Short shoe on the front, that’s the way Mr. Berry my first auto shop teacher instructed 40 years ago and the rule has served me well.
I too was trained to install the longer lining rearward. My auto repair instructor - Mr. Hayden, a drunken Irishman - seemed quite insistant on the point. However, those who can’t do teach?
Now, I would like to know:
(1) Why does one shoe have less material?
(2) If the shoe with less material was designed to be placed forward, what was the engineers’ reasoning for that positioning?
Rod Nox answered your question (and recieved 5 stars for his answer)
When you press the brakes while going forward, the top of the rear shoe stays >firmly seated on the pin at the top of the brake backing plate.
You say the ONLY outward motion the rear shoe receives (while the vehicle is in a forward motion) arrives from the front shoe?s downward motion - through the adjuster?
I?m sorry, but I do not see what you write as a likely scenario. If your viewpoint were a part of reality the upper portion of the rear shoe would know virtually no wear, if any, while the lower portion received an amount that would be unacceptable.
I think Manolito’s partly right. When you push the brake pedal, both shoes move out until they contanct the drum. At that point, the friction between the drum and the shoes rotates them both, forcing the rear shoe back to the pin and the rear piston back into the brake cylinder as the front piston pushes the front shoe further out.
If the front shoe is being forced outward, more so than the rear shoe, it would be the front shoe which should have the longer friction material.
Add to this:
Bolted together as one cohesive part, are the rear-wheel, brake-drum and axle-shaft. When the brakes are applied it is that cohesive part that brutally grabs at the road - an action that forces this wheel/drum/axle-shaft assembly to violently leap relatively rearward - pressing the inner surface of the brake drum most-so upon the forward-facing shoe.
It appears that the two sides of the debate have made their cases. Now it is time to find the facts. I think it is time for the OP to do the experiment. Measure and record the lining thickness of the short and long shoe. Install the long shoe forward and short shoe rearward (install in the same orientation on each axle side for safety). Drive the vehicle 5K to 10K miles. Remeasure the lining thicknesses.
I postulate that the forward placed long lining will have worn significantly less than the rear placed short lining. I am also an adherent to the long shoe going to the rear and the short shoe going to the front. This is contingent on only one anchor being above the wheel cylinder. All of the relinings I have done that way have worked well; had effective braking; and worn evenly in that configuration.
IIRC 60ish VW beetle rear brakes had a double wheel cylinder above but there was a solid anchor at the bottom. The shoe linings were the same length. However, the front shoe always wore faster that the rear. On yearly inspection, the front and rear shoes could be exchanged to even out the wear. Just thought I would muddy up the water more.
Let us know the results of your experiment.
That short lining was probably invented because the longer ones would make the brake grab. Another possibility is that the top end of the lining would wear down rapidly. The short lining is usually thicker too. It prevents the top end of the shoe from wearing a groove down the center of the drum. It’s better to keep the metal away from the metal. If the tip scrapes the drum, the lining isn’t making full contact.
I concede to the group on this then(why does any manu still use drums on the rear?)-Kevin
Because they work well and the plant and equipment to make them was paid for a long time ago so manufacturing cost is low. They work better than disc brakes in dirty, muddy, wet environments. But as overall car designs change, drum brakes are passing into automotive history…
I have worked chain brake repair (here in Tucson the main one is Brake Masters). The only way to move up the ladder as a “mechanic” was to become fast at rear drums. Believe it or not many people are challenged by rear drum brake shoe replacement, or at least going fast at it. I knew a Chevrolet heavy line mechanic that could replace rear shoes 10 min. a side, but he could not figure out how to unlock the radio after he had the battery disconnected.
I will admit that it has probably been five years since I did a rear drum brake job. So many cars have gone to disc brakes that those needing shoes are few and far between.
Don’t the shoes still have “PRIMARY” and “SECONDARY” imprinted on the edge of each shoe? No more arguments, just read the shoe and put the primaries on the front sides.
After reading this discussion… One must first understand that not all hydraulic drum brakes are actuated the same… How the brake shoes are anchored and how the wheel cylinders are situated will determine which shoe is the “leading shoe”
there are many iterations of drum brake architecture. so first you must identify and understand which one you have … before you can determine which shoe goes where… that is the nucleus of the contrary replies given so far.
there is a Simplex architecture
there is Duplex architecture
there is Uni-servo architecture
there is Duo-servo
and there is Duo-Duplex
see the diagram it should clearify which shoe is the leading shoe… and also why some shoes are identical and dont require a" leading shoe"
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also… The industry situation that finds drums brakes so common on the rear of most vehicles… is because the drum brake set up allows for a simple emergency brake function. This is why many manufacturer’s stayed with drums on the rear for so long… when disc systems became a clearly better choice.
the drum allows for a simple solution to employ an emergency brake.
In fact today often when you find a vehicle with disc brake systems on the rear… you will often find (designed and installed into the bell of the rear rotor) ,a minor drum brake architecture. It’s used to employ the emergency brake on an otherwise rear disc brake set up.
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jimfoxmail_141794,
Thank you so much for the diagram you posted!!! I heard all these different types of brake systems mentioned when researching this subject for my old van, but no one explained how each type works.
now I know I have duo-servo rear brakes and the larger padded shoe does on the rear. It is amazing how such a small thing can be such a powerful aid.
Thanks again,
DW
This is a discussion from 10 years ago - and I wonder why I didn’t comment at the time
- BUT -
I was going to post that it made a difference where the cylinder was. While most cylinders are on the top, some are on the bottom.
AND THEN Jim Fox posts an even better point.