Old brake shoes different length, new brake shoes equal?

[Julien Abrahams]

Dear all,
I've received new brake parts for my '67 Deville: new hoses, linings and wheel cylinders. When I took the drums off, there was a difference between the length of the primary and secondary shoe. The new linings however, are equal in length, the only difference being that on one shoe, the lining is placed more towards the top and the other one is more towards the bottom. They come from Rockauto, and up until now, I never have been sent wrong parts. So, which one is the primary one? I think that the shoe with the lining more toward the top should be at the rear (towards the back of the car) and the one with the lining more towards the bottom should be towards the front of the car. The manual says nothing about equal/unequal length shoes. Anyone have experience with this?

[TJ Hopland]

I have never seen that either but it makes you wonder if that higher mounting does the same thing as the shorter shoe.

I will stay tuned to see what others think. 

[tomo]

Look for a ink stamping on the shoes designating the primary shoe. If there is none, I would call Rock Auto or the tech line at the manufacturer for the answer. Installing them wrong could affect performance as the coefficient of friction is probably different for the primary and secondary shoes.

If you cannot get answer and these are the only shoes available, put the shoes in the drum so there is contact at the center of the shoe, the secondary shoe should have a larger gap at the ends than the primary shoe. The primary lining is usually oriented at the top of the shoe and the secondary is centered on the shoe.

[Scot Minesinger]

I think the shorter linings do not allow for e-brake hook up, plus obviously less surface reduces braking power.  Get the same size parts.  The shorter ones on my 1970 had to be returned because no e-brake hook up.  Just another it is all about the money thing, $2.00 cheaper to make.

[Julien Abrahams]

I did a little research on the internet, and from that I can conclude that normally, the shorter shoe goes toward the front of the car. My reasoning was that the shoe which has the lning more towards the bottom, would be equal to the action of the shorter shoe. And just for the record, the new shoes are somewhat longer than the shortest lining on the old shoes, and about 1/2 " shorter than the longer lining on the old shoes. So, it is really something in the middle. .
I sent an e-mail to Rockauto, so just wait and see what their advice will be. Will keep you guys posted.

[bcroe]

I believe the turning of the wheel tends to reinforce the braking on the longer shoe
(in back), tends to reduce it on the shorter (front).  The larger shoe compensates
for more wear.  The action is related to the pivot point.  If the pivot were on top
and the brake cylinder on the bottom,  the longer would need to be in front. 

Bruce Roe

[Whit Otis, 1188]

The type of brake shoe set up you described is used on Cadillac's and many other cars, and is known as "Self Energizing Brakes."  The primary or "leading" shoe is the shoe with the shorter lining and goes towards the front of the car.  When the brakes are applied, the primary shoe contacts the drum and the "drag" forces try to rotate it in the direction of drum rotation.  The primary shoe will move slightly off the anchor pin at the top of the backing plate and since there is no anchor point at the bottom where the star wheel adjuster is located, it (the primary shoe) applies additional force to the rear shoe that has the longer piece of lining.  The direction of rotation and additional force on the secondary shoe pushes it against the anchor pin which is there to keep it from moving any further in the direction of drum rotation. Basically the whole shoe assembly moves or "rotates" slightly on the anchor pin at the top of the backing plate.   The longer lining is on the rear shoe just to provide additional wear characteristics since it gets the most force applied to it and also because most braking is done in the forward direction.  The system is also self energizing in reverse, but the primary shoe and it's shorter lining don't have to worry so much about lining wear in reverse due to lower speeds and less frequent application.  That's it in a nutshell.  It is important to be sure that when you replace your shoes that the shoe to drum clearance is correct as this provides for proper braking force, and keeps the whole assembly centered.  If your anchor pin is an "eccentric" then it is adjustable and is there to help you achieve a centered and consistent shoe to drum clearance.  Be sure to consult your shop manual for proper installation and adjustment of all components.  Done correctly, you will have a car that stops properly with no pulling to left or right.

Whit

[Philippe M. Ruel]

As explained by Bruce and Whit, on the floating-shoe system we have on our cars, the secondary (rear) lining should be longer to compensate for wear.
It isn't even mentioned in shop manuals as it was a part of mechanics' training.

Read this very clear explanation from Tim Gilles's Automotive Chassis: Brakes, Suspension, and Steering

[Julien Abrahams]

You learn something new everyday. Both explanations are great! Now it is completely clear how (these) drum brakes actually work.
I contacted RockAuto, sent some photo's and it turned out that they simply sent a wrong set of shoes. They will send a new, different set, a.s.a.p. (which I presume will be Monday). Apparently something went wrong at Centric, as the part numbers are correct.
Unfortunately I already put the new shoes on, on the right hand side of the car.  . Well, just have to take it apart again.
I also noticed that on the left hand side of the car, somebody made a couple of mistakes. Not only are the shoes installed the wrong way round (the long shoe is now towards the front of the car), but also that the stabilizer plates are under the shoes (the manual clearly says that you have to put the shoes on first, then put the stabilizer plates on top, and then secure everything with the pins, springs and cups) and the springs (which are color coded) are installed all wrong.  . 
I just have a short question on the auto adjustment system (star wheel and pawl). The manual states that when everything is put together, the pawl should engage the star wheel. Do they mean that the pawl should rest on the star wheel at all times? I noticed that on the left hand side.where I only took off the drum to use as a reference for the springs on the right hand side, I could rotate the star wheel both ways as the pawl did not engage the star wheel. It is very close (about 1/16th of an inch), but not resting on it. Is this the way it should be? I know that this system is suppose to work when the brakes are applied while driving in reverse. Taking the info from Bruce and Whit into account, would that mean that the pawl is not supposed to rest on the star wheel, but moves towards it when the shoes move (as when the brakes are applied in revers)?

[curly]

The pawl should rest on the star.  When the brakes are applied in reverse, the self energizing action moves the shoes in such a way that the pawl is lifted up.  When the brakes are released and the brake shoes go back to the 'rest' or normal position, the pawl will come back down and turn the star---- but only if there is enough wear in the linings to move the pawl far enough. 
If the linings are worn or out of adjustment, there will be enough movement of the shoes to move the pawl, other wise the adjustment won't take place.

As far as the problems you found, it is my experience that most DIY folks don't know about the Primary/Secondary system and will mount the shoes any way they can and since the shoes are interchangeable it happens alot. The one I remember best is the 67 El Camino with 4 wheel drum brakes.  One wheel correct, one with the shoes on backwards, one with 2 primary shoes and one with 2 secondary shoes. 

T Lewis

[Julien Abrahams]

Funny story About THE El camino . But how do you get the pawl to rest on the star wheel then? Or will this happen automatically when you put the springs and cups etc on?

[TJ Hopland]

The cable or rod that hooks to the top of the arm and then to the anchor pin is what makes it engage to the star wheel.  It should work out once you get it all back together.

Do you have the special tool set?   I did a few sets of brakes without em.   Just not worth the bloody knuckles.
This is kinda what I would consider a minimum set:
http://www.summitracing.com/parts/shc-947388?seid=srese1&gclid=CIGihPDeo74CFcQ7MgodpkcAJQ

The screwdriver looking thing is to put those little nut sort of things on the pins with the springs under em.
The bent pry bar thing is to adjust the star wheel with the drum installed.
The crank handle thing is to either release or install the springs on the anchor pin.

[curly]

I have used the tools that TJ linked, but I prefer to use brake spring pliers because the size gives better leverage for installing the spring.
I guess it is a matter of taste, I learned to do brakes with the pliers.
http://www.sears.com/craftsman-brake-spring-pliers/p-00945494000P

The black cup is to remove the springs from the anchor pin and the other side is used to install the springs.  I have never learned what the hooked end is for.   Beware china brand versions of this tool, the cup will be a cheap casting, too thick to do the job.

T Lewis

[TJ Hopland]

I have a couple of the pliers like one too.  I have used the hook a few times but I don't think I was using it correctly.   They are slightly different from each other and sometimes one works well and on other brakes the other works best.   

[tomo]

The hook end is used to install the top springs onto the post above the wheel cylinder. It is much easier to use than the spring pliers. The black end is used to remove the springs. The pliers are use with the Bendix brakes to replace the top spring. The Bendix brakes use a fixed anchor at the bottom of the shoes. These anchors must be adjusted to give the correct shoe contact. The self energizing brakes float at the bottom and have the anchor at the top.

To remove the springs, slip the black end over the post and turn the tool to expand the spring and then remove the spring.

To install the spring slip the hooked end ov the spring over the tool and place the hooked end of the tool over the post and use the tool as a lever to slip the spring over the post.

[bcroe]

To remove the springs, slip the black end over the post and turn the tool to expand the spring and then remove the spring.

To install the spring slip the hooked end ov the spring over the tool and place the hooked end of the tool over the post and use the tool as a lever to slip the spring over the post.

Someone ought to post a picture (Youtube?) of that tool in action; not sure I have it right.  Bruce Roe

[Julien Abrahams]

Just a quick update on the brakes here. Rockauto sent me a new set, which are exactly the same as the ones they sent the first time. Contacted them again, and it turned out that Centric no longer produces the short and long shoes. Instead, they have equal length lining material, placed differently on the shoes. The primary shoe apparently is the one where the friction material is more towards the bottom of the shoe. Well, I just have to find some time this weekend to see if I can install the new brake shoes, wheel cylinders and hoses. Just have to wait and see how the "pawl engaging the star wheel" goes.
I will keep you guys updated.

[Julien Abrahams]

Well, everything is back together, and as far as I can tell, the brakes are now OK. Once you have done it once or twice then it is not rocket science. The self adjuster problem (where the pawl would not engage the star wheel) actually worked itself out: if you put the springs and link together the right way, it does engage by itself. Nice .
Well, now that is sorted, I can crack my skull again with regard to the carb. It still has a vacuum leak, and I don't know where exactly. However, I think it is the air horn gasket which is too thin. The float bowl is warped a little and when I put the airhorn on the float bowl without the gasket, there's a 0.7 mm gap. And I think that the air horn gasket is actually 0.7 mm. So I think the solution is to get another rebuild kit, and stack two airorn gaskets on top of each other. I'm just running out of ideas :S.

[Philippe M. Ruel]

The float bowl is warped a little

Plane it.

There is a recent thread on which you posted ideas involving mirrors and glass. Time to put words into action .

[Julien Abrahams]

I've actually made a new thread for the carb issues .
And its not possible to plane it: the primary venturis stick out a couple off mm, so it is not flat at the top. The airhorn has already gotten the "mirror" treatment .