Hooniverse 101 is intended as an introduction to auto maintenance and function, so as to give inexperienced car owners a leg up on either tackling simple maintenance tasks themselves, or being better informed when going to a shop, potentially helping to not get ripped off. Today, in part 2, we are wrapping up our discussion on the function and maintenance of the drum brake.
Out With The Old, In With The New
When we last left our poor Datsun 240Z, it was up in the air with its shoes pulled off. Now that we’ve completed our inspection of the wheel cylinder and bearing surfaces, we’re going to start reassembling the brakes, and will be replacing a number of parts.
If everything looks good then it is now time to lube up and dive in with the new shoes. In the case of the Datsun, you’re expected to put a little high-temp grease on the supporting blocks on the backing plate (there are three on each side, looking like little dashes) as well as on the pivot points.
Once that is done you’ll need to decide which spring goes where in re-assembly and this is where pictures and the properly assembled other side become invaluable. In my case, the black spring with the s-shaped ends proved to be the one that is impossible to install with the shoes in place so I slotted that in while they were off the car. The spring and shoes combo then gets put in place, with the bottom of the shoe correctly slotted into either side of the wheel cylinder.
Now it gets tricky and this is where an extra set of hands becomes valuable, but not required. First, slide the anti rattle pins in through the back of the backing plate and through the aligning holes in the middle of the shoes. Assemble the rear seat, spring, and front cap and slide it over the pin ensuring the flat slots through the front cap.
Next, hold both shoes in place and, using your long nose pliers, grab the flat of the pin while you push down on the cap with your thumb and forefinger. Twist the pin to seat it in the cap. The second shoe will prove much easier.
Now comes the really hard part so put on your muscles and get ready to use them. The remaining spring now needs to be stretched in place. I do this with the brake shoes off their pivot block perches, just to allow a little more ease. I first slot the spring into one shoe and then, using the hook (Arrr!) of my brake tool, pull the spring to the lip of the hole on the other shoe and then seat it with the end of my mallet handle. Then I use my channel locks to pull the shoes into their perches on the pivot block.
Now you’re done with the hard stuff. . . for this side at least. Check your work, making sure everything is in its respective slots both top and bottom, and that the anti rattle pins are seated fully 90-degrees in their cups.
Slide the drum back in place and give it a spin to ensure that there are no areas binding, but don’t put the wheel on just yet.
Let It Bleed
If you haven’t opened up the hydraulic system any then there’s little need to bleed your brakes after changing the shoes, but it never hurts to go in and give the system a good burp any time you’ve messed with the brakes.
The purpose of bleeding the brakes is to remove air from the system. Hydraulic fluid doesn’t compress, air does. Air in your hydraulic lines means that when you press the pedal, the air gets compressed rather than the brakes and you won’t stop. You’ll also want to bleed them out in the event you want to change the fluid en toto.
To bleed your brakes you need to follow a pattern which is to start the farthest away from the Master Cylinder working your way to the wheel that’s closest. There are a couple of ways to do it, one requiring a vacuum pump which allows you to undertake the task solo, should you be the Earth’s last inhabitant or an angry loaner. The other is to enlist a friend, family member, or street person promised a can of beer to push down the brake pedal while you selectively open and close each brake’s bleeder.
Whether you choose to go the introspective vacuum approach or the pump and dump, one thing’s for certain, you will need a flare wrench. This is an open-ended wrench that has an extra pair of flats over a standard wrench, and which will prevent the fragile bleeder from getting rounded over, which would be a bad thing,
In my case, all the bleeders are 10 MM. Let’s go ahead and walk through the friendlier method. Your goal is to remove any air from the brake lines, and to do that we want to pressurize them, just like applying the brakes.
First pop the cap off of your Master Cylinder – it’s that reservoir that’s likely ahead of your steering wheel and perhaps even markets as BRAKES. Look at the side of the reservoir, there’s likely a pair of lines marked on there, which are minimum and maximum fluid level. Top up the reservoir with your car’s required brake fluid.
Now enlist a friend to sit in the car and roll down the window so you can hear one another. You’ll need to reach under the car (again make sure it’s securely supported before sticking your mellon under there) and place your flare wrench at the farthest point on the bleeder nut (it looks like a hex nut with a nipple on it) allowing a counter clockwise arc.
Once the wrench is in place, attach a length of hose – I told you that you would need a length of hose, right? – well you will. Attach one end of the hose to the nipple on the end of the bleeder nut, and the other end submerged in a jar with about an inch of brake fluid in the bottom.
Ask your friend to pump the brake pedal one-two-three times, and then to hold it down. Once they are pushing steadily down on the pedal, turn open the bleeder valve. You will hear a sputter of air and see bubbles in the jar fluid, as the air is pushed out by the pressure from the pedal. Meanwhile the brake pedal should fall to the floor under your friend’s foot. You’ll need to repeat this a couple of times until no more air comes out, and then on each of the three remaining axles.
Once you’ve done all that, it’s time to take the car for a test drive, but be very careful here as the brakes may need some pumps to fully seat the new shoes and ensure everything is working okay. Remount the wheels hand tightening the lug nuts and then drop the car off the jackstands. Torque the lugs to specs once the weight of the vehicle is on them to prevent spinning. Now you are ready get in and start it up.
Don’t however go anywhere just yet. First pump the brake pedal and make sure that it feels solid and doesn’t have an excess of travel. Next apply the hand brake and see if it is functioning as expected. If it exhibits too much travel then it will need to be adjusted, which will require a visit to your service manual to determine the details of just exactly how to do so. It will likely self-adjust as you back the car up and apply the brakes.
Now, slowly move the car and, ensuring that it is safe to do so, apply the brakes. Listen for any weird grinding or hissing noises. Once you are sure that the brakes are properly seated and working as they should, go ahead and repeat the last action at a slightly higher speed. Note if there is any feeling of grabbing or pulling.
If everything feels good, head back to your work area and stop the car. Get out and do a visual inspection of your work. Are there any signs of fluid leaks? Recheck all your lug nuts and if you need to adjust your hand brake cable this would be a good time to do that.
If everything checks out in both your visual and driving test, then you have successfully changed your brake drums, and can check that skill off your bucket list. Being able to undertake these basic auto maintenance tasks will not only fill you with a sense of accomplishment and earn you bragging rights at the Sports Bar, but they’ll also let you save a load of money over having a shop do the work. If you are more experienced and have additional tips to share, please feel free to do so below.
Images: ©2013 Hooniverse/Robert Emslie