Drum brake chatter

[Ron Gusack]

Right rear shoes have marks going across the shoe lining. The marks are about an inch apart. I can feel it in the car when I brake pretty hard. I recently put secondary shoes on both the primary and secondary sides. What would cause this? Left rear looks fine.

[Eman]

New drums or old? Did you measure the drums with a drum mic if they are used? Remove the shoes and place them in the drum, do they "fit" the drum or can you rock them in the drum when you place pressure against the machined surface of the drum? If a drum is oversized it will not have the same arc as the shoes, this is where arcing brake shoes used to come in years ago.

[Ron Gusack]

I didn't mic the drum but the shoe fit is very close to touching the full arc. There's about a 1/16 inch gap at the very end of the shoe that's not making contact.

When racers put secondary shoes in both positions, do they do it to both the front and rear wheels?

[Mike Pearson]

The best thing you can do is get rid of the drum brakes and go to a decent disc brake set up. You wont believe the difference in stopping power. One of the best improvements that I have made on my car.

[Ron Gusack]

I'm more concerned with it holding on the starting line and I've been told drums were better than discs for that. I foot brake and sometimes the brakes won't hold the car at much above 3200. This chatter problem didn't start until I put long shoes in all eight spots. I'm wondering if the secondary shoe on the primary side is the problem.

[bigfoot584]

Ron, years ago we use to have to put 1/8" to 3/16" bevel on the leading and trailing edge of shoes to help with that sometimes, also I wouldn't run both long shoes on the rear but I would in front. We also would take a hack saw and put a diamond pattern across the face of the shoes spaced out about an inch then turn saw other direction come back the same distance, go about 1/4 to 1/3 into shoe surface be careful on riveted shoes for depth, this helps chase some of the heat out. Try taking 80 grit sand paper and scuff rear shoes and drums then clean well with brake clean before you go out again, it's possible you had oily finger prints on one or other.
Good Luck

[Ron Gusack]

Thanks for the tips Bigfoot. I took a file and beveled the lead edge of the primary shoe, but it was a very slight bevel. I've only been 106 in the 1/8 mile since I changed shoes and it only does it if I hit the pedal pretty hard. I'm holding off 1/4 mile stuff till I get it figured out.

[JHeath]

Good advice from Bigfoot, I used to do that back in my Firestone brake mechanic job. People would come in and say, my car pulls to the right, we would say, step on the left side of the brake pedal....