The Stovebolt Site Forums The Shop Area Driveline 55 GMC 100 front brake drum size

I have a 55 GMC 102 truck that has front drums that I "think" are oversized. They are measuring 11.170" inside diameter and I cannot find a maximum size anywhere on the internet. The only stamping on the drum is located on the face and it says "W 20" Does this mean they can be bored .200" over the nominal 11.00"? Other than that there are no markings anywhere.
Cannot find any information......

Should be stamped on the edge like this

When I posted earlier the passenger side was off and had no markings, once I got the drivers side off it was different and had the markings that you posted. Sure enough I measured it, and it was on the high (11.090). The passenger side is 11.170" so I am going to replace both sides. I can see the "homemade" looking rivets on the driver's side so I know it was replaced at one time or another. Maybe the passenger side (that has the minimal markings) is still original?!
Thank you so much for posting the photo! I appreciate it!

DB,

FWIW, check out this link to a MA law regarding maximum oversizing of vehicle brake drums.

MA Law on Brake drum turning limits

Provides very detailed rules to follow. Since your truck is before the 1971 manufacture date cut off, it is essential that you find the maximum size limit markings on the existing drum to make a final determination. Without that marking, I doubt any shop will even consider cutting your existing drums.

These drums are reproduced and available through most of our normal vendor sources.

Thinking easiest option is choose safety first IMHO.

Hope you find this info helpful.

Dan

EDIT: See you have posted while I was putting this reply together. Good on you for deciding to replace them!!!

It has been max 90 thousandths over for as long as I can remember (back to 1967 at least). Having said that, drums are darn cheap for bendix brakes on light trucks, like $40. At summit racing for ACDelco’s.
In working with my local machinist on converting my 46 1/2 ton to front bendix (long story, truck came to me with bendix rears, huck fronts), plan is to secure our brand new drums to the hubs and turn them just enough to be sure they are centric to the axels.

Chuck