WTF! Help! Pontiac 12 bolt 31 spline rear end

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kid7755
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WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by kid7755 » Fri Apr 24, 2015 11:05 pm

Working on a customer's 67 poncho Grand Prix. Rear end has 10 bolts in cover so I assumed it was the 8.2 BOP ( yes I'm a dumb ass for assuming). Ordered powertrax posi lock for 8.2 but obviously does not fit. This thing is a 12 bolt with 31 spline axles. What can I do so it is not a one wheel burner. Can't put spider gears back in without losing sleep one is galled a fair amount on the cross pin. Any advise???? #-o

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by cgarb » Sat Apr 25, 2015 12:38 am

I had one of those also, goofy B.O.P. rears. Mine was a drag only set up and what i did was fire up the welder...not the best option but i wasnt making a ton of hp then and it did work. Good luck sir.

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by Pontiac_Puller » Sat Apr 25, 2015 12:56 am

It sounds to me that at some point that car received an axle swap.

If what you said is true, it looks like a 8.75" axle, not to be confused with the Chevy 8.875". They only made them a few years, and not until the 70's. A few parts are available, such as bearings, but no other hard parts.

Look like this? Should be a 10 bolt cover, 12 bolt ring gear, c-clips?

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kid7755
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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by kid7755 » Sat Apr 25, 2015 3:20 am

That looks like cover. No c-clip.

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by kid7755 » Sat Apr 25, 2015 3:22 am

The owner bought the car new and never swapped axle.

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by pdq67 » Sat Apr 25, 2015 12:15 pm

8.75" dia. ring gear... Interesting!! NO "C"-clips....

A GM "sorta" 12-bolt with no clips!!

Wonder how much of a "real" 12-bolt car rear end will fit in it??

Where is Freddie, (aka, big gear head??)..

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by pitts64 » Sat Apr 25, 2015 2:05 pm

Brad at Fabcraft sells parts for them... If it's not going to be drag raced, the standard rear end is best for street cruising...

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by Chipped tooth » Sun Apr 26, 2015 3:57 pm

That's the typical bop 12 bolt..... It's a odd duck.

I would try to sell it to a restoration buff and take that money and buy something more common.

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Re: WTF! Help! Pontiac 12 bolt 31 spline rear end

Post by kid7755 » Thu May 07, 2015 9:32 am

Thanks guys for your info. I searched high and low even for some good used parts with less wear. Have to put it back together as is. It'll last the summer if he keeps from burning one tire. Gonna swap it out this winter.

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