63 Avanti Rear Brake Drums - what gives?

[brian6373]

I'm having the exact same problem! I have new shoes, wheel cylinders, and new finned brake drums for the 10" rears on my all drum brakes. The tops of the brake shoes are against the wedge, and the adjuster is all the way in. The parking brake cable is slack. I also insured that the shoes were centered. I compared the old shoes with the new ones and out of the four shoes they all looked to be about the same thickness as the new shoes, except for one that had about 50% of the lining worn down. The drums just won't go over the shoes! The drums and brake shoes are from S.I. I noticed that the drums were made in China, and we all know how the Q.C. from there can be somewhat lacking. I'm taking the drums down to the machine shop tomorrow and have them measured. If it turns out the drums are ok, I guess I'll take the belt sander to the shoes and "calibrate" them! I'll post more after I find out tomorrow about the brake drums.

Brian

[37CoupeE]

Arcing the shoes is done on a machine that clamps onto the shoe and grinds the lining to the correct arch.
This is set by locating of the shoe to the grinding wheel.
Many shops had them in the past to properly fit shoes.
My dad picked up one years ago when a shop was tossing it out because of the worry of asbestos in the linings.
Still have it though, because it does come in handy sometimes.

[Warren Webb]

I have seen the backing plates grooved too. Doesn't sound like your problem here but I would check anyway, just to be sure.

[DEEPNHOCK]

Watch this video.
It gives you a real good idea of the brake shoe, wheel cylinder, and flywheel rebuilding/machining process..

[brian6373]

Yes, the shoe platforms were badly grooved when I took off the backing plates. I ran a bead of weld and ground down the welds to restore the flat surface that the shoes ride on. Good thinking Warren! Too bad I'm not close to you 37coupeE, I could take my shoes over to you for a demonstration! Great video! I would kill for some of those machine tools! So, if the drums are good I need to reduce the shoe size. As we don't have any old school brakes shops around here that will arc brake shoes. What's a fella to do? Thanks for the help guys, Machine shop opens in about an hour, and I'll find out about the brake drum I.D.

Brian

[brian6373]

Just got back from the machine shop. He measured the drums and they were .030 under 10". I told him to turn the drums so they were within specs. I'll get them back in an hour or so, and give them a try. I called the nice folks at S.I. and they offered to exchange the drums. Since both drums were the same undersize I figured that the ones in their warehouse are identical to the ones I already have with the same undersize problem. I didn't think that was a good solution. I counter-offered that they could reimburse me the cost of turning the drums to the 10" that they're supposed to be. They said they would have to talk to the owner first and get back to me. To be continued...

Brian

[DEEPNHOCK]

Here's a 'Brakes 201' tip for you.
Try not to cut any more cast iron off of your drum than you have to.
The legal max cut is .060" by federal and state law.
(A 10" drum cannot be cut more than 10.060"..an 11" drum can be cut no more than 11.060"....)
You are best to just have your machine shop 'clean them up' and 'make them round'...
If he can do that with a .005" cut...great!
Oversized (thicker) linings are easy to sand down (with a shoe arc machine).
You can get a precise fit to the drum that way.
Hogging out a drum to fit an oversized lining is crazy, as drums are way harder (read that $$) to replace than a brake shoe is.
HTIH
Jeff

Just got back from the machine shop. He measured the drums and they were .030 under 10". I told him to turn the drums so they were within specs. I'll get them back in an hour or so, and give them a try. I called the nice folks at S.I. and they offered to exchange the drums. Since both drums were the same undersize I figured that the ones in their warehouse are identical to the ones I already have with the same undersize problem. I didn't think that was a good solution. I counter-offered that they could reimburse me the cost of turning the drums to the 10" that they're supposed to be. They said they would have to talk to the owner first and get back to me. To be continued...

Brian

[bezhawk]

You absolutely have the WRONG DRUMS!!!!! A DISC BRAKE REAR DRUM IS 11". I have several NOS in stock.

[StudeRich]

Wow a Disc. Brake Avanti with a rear end swap from a DRUM BRAKE V8 Lark or Hawk, not a good fit for front Discs.

These would be the self energizing Bendix star wheel adjusted type, if that is so I would try reversing the Wedge at the top anchor to prevent that action. And then 11 inch rear Shoes for Front Discs will not fit a 10 inch Drum either.

But it still seems to me if you ordered New Avanti Rear Drums why would you have Lark Hawk 10 inch drums?
Something is not right here but without seeing the Backing plates I can't tell what is going on here.

[Dwain G.]

The 10"drums belong to another poster that entered this thread.
On both cars, if the adjusters are backed off all the way and the equalizer bar (flat piece between the two shoes) has some slack to move back and forth a tiny bit, then yes, you are going to have to find someplace that will arc grind the shoes. Take the drums and shoes to a commercial clutch and brake shop.

[StudeRich]

OK, thanks Dwain, I stand majorly CORRECTED!

[bezhawk]

There is no equalizer bar, star wheel or anything like that on disk rears, the bottom is anchored they are not self energizing.

[StudeRich]

bez, you and I have two different Cars mixed up from two different posters on the same topic!

See Post #25.

[bezhawk]

bez, you and I have two different Cars mixed up from two different posters on the same topic!

See Post #25.

Then somewhere the subject was changed. The original posting header mentions an Avanti

[Dwain G.]

Disc or drum, they both have what I called an equalizer on the rear brakes. The parts book calls it a "Link, rear brake shoe operating".