The 1947 - Present Chevrolet & GMC Truck Message Board Network

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)

- The 1967 - 1972 Chevrolet & GMC Pickups Message Board (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=3)

- - 12 bolt (https://67-72chevytrucks.com/vboard/showthread.php?t=612919)

How do you tell the difference between a "car 12 bolt" and a truck 12 bolt. I know I have a truck 12 bolt but I am just curious as to how you tell the difference between them without pulling the diff cover. The car was 8.5 inch ring gear, and the truck was 8-7/8 inch correct? Is there any tips or tricks to tell the diff? Hahahahaha get it

I know the 73 up truck had a bigger pinion bearing. Not sure if that hold true for the pre 73

Quote:

Originally Posted by 1971 cheburban (Post 6480025)

The pics of the diff cover gasket say it all. Both 12 bolt diffs have an 8.875 in ring gear, but the housing is a different shape. The 8.875T is the truck, the 8.875P is the passenger car.

Ok to expand the question, what's the difference between a 67-68 12 bolt and the 69-72ones? I heard one is wider than the other? Does anyone know exact dimensions?

I think the 67-70 axles were 55 1/2 inches wide and the 71-72 were 57 inches wide but not 100% sure.

You have the 6lug and 5lug thing going on too.

Quote:

Originally Posted by Titus0 (Post 6481680)

Ok to expand the question, what's the difference between a 67-68 12 bolt and the 69-72ones? I heard one is wider than the other? Does anyone know exact dimensions?

The width change came in 1970.

I thought the older axle was the longer one allowing for wider wheels in the back. Mine is a 12 bolt truck axle, but im not sure the year as the truck is kinda a frankenstein.. Im wanting to buy new wheels soon and i want 10" wide in the rear, but dont wanna have to deal with a clearance issue.. This is why i wondered the difference in axle widths,, It's a 5 bolt btw..

Quote:

Originally Posted by Titus0 (Post 6482830)

It is not that simple. The rear drum brakes came in two different configurations. 63-69 are narrower than 70-up by 1.5" BUT that is with 2" wide brakes and not 2.75" wide brakes,

The width differences are not because of different shoe width, the 2.75" wide shoe backing plates are deeper inset to make those axles same overall width from WMS to WMS as the 2" wide shoe axles.

All 70-up axle shafts and housings are same width regardless of shoe width,
the housing width is what changed, IE tube length, in 1970, then in 71 for 2wd's the wheel studs changed to 5 lug pattern with 1/2" studs, away from the 69 older 6 lug 7/16" studs pattern same for 2wd and 4x4