Discs and a dual brake system at home in a weekend
Jerry Slattery & Associates - March 08, 2012 10:00 AM
Master Power Brakes will build custom disc brake kits for the mid-to-late ’50s and ’60s classics and muscle cars. This direct replacement kit uses the same original (front) drum brake spindles loaded with (’77-’88) 12-inch Impala/Caprice disc brakes. The new kit includes a new double-diaphragm, eight-inch booster and dual chamber master cylinder and pre-set combination valve for the new disc-drum system. It can be installed at home with basic hand tools in a weekend.
The original single chamber master cylinder features a four-bolt mounting pattern that is used to mount the new vacuum booster bracket. This single line to the original master cylinder will be used on the new dual chamber master cylinder for the front disc brakes.
Our project car did not have power drum brakes, but some ’60 Pontiacs like this one came with a power brake booster and drum brakes. Since the owner, Dave Elwell, had another ’60 Pontiac donor for parts with a booster (shown), MPB asked us to send the stock spindles and the booster so they could duplicate the position of the booster bracket and the pushrod location on their new double diaphragm, eight-inch booster.
To install the new disc brake kit, you only have to remove the spindle from the ball joints along with the brake hose and the tie rod. You don’t have to remove the spring and shock.
Looking at the back of the ’60 Pontiac drum brake spindle, you can get an idea how MPB built the two-piece caliper brackets using only the three stock holes that held the original backing plate to the spindle. To fit the newer rotor bearings on the earlier spindle, MPB used bearing shoulders and spacers to position the new bearing in the correct places. This increased the front track width about ¾-inch more on each side.
MPB makes sure you have a quick-and-easy installation. After installing the spindle on the lower balljoint, use a floor jack to push the spring together a little and install the upper balljoint nut. Only the tie rod, brake hose and the two balljoints need to be removed and replaced for this 12-inch disc brake conversion. No alignment should be necessary.
New brake hoses, clips, brackets and even an adapter from 3/16 steel brake lines to ¼-inch is supplied in the kit. This will adapt the new brake hose to either size depending on the vehicle’s brake line size. MPB supplies extra parts if you need them; like this new frame bracket and clip for each front hose.
The pivot arm pivots at the bottom, locates the brake pedal pushrod in the center and actually pushes on the booster at the top. This offers about half the pedal travel to stop the car, eliminates about half the pedal freeplay and always gives a nice feeling pedal near the top. And, the four-bolt bracket keeps the booster off the firewall to clear other components and wires.
Dave Elwell wanted to turn the combination valve around under the master cylinder so he created his own bracket to hold it. He also made his own lines from the combination valve up to the master cylinder ports. The short line out of the back of the valve is all it took to connect to the frame line to the rear. The kit comes with a mounting bracket.
The junction on the top of the frame rail where the stock front and rear lines connect is really a four-way block. The port to the rear has been plugged and the line is bent upward to meet the new short line coming out of the rear of the combination valve in the last photo. The line coming up will connect to the front of the combination valve.
It’s a good idea to measure the old pushrod to maintain the same length before installing the new unit. Install the new unit temporarily and measure for the new lines and bend them to fit.
To bench bleed the master cylinder, you’ll need to remove it from the booster, save the two plugs in the master cylinder ports and install the unit in a vice. The plastic fittings and hoses coming out of those ports are from a bench bleeding kit (about $5 to $6 at a parts store). The hoses go back into the reservoir chambers to bleed the air out of the plunger bore. Fill both chambers with DOT-4 fluid. Using a Phillips screwdriver, slowly push the master cylinder piston in and out until no more air bubbles come out, then use the plugs to seal the openings, keeping the fluid inside the piston until you’re ready to install all the new lines. With all the lines installed and the pushrod connected to the brake pedal, it’s time to bleed the system at the wheels. This will bleed any air out of the combination valve too. Be sure to keep fluid in the master cylinder when bleeding the system.
When we were finished with the installation, we put the gauge back on the brake pedal and went for a test drive. It took about half the effort to stop the car with power brakes. From 60 mph it took 55 pounds of effort and from 35 mph only 45 pounds. These were normal in-town driving stops. The rear system that locked-up in the first test was rebuilt for a true indication of what the total system could really do with a disc/drum system.
Dave Elwell’s Bonneville Hardtop came stock with manual four-wheel drum brakes and 14-inch wheels. He wanted to upgrade the brake system with front discs and keep the stock rear drum brakes.
Master Power Brakes builds custom front disc brake kits for mid-’50s to mid-’70s full-sized cars and two-wheel-drive trucks. They provided everything he needed to complete the job in a couple of days using basic hand tools, a tubing bender, jack stands and a floor jack.
As you look at the kit photo, notice the spindles are fully assembled. We sent our original spindles to MPB and they loaded and assembled the spindles and sent them back to us. This makes the front spindle swap a real snap, about 20 to 30 minutes a side to install. The trick here is to know how to release the ball joints from the spindles. A sharp hit with a big hammer around the cast steel spindle taper on the top and bottom of the spindle is all it takes.
There are no bearings to pack or calipers to load with pads, no assembly at all. To do this job, you’ll only need to remove the upper and lower ball joints, steering tie rods and the two hoses. The coil springs or the shocks do not have to be removed for this installation. If you loosen the upper ball joint nut slightly (but don’t remove it), and hit the cast steel spindle around the ball joint taper and remove the ball joint from the hole, then you can tip the spindle out and get to the lower ball joint much easier. Be careful, as there is a lot of force on the coil spring. As Dave did, this is a good time to replace upper and lower ball joints while everything is apart. MPB even provides new hoses, brackets and clips that go on each frame rail.
To keep the same Pontiac five-on-five wheel bolt pattern, MPB uses the ’77-88 Impala/Caprice 12-inch diameter rotor and GM caliper on stock ’60 Bonneville spindles. Don’t think you can just find a couple of 12-inch GM rotors and calipers and bolt them on. MPB has engineered this kit to fit by adding bearing spacers and shoulders to accept the later bearings on the original spindles.
They’ve even built a two-piece caliper bracket that uses all three original backing plate holes. This way, there is no cutting or grinding involved. Just reinstall the same spindles back to their original positions. The new disc kit will add about ¾-inch on each side to the front track width. For power assist, they provide an eight-inch, double-diaphragm booster and preset combination valve. You will have to install the combination valve under the new 11/8-inch diameter master cylinder and booster and then plumb it into the car’s existing brake system.
The pre-set combination valve hangs under the master cylinder via a bracket and two pre-formed lines (provided in the kit) that go between the master cylinder and the combination valve. As you can see in the photos, Dave made his own (sling-shot shaped) bracket to hold the valve under the master cylinder. The next exercise is to connect the new brake lines into the old brake line system. The best way to do this is to temporarily install the booster and master cylinder and adjust the pushrod to keep the pedal in its normal position.
This is the time to measure for the new lines and get them bent to fit the new system. The goal here is to have two lines up to the combination valve from the “T” on the frame. You can accomplish this in two different ways. At the “T”, you’ll tie into the old system, bringing one line from the front and one line to the rear up to the new combination valve. In the photos, you’ll see the “T” on the top of the frame just below the old single chamber master cylinder. Remove the rear line from the “T” and plug that hole in the “T”. This original rear line will receive a union and a new piece of brake line to reach the combination valve above. The existing single chamber four-bolt master cylinder line can now be used as the front brake line. Or the second way to plumb this, as Dave did, is to make two new lines to the master cylinder (from the frame lines) and eliminate the original “T” for a nicer looking job when you open the hood. You’ll notice in Dave’s installation he turned the combination valve around on his new bracket and made his own short lines between the master cylinder and combination valve.
Once you have fitted and installed the combination valve under the master cylinder using the bracket in the kit or your own bracket, you can remove the valve and booster from the master cylinder and place it in the vice and bench bleed it. The goal here is to get the air out of the master cylinder’s plunger bore. In the two bottom front and rear (threaded) outlet holes (of the master cylinder) you can use the two short pre-bent lines from the kit if you don’t have a bench bleeding kit.
Add a couple short pieces of hose (about three to five inches long) to extend these lines, one into each master cylinder chamber. Next, fill the two chambers with DOT-4 fluid and using a Phillips screwdriver, slowly push the plunger into the master cylinder. The bubbles will come out of the two lines that empty back into the master cylinder’s reservoir bowls and sometimes out of the bottom holes in the reservoirs. Push the plunger in and out until no more air comes out and then using the plugs in the kit, plug the outlet holes. Now it can be installed back on the booster with the valve and the assembly bolted to the firewall for the last time. Connect the new lines to the master cylinder and combination valve and bleed the entire system at the wheels.
If you’ll notice in one of the first photos, the original master cylinder is mounted to the firewall with a square four-bolt pattern. Master Power Brakes installed a four-bolt mounting bracket to the back of the booster to fit this old pattern. Take a look at the back of the bracket. It does much more than mount the unit to the firewall. There is an arm that pivots at the bottom of the bracket, while the top of the arm pushes into the booster and the brake pedal push rod connects in the center of the arm.
This ratios the pedal travel by 50 percent, offering less travel, making the pedal feel like it has less free play and always at the top. The offset symmetrical four-bolt pattern actually gives you four offset positions, so it can be rotated to clear objects on the firewall or the valve cover if necessary. These brackets are very useful for under-floor brake assemblies where the master cylinder needs to be away from the rails for the addition of a booster diameter larger than the master cylinder. They are available in a number of different offsets.
Before we installed the Master Power Brakes front disc kit, we put a pressure gauge on the brake pedal and went for a test ride to see what kind of leg effort it took before and after the install. This Pontiac had been sitting for about three years and the brakes were stiff and not moving too well. This old system could use a lot of improvement and that’s what the MPB kit will accomplish.
Dave rejuvenated the rear brake system so we could see what the fronts could really do with all fresh parts. The first stop from 50 mph took around 160 psi and locked-up the right rear. The second stop from 50 mph took 80 pounds of leg effort, while the third stop from 50 mph took 90 pounds of effort. After the new system was installed, we took another test ride and did some normal stops. At 35 mph it took 30 to 35 pounds of leg effort to stop and at 40 mph close to 45 pounds; at 60 mph about 55 pounds of effort. This is about half the effort it took to stop the car than it did with the old rusty drums and old wheel cylinders.
While he was at it, Dave replaced the ball joints and painted the A-arms and all the brake parts. The original 14-inch steel wheels could not be used with the larger GM 12-inch rotors and calipers; 15-inch wheels had to be used on the front. If you want to use the original 14-inch hub caps you’re out of luck. The MPB kit did a great improvement to stop the big Chief and made the brake pedal very predictable with a higher feel and less travel.