Technical Bendix brakes. Leading / trailing shoes have different spring tensions from shoe to top post.

Technical question I suppose and I searched quite a bit and got a pretty equal split of answers.


I’m working on my wife’s 64 falcon v8. It’s been sitting a long time and I wanted to clean and inspect the brakes before I put any miles on it. The drivers side and passenger sides have different spring orientation. The springs in question are the yellow and blue springs that connect the shoe to the top post. One of them also locates the half round cable pivot for the self adjuster.


one side of the car has the stronger blue spring with more tension located on the shorter lining leading shoe.


The other side has the weaker yellow spring located on the leading shoe. Obviously the springs are different tension by design.


Being a self energizing drum brake system, these spring tensions are pretty important. Logic tells me that the lighter tension yellow spring should be on the forward leading shoe. When the wheel cylinder starts to spread, the pressure would push the lighter tension spring first engaging the leading shoe into the drum and friction would “self energize” the trailing shoe (longer lining) providing maximum pressure against the top post.

Am I all wrong here?

 

Rule of thumb the primary shoe (leading) has less tension so it engages the drum first and acts as a servo to push the secondary shoe. The primary spring goes onto the anchor first as well for the same reason as the post is tapered outward and by design the first spring installed has less tension.
From what I see the brakes in your photos looks to be correctly installed!

 

Yup, lighter tension spring on the primary shoe. Servo acting brakes have primary and secondary shows. Leading-trailing is a different brake design.

 

Yellow spring was on the right on the first side that was done, so it only made sense to put it on the right on the other side You've got to be logical.

 

Thank you for the feedback. I wonder how many drum brakes were assembled incorrectly over the years. Those folks that didn’t stop to think how they actually work and just slapped them back together however . Probably contributed somewhat to the perception that “drum brakes suck” adage. If properly assembled with proper clearances they work quite well for their design. All of my drum brake vehicles stop with minimal effort. This mismatched spring situation was the first I’ve seen so I wanted to learn more.

thanks all!