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I have 68 Cat wagon with an open 2.56 rear end in it now ..I am looking to put posi in it...how low can I go in ratio and still be able to drive it on the highway with out excessive rpms?..and what would be the cheapest way to do that sticking with all GM parts...I have 2 sets of wheels for it ..taller wheels for trips and low profile for city cruising..any and all advice or suggestions are welcome..thanks in advance..Jeff

Ok Jeff, 68 Catalina wagon is going to be a tough find for gears and even the posi unit.
Here are the ratio available from the factory. NO gears at the moment are available from the after market...BUT they ARE coming.

Carrier breaks I am a bit foggy on...Yes even I do not know it all...lol. Here is my guess. I will contact a gentleman down in Texas that is actually making these gears to get the proper series break in the posi / open carriers of the ratios. My GUESS is BELOW the way they are separated

1968 Big Pontiac 2.29 39/17 UA VA
1968 Big Pontiac 2.41 41/17 UB VB
1968 Big Pontiac 2.56 41/16 UC VC

1968 Big Pontiac 2.73 41/15 UD VD
1968 Big Pontiac 2.93 41/14 UE VE
1968 Big Pontiac 3.08 40/13 UF VF

1968 Big Pontiac 3.23 42/13 UG VG
1968 Big Pontiac 3.42 41/12 UH VH
1968 Big Pontiac 3.55 39/11 VJ
1968 Big Pontiac 3.73 41/11 VK

I have a 12 bolt full size Pontiac posi on the shelf but i am sure it is not a very steep carrier probably the highest gear would be 3.08 on it.

Jim

thanks for the info Jim....looked in my service manual and it says the breaks are 2.29 ,2.41 2.56 and one for the 2.73 2.93 3.08 and one for the 3.23 3.42 3.55 3.73 and 4.11.......will the 12 bolt fit right in place of 10 bolt? with no modification? if it is a 3.08 what is your opinion is it to high of ratio for highway driving?..dont want to be at 3500 rpm's going 55 mph.....is the 12 bolt for sale?thanks for your patience I am in a novice at this and trying to figure this out as I go...Jeff

Ok fixed the carrier breaks and appreciate the Helpful book work for everyone with the full size Pontiac 10 cover 12 bolt ring gear rear with 31 spline bolt in axles.
I am a bit confused as to what your asking about the 12 bolt fitting in the 10 bolt? Please elaborate on that? Do you have a 10 bolt or a 12 bolt rear under your car?

If you have the a 10 bolt cover under a full size car you will have 12 bolt ring gear. Jim

sorry for the confusion Jim....I have the 10 bolt under my car looks like the one in the photo you just posted....the 3.08 posi you have is it from a full size Pontiac? ...it is my understanding that 66-69 full size rear ends will fit under my wagon... will the 3.08 allow for long highway trips with out high rpms? Thanks in advance Jeff...

would the 3.08 pontiac posi be for sale ..if so what would you want for it?....thanks... Jeff

gonna be about 300.00 for that unit.

We should do the flange measurement first before anything to be sure the units are correct. Jim