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Old 11-03-2008, 06:14 PM   #1
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1984 27' Airstream 270
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gear ratios

My 1984 Excella 270 with a 14 bolt corp. axle with 4:56 gears. Has anybody switched to 4:11's? Drag racers and rock climbing 4x4s have 4:11 ratios so they are available and I'll bet the 4:56 would make an offroad vehicle climb that much better and my 454 should more than enough power to use the slightly lower gears?
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Old 11-03-2008, 06:25 PM   #2
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Not sure I'm understanding here!

My 1/2 ton sierra 4x4 has 4.11 diffs. Yours are actually lower than mine - unless I am very confused, which isn't entirely impossible!


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Old 11-11-2008, 07:45 AM   #3
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Craig, that's one low rear end... but lots of Moho's had 4.56's.

What do you turn (rpm) at 55 mph?

Check out Jegs or Summitt Racing for Ring and Pinion sets.

Make sure you get someone to do this swap who has experience and the right tools. As I understand it you can tear up a new rear end if it's not installed and meshed just so.
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Old 11-11-2008, 07:55 AM   #4
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If I understand your question, you want to swap your lower-ratio gears for something a little more highway-friendly. The ring gear and pinion gear need to be installed together as a set, and need to be "set up" or preloaded. Most pinion gears use a crush sleeve and/or shims to accomplish this. It is something you can do, but requires more than basic automotive knowledge.
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Old 11-11-2008, 08:42 AM   #5
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I don't think it's something you need to worry about with a '84, but when I took a look at new gears for the rear of my Titan, I was told I would need to have the dealer reflash the ECU.
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Old 11-11-2008, 10:43 AM   #6
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Quote:
Originally Posted by hampstead38 View Post
I don't think it's something you need to worry about with a '84, but when I took a look at new gears for the rear of my Titan, I was told I would need to have the dealer reflash the ECU.
That's why my '02 Silverado will continue with the OEM 3.73 gearing. I am not sure if the '84 has an electronic speedometer or not, if it does, it will need a different VSS. If it doesn't, it will need a different speedometer drive gear. Both are located in the same place, in the tailshaft of the transmission.
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Old 11-16-2008, 10:06 PM   #7
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Before you mess around with changing the diff, do a bit of calculating - - figure out how much distance 1 rev moves the rig - remember that to do this, you need to know the diameter of the tires. I once had a Chev G20 van that came with a 2.73:1 diff. It was useless for towing, so I bought a set of 4.10:1 gears, but I increased the tire size so that it was effectively the same as a 3.96:1 rear.

BTW, if you do change the diff ratio, you will also have to change whatever is used to calculate your speed and odometer, either a small gear, or, more likely, you will have to change the DRAC (digital ratio adapter controller), a small module that interfaces between the sensor and the speedo.

Personally, I would be inclined to keep what you have. With the Chev van, I actually got better mileage with the 4.10:1 than the 2.73:1, not to mention the power to pull a heavier load. By moving to a numerically lower ratio you will lose load carrying capacity of your rig.
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