Show Stoppers: Restoring Drum Brakes - Pontiac Enthusiast October, 2010

This is an archive of John Kryta's write up for Pontiac Enthusiast October 2010. It has been unedited from its original form.

Pontiac Enthusiast

Show Stoppers: Restoring Drum Brakes

The focus of this article is a 1969 GTO, but much of it applies to all 9 1/2" GM rear drum brake restorations.
There is nothing exciting about drum brakes, although most cars have them even today. I thought there was a time were all newer cars and trucks would have 4 wheel disc brakes making the drums obsolete but to my surprise my new 2010 GMC truck has rear drum brakes. When I questioned why the discs I found out that all the GM trucks went back to drum brakes in the rear. There were many problems with disc brakes and the good old industry trusted drums remain - said the sales man.

I am not here to debate whether disc or drum is better or what came first the chicken or the egg. I just know millions of GM cars were outfitted with them. The car we are working on is a 69 GTO with 9 ½” drum brakes. It turns out that this is the same unit that is used on all GM mid size cars in the 60’s and 70’s. GM used this unit on all 64-72 A-bodies which includes the GTO, Tempest, Lemans and the other makes like Chevelle, 442 and Skylark. It was also used on the F/X body cars that includes 67-81 Firebird, Trans Am and 71-74 Nova Style Ventura / GTO. So pretty much the entire, small to mid size line up had 9 ½” rear drum brakes. The big Catalina and Bonneville got the slightly larger 11” brakes. There are a few minor changes from car to car which include a 1/16” bigger or smaller wheel cylinder and the length of the parking brake cable but the internals are all the same.

Inline Tube - 9 1/2" GM Rear Drum Brake Restore

Drum brakes are one of those areas that nobody wants to work on. There are so many springs and other parts that have to go together, it is a nightmare. If the parts are rusty it makes it 100 times worst. This article will show the complete rebuild of the very common 9 1/2" GM rear drum assembly. This assembly was used on countless cars in the 60's an 70's. Applications include:

1964-72 GM A-body Chevelle, GTO, 442, Gran Sport, Monte Carlo, Grand Prix
1967-69 GM F-body Camaro, Firebird, Trans Am
1968-74 GM X-body Nova, Ventura, Apollo, Omega
1970-81 GM F-body Camaro, Z28, Firebird, Trans Am

Now that your brakes are 30 - 40 years old it is time to take a look and see what is left. If the shoes are worn out maybe it is time to replace all the hardware since it all has to come apart to get the shoes out. Another thing to remember is there is a difference between the right and left side so do one side at a time and do not mix the parts together. Inline tube offers a complete line of drum parts so if you just need a spring kit or a wheel cylinder it is no problem. If your system is in need of a complete overhaul Inline Tube also offers the complete set assembled and ready to bolt on. The complete set comes as a unit with all the correct color coated springs, plated hardware, parking brake arm and other hardware that is not available anywhere. When you consider the cost of rebuilding all the pieces including turning the drums and re-painting or plating the parts the complete unit really takes the work out and saves money. The complete unit is around $400 or all the parts could be as much as $600 and you still have to do all the assembly. By following the steps below you can rebuild you components just like an experienced mechanic. Inline Tube offers all the pieces of the rebuild or the bolt on unit ready to bolt onto your classic.
Here is an original drum brake set off a 69 GTO, all the parts are in great shape and will make this restoration much easier. When you take apart the drums you must evaluate the parts and consider the condition and the time it will take to restore an old part verses the cost of a new part. In this restore we have taken the harder road and are going to restore the old parts. All the springs and hardware have been bead blasted and repainted the factory correct colors and the parking brake arm, and other hardware has be phosphated. A few parts have been sent out to be silver and gold zinc plated which takes a week to get back.
When working on drum brakes no special tools are necessary but there are 2 tools that can really save some time. The red handled tool will help to get the shoe springs held down and turned into place. Pliers can be used in place of this tool but often scratch up the parts. The second tool is the spring bar. This tool is designed to get the springs back into place, it has a special end so the spring slides into place. A screw driver after several attempts and a possible pinch of the finger will achieve the same result. The hardware is now back from being plated and the color hardware is now dry. The wheel cylinders were rebuilt in the article Wheel Cylinder Rebuild or click here to view.
This is the left assembly we are working on. The drum shoes are riveted and glued just like factory, provided by Inline Tube. The backing plate is phosphate with the back painted black. At the factory the brake assembly was installed to the axle with the drum and then the black paint was sprayed on everything. The first step is to snap the parking brake cable into the backing plate and next the wheel cylinder can be bolted in.
The shoes look alike and will fit either side so be careful to install correctly. The shoe with the long pad goes to the rear of the car. At this time the parking brake cable must be hooked to the parking brake arm and hooked into the rear shoe. The adjuster arm is set into place with the orange spring ready to be hooked in.
With the special red tool push the spring down and twist while holding the pin on the back side. It will lock into place. Now install the small red spring at the base of the adjuster and hook the 2 shoes together with the other red spring and the cylinder adjuster between the shoes. The teeth of the adjuster will line up in front of the hole in the backing plate, beneath the adjuster arm. Hook the brown spring from the adjuster arm to the backing plate stud but be sure to install the washer with ears first. With the bar tool or screwdriver install the pink spring from the shoe to the backing plate stud.
Half the assembly is now done and the other half will have to have the blue shoe. Hold down spring installed and the light blue spring installed from the shoe to the backing plate stud. Flip over the assembly install the blue bleeder cap and rubber dust plug.
We now assemble the right hand side which is a mirror image of the other side. This can be tricky since many of the parts look exactly the same but are the opposite. The steps are the same as above. Again remember to install the long shoe to the back of the car.
The cylinder adjuster teeth go over the open slot in the backing plate and should be in the full closed position. These are self adjusters so when the car is all put back together in reverse motion lightly apply the brakes and the shoes will automatically adjust out to the right position. As the shoes wear down and the car gets put in reverse the adjusters will continue to take up the slack in the system.
The drum assembly is held to the axle flange by four bolts. To install the backing plate the axle must be removed. This is again held on by the four flange bolts. For Pontiac, Buick, and Oldsmobile the axle is held in by the bolts, on Chevrolet products there is an additional c clip that will have to be removed. This c clip is located under the rear end cover. Drain the oil, remove the cover, pull the clip, then remove the axles.
The drums have been installed and the axle is ready to be installed in the car.