Bigger, Better … Stoppers
Story and photography by Jerry Slattery & Associates
The 1960 Bonneville was so big, you’d swear it has front-and-rear runways! They don’t make hoods and trunk lids this long anymore with a hardtop conning tower. The only thing missing is the radar unit coming out of the top!
Owner 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. MPB builds custom front disc brake kits for mid-’50s, ’60s and up to mid-’70s full-sized cars and two-wheel-drive trucks. They provided everything he needed to complete the job using basic hand tools, a tubing bender, jackstands and a floor jack in a couple of days. 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 20-30 minutes per side for the 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 the R-and-R, 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 first and hit the cast steel spindle around the ball joint taper, then remove the ball joint from the hole, you can tip the spindle out and get to the lower ball joint much easier. Only use a pickle fork as a last resort. 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 5-on-5 wheel-bolt pattern, MPB uses the ’77-88 Impala/Caprice 12-inch diameter rotor and GM caliper on stock ’60 Bonneville spindles. But 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 an even wider Wide Track stance.
For power assist, MPB provides 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 preset combination valve hangs under the master cylinder via a bracket and two preformed lines (provided in the kit) that go between the master 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. Next comes the plumbing exercise 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 and then 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 can 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 can see the “T” on the top of the frame just below the old single-chamber master. 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 eliminate the original “T,” and instead, use one union to extend the front brake circuit’s original line up to the master and another union to do the same with the line from the rear circuit. This results in better looking installation for when you open the hood. You’ll notice in Dave’s installation that he turned the combination valve around on his new bracket and made his own short lines between the master and combination valve.
After 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 and place it in the vise and bench bleed it. The goal here is to get the air out of the master cylinder’s plunger bore. In the master’s two bottom front and rear (threaded) outlet holes, 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 chamber of the master. Next, fill the two chambers with DOT 4 fluid and use a Phillips screwdriver to slowly push the plunger into the master. The bubbles will come out of the two lines that empty back into the master 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 plug the master’s outlet holes with the plugs provided in the kit. Once bled, the master can be installed back on the booster with the valve, and the assembly can be bolted to the firewall for the last time. Connect the new lines to the master 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. MPB 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 pushrod connects in the center of the arm. This mechanism reduces pedal travel by roughly 50 percent, making the pedal feel like it has less free-play and is 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-the-floor brake assemblies where the master needs to be away from the rails for the addition of a booster diameter larger then the master. They are available in a number of different offsets.
Before we installed the MPB 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 lbs of leg effort, while the third stop from 50 mph took 90 lbs of effort. After the new system was installed, we took another test ride and did some normal stops; at 35 mph it took 30-35 lbs of leg effort to stop, and at 40 mph we used close to 45 lbs of effort, while at 60 mph it took about 55 lbs to stop. 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. Unfortunately, the original 14-inch steel wheels didn’t clear the larger GM 12-inch rotors and calipers; 15-inch (or larger) wheels had to be used. To our dismay, even the hub caps had to be changed, as the ones for the 14-inch wheels wouldn’t fit on the 15-inch wheels.
In the end, the MPB kit greatly improved the big Chief’s stopping power and made the brake pedal very predictable with a higher feel and less travel.
1 MPB produces custom disc brake conversion kits for the mid-to-late ’50s and ’60s classics and musclecars. This direct replacement kit fits the original drum brake spindles with (’77-’88) 12-inch Impala/Caprice disc brakes, thanks to some custom brackets and adapters. The kit also includes a new dual-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 handtools in a weekend.
2 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 will be used for the front disc brakes with the new dual chamber master.
3 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 dual diaphragm eight-inch booster.
4 To install the new disc brake kit, we only had to remove the spindle from the ball joints along with the brake hose and the tie rod. We didn’t have to remove the spring or shock, which makes the job much easier and faster.
5 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 by about ¾ inch on each side. If you have wider-than-stock wheels or tires, you may need to check tire-to-fender clearance.
6 New brake hoses, clips, brackets and even an adapter from 3/16-inch 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.
7 MPB makes sure you have a quick-and-easy installation. After installing the spindle on the lower ball joint and threading on its castle nut, use a floor jack to push the spring together a little and install the upper ball joint nut.
8 Only the tie rod, brake hose and the two ball joints need to be removed and replaced for this 12-inch disc brake conversion. No alignment should be necessary if you measure the length of the tie rod assemblies and adjust the assembly to the same length with the new tie rod end.
9 MPB supplies extra parts if you need them; like this new frame bracket and clip for each front hose.
10 The completed front disc conversion uses all stock holes, original ball joints (that we replaced) and keeps the same 5-on-5 wheel-bolt pattern that our Pontiac originally had.
11A & 11B Notice how the offset mounting bracket has ratioed the pushrod by about 50 percent. 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 of its travel. And, the four-bolt bracket keeps the booster off the firewall to clear other components and wires.
12 While the MPB kit comes with a mounting bracket for the combination valve, Dave Elwell, the car’s owner, wanted to turn the valve around under the master cylinder, so he fabricated his own mounting bracket for the job.
13 Elwell also made his own lines from the combination valve up to the master cylinder outlets. The short line out of the back of the valve is all it took to connect the existing line to the rear brake circuit.
14 The “T” on the top of the frame rail where the stock front and rear lines connect is really a four-way block: The port at the rear of the block has been plugged, then there are two ports used for the front wheels (one each), plus a port that runs up to the master.
15 This view of the “T” shows a line running up to the master from the “T,” just as one originally did, though we replaced it with a new section of line for a better appearance. The line visible at the top of the photo was a short section of new line that we joined to the rear brake circuit with a union fitting.
16 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. Then bend them to fit and get ready to bench bleed the master cylinder next.
17 To bench bleed the master, you’ll need to remove it from the booster, save the two plugs in the master’s outlets and secure the master in a bench vise.
18 The plastic fittings and hoses coming out of the master cylinder’s 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.
19 Using a Phillips screwdriver, slowly push the master cylinder piston in-and-out until no more air bubbles come out, and then use the plugs to seal the openings, keeping the fluid inside the piston until you’re ready to install all the new lines.
20 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.
21 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 lbs of effort and only 45 lbs from 40 mph. 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.