I'll readily admit I've been spoiled by modern, self-adjusting brakes. On an old Willys, the brake shoes must be manually adjusted to compensate for lining wear. If the clearance is too much, excessive pedal travel will be required before the shoes contact the drums. This can give the misleading impression of air in the lines. While not difficult, few people are familiar with the adjustment process anymore.
Some of these pictures show the brakes on my full-floating rear axle conversion. The brakes are the same as the stock semi-floater rear axle. (On the stock rear axle, don't forget the Grease Retainer and Protector
.) The front brakes are nearly identical except for larger diameter brake cylinders.
Later models have only two upper adjustment points per wheel, but the CJ-2A and CJ-3A have two at the top and two at the bottom. Here is an exploded image showing the adjustable lower anchor pins on my CJ-2A. The cam (outlined in red) has an odd-shaped inner opening to engage the anchor pins. By rotating the anchor pins, the cam turns and the pivot points can be adjusted for the two brake shoes. This view shows the inboard side of the brake shoes and anchor pins. The wheel cylinder was shown for illustration purposes, but it should have been spun around so the side with the brake line connection was visible:
Here is a close-up of an upper eccentric, with the backing plate in the background. The upper eccentrics limit how far the shoes retract. Note the notch in the shoe guides which keep the edge of the shoes from touching the backing plate
The anchor pins and eccentrics have a dimple at the tip of the shank. The dimple points to the area of maximum offset, allowing you to keep track of which way they are pointing. Here is the dimple highlighted in red on one of the upper eccentrics:
If the backing plates have been removed for any reason, you can pre-assemble all the parts from the comfort of your workbench. Installation of the brake parts is much easier that way. Brake spring pliers make easy work of stretching the spring for installation:
The completed assembly is installed on the axle in this picture. The upper eccentrics are not visible behind the brake shoes :
Here is a view of the backside of the backing plate. Remember with four adjusting points, the two anchor pins at the bottom change the pivot point for each shoe and are adjusted first. The upper eccentrics only control how far the shoes retract. This picture also shows the plug which replaced the grease fitting
for my rear axle full-floater conversion
The anchor pins fit in a recess in the backing plate, making access a bit tricky. This picture of the front axle shows how an open end wrench can barely grip the 3/4" locking nut and has limited movement before hitting the backing plate. Access is worse on the front axle due to the adjacent kingpin bearing cap:
An offset 12 point box end wrench works best. Note how it fits in the recess of the backing plate:
Due to the limited clearance with the kingpin bearing cap, the head of the box end wrench cannot be thicker than .375". The wrench on the left in this picture is a standard box end without the offset, which won't fit in the recess. The middle wrench is too thick and won't pass through the gap. The wrench on the right has a thin enough head to work perfectly. You may have to grind down an inexpensive 3/4" wrench to fit:
The CJ-2A and CJ-3A have a neat gee-whiz feature for checking brake shoe clearance. A slot is cut in the face of the brake drum, allowing the use of a feeler gauge. This view, of the inside of a brake drum, shows the feeler gauge inserted from the other side:
With the brake drum installed, here is the feeler gauge from the outside. These slots were eliminated on later models and it is easy to understand why. It is time-consuming to set clearances this way. It was far easier to get the same results by spinning the brake drum and backing off the shoes slightly to eliminate drag, the process used on later models:
After installing new brake shoes, expect pedal travel to increase as the highest points on the shoes wear to match the drums. After a few hundred miles for the shoes to seat properly, go back and readjust them.