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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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| | | | Joined: Apr 2010 Posts: 45 'Bolter | | 'Bolter Joined: Apr 2010 Posts: 45 | Good evening Guys. I have lurked around here the last couple of years and have learned a lot. First off, I have a 1948 3600 with a 250 6 cyl, 200r4 auto with a lockup, with the original 4.56 rear. I can run 65 mph at about 2400 rpm's. I still have original front and trar suspention, with the exception of swapping out the old knee shocks for tubes. I want to keep the 8 lug. I have found a (as described) 3.73 8 lug rear out of a 1981 G30 van. I have read much here about the options for rearends and I think I have found the best solution. I will try to add a picture. What do ya'll think? Am I on the right track? 1 ton REAR chevy | | | | | Joined: Sep 2001 Posts: 29,270 Bubba - Curmudgeon | | Bubba - Curmudgeon Joined: Sep 2001 Posts: 29,270 | jjrockbush,
What is the diameter of your tires? | | | | | Joined: Apr 2010 Posts: 45 'Bolter | | 'Bolter Joined: Apr 2010 Posts: 45 | jjrockbush,
What is the diameter of your tires? 29.6" 265/70/15 | | | | | Joined: Feb 2004 Posts: 29,852 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,852 | That would be a good gear ratio option for a direct-drive transmission like a TH 350 or 400. The overdrive 2004R will make the engine struggle to maintain highway speed as you'll be way below the optimum torque range, and gas mileage will suck like a Hoover upright vacuum cleaner.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Apr 2010 Posts: 45 'Bolter | | 'Bolter Joined: Apr 2010 Posts: 45 | I estimate that at 65 it will be running abot 1700 rpm. too low? | | | | | Joined: Feb 2004 Posts: 29,852 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,852 | 2000-2500 at 65 would be a better speed, as the manifold vacuum at 1700 will be so low the power valve in the carburetor will stay open all the time.
It's possible to over-gear an engine to the point it can't develop enough torque to pull the vehicle along a level road reliably, and even a slight hill or an attempt to accelerate or pass puts it into a "lugging" situation where more throttle opening doesn't produce any more RPM. Both performance and gas mileage take a big hit at that point. With that rear end you'll be spending a lot of time downshifting, and forget about ever getting the torque converter clutch engaged.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: May 2004 Posts: 11 New Guy | | New Guy Joined: May 2004 Posts: 11 | Don't want to steal this at all!
I do have the same interest on the 81 G30 gears. But with a stock 350/400 auto. and a 30" 17.5 tire?
Last edited by benson; 12/03/2015 1:00 AM.
| | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | What is the width of that van axle compared to the original (which is about 63")?
It also looks like a semi float rear which I personally wouldn't want for a 3/4 ton or larger.
A full float "14 bolt" rear can be had the right width and with gear options to suit. I'm gearing up* for a 14 bolt swap myself and will document it well in the coming weeks.
Grigg
*pun intended | | |
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