Re: [FWDLK] rear brake shoes and arching them

I suppose that I should join the conversation; my experience was wrought in the late 50’s to late 90’s, and filled with Chrysler Center Plane Brakes, Self-Energizing (Bendix Brakes), common for Ferd & GM for years, and for most cars until around 1967-68, when Disc Front Brakes became the norm. The rear brakes had additional designing problems with applying Parking Brakes and placement of the calipers. The “Arcing” of brake shoes was common early in the developing of the system during the 40’s & 50’s. Virtually every Brake Shop had, along with their Drum Lathe, an Arc Grinder. There were many precautionary attachments to prevent the poisoning of the users (and anyone else around). Unfortunately, many mechanics were endowed with a case of asbestos poisoning, degree determined by amount of contact. (Some goofy mechanics thought they were to good to get sick, and in to much of a hurry to take the suggested precautions. Silly Bumbleheads! ... *cough, *cough, *cough; excuse me, I don’t know where that came from!!)

All of the details about the measurements already given were true, and varied slightly between the technicians. But the reasons for the careful measurements was because of variations in the lining thicknesses, and the most obvious problems occurred from the “Self-Energizing”, most common style. But the .020” number stayed around for a convenient reason. Instead of making the shoes fit the drums, it became a general practice to “Cut the Drums”, (or “Turn the Drums”) to within .020” of each other, side-to-side. If the shoes on both sides make the same contact to start the wear pattern, they would likely wear very evenly through their lifetime of wear, and do it without pulling or grabbing and causing uneven braking. I think most mechanics remember that the maximum diameter of the inside of a resurfaced drum was to be not more than .060”. By closely monitoring the total inside diameter of both drums while turning, the technician could rely on the customer getting the most from his brake system, and at a reasonable labor charge, while avoiding the smoky and offensive odor of the Asbestos Dust permeating the shop.

As already stated by a previous post, the Center Plane type Brakes were much less sensitive to the Equal Contact issue, since their contact was from different forces; which could some day be another subject.

Sorry for rambling, I do enjoy taking about technical subject of by-gone eras.

mike higgins

From: John Hagen

Sent: Saturday, June 29, 2013 1:53 PM

To: L-FORWARDLOOK@xxxxxxxxxxxxx

Subject: Re: [FWDLK] rear brake shoes and arching them

Well I never had to replace any of those tranny mounted parking brakes but I think it would be a good idea. Those dang things often didn’t hold all that well until they were “burnished” in. I did this by GENTLY applying the parking brake while driving forward slowly. And I mean gently as you sure as hell don’t want to lock them up or, more likely, overheat them. It’s the sort of thing you do a few days in a row for short distances. You test them by going to a somewhat steep hill somewhere and applying the parking brake while sitting in the car to be sure it holds. Once it does you are finished.

Do you need the drums when arcing the service brakes? Well you need to be able to measure them (you can’t go by the fact that you have an 11 or 12 inch drum, you need the actual measurement) and then to test fit the shoes after arcing so, yes, you do. There are special tools for measuring brake shoe diameter that are simple to use. You don’t need an inside micrometer here; we’re not building a watch.

John Hagen

From: John Hagen [mailto:sprinthag@xxxxxxxxx]
Sent: Saturday, June 29, 2013 2:51 PM
To: 'debenson2'
Subject: RE: [FWDLK] rear brake shoes and arching them

Well I never had to replace any of those tranny mounted parking brakes but I think it would be a good idea. Those dang things often didn’t hold all that well until they were “burnished” in. I did this by GENTLY applying the parking brake while driving forward slowly. And I mean gently as you sure as hell don’t want to lock them up or, more likely, overheat them. It’s the sort of thing you do a few days in a row for short distances. You test them by going to a hill somewhere and applying the parking brake while sitting in the car to be sure it holds. Once it does you are finished.

John Hagen

From: Forward Look Mopar Discussion List [mailto:L-FORWARDLOOK@xxxxxxxxxxxxx] On Behalf Of debenson2
Sent: Saturday, June 29, 2013 2:05 PM
To: L-FORWARDLOOK@xxxxxxxxxxxxx
Subject: Re: [FWDLK] rear brake shoes and arching them

Is it the same thing on parking brake shoes as well? And to do this do you need the drums with the new shoes to do the arcing?

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