Posted by Gordon Maney on Tuesday, July 31, 2001 at 7:41PM :
In Reply to: I know this has been asked 100 times but... posted by Tim Way on Tuesday, July 31, 2001 at 7:00PM :
The spec from the military manual is 14.220 inches as the wear limit (maximum diameter). The brake drum is nominally a 14-1/8, which is 14.125, so they are letting you go almost Ō100 over,Ķ using the machinistÕs conversational language.
If you have someone turn them, remember to have them turned on their own hubs, firmly attached to those hubs, and with the bearing races firmly in place, properly seated, and clean.
Proceed gingerly. The guy at the muffler shop who hopes to discard the typical customerÕs drum so they can sell them another one fails to realize that if he scraps the typical Power Wagon ownerÕs drum(s) he will get his head crushed by one of the ruined drums wielded by the irate owner.
If you have a few deep scores, just leave them and machine the rest of the surface. Yes, ideally, you need to turn the entire face of the drum, it canÕt be over the ax diameter, it must be round, it canÕt be a tapered bore, and so on.
You understand there is enough mass in that drum so that even at the ax diameter it is considered and rated as safe. Consequently, if it is turned .010 inch past that, it does not mean you will be killed in your first trip.
Realistically, there are few Power Wagons in use with drums that would pass measurement.
What am I saying? Measure the drum for sure, and donÕt let someone turn the drum clean on the first pass. Go slowly, take .010 or .015 at a pass. He wonÕt like that because if he charges $X.XX per drum, he is making less per hour that way. If the guy does not like your requirement, then find someone else.
I have had trucks where I got the drum clean and under ax with a couple of score lines, that is fine. I have had trucks where I had most, like 85%, of the surface width clean and at ax, and that was fine. Just donÕt hand the drums to a guy to turn and not watch him. He will ruin your drums, most likely.
Also, if the shop does not have an actual drum micrometer for that size drum, donÕt let them touch it.
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