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Old 05-16-2009, 06:46 PM
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swapping 2.56 gears to 3.50 gears

Can I still use the carrier that I'm running with the 2.56 gears? The rearend is a 8.2" 10 bolt 1970 Chevelle. What RPM would I be running with the 3.50 gears and a 350th tranny @ 60mph with stock tire height? Also, can you keep the original drive shaft unaltered if the 350th was swapped for a 200r4? I have a 700r4 I was thinking of using but is longer. Which one is the easier swap - 700r4 or 200r4? Which one is better?
Thanks
Jay

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Last edited by shmiv; 05-16-2009 at 06:56 PM.
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Old 05-16-2009, 06:54 PM
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Are the 3.50 gears out of another 8.2 ? Cole
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Old 05-16-2009, 06:58 PM
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Yes the gears are out of a 8.2" rearend
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Old 05-16-2009, 07:04 PM
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As long as its the same style rearend there would be no reason why it shouldnt work. Cole
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Old 05-16-2009, 07:31 PM
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The 3.50 gears won't work on the carrier for the 2.56 gears without using a ring gear spacer, or using a 3-series differential carrier.

Can't tell you what rpm you will be running without knowing the actual tire size and what rpm you run now with the 2.56 rear @ 60 mph.

You can keep the drive shaft with the 200R4, it is the same. Most racing trans builders say they can beef the 200R4 up to handle more, guys are running them in low 8-second 1/4 mile Turbo Buick Grand Nationals. But, 200R or 700R, the cost really goes up sharply to make them handle 450 or more HP.
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Old 05-16-2009, 07:50 PM
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[QUOTE=ericnova72]The 3.50 gears won't work on the carrier for the 2.56 gears without using a ring gear spacer, or using a 3-series differential carrier.

Thanks Eric. I was trying to remember how that works. the difference is the space between the ring gear / pinion center . Cole
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Old 05-16-2009, 08:42 PM
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Quote:
Originally Posted by shmiv
Can I still use the carrier that I'm running with the 2.56 gears? The rearend is a 8.2" 10 bolt 1970 Chevelle. What RPM would I be running with the 3.50 gears and a 350th tranny @ 60mph with stock tire height? Also, can you keep the original drive shaft unaltered if the 350th was swapped for a 200r4? I have a 700r4 I was thinking of using but is longer. Which one is the easier swap - 700r4 or 200r4? Which one is better?
Thanks
Jay
The 2004R has a better 1st to 2nd gear spread than the 700R4. It's lighter & takes (slightly) less HP to turn.
Here's a calculator that shows rpms/speeds with different ratios.> http://hotrodworks.net/hotrodmath/quarter.html
Just input your Info. 2nd calculator, also chart below it shows ratio/speed changes.
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Old 05-16-2009, 09:02 PM
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yes 2.56 and around 3.42 and up are different series from each other

the reason is that the ring gears are different thickness for each series and thus the ring gear mounting flange on the unit is in a differnet location to make up for this, because series 4 pinion gear heads are smaller diameter, around 9 teeth,

vs series 3 pinion heads in which are larger diameter and have more teeth with the taller ratios such as 2.56 and 2.73




3.50 is a ford ratio

gm will be 3.31 3.40 3.42 3.73


2.56 is series 3

around 3.42 and up are 4 series
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Old 05-16-2009, 09:26 PM
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Fast68, GM 8.2" 2.56 gear is not three series.

GM listed a 3.55 for the 8.2" 10 bolt.

4 series for the 8.2 is 3.90-up IIRC
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Old 05-16-2009, 10:18 PM
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8.2" 10-Bolt Factory gears.
2-Series = 2.56, 2.73
3-Series = 3.08, 3.36, 3.55, 3.70, 3.90*
4-Series = xxxxxxxxxxxxxxxxxxxxxxx N/A
*- S/O
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