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......
55 GMC 3100 2nd Series 71 GMC 1500 Super Custom 1956 Thriftmaster 1954 Blue Flame 1962 Thriftmaster
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!
55 GMC 3100 2nd Series 71 GMC 1500 Super Custom 1956 Thriftmaster 1954 Blue Flame 1962 Thriftmaster
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!!!
Last edited by Gdads51; 01/20/202311:30 PM.
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
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.
