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 Post subject: 904 gearing
PostPosted: Sun May 18, 2008 7:01 pm 
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Supercharged
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Joined: Sat Feb 16, 2008 1:25 pm
Posts: 5611
Location: Downeast Maine
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Are there different gear ratios that can be fitted to a 904 Automatic transmission?

If so, how can one calculate what the transmission has for a gear ratio.

Presently I have a 3.55:1 8 3/4 rear end. My goal is to create a taller final ratio by transmission recalibration to improve gas milage.

I know, I can hear you; "just change the rear end". My 904 currently is fitted with a reverse valve body, and needs to be returned to normal operation. In this case a change of transmission gear ratio would be easer if possible.

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 Post subject: Re: 904 gearing
PostPosted: Sun May 18, 2008 7:16 pm 
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Joined: Thu Oct 31, 2002 5:39 pm
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There are only two ratio sets available. Through 1980, the ratios were:

2.45, 1.45, 1.00

Starting in 1981, the ratios were:

2.74, 1.54, 1.00

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Last edited by SlantSixDan on Sun May 18, 2008 7:50 pm, edited 1 time in total.

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 Post subject:
PostPosted: Sun May 18, 2008 7:43 pm 
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Supercharged
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Joined: Thu Jan 27, 2005 8:32 pm
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Location: Portland-ish
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As you can see by the info Dan posted there is no change possible to the final (high gear) ratio of the A904 as it's direct drive. You're stuck with a rear axle gear change, adding an overdrive or changing to an overdrive transmission. The only overdrive transmission that directly bolts up is the A833OD manual 4-speed. Adding a Gear Vendors OD to the A904 is also possible, but expensive.

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 Post subject:
PostPosted: Sun May 18, 2008 8:04 pm 
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Joined: Tue Jun 27, 2006 8:21 am
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Location: Orlando, FL
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Go with the Gear Vendors overdrive. It's spendy buy you'll really like it. Your final drive would be like having a 2.77 gear with it.

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 Post subject:
PostPosted: Sun May 18, 2008 8:23 pm 
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Supercharged
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Joined: Sat Feb 16, 2008 1:25 pm
Posts: 5611
Location: Downeast Maine
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Maybe I'll liberate two of the 17" wheels shod with P235/65 rubber on the wife's Nitro... That would change the ratio a bit.

What was I thinking... Any damn fool knows that these old three speed transmissions have a 1.00 final drive. Gezz... I must have spent too much time clay baring & waxing the fleet today. Sorry to waste everyone's time.

Smicomatose Maineac

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