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[GMCnet] 3.21 final drive, any opinions [message #304844] Wed, 03 August 2016 15:50 Go to previous message
glwgmc is currently offline  glwgmc   United States
Messages: 1014
Registered: June 2004
Karma:
Senior Member
With two coaches (a 77 Clasco and a 78 Royale, both 455) and lots of driving all over north America every year I really like the 3.67 ratio from a 3.5 chain in the transmission plus a 3.21 planetary gear final drive. You can achieve the same outcome with a 3.7 final drive alone. I rarely shift into second gear going up hill with either coach, drive about 65 on average and get right around 8.5 on regular crap gas in both coaches. I do regularly add an ethanol conditioner to the “fuel” to try to mitigate some of the ill effects from 10% alcohol. My mileage went up a bit when I changed from the 3.07 to the 3.67 in both coaches. Both coaches drive far more like cars with this gearing than either did with the 3.07. Quick merging into traffic, easy overtake on the freeway - just generally a lot peppier feeling. I don't tow anything.

Jerry
Jerry Work
The Dovetail Joint
Fine furniture designed and hand crafted in the 1907 former Masonic Temple building in historic Kerby, OR

glwork@mac.com
http://jerrywork.com
=================
Message: 7
Date: Wed, 03 Aug 2016 11:16:12 -0600
From: Todd Perkins
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] 3.21 final drive, any opinions
Message-ID:
Content-Type: text/plain; charset="utf-8"

great questions. I drive in the 70s pull 3,000 to 5,000 loads also.

Another question is what kind of mileage before and after would be interesting. I'm getting around 7 MPG. Too many WOT runs up the hills I guess. I
assume i would get a little better buy staying out of the secondary throttles :)


please share what you find.


Todd
--
Todd

Owner of a 1976 Eleganza II 26?
other toys:
93 Vette
84 Goldwing

and gone but not forgotten
72 CB750 Chopper
96 Caprice Classic
34 Ford roadster
94 Fleetwood
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Jerry & Sharon Work
78 Royale
Kerby, OR

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