I have an 89 GTA with a 9 bolt rear and I'm swapping in another 9 bolt

The last person cut a slot to remove the old bolt where the rod bolts onto the rear, so I had a plate welded in, thought I'd just get a longer bolt.

Well now I see these bolts have a shoulder that ends part way though. I'll probably just buy a standard bolt since the original one is too short with the plate, but I'm wondering if there's any purpose of having that type of bolt there.

thanks,
-Dan

 

Shoulder bolts are generally used when two mounting plates or parts have the potential for significant side or shear loads. The shoulder projecting through both parts prevent the load from transferring thru screw threads which could cause the holes to get chewed up resulting in excess bolt/hole clearance.

You can get shouldler bolts of various sizes & lengths from Lowes or a specialty screw company or order online from McMaster Carr Supply Co.

 

It can also be for factory assembly .
In this case they only wanted the bolt to go in one way.

 

it's weird that if they wanted that they put it so it would go in from the back, it would make more sense to go in from the front if it came loose

 

The PHB bolts do go in from the front(rear coil spring side), nuts are on the rear side just like the front "A"arms.