I just installed a new 12 bolt in my car and notice that the center of the yolk is not centered in the frame. It appears to be off to the passenger side by approx 1/2 inch. I realize that the yolk is not centered on the actual housing so is the rear end also ofset by the 1/2 inch. The body is off the frame. The car has never been in a accident and the actual measurements coner to corner are within 1/8th of an inch.

It would help if we knew what the 12 bolt was out of, 64 never had a 12 bolt.??????

The 64 book call's for a 1.50 offset

I am not sure what year the 12 bolt is. The car has rear discs and if I put a straight edge on the hub of the rotor and measure to the outside of the frame rail there is a 1/2 inch difference side to side. I measure another vehicle I have (71 chevy 4x4 truck) from the brake backing plate to the leaf spring mounts and it also has a approx. offset of 3/4 of a inch.

Originally posted by LeoP:
64 never had a 12 bolt.?????? I used to think that too and was corrected right here on TC. Apparently some 64's did get 12-bolts.

But more to the question at hand, the yoke should not be centered on the frame. I'm unsure as to how much the offset should be but some answers above should be helpful.

When measuring at the backing plate to the frame rails, the rear should be centered. The side-to-side distance from the backing plate to the frame rail on each side should be equal.

Thats what I would think but there is approx. 1/2 inch difference between the drivers and passenger sides.. I also measured a few other cars and they also seem to be anywhere from 1/4 inch to 3/4 off. Would adjustable upper control arms help center the rear in the frame. Anyone with any other ideas. It would be intersting to actually have a few people measure from the backing plate to the frame to actually see if the rear is centered.

Posted by Rich-L79:
>Originally posted by LeoP:
64 never had a 12 bolt.??????<
>>I used to think that too and was corrected right here on TC. Apparently some 64's did get 12-bolts.<<

Count me among the skeptics.
Is this in the archives?
I looked, didn't see an article like that.
Any 64 I've seen with a 12 bolt had it swapped in.
Could have been done 35 years ago, but that still doesn't make it OEM.

Some guy tryed to sell me a 12 bolt out of a 64 once. They did install them, I believe they were only installed in the 4 speed chevelles.

I would like to see the 64 cast date. Early 65 cast dates are hard to find. Has anyone ever seen a A-Body 12 bolt with a 64 cast date?

Originally posted by chev65elleSS:
Some guy tryed to sell me a 12 bolt out of a 64 once. They did install them, I believe they were only installed in the 4 speed chevelles. I think that if 64 4 speed cars came with 12 bolts we wouldn't wonder about this at all because there were certainly enough of those built.
Now OTOH, if only the high horse 327 4 speed cars used a 12 bolt, late in the year, maybe, as that would drop the production totals way down enough to make them scarce.
I had an SS parts car which was alledged to be a 327 (hp unknown)4 spd , from the factory, and I have the rear and it's a 10 bolt.
One has to be careful of what one is told. I've found the owners of cars at shows don't necessarily know a lot and if they shelled out big bucks for a car, then questioning the correctness of parts on the car throws some of them into a defensive stance "of course it's right!" ;)
And what the guy trying to sell something tells you, well......... :eek:

I didn't here this from the seller, I read it somewhere along time ago, I think it was on a rearend ID site, but it doesn't seem like they would put a 12 bolt in an auto trans, probably for the high performance ones. Did they have 12 bolt in Auto's in 65? Maybe the date on the 12 bolt he was trying to sell me was dated 64 like some of the early 65 chevelle parts that were already being made at the end of 64. In my 65, when I pulled out my clock for a tach, the date on the clock says "Sep 10 64" on the back. Maybe your right but who knows for sure? Anyone?

Originally posted by chev65elleSS:
>> Maybe the date on the 12 bolt he was trying to sell me was dated 64 like some of the early 65 chevelle parts that were already being made at the end of 64. In my 65, when I pulled out my clock for a tach, the date on the clock says "Sep 10 64" on the back. <<

A Sept 64 date is certainly a 65 model year part.
I have a 64 wagon with the date 08E, last week of August 63.
Have to watch those model year changeovers.