1968 GS400

My friend is starting a resto on a '68 GS400 and it has a 12 bolt open rear. He insists it is original, but I thought only Canadian built cars recieved those. His (he tells me) is a Freemont built car.

Is it possible to have a 12 bolt originally in that car? Thanks.

 

Ask the owner to check the casting numbers on the center section and the codes and date that are stamped on the axle tube. I suspect it will give the answer.

 

While my knee jerk reaction is to say it wasn't born there, I have been around long enough to know better than to assume anything anymore. Having said that, one thing I have always understood, is that all the Canadian GS's and perhaps even the Skylarks in 68 and 69 had 12 bolts. As mine does. It was an open 3.08 (I did an actual tooth count math problem and it came to 3.08). But I suppose this doesn't necessarily mean that a 12 bolt couldn't have found its way into a U.S. built car. Stranger things have definitely happened.

 

I'll check the casting numbers.

 

be sure to get the stamped code from the axle tube as well.

 

I agree. It wasn’t supposed to and shouldn’t have (and likely didn’t!) but never say never. That said, if it was factory, it should have the big Buick style yoke (my ‘68 was built in Flint with a 2.93 posi; it now has a 3.55 12 bolt from a ‘69 Canadian GS and it went in without changing U joints).
Patrick

 

BIG BLOCK YOKE? BOP
Chevy in 1970 -1972 were the ones with a big and small block yoke 1310 and 1330 (big block chevy)
The BOP only had one yoke...The BOP Mechanics 3R yoke. That is it. ALL 12 bolts originally in BOP rears will have this standard BOP yoke 1.125 cup u bolts and 4 nuts and lock washers.

Maybe I read that wrong...'BIG BUICK STYLE YOKE'
Jim
JD Race

 

The casting # looks like 69 Chevy? Looked on google. I forgot to get a pic of the yoke. Tried to see what the ratio was but it turn 1 1/4 drive shaft for 1 tire revolutions, makes no sense there.

 

That’s a 12-bolt Chevy for sure. Get a picture of the yoke.

 

It is marked R8 That is BOP coding. It was original in a BOP car.

 

It is a 1969 casting number 038

 

Type "C" differential

2.56 41-16 R8, TR R9, TW, TH

2.73 41-15 RA, TT RB, TJ

3.08 43-14 RC, T4 RD, T5

3.31 43-13 RE, T6 RF, T7
Vista Cruiser w/400, 442 4.33 39-9
TW, TY


Here is your info.... 2.56 Oldsmobile rear in your Buck car. Sorry Not original to the car. UNLESS they again just plain goofed in the factory build when going down the assembly line... Jim
JD Race

 

Thanks. I was trying to run numbers and kept running into roadblocks

 

Just to make sure. It uses all chevy 12 bolt parts?

 

Yes. All 12-bolt Chevy parts.

 

ditto. yep THE yoke is what makes the 12 bolt chevy into 64-70 BOP swap easy... until you hit the 71 72 8.5 road block...lol.(driveshaft length issues etc.
Mechanic3R (1 1/8" cups)