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#1 |
Registered User
Join Date: Jan 2015
Location: Wellington, New Zealand
Posts: 47
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1971 K20 Gearing Query
Hi everyone.
Firstly thank you for the great active community here - I've learned a bunch from the numerous threads. I've recently imported a 71 K20 (3 speed auto with a 350 GM Goodwrench) to New Zealand and now we've got through compliance we're finally on the road! I'll get some shots for you guys shortly :-) Overall she drives really well, however at 60mph on the motorway she's really working at around 3,000 rpm. I'm currently running some 33s which leads to a gear ratio of 4.9 which seems quite high compared to the 4.1 I understand they were built with (dodgy tach?). She previously had 37.5s (I had to swap them out for compliance and didn't drive her with them on), so am looking for some advice on which would be the best option to work through: 1. Change the gear ratio (keen to hear what you guys are running) 2. Look at a new trans, e.g. 700r4 (keen to hear if there are any major challenges to keep an eye out for). Thanks in advance for your hel[p, Vaughan |
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#2 |
Registered User
Join Date: Jan 2015
Location: Wellington, New Zealand
Posts: 47
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Re: 1971 K20 Gearing Query
Sorry guys - forgot to mention I have an Eaton axle (as per those in the thread
below) if that helps in anyway. http://67-72chevytrucks.com/vboard/s...d.php?t=339732 Thanks, Vaughan |
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#3 |
Registered User
Join Date: Jan 2015
Location: Wellington, New Zealand
Posts: 47
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Re: 1971 K20 Gearing Query
Well after all that it looks like the Eaton was shipped with a 5.14 for the 3/4 ton trucks (http://www.stovebolt.com/ubbthreads/...&Number=870449), so that explains that 4.9 I came up with :-)
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#4 |
The Older Generation
![]() ![]() ![]() Join Date: Aug 2006
Location: Montezuma, Iowa
Posts: 25,481
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Re: 1971 K20 Gearing Query
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First off, welcome to the board. Sometimes there isn't much traffic on here on the weekends. Not much available for the Eaton's as far as the gears go. The 4.10's are about as high as they go. The 700r4 would probably be your best bet. Here is some reading on it while you are waiting on other members to chime in with their experiences.... http://67-72chevytrucks.com/vboard/s...ad.php?t=33266 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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#5 |
Registered User
Join Date: Apr 2011
Location: Klein Texas
Posts: 3,852
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Re: 1971 K20 Gearing Query
I'm pretty sure 4.56 or 4.10 were the only choices of gear ratio from the factory. It doesn't mean that someone didn't install something else.
I agree with the Doc, an overdrive transmission is going to help. It's easier, on a 4WD, to move the engine forward to accommodate the longer transmission than to push the transfer case backwards.
__________________
My Classics: '72 K20 Suburban + '65 Dodge Town Wagon '72 Corvette Roadster +'67 Corvette Roadster '73 Z-28 Camaro '63 Ford SWB Uni Pickup '50 Ford Coupe |
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#6 |
What?
Join Date: Jun 2007
Location: Southern California
Posts: 7,617
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Re: 1971 K20 Gearing Query
Welcome to the forum!
The Eaton HO52 rear axle in these trucks could have been ordered with either 4.10, 4.57, and 5.14. Being that yours is a K20, chances are it is 4.57 ratio unless swapped out. There isn't much of a market on Eaton HO-52 & 72 axle parts, let alone new ring and pinion kits. If you are looking to go to a taller gear for better highway manners, then I would start looking for a GM full floating 14 bolt rear axle. This axle housing will have more options for gears, and the replacement parts will be much easier to source.
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Chris 1968 K20 Suburban 1972 K10 LWB PU |
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#7 |
Registered User
Join Date: Jun 2013
Location: Somewhere
Posts: 3,073
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Re: 1971 K20 Gearing Query
Rather than guessing, pull the cover off the front diff and get the numbers off the ring. The gear oil needs changed anyway.
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Tags |
1971, gear ratio, k20, suburban |
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