Service brake cross shaft arms

Dean Lemoine

Dean Lemoine

Senior Member
I started adjusting the brakes to my 29 Tudor after rebuilding the cross shaft. My question is: What position should the cross shaft arms be in once the brake rods are installed? As always, thanks in advance for any and all replies.
 
I am going to expound on Will's & Bill's comment a bit. In the perfect world, when the brake shoes are 'locked' against the drum, vertical is the position you would like the arms to be located in at that time. The reasoning is you get much better leverage on pulling the rods. Otherwise, if located vertical to begin with, the levers have over-centered when they are pulling the rods.

Now what many do not realize is worn shaft bushings allow the shaft to move which removes the fulcrum action. Also, when you look at the A-2482-* Brake Cross Shaft print, you will see that both ends of the shafts are in a straight line. When inspecting many of these shafts, I have noticed they are bent. My theory is this is caused by a worn or broken rear engine mounts which has allowed the torque tube to hit the cross shaft. The shaft really needs to be straightened and the clevis pin holes on the A-2514 Arm along with both the A-2496 & A-2497 Arms being welded and resized back to the correct size.

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Thanks guys. Given this info and all the info on the Barn, adjusting everything was much easier than I thought it would be.
 
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If the plunger end of the brake pedal rod is a small fraction from touching the inside rear of the center crossmember , the cross shaft arms will be in the correct position pointing straight up and down. Ford Wanted a small gap between the plunger and the rear inside of the center crossmember To prevent the plunger from squeaking against the crossmember .
 
Brent, The torque at the end of a lever does not vary depending upon whether it has gone over center or not. [FONT=&quot]M[/FONT][FONT=&quot] = Fd[/FONT][FONT=&quot], where F is the force at the end of the lever, d is the distance between the force and the fulcrum, or the length of the lever, and M is the turning force known as the moment or torque.[/FONT] The torque is purely a function of the length of the lever and the force being applied to the other end. It is true, though, that for a lever moving in a 90 degree arc from vertical to horizontal, that there are both vertical and horizontal components to the circular movement at the end of the lever. The closer you are to vertical, the horizontal component of the distance traveled is greater for every degree of circular movement, and that horizontal component decreases the further you move away from vertical. Translated to Model A terms, as the brake cross shaft lever just starts to move away from vertical, it pulls the brake rod the greatest horizontal distance, and the horizontal distance it can move the rod decreases as the angle of the cross shaft lever increases. But the force at the end of the lever remains constant. So perhaps, if you have a really sloppy brake system where the bushings are worn out and the clevis pins are loose, you will need a greater horizontal pull on the brake rods to take up the slack before the force at the end of the lever is transmitted to the brake shoes. Starting the brake cross shaft lever a few degrees on the other side of vertical so that it goes over vertical as it pulls will give you the greatest length of pull to take up that slack. But if your bushings and clevis pins are tight and there is no lost motion, there will be the same braking force at the end of the lever whether is starts from or ends at a vertical position.
 
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