probably go with what is on the SPID. If you have nothing on the SPID, then you got the standard gear for your configuration (3.73). 3.07 and 4.11 were optional. And btw, WELCOME to the board, glad to have you here. Show us some pics when you can. Last edited by jocko; 02-16-2015 at 08:42 PM. |
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#10 |
Registered User
Join Date: Dec 2009
Location: El Dorado Ca
Posts: 3,374
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Re: Gear Ratio
jack up the rear of the truck,it takes two people to do this..make a mark on both rear tires and the driveshaft.then both of you at the same time slowly rotate the tires forward til you make one revolution,while turning the tires,one of you need to count the number of revolutions of the driveshaft....for a 3:73 the driveshaft will rotate 3 3/4 times, a little more than 4 times for a 4:10 ratio and so on...
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#11 |
Registered User
Join Date: Aug 2010
Location: Edwards, CA
Posts: 7,503
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Re: Gear Ratio
By the numbers.
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#12 |
Parts and more parts
Join Date: Nov 2003
Location: Lebo, Kansas (middle of nowhere
Posts: 6,821
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Re: Gear Ratio
Is the truck still driveable? If so, can you get the RPMs that you are turning when driving a set speed, such as 2300 @ 70 MPH. With this information the rear end gearing can be calculated. If the transmission is a TH350, then the output shoft on it is counted as a 1.0 % and if it is an OD tranny, then the output would be a 0.70%. If you have the tire diameter to include into the calculation, then you can complete the calc.
Rear end gearing = ( RPM x tire diameter ) divided by (MPH X Trans output X 336)
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Frank |
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#13 |
Registered User
![]() Join Date: Dec 2011
Location: Hope Mills, NC
Posts: 62
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Re: Gear Ratio
I have been looking into this as well. I have a 3ott (1:1 final gear), a 3.08 gear and 23/75/15 tires. At 70 mph I am turning 2500 rpm. If I changed my tire size to 265/65/18, the new wheels and tires from a 2013-2015, I would drop below 2300 at 70. I would also lose a little takeoff power. Not a big drop for the price of the wheels. It's really hard to beat an overdrive with a 4th or 5th gear.
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