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Old 04-30-2021, 10:17 PM
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Default 69 GrandPrix 12 bolt??

Looking for new axels for pur 69GP but everything i see is listed for Chevy. Any know if the rear-end is same a A-body's?
Im finding 68-72 a-body
Or 66-70 Impala

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Old 04-30-2021, 11:38 PM
1969GiPper 1969GiPper is online now
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Quote:
Originally Posted by slowbird View Post
Looking for new axels for pur 69GP but everything i see is listed for Chevy. Any know if the rear-end is same a A-body's?
Im finding 68-72 a-body
Or 66-70 Impala
To the best of my knowledge a 12-bolt rear end was not available in a 1969 Grand Prix.

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Old 05-01-2021, 07:08 AM
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70 GP cettainly got the 12-bolt for 455 4-speed.

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Old 05-01-2021, 07:12 AM
'ol Pinion head 'ol Pinion head is offline
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Quote:
Originally Posted by Half-Inch Stud View Post
70 GP cettainly got the 12-bolt for 455 4-speed.
All '70 factory 455 equipped GP's & '70 400 manual trans received McKinnon plant built 12 bolts.

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Old 05-01-2021, 07:23 AM
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A 12 bolt is a 12 bolt is a 12 bolt basically in terms of Chevy only 12 bolts.

It first came about in 64, but there are Truck versions and passenger car versions and not all the parts between the two will interchange!

All the GM Trucks that used this 12 bolt rear had leaf springs, so the needed change over to run it in a coil spring car would be very clear in the rework done!
If I recall right the Truck rears take a different size pinion Bearing then the passenger car rear ends?

This GP in question is likely a very late 69 model and it would have been a 428 4 speed model if this rear is original to it.

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Last edited by steve25; 05-01-2021 at 07:54 AM.
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Old 05-01-2021, 07:31 AM
'ol Pinion head 'ol Pinion head is offline
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slowbird, if the rear is a c-clip axle real 12 bolt, it's either a traditional "Chevelle" style 12 bolt or it could be a McKinnon plant built 12 bolt, which took a different c-clip axle, the centering hub that locates the drum is slightly different diameter than the oem axle used in typical '68-72 Chevelle 12 bolt rear. Have versions of both.

If by some chance the "12 bolt" rear has a smooth 12 bolt cover, it's not a 12 bolt, but a '67-70 Type "O" Olds 8.4" 10 bolt rear. These have bolt-in axles, & there are 3 different style of axles (& housing ends)
-28 spline sealed axle bearing,
-31 spline sealed axle style, as well
-28 spline tapered axle bearing ('70 Cutlass & 442 only)

The Type "O" Olds 8.4" 10 bolt rear is often mistakenly referred to as a 12 bolt. The Olds crowd is the absolute worst at advertising the Type "O" as a 12 bolt. As the pinion length is the same & the Type "O" uses a 3R pinion flange, this style rear was often swapped into Pontiac A-body's. Having had '69 & 70 GrandPrix partscars which had Type "O" rears swapped in, it would be smart to carefully examine & identify what rear is now in your '69 GP, then can pinpoint what axle you need.

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Last edited by 'ol Pinion head; 05-01-2021 at 08:00 AM.
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Old 05-01-2021, 08:11 AM
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Sorry guys for the confusion, the rear is out of a 70GP. With c-clips
So the A-body Chevelle axels should be the correct replacement?
Thanks

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Old 05-01-2021, 01:31 PM
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1970 GP rear end with C-clips would be a McKinnon 12-bolt.
I guess all 1968-72 A-body 12-bolt C-clip axles will fit but the correct McKinnon axle are said to be stronger.
I´m sure OPH has a track on this.
And, https://tomsdifferentials.com/ has good axles.

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Old 05-01-2021, 01:38 PM
'ol Pinion head 'ol Pinion head is offline
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With the 12 bolt rear being original to a '70 GP, it should be a McKinnon built 12 bolt, the factory c-clip axles in the McKinnon built 12 bolts for '68-70 Buick & Olds usage & '70-72 Pontiac usage have a slightly larger diameter pilot where they go through the brake drum. A new pair of Moser 12 bolt axles for a '68-72 "Chevelle" or 70 1/2 Fbody will have a slightly smaller diameter pilot, but will work, or if concerned about the slight difference, one can run "Chevelle" style drums.

Someone was asking a month or so back about the pilot hole diameter of the different 9 1/2" rear drums, I'll pull some factory axles out of the racks & post the two measurements later this weekend.

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Old 05-01-2021, 09:32 PM
gtospieg gtospieg is offline
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Steve25...not ALL chevy trucks with 12 bolts had leaf springs, they also came with coil springs. I have 2 friends with factory coil spring setups in their c10s. Just sayin

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