Drum 2 disk brake conversion. Stop That Car!

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1 Page 1 of 9 Stop That Car! From the February 1993 issue of "Petersen's Musclecar Restoration and Performance". Illustration by: Dennis Ellefson GM BUILT PLENTY OF CARS WITH FRONT DISC BRAKES. IF YOUR A-BODY WASN'T ONE OF THEM, IT'S EASY TO CONVERT IT WITH A KIT FROM H-0 RACING by Sue Elliott Anyone who's driven a real musclecar knows about power. And anyone who has driven a musclecar with front disc brakes knows about, and appreciates, stopping power. Unfortunately, not all musclecars came so well-equipped. If your'64-72 GM A-body is one of those four-wheel-drum-brake cars, you can take matters into your own hands. In fact, it's easy to make the switch to front discs. All you need is a set of donor disc brakes and spindles plus a conversion kit from H-0 Racing Specialties. The kit (PN SB-55 for'64-70 cars, SB-56 for'71 72 cars), which costs $99.50, includes outer tie rods, upper and lower ball joints, and all the hardware needed to make the changeover. When it comes to finding a set of disc brakes and spindles, your best bet is to scour the junkyards. Ken Crocie of H-0 Racing recommends getting a setup from a'70-81 F-body (Camaro, Firebird), '73-77 A- body, '75-77 X-body (Nova, Omega, Ventura, Apollo), '73-92 B-body (Caprice, Delta 88, Bonneville, Le Sabre, etc.), or'73-92 rear-drive C-body (large Cadillacs, Olds 98s, Electras, etc.). All of these cars' spindles are the same dimensionally. However, the smaller cars generally have 11-inch rotors with a 4 3/4-inch bolt circle, the same as a stock'64-72 A-body. The B- and C- cars sometimes have 12-inch rotor with a 5-inch bolt circle. You will need to have these rotors redrilled to use them with existing wheels. Switching to these later-style spindles will improve not only your car's stopping ability, but its handling, too. Because these spindles are about 1 1/2-inches taller than stock, they'll give your car a better camber

2 Page 2 of 9 curve, which allows the outside wheel to remain more upright as the body rolls in turns. A FEW WORDS OF WARNING: There is no doubt that this conversion will improve your car's stopping and handling abilities, and a swap to latemodel spindles will ensure an adequate supply of replacement parts (bearings, seals, rotors, pads, caliper kits, hoses, etc.). However, there are still a few caveats to consider. For starters, this conversion will slow your car's steering ratio about 11% and increase its turning radius. Also, if your car's suspension is stock, "toe steer" will be a problem. (If you've firmed up your suspension, don't worry about this.) You'll want to check your existing wheels for fit with the new spindles, as well. Not all stock wheels will clear the caliper and hub. And because this spindle conversion requires approximately 3/4 inch more shim pack than stock, you must check that the upper control arm, along with the shaft assembly, can be moved inboard 3/4 to 1 inch. (Big-block Chevys and 455 Oldsmobiles are the most likely to have a problem.) If the upper control arm and shaft assembly cannot be moved that far, you have a few expensive alternatives: 1) use shorter upper control arms; 2) lower the car; 3) have custom offset lower control arm bushings made up; or 4) move the engine or modify the headers (the usual point of interference). A less expensive alternative is to use early style disc brakes instead. These can be found on '67-69 F-bodies,'67-72 A-bodies, and '68-74 X-bodies. While you won't reap any handling benefits from a conversion to these stock-type spindles, your car still will stop more reliably. PREP WORK: Once you've found the disc brake setup from a junker and made sure it will fit on your car, you'll have to do some preparation work. Pick up some new bearings and brake pads from an auto parts store. Rebuild the calipers or buy a rebuilt pair from a brake house. If necessary, turn or replace the rotors. And it's a good idea to have the spindles Magnafluxed, too. You'll also need to swap your old rubber drum brake lines for a pair of new rubber disc lines. While a number of brake lines will work, H-0 Racing's experts recommend purchasing a pair of rubber lines for a'72 Pontiac Grand Prix at your local auto parts store. Because of their length, they're easy to work with, and they have the correct banjo fitting on the end. You can retain your car's original single-outlet master cylinder, but it is not recommended. Any factory master cylinder will work, although different units provide different pedal feel and pedal travel. Ken recommends switching to the '70-72 F-body unit, if possible, and notes that power brakes are not mandatory; in fact, power disc brakes were optional on '70-72 Camaros, while manual disc brakes were standard. If you decide to use the drum brake master cylinder from a'68-71 car, you'll need to remove the residual pressure valve. In addition to choosing the right master cylinder, you also must obtain a disc/drum proportioning valve, which will help keep the rear brakes from locking up prematurely. You could simply take the proportioning valve off the disc-brake donor car, but a better idea is to use an aftermarket adjustable unit, so you can set up a perfect front/rear brake bias. Adjustable proportioning valves are available through the GM, Mopar, and Ford high-performance parts networks, as well as through a number of aftermarket sources. While you can do virtually all the work involved in this conversion your self, Ken recommends taking your car's upper and lower A-arms to a machine shop or local auto parts store to have the new ball joints installed. If you choose to install the ball joints on the upper A-arms yourself, don't forget to change the bushings.

3 Page 3 of 9 Once you've chased down all the parts for this conversion, you should be able to complete the entire installation in less than three hours. To help make this easy bolt-in a little easier, Dave Miller walked us through the conversion process on a'64 GTO at H-O Racing. 1. Start with the car up on jackstands and the front wheels off so your drum brakes are exposed. (Naturally, you'll want to work on one side at a time.) the shock at the top of the top of the frame. 2. Begin the disassembly process by disconnecting

4 Page 4 of 9 3. Next, loosen the two bolts at the bottom and remove the shock. drum brake assembly. 4. Disconnect the tie rod end so you can swivel the

5 Page 5 of 9 bushings. 5. Disconnect the anti-roll bar strut mount bolt and 6. Remove the retainer clip so that the brake line slips out of its support bracket. Tip: To keep all the brake fluid from draining out during the conversion, a cap such as the one used here (arrow) comes in handy.

6 Page 6 of 9 7. Be sure to secure the spring with a safety chain when you prepare to remove the drum brake assembly. Remove the cotter pins at the ball joints. Loosen the ball joint nuts to two turns. Lower the jack about a 1/2 inch below the lower A-arm. Strike the spindle sharply with a hammer to break it loose. Raise the jack back up to take the tension off the ball joint nuts, then remove the nuts. brake assembly. 8. Lower the lower A-arm carefully and remove the drum

7 Page 7 of 9 9. Now carefully lower that A-arm the rest of the way to remove the spring. (A spring compressor may be necessary.) Then disconnect the lower A-arm. 10. Disconnect the upper A-arm by loosening these bolts (arrows). Then take both A-arms to a machine shop to have the new ball joints installed. 11. Once the ball joints have been installed and you've done your prep work, you're ready to begin the installation process. Start by reinstalling the A-arm and spring. Once again, use a safety chain. 12. Next, attach the disc brake assembly spindle to the new ball joints. Torque the nuts on the ball joints to factory specs (lower A-arm: 70 lbs.-ft. nominal, 100 max to install the cotter pin; upper: 40 lbs.-ft. nominal, 70 max.). Then insert the new cotter pin

8 Page 8 of 9 the new disc brake line. 13. At this point, it is OK to remove the safety chain. Then connect 14. Replace the anti-roll bar strut bolt, then replace the shock. 15. Unscrew the old tie rod and install the new one from the conversion kit. Screw it into the adjustable sleeve approximately the same distance that the old tie rod went in, so your alignment won't be too far off. Torque the adjuster sleeve to 20 lbs.-ft.

9 Page 9 of Put the boot on the tie rod end, then insert it into the spindle. Replace the nut and torque to lbs.-ft. for alignment. Insert the new cotter pin. 17. When you've finished the installation, turn the wheels lock to lock and check to see that the brake line isn't stretching or rubbing. Then bleed the brakes (consult your factory shop manual for correct procedure), and make sure everything is tight before you take the car off the jackstands. If everything looks good, test the brakes in your driveway, then go directly to an alignment shop.