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Discussion Starter #1
Looking at changing up my ratio for the 66 from a 2.56 to 3.08. I have the original rear axel with the 3.56 but seems thats a little high for highway speeds. Anyone know a rough estimate on how much changing up the ratio?
 

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while yall are on the subject my tempest has 2.56 none posi rea but with the roads around here id liek to have posi but i wish to keep the 2.56 geaing but all the posi chunks for the 10 bolt rears have a ange of gearing listed thay will work with, the only 2.56 posi i have found is a full sized posi chunk out of a late 60's to mid 70's car, will it fit my 66 10 bolt? or were would i find what im looking for?
 

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while yall are on the subject my tempest has 2.56 none posi rea but with the roads around here id liek to have posi but i wish to keep the 2.56 geaing but all the posi chunks for the 10 bolt rears have a ange of gearing listed thay will work with, the only 2.56 posi i have found is a full sized posi chunk out of a late 60's to mid 70's car, will it fit my 66 10 bolt? or were would i find what im looking for?
The 2.56 gearing uses a series 3 carrier. It will support all the way up to 3.23's. Anything above the 3.23's uses a series 4 carrier.

I would think what you have will fit but I'm with Rukee. Call the pro's !!!

Good Luck

Jim:cheers
 

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The 2.56 is a 2 series carrier. It will support 2.56 and 2.73 gears. The 3 series carrier is 2.93 thru 3.23. The 4 series carrier is 3.36--4.33. Should be fairly easy to find a 2.56--2.73 LSD for your ride. Good luck.
 

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Looking at changing up my ratio for the 66 from a 2.56 to 3.08. I have the original rear axel with the 3.56 but seems thats a little high for highway speeds. Anyone know a rough estimate on how much changing up the ratio?
You have 2.56 or 3.56 in your car now? I've never heard of a 3.56, heard of 3.36 gears.
Yes, 3.55s pulls more RPM at speed and acts like you need another gear, but the acceleration will offset the RPM. 3.08 or 3.23s are a good compromise gear.
 

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thanks guys, i like the 2.56 geaing but i would liek to have two drive wheels instead of one. aint it great that thares so many repro and aftermarket parts for gm car? and just ahs these cars get old enough to have to be called outdated thay come out with all these aftemarket parts that will insure these cas can be on the road in another 40 years.
 

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Discussion Starter #9
You have 2.56 or 3.56 in your car now? I've never heard of a 3.56, heard of 3.36 gears.
Yes, 3.55s pulls more RPM at speed and acts like you need another gear, but the acceleration will offset the RPM. 3.08 or 3.23s are a good compromise gear.

There is a 2.56 in there right now but it is not the original. The original I am told is a 3.56 but was switched due to the RPM's. I was looking at getting the one in there now, the non original and switching it to a 3.08 to get more RPM at speed. What would be better ratio to go with 3.08 or 3.23?
 

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Pontiac never offered a 3.56 gear in any A body. It was a 3.55 ratio that was fairly standard on the '65--'67 stickshift cars.
 

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If your car is a stickshift, I would put a 3.23 gear in it. If it's an auto, I'd go with the 3.08. Just my personal taste...
 
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