Brake Shoe Orientation

Jim Johnston

Jim Johnston

Senior Member
While troubleshooting the front brakes (pulling to one side) on a friends hydraulic brake equipped Model A I noticed the brake shoes, as installed, had the bigger shoe (the one with the most lining) on the front side. I remember being taught that the bigger, or primary shoe, should be on the rear side. Can't seem to find anything in my manuals to support this. Would appreciate any wisdom or comments. THANK YOU.
 
This is a common question. I know it seems odd but yes, the brakes are correct. The long shoe is to the front which is the opposite of the more modern type of shoe arrangement with the longer shoe in the back.

Tom
 
On self energizing brakes (wagner type) the long shoe goes to the rear because it grabbing rotates the unit (slightly) and helps energize the front.

On non-self energizing brakes (lockheed) there is no assistance and the long shoe goes to the front where it can do the most good. That was how it was explained to me.
Gary in Mozarks

See below, I stand corrected
 
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Gary in Mozarks said:
On self energizing brakes (wagner type) the long shoe goes to the rear because it grabbing rotates the unit (slightly) and helps energize the front.


Gary in Mozarks
Click to expand...

You are correct that on Self Energizing Brakes, the "long" shoe goes to the rear but for a different reason.

When the brakes are energized, the front (leading) shoe tries to rotate with the drum and in turn applies a force to and thus energizes the rear (trailing) rear shoe thru the adjust link at the bottom of the brake assembly. The anchor pin above the wheek cylinder prevents the rear shoe from rotating. If it was not for the fact that you have to have some brakes when you back up, there would be no need for a wheel cylinder piston to apply the rear shoe.

Trailers with hydraulic brakes normally have single piston wheel cylinders, only for the front (leading) shoes.

Ford first used "Fixed Anchor" brakes on Ford and Mercurys thru 1948. With this design, most of the braking is done with the front "leading" shoe and very little with the Rear "trailing" Shoe.

Lincoln used Bendex Self energizing Brakes which are MUCH BETTER where the front shoe actually applies the rear shoe. This results in more total braking force.

I have been told that Henry did not put the superior Bendex Brakes on all his cars because he did not want to have to pay all the Royalties to Bendex. In 1949, Henry finally put self energizing brakes on all this cars.

Just my understanding.

Chris
 
The attached pictures are from a 1939 United Service Motors repair and tune-up manual. The big shoe always goes to the front on Early Fords and should match up with the big end of the wheel cylinder, this is the forward braking shoe. The smaller shoe is the reverse braking shoe and does not require as much stopping force so the wheel cylinder is smaller on that shoe.
If you do not have the bottom adjustments you have the later '42 to '48 Ford brakes. Ford eliminated the bottom adjustment so the brake shoes could float up and down and center themselves with the drums. Ford called these later brakes "self centering" to confuse the issue with the better designed self energizing Bendix brakes.
The first thing to check is the front tire pressures and the tire wear pattern. You want identical pressure and tread on each side. Next check the wheel bearing adjustments, play in the king pins, steering components, spring u-bolts, shackles, the rubber ball on the wishbone. anything that would allow the axle and wheels to move slightly when the brakes are applied. Make sure the caster, camber and toe-in are correct.
If you don’t find anything mechanically wrong move on to the brakes Which ever side it is pulling towards has more stopping power. Check that the lining adjustment is correct (see attachments). The brake drums should be within .010 diameter of each other. Check the wear pattern on the lining and make sure you are getting a full contact pattern on shoes, they might not be arched correctly to the drums. Grease or excessive brake dust on the lining will cause a pull. Measure the length of the lining on each side and make sure they are the same length, it will pull to the side with the most lining. Who ever relined the shoes might have riveted a little longer piece of lining on one shoe. Even different brands of drums can cause a pull, the difference in the metallurgy can have an effect on how aggressively the lining grabs the drum. Drums that have been overheated with cracks and heat spots can cause pulling. A grooved drum can have more surface area contacting the lining than a smooth drum. You want everything to be identical on each side.
On the hydraulic portion of the system, a frozen or rusty wheel cylinder will cause the brakes to pull, possibly violently. A little air in the fluid on one side could cause a brake pull to the opposite side. Brake fluid should be flushed and replaced every two years because it is hydroscopic, meaning it absorbs water, some reports say it will absorb 2-3% water a year. Master cylinders and wheel cylinders will virtually last forever if you change the fluid every two years. The only way rust can get in there is if moisture and oxygen are present.
Even when everything are perfect you still might get a slight pull. Then you start fiddling with the adjustment to see if you can even things out. I jack up the front end and put a pedal jack on the brake pedal to create a slight drag on the brakes and then adjust them until they have the same drag on each side. You can make a brake pedal jack out of caulking gun by cutting off the part that holds the tube. You might have to weld something to extend the rod. You can also try swapping the front tires, sometimes that fixes a slight pull.

Jerry
 

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"If you do not have the bottom adjustments you have the later '42 to '48 Ford brakes. Ford eliminated the bottom adjustment so the brake shoes could float up and down and center themselves with the drums. Ford called these later brakes "self centering" to confuse the issue with the better designed self energizing Bendix brakes."

There is also great confusion as to which year Ford/Merc went to "self-centering" brakes, which was actually 1946 models introduced in 1945, as evidenced by the 51-A part number prefixes. The brakes for 1942 continued to be those with adjustable lower anchor/eccentrics, the purpose of which is to center the (correctly arc'd) linings in the drums. The change that occurred in 1942 was that the forward pistons in the front wheel cylinders were enlarged from 1-1/4" (Part number prefix 91-A) to 1-3/8" (Part number prefix 21-A) in an attempt to increase front braking, since the cars had become larger/heavier. All new replacement cylinders are 1-3/8" so must be replaced in pairs if the vehicle still has the 91-A cylinders. Rebuild kits remain available for the 1-1/4" cylinders.
 
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"In 1949, Henry finally put self energizing brakes on all this cars."

...it is my understanding that Henry had expired in 1947... musta been II...
 
Richard (EV8G) said:
"In 1949, Henry finally put self energizing brakes on all this cars."

...it is my understanding that Henry had expired in 1947... musta been II...
Click to expand...

Ah Henry II, the second saviour of the Ford Motor Company, and Clara, Henry I's wife threatening to sell her voting stock if he didn't hand over the reins to II instead of giving control of it to Harry Bennett as he'd wanted!
 
When the driver applies brake pedal pressure at the master cylinder, fluid disperses to each wheel cylinder. The curved top ends of each shoe fit against the round anchor pin. As the pistons move outward in the wheel cylinder, the shoe lining contacts the drum. The linked shoes attempt to rotate with the drum. With the vehicle traveling forward, the rear shoe stops against the anchor pin. Backing up, the front shoe stops against the anchor pin.

The obstructed rotational force now redirects, pressing the shoes outward against the drum. This additional force, referred to as “self-energizing”, is beyond driver input and hydraulic pressure. When self-energizing force can apply in either direction of rotation, the system is called duo-servo.

536326


As the vehicle moves forward, the self-energizing force is greater at the rear shoe. To keep lining wear even, the rear shoe’s lining is longer and sometimes of different composition than the forward shoe. With a shorter lining on the primary or forward-facing shoe, self-energizing force is slightly less when the vehicle moves backward. Since the vehicle does not back up at high speeds, braking is sufficient in either direction.
 
glennpm said:
When the driver applies brake pedal pressure at the master cylinder, fluid disperses to each wheel cylinder. The curved top ends of each shoe fit against the round anchor pin. As the pistons move outward in the wheel cylinder, the shoe lining contacts the drum. The linked shoes attempt to rotate with the drum. With the vehicle traveling forward, the rear shoe stops against the anchor pin. Backing up, the front shoe stops against the anchor pin.

The obstructed rotational force now redirects, pressing the shoes outward against the drum. This additional force, referred to as “self-energizing”, is beyond driver input and hydraulic pressure. When self-energizing force can apply in either direction of rotation, the system is called duo-servo.

536326


As the vehicle moves forward, the self-energizing force is greater at the rear shoe. To keep lining wear even, the rear shoe’s lining is longer and sometimes of different composition than the forward shoe. With a shorter lining on the primary or forward-facing shoe, self-energizing force is slightly less when the vehicle moves backward. Since the vehicle does not back up at high speeds, braking is sufficient in either direction.
Click to expand...

Glenn ..... That was an exquisitely-well-stated explanation of how the physics of a "Self-Energized" brake actually works.

Coop


.
 
When adjusting self-energizing brakes through the oval hole at the bottom of the backing plate, do you ratchet the little wheel inside up or down to tighten the brakes? i it the same on both sides of the car?
 
drolston said:
When adjusting self-energizing brakes through the oval hole at the bottom of the backing plate, do you ratchet the little wheel inside up or down to tighten the brakes? i it the same on both sides of the car?
Click to expand...

I have honestly never paid attention as to whether the star-shaped wheel is made with RIGHT-HAND thread or LEFT-HAND thread, OR whether they differ from side to side. I'd be willing to bet a half a dollar that they are likely all RIGHT-HAND threaded. IF that is true (to be determined when you have the brake drum removed), you would need to RAISE the little fingers on the wheel to DECREASE the clearance between shoes and drum. Your mileage may vary!

Coop


.
 
drolston said:
When adjusting self-energizing brakes through the oval hole at the bottom of the backing plate, do you ratchet the little wheel inside up or down to tighten the brakes? i it the same on both sides of the car?
Click to expand...


The star wheel and attached threaded shaft are screwed into the threaded barrel. Look in the adjustment hole and determine the direction of the barrel. Also note that the adjustment hole is offset, being closer to the brake drum on one side. The barrel points in the opposite direction.


Looking down the barrel, if you turn the star wheel CCW, it un-threads, making the assembly longer and tightening the shoes to the drum.


536419
 
My shoes are old relined Fords, they are 1940 rears, when they relined them they made the lining the same size on both front and rear shoes. Is this an issue?
 
Richard (EV8G) said:
"If you do not have the bottom adjustments you have the later '42 to '48 Ford brakes. Ford eliminated the bottom adjustment so the brake shoes could float up and down and center themselves with the drums. Ford called these later brakes "self centering" to confuse the issue with the better designed self energizing Bendix brakes."

There is also great confusion as to which year Ford/Merc went to "self-centering" brakes, which was actually 1946 models introduced in 1945, as evidenced by the 51-A part number prefixes. The brakes for 1942 continued to be those with adjustable lower anchor/eccentrics, the purpose of which is to center the (correctly arc'd) linings in the drums.

My question;
I have a early production '32 rear end with the bottom adjusters. (39-42?)
Since it seems the bottom adjusted rear brake system is a problem to adjust properly. Plus, no one around here locally knows how to "arc brake linings". Could I simply elemiate the bottom adjusters and use the '48 style bottom anker system? Thanks
Click to expand...
 
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