Proper Brake Rod Adjustment

3

'31 Patina

Senior Member
Can someone direct me to the proper steps on adjusting the brake rods on a '31 coupe? I have the Les Andrews vol. 1 manual and I'm reading through the service adjustment section for brakes but I'm just not fulling understanding the brake rods.

The cross shaft actuating lever on the car isn't in a vertical position like the manual suggest. The actuating lever is at a slight angel when there isn't any pressure on the brake pedal but when you put full pressure on the pedal then the lever is in the vertical position like it should be.

I'm in the process of re-doing the brakes but before I start I want to fully understand how to adjust the brake rods properly.

Also when the brake rod is attached to the front brake actuating arm should the arm be straight up or at the 15 degree forward tilt? Or is the front brake actuating arm supposed to be at a 15 degree forward tilt when the rod is NOT attached to it.

I'm learning as I go and I'm following the manual but sometimes it helps to hear other verbiage so I can understand it better.

Thanks for the help!
 
The front brake levers should have forward tilt for mechanical advantage. the rods are adjusted so they only just take up the slop in the lever freeplay. If the rods do not take up freeplay and reside 15% forward you can take up the slack in the backingplate area. I don't have the Les Andrews book so don't know about what he calls for but I have brakes.
 
The way I read it, 15 degrees before the rod is attached. That note above says that angle will be corrected with a new operating pin. And my levers on the cross shaft are not perfectly vertical either. I'll be interested to read the replys you get because I'm not totally satisfied with my brakes after a total rebuild.
 
You need to start inside the brake drum. Make sure the brake shoes are good. The roller tracks, the operating pin, etc. must all be in like new condition. The operating pin is often worn, so the lever won't be 15* forward. Once everything inside the drum is good, including the brake drum, then adjust the wedge so the brakes just have a very slight drag. Do all 4 wheels, then lightly pull the slack out of the linkage and adjust the brake rods so the pin just slips in.
 
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Okay so my front brake rods are disconnected from the actuating arm and the arm has a 15 degree forward tilt. How far do I pull the arm back and reconnect the rod? The manual says to pull the arm back to take up free travel. What does "free travel" mean? Am I just taking the extra play out of it?
 
Do the brake shoe to drum tightening before attaching the brake rod. the angle is set with the actuating rod or pills to take up slack. the fifteen degrees is ideal but not set in stone as all cars have some different wear and characteristics. the fifteen % are after the slop is taken up, turn the brake rod eye so the pin just slips in. you can lock the rod clevice eye a bit out of plane with the lever eye and take out rod rattle while you are at it.
 
Use your little finger to lightly push the brake lever rearward (should be about 15* forward tilt) and at the same time use your other hand to very lightly pull the brake rod forward. This take out the FREEPLAY and now you can turn the clevis until the pin just slips in.
 
Thanks guys for clearing this up and helping me further understand what I need to do and how to do it.

How important is it that the cross shaft actuating lever is in the vertical position? I'm reading this in the Les Andrews manual. It's step #4 of the service brake adjustment.
 
'31 Patina said:
Thanks guys for clearing this up and helping me further understand what I need to do and how to do it.

How important is it that the cross shaft actuating lever is in the vertical position? I'm reading this in the Les Andrews manual. It's step #4 of the service brake adjustment.
Click to expand...

You get the maximum leverage when the arms are vertical. How far from vertical are the arms?
 
'31 Patina said:
How important is it that the cross shaft actuating lever is in the vertical position? I'm reading this in the Les Andrews manual. It's step #4 of the service brake adjustment.
Click to expand...

I would think he would include an instruction for adjusting the brake pedal to cross shaft rod as that is your starting point. The rear of the pedal to cross shaft rod should have a large 'button" on the end which will operate the stop light switch on '30-31 models. The length of this rod should be adjusted so when the pedal is UP against it's stop, the button at the rear will be 1/32"-1/16" from the inside rear wall of the cross member. This SHOULD place the end levers in the proper position.
 
Marco Tahtaras said:
I would think he would include an instruction for adjusting the brake pedal to cross shaft rod as that is your starting point. The rear of the pedal to cross shaft rod should have a large 'button" on the end which will operate the stop light switch on '30-31 models. The length of this rod should be adjusted so when the pedal is UP against it's stop, the button at the rear will be 1/32"-1/16" from the inside rear wall of the cross member. This SHOULD place the end levers in the proper position.
Click to expand...

The Les Andrews book doesn't tell how to adjust the brake pedal to cross shaft rod. After having the shoes relined, drums truned, shoes arched to drums, new rods and other brake parts I made the mistake of putting everything back together without starting with adjusting the brake pedal to the cross shaft.

I followed the Les Andrews instructions on how to adjust the brakes and when I went to use the board with notches cut in it (the tool used to put pressure on the pedal while you adjust the brakes accordingly) I found that my brake pedal was already half way forward but the cross shaft was in the vertical postion. So I assume I need to adjust the brake pedal to the cross shaft? How do you do this? Should I disconnect all the rods and start over?
 
I am aware this is an old thread. And, sadly, I realize many of the original posters will never read my question.
But, I have the same conundrum as the last paragraph from the last post.

I understand the mechanical advantage that the lever arm receives starting at 15 degrees forward.

And I reviewed and worked the formula:
T = F r sin(a)
where
T = torque
F = force in the brake rod
r = length of the actuating arm
a = angle between the arm and the rod’s line of pull

The result of a 15-degree advance of the lever arm results in a 3.6% increase in torque at each lever arm.​

But, what about the cross shaft and its levers?

The service bulletin and Les Andrews state that the cross shaft should be aligned to ensure the levers are vertical. The lower arm is connected to the front brakes, and the upper lever arm goes to the rear brakes. I also discussed this with Larry Shepard, and he, too, said to align the cross-shaft lever arms vertically, or at 0 degrees.

Why not adjust the shaft so the rear/upper arm is forward 15 degrees, and that will automatically advance the lower/front brake arm 15 degrees, also.

Will there not be the added 3.6% increase in torque from the formula for each lever arm, here, too?

Please help!

Gratitude for any help,

Diastole in the Smokies
 

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Tom Wesenberg said:
You need to start inside the brake drum. Make sure the brake shoes are good. The roller tracks, the operating pin, etc. must all be in like new condition. The operating pin is often worn, so the lever won't be 15* forward. Once everything inside the drum is good, including the brake drum, then adjust the wedge so the brakes just have a very slight drag. Do all 4 wheels, then lightly pull the slack out of the linkage and adjust the brake rods so the pin just slips in.
Click to expand...

Right on. EVERYTHING MUST BE RIGHT!

There is no easy way other than that.

Once completely rebuilt, you just need to adjust using the adjustment nut.
 
Formula should be T=F r cos(a) where a is the angle from vertical. So when vertical the angle is zero and the cosign is 1 and the maximum torque is applied. The 15 degrees in the front is so that the arm is vertical when the brakes are at their maximum braking effort. The formula when torque is applied to produce a force in the rods, such as in the center at the cross arm, is F=T/r cos(a), again where a is the angle from vertical. As you can see the maximum force is when the angle is close to 90 degrees, such as the mechanism in Vice-Grip pliers. You don't want to go over center so it is best to steer away from 90 degrees. If the arms are vertical when no torque is applied, as the instructions say, the force in the rods will be a little more when the arms tilt over during maximum braking.

There will be a pop quiz tomorrow at 9:00 AM.
 
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I agree

But, using the same math and mechanical advantage of the actuator arm why would this not apply to the service brake cross shaft levers?

Advancing the linkage between the brake pedal and the cross shaft would advance the cross shaft levers 15° so as brake pedal pressure was applied would we not get the same mechanical advantage and the same 3 to 4% increase in torque per wheel??

The service bulletins by Ford, Les Andrews, and in conversations with Larry Shepard everyone says the cross shaft brake levers should be vertical or 0°
The math suggests advancing them 15°
Any thoughts?

Gratitude

Diastole
 
Will there not be the added 3.6% increase in torque from the formula for each lever arm, here, too?

No, the cross rod will give the most force to the rod when the lever is vertical. In that instance the cross rod is the driver and the rod is getting pulled. The formula for torque increase up at the front wheel where the rod is the driver and the lever is being driven has to be inverted in order to apply at the cross shaft.

It is kind of like on a ten-speed bike. To get the most force at the wheel you want the smallest sprocket at the pedals and the biggest sprocket back at the wheels. The front sprocket is driving the chain and the back sprocket is being driven by the chain. The math is inverted regarding sprocket size and torque multiplication. To put the bike in high gear you go to the biggest front sprocket and the smallest rear sprocket.
 
Here is a thought experiment that might help you:

To get the most force to the front brake with the least pressure on the pedal you can imagine a system where the arm on the cross rod was shorter and the arm at the front wheel was longer. The short lever at the cross rod would give the actuating rod less motion but more force. Up at the front the actuating rod would turn the lever less degrees but the torque would be multiplied. You would be increasing the force at the brake shoe by making the rear lever shorter and the front lever longer.

If you change from the lever doing the driving to being the one being driven, you have to change from dividing to multiplying by the lever length (to get the force increase).

This is just a thought experiment, if you tried re-engineering the system this way the brake pedal would be in danger of going all the way to the floor before slowing the car down. But you would have a lot of force on the brake shoes, if you got them to work before the pedal hit the floor!
 
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