is it safe to drill a 3/8 or 7/16s hole through my monoleaf to make a centerpin so that the rearend will not shift left ot right? i bought a aftermarket housing that didnt come with gm perches. they said just u bolts and run them through the perch on the bottom side of the monoleaf. i tightened the hell out of the u bolts and still first nite at the track my rearend shift to the right causing my brake caliper to rub into my airshock. the only way i can figure is 2 drill my monoleaf i just want 2 know if any1 has done it and how safe it would be?

The OE monoleaf has a welded center post on the bottom. This 1/2 in dia post aligns with a hole in the shock plate. However, the OE set-up is the post fits into a pad socket, then the outer diameter of the socket, 1 inch dia, fits into the hole in the shock plate.

It is this interface keeping the rear axle aligned. I would not drill the spring, personally.
You could make a new shock plate from 1036 steel plate and drill for the post, 1/2 inch diameter and remove the pads. Or if you use a traction bar, make a spacer to go from the 1/2 inch dia to 1 inch dia.

Are the perches welded to the axle tubes?

ye the are welded but they r universal style perches. the perch has no lip to go over the leaf on either side 2 keeep it from goin right 2 left

the perch has no lip to go over the leaf on either side 2 keeep it from goin right 2 left

Make some locating pieces, just a simple channel that indexes into the perch and keeps the spring from sliding athwartships. The Lincoln Versailles use this arrangement.

That "tit" is like 3/8" dia. x 3/8" long and fit's in a tight thin sheet metal cup that fit's in an about a 5/8" hole in the bottom plate along w/ the bottom rubber pad lining the cup!

DON'T drill holes in your springs!! If the tit's are still there, then use stock bottom shock plates and you will be fine!!

If the tit's are GONE, then either buy new mono replacements OR the cheaper, three-leaf mono replacements that place's like good spring shops and JCW sell's worth the money and be done w/ it..

And I used 5-leaf, '68, 'Bird multi's by using Grade-5, 5/16" dia. x what was needed rethreaded and cut off carriage bolts that I ground the square off from under the heads and then whacked hell outta them in my multi's to seat them fine w/ my stock mono rearend mounts for years and years!!

Know ALL about this crap!!!

pdq67