#1  
Old 03-22-2021, 03:08 AM
Ponty Ponty is offline
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Join Date: Jun 2020
Posts: 11
Default 68 Bonneville rear diff info.

I've just recently bought a 1968 Bonneville coupe. 400CI, TH400. On the LHS of the axle tube the letters "VC" are stamped into it. From what I've been able to find out the diff ratio is 2.56. With the diff being an LSD type. The diff cover has 10 bolts in it. Now is this diff an 8.2" or an 8.875"? (with a 12 bolt ring gear). I thought all diffs for these full size cars from 65-76 were an 8.875". I've been told conflicting stories. I'm looking at changing this ratio to a 3.55. So am I correct in saying I'll also need a 3 series carrier ? Are these gears & carriers available anywhere as an aftermarket option? Still new to Pontiacs, still learning. Thanks.

  #2  
Old 03-22-2021, 09:08 AM
20milecar's Avatar
20milecar 20milecar is offline
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3.55 won’t be fun on the highway. Your rear end should be an 8.2 BOP. And you will need a 3 series carrier. I have a set of 3.36 gears and Posi on the way for my 67 Bonneville. (641) 751-8060 Call this guy, got a full gear set and everything to do the rear end for $550 with posi. Here’s a handy gears to speed calculator https://www.randysworldwide.com/calculators/rpm

If you’re looking to get rid of the posi 2.56, I may be interested as I’ll be going back to the long legged gears after I rebuild my motor.

  #3  
Old 03-22-2021, 09:28 AM
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camerjeff camerjeff is offline
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I have never seen a 8.2 on a full size Pontiac, all 65-76 B-Bodies should have a 10 Bolt (with 12 bolt carrier) 8 7/8" or 8.875" axle. Starting in 77 they went to a Lighter 8.75" axle.

Both are tough to find ring an pinion gears for.

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