Adjusting drum brakes

[gogmorgo]

Brake Shoes:
 

It’s a pretty basic process, common to all vehicles with drum brakes and some with a parking brake inside a rotor, but I didn’t see a specific thread about it so figured I’d do one. 
Why do you need to adjust them? As your shoes and drums wear, you lose some of the wear surface. This means there’s a bigger gap between the shoes and drums, and the brake components need to travel further to do anything. Eventually they get to the point where they have to travel so far that they don’t apply much pressure when they get to the drums. This is an issue that seriously affects brake performance, to the point where if something happens to your front brakes you may lose brakes entirely. It also puts much more stress on the front brakes, beyond what they were intended to deal with, especially if you’re carrying a load or pulling a trailer. The brake shoe adjustment also affects the parking brake. If they’re too far out of adjustment the parking brake will not hold. So we adjust the brakes to get the shoes back to close proximity to the drums. 
 

Adjusting brakes is something that should be done every so often. It would have been part of the annual “tune-up” maintenance that was normal for cars in the past, but that modern cars don’t really need and society has mostly forgotten about. 

“But they’re self adjusting!” Right. In theory, yes, but in practise not so much. They only self-adjust in reverse, and you need a pretty aggressive stop in reverse to make it happen. Most people don’t go fast enough or brake hard enough in regular driving to make it happen. If you can find an open space where you can safely get up to 10-15mph in reverse and do a hard stop or three, this may be enough to get your brakes back into adjustment on their own, assuming all your brake hardware is in good shape. This is not always the case, so what do you do? We adjust them manually. 

 

You need to do this with the parking brake released, so make sure you have proper safety mechanisms in place so you can get underneath the vehicle without running yourself over or the truck falling on you. Chock the front tires, jackstands under the frame, etc.

 

Start with one of the rear wheels. Locate the rubber plug on the back of the drum brake backing plate.

It’s an oval sort of shape, and similar to the plug in the bottom of a piggy bank. I like to use a small screwdriver to dig them out of the holes, but anything with a pry-bar action will work. 
 

When you look into the hole, you should be able to see the adjuster star wheel. You’ll probably need a flash light, because, you know… hole. 

It’s difficult to photograph because hole, but you can see the shiny teeth on it in the hole. This is what it looks like:

Heads up, this picture is rotated 90° from how it sits in the hole. Note how the teeth are ramped, one side is much steeper than the other. The self-adjuster pushes down on the straight edge, then travels back up the ramp, like a ratchet. As it turns, screw threads push the tip out, which pushes the brake shoes closer to the drum. To turn it manually, you need to reach into the hole and push against the flats on the star wheel. Usually you would lever off the side of the hole. There is a tool for this, called a brake spoon:

It’s basically a double-ended pry bar. The bends in it make it easier to get into some more awkwardly positionned adjuster holes. You don’t strictly speaking need it. You can use a screw driver or any other sort of prying device, but the spoon definitely makes it easier.

Depending on how long it’s been since the adjusters last turned, it may take some force to get them started moving. Usually once you get them spinning they’ll move pretty freely. If they’re totally seized and you can’t get them to budge at all, you may have to take the wheel and drum off to free up the adjuster. If that’s the case, I would probably come armed with all new hardware, probably shoes and drums as well, because things won’t be pretty in there, and drum brake hardware is cheap. Usually the adjusters come separately from the hardware kit, and they’re different left to right. Make sure they’re lubricated when they go in so they won’t end up seized. But that’s a different thread.

 

How far do you turn the adjusters? Good question. You want to go far enough the shoes are almost in contact with the drums, but not too far or you’ll just have brakes stuck and dragging. What you’ll want to do is lift the wheel off the ground so you can spin it, and then adjust the brakes until you can feel a very slight drag. Go a few clicks, spin the wheel, few clicks more, spin it again, until the brakes are dragging ever so slightly.

At this point, go into the vehicle and push the brake pedal, then go back under and make sure you still have the slight drag. If the drag goes away, keep adjusting until it comes back, and then repeat. In a perfect world, turning the adjuster moves both brake shoes, but the world isn’t perfect so you’re probably only moving one of them, which means you’re only getting your brakes halfway adjusted. Applying and releasing the brake moves the assembly back to centre, so you can continue adjusting until both shoes are dragging slightly. When it’s where you’re happy with it, pop the rubber plug back in. 

 

Now you move onto the other rear wheel. Once you have them both adjusted to a slight drag, take it for a spin. If your brakes were pretty far out of adjustment, you should notice the increased braking performance right away. Congrats, you just adjusted your brakes! Don’t forget to pop the rubber plugs back in.  

It’s worth pointing out that if your brakes were out of adjustment for long enough that corrosion built up on the braking surface of the drum, you’ll find yourself having to adjust the brakes again in pretty short order. This is normal (ish). What happened is that when the corrosion got scrubbed off, the drum diametre increases, so the drum is effectively further away from the shoes. Adjusting them again will correct the situation.

 

Parking Brake:
 

If you were adjusting the brakes to try to get the parking brake working, and you’re now stopping on a dime but the parking brake still doesn’t hold, good news is there’s adjustment in the parking brake cable, too. It’s important to make sure the brakes themselves are adjusted correctly before attempting to adjust the parking brake cable. That may be all the parking brake needed after all.

It’s also not usually necessary to adjust the parking brake cable other than initially setting up a new cable. The cables do stretch over time and with use if they survive long enough without seizing, but it’s not something that you should need to be doing more than once every ten years, if even that. Again, the primary adjustment point for the parking brake should be your rear brakes, and once the initial setup is done, you shouldn’t need to touch the cable adjustment again until you’re replacing cables. 
 

There’s only one point of adjustment for the cable, and it handles both sides.

This is the equalizer assembly. On a Comanche it’s located above the rear driveshaft, next to the fuel tank. You’ve got three parking brake cables that meet here. The two in blue go to the brake drum at each rear wheel. The one in red goes forward to the parking brake pedal. It’s called the equalizer because when you pull on the forward cable, the bar then will distribute equal tension to both brake cables, and in theory equal brake force.

The adjustment is in the red cable. The end of the cable is threaded, and it’s adjusted by turning a nut, circled in green. The nut is usually double-nutted, so you’ll need two wrenches. The nut against the bar is the adjustment, and the second nut locks the adjuster nut in place. Back off the first nut, then tighten the second one to adjust the cable tighter.

The wrench is on the adjuster nut, and the vice grips are holding the cable, just ahead of the threads, to stop it from turning while I adjust the nut. Given the location under the vehicle this adjustment can be particularly recalcitrant, especially if you see road salt. Penetrating oil is usually a must. 
You want it to be tight enough to take up almost all the slack in the cable, but not so tight that it’s applying and dragging the brake with the parking brake pedal fully released. Once it’s adjusted, tighten down the lock nut. 
If you run out of cable adjustment and the parking brake still won’t hold, double check that the brakes themselves are correctly adjusted. If they are, then you likely need new cables. Good news is they’re still available from a handful of retailers, at least at the time I’m writing this.