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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend> swapping 2.56 gears to 3.50 gears
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Topic Review (Newest First)
05-16-2009 09:18 PM
SSedan64 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
05-16-2009 08:26 PM
ericnova72 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
05-16-2009 08:02 PM
fast68 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
05-16-2009 07:42 PM
SSedan64
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.
05-16-2009 06:50 PM
eloc431962 [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
05-16-2009 06:31 PM
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.

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.
05-16-2009 06:04 PM
eloc431962 As long as its the same style rearend there would be no reason why it shouldnt work. Cole
05-16-2009 05:58 PM
shmiv Yes the gears are out of a 8.2" rearend
05-16-2009 05:54 PM
eloc431962 Are the 3.50 gears out of another 8.2 ? Cole
05-16-2009 05:46 PM
shmiv
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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