BRAKE ADJUSTMENT AND LINING PREP
'54 PACKARD CLIPPER
by Ross

ADJUSTMENT

54s still have the eccentric adjustment at the anchor pin on each of the backing plates to center up the shoes in the drums. Always a good idea to readjust them when fitting new shoes to give the best contact. With them adjusted, and a bit of wearing in, you probably won't have to have the shoes arced.

There is a long and tedious procedure in the shop manual for doing this which over the last 20 years I have boiled down to this:

Loosen the locknut (15/16) and turn the eccentric (7/16)to its neutral position. You will see that the eccentric's shank is cut at a slight angle. The high point should be toward the rear of the car. Tighten the normal adjuster til the drum is dragging heavily. Now move the eccentric back and forth a bit to obtain the least drag. You might have to tighten the adjuster a bit more and repeat the process to find the point of least drag. Tighten the locknut and then adjust the brakes normally. This will give the best possible contact pattern.

Important: when doing the rear brakes, disconnect the e-brake cables at the equalizer before beginning. Only connect and adjust the cables after the individual wheels are adjusted. If the cables are pulled you will not get a correct adjustment.

Arcing is grinding the shoes slightly to perfectly match the actual inner diameter of the drum so the entire shoe makes contact from the start. Without it, eventually the contour or any high spots on the shoe will wear down so the entire surface makes even contact but takes awhile.

It used to be a routine part of the job and every good brake shop, garage & larger parts store had the machines. The service has apparently fallen out of favor -- most likely due to regulations on dust. The theory now is the shoes come biased or pre-arced and you change the drum to match the shoe if the diameter doesn't match. Obviously the people behind the theory have no Packards or cars hard to find drums for.


LINING PREP AND "ARCING"

When drums are cut the radius of the drum surface becomes larger than the radius of the linings and thus, until such time as enough material has been worn from the linings, only a portion of the lining contacts the drum, so you very inefficient brakes and also very prone of localized overheating of the lining.

"Arcing" is a grinding method that grinds the lining to match the diameter of the drum so that full lining-to-drum contact is obtained from the get-go.