Hey All,

Anybody have any data that says the size of the hole to drill in the front hub in order to accept an 88 stud?

Thanks

Bimp (pink panther)

From what I have read, the hole should be .010" less than the knurl. I'd wait for someone else to chime in before proceeding because I can't find where I read it.

Dick

Several years ago I had regular access to a vertical mill, so I machined up a jig and redrilled my '88 front hubs on the mill. I just went out to the shop and double checked, and I'm pretty sure I used a 31/64 (0.484 inch, 12.3 mm) drill for the final (finish) pass, and the OEM studs pressed in very nicely. I did use anti-seize to facilitate assembly.

According to the catalogs, the M12x1.5 GM wheel studs have a knurl diameter of 0.509 inch (12.9 mm), which would imply that the hole should be about half an inch (0.500 inch, 12.7 mm) in diameter. But having actually done it, I think that a half inch hole might be a little too large. Consider that the actual finished hole size usually ends up slightly larger than the nominal drill size. I guess you could always drill to 31/64 and then ream to a slightly larger final size, if desired. YMMV.

[This message has been edited by Marvin McInnis (edited 04-13-2010).]

Thanks for the info!

Just wanted to share that I did get a reponse from another outfit...they indicated that the hole size would be .005 less than the knurl diameter. So, for this application it would be,,,

.509 - .005 = .504 hole size

Given the "odd" size of the GM knurl (0.509 inch), it makes sense that they probably would have tooled for a standard 0.500 inch hole size. In that case the best strategy for redrilling the hubs would seem to be: 1) pilot drill, 2) drill up to 31/64 (0.484 inch), 3) slightly chamfer both faces of the hub flange (for stress relief and crack resistance), 4) ream to 0.500 inch, and 5) press in the studs.

Remember, you can always enlarge an undersize hole, but you can seldom go the other way. You might want to do a practice run on a piece of scrap steel or aluminum before drilling the hubs themselves.

[This message has been edited by Marvin McInnis (edited 04-15-2010).]

Marvin, I think your approach is right on.

Hmm...31/64...that sounds familiar...isn't that also the hole size for drilling out the door hinges for new bushings?

Thanks again!

T