Rear Disc Brakes on the Cheap: Convert Your 64-and-up RWD Pontiac Using New and Used Pieces

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1 Rear Disc Brakes on the Cheap: Convert Your 64-and-up RWD Pontiac Using New and Used Pieces BY Don Keefe, with info supplied by Imran Chaudary and Andy Pooni Photos by the author, Andy Pooni and Imran Chaudary Diagrams Courtesy of GM Media Archive Imran Chaudary s 11-second 69 GTO now stops as well as it goes, thanks to a cleverly designed four-wheel disc brake system that uses boneyard and over-the-counter parts, available at any parts store or GM dealer. Editor s Note: This article was originally written in 2006 and over the course of this summer, we received quite a few inquiries about it. We therefore decided that it would be a worthy candidate for reprinting. The prices may have changed somewhat in the years that have passed but the part numbers should still be accurate. Owners of early Pontiac A, B and F-bodies have a lot going for them: great looks, powerful engines and instant street credibility, especially for the performance versions of each series. The only real drawback is that they don't really drive like new cars. By modern standards, the handling is only so-so and the brakes are several feet short of spectacular. True, the addition of disc brakes in '67 did help quite a bit, but they still are not up to what one would find in a base-engined minivan. They certainly aren't adequate if even modest gains in horsepower are achieved. Bringing performance up to modern standards is pretty much the whole idea behind the Pro Touring movement. Making an early GTO accelerate like a new one is not very difficult- several are already there in stock form. Getting one to handle and stop like a new one, well that's a little more of a challenge- and it's one that many 46 Page

2 are taking up and finding worth the effort. Sometimes, effective upgrades for earlier cars can come from inexpensive factory components. Whether you re building a corner-carving GTO or just want something that will stop shorter than your current disc/drum setup, we have a solution that will cost less than $500 total. You ll also be able to run a factory-style 15-inch wheel on your car, though a 14- incher will not quite clear the caliper. Canadian GTO restorer and Pro Touring enthusiast Imran Chaudary, has developed an affordable and relatively simple rear disc-brake conversion for 1960s and 70s-era GM cars that use parts originally designed for latemodel compact GM pickups (Chevy S-10/GMC S-15) and SUVs (Chevy Trailblazer/GMC Envoy). The system works for 8.2 and 8.5- inch 10-bolt and GM 12-bolt rearends. Imran has this system in his street-driven 11-second 1969 GTO (a former High Performance Pontiac Shootout participant) and has racked up more than a dozen years of trouble-free performance. Keep in mind that even though these are considered compact trucks, they can easily tip the scales at over 4,500 pounds, so it s not Go to your local wreckers or GM and find a pair of rear disc-brake backing plates for S-based two-wheel-drive trucks and SUVs. Rear disc brakes were an option in those years. These brackets also have an integrated parking brake in them. They work by expanding a brake shoe against the inner portion of the rotor. When disassembling the bracket at the wreckers, take special care to salvage the parts for the parkingbrake assembly. You should be able to pick them up for around $50 a pair. Page 47

3 While at the salvage yard, also look for a set of brake-pad retainer cages (shown with pads installed), GM PN These items can be difficult to find, though they are available new from GM for $ each. like these brake systems will be for their own cars and have overtaxed with even the weight ofa late 60s Bonneville. the conversion won't break the recorded similar results. Best of all, This setup also went into fellow bank and is fairly simple to accomplish. Canadian Pontiac fan Andy Pooni's Pro Touring 1965 GTO. Several "It's really amazing how well other friends have used this combo these new parts go together with This new dust shield from GM costs $19.70 (each), so it makes sense to discard the old ones. Before you do, be sure to compare them to the new ones, as there are two different designs, depending on whether the backing plates locate the calipers at the 11:00 or 2:00 positions. the older rearends," Chaudary said. "I guess that when it comes to pieces like rearends and axles, there is a lot of carryover from year to year and even generation to generation. When you have the critical dimensions laid out and tooling to pay for, it doesn't make sense for GM to change things if they don't have to." When you realize that the S-10s were designed to use the same front suspension pieces as the Chevy Caprice, and the Chevy Caprice is an outgrowth of the A and G Bodies, which were closely related to the A- and G-body platforms, you begin to see how these seemingly unrelated vehicles actually share some vital DNA. For this particular setup, most of the componentry can be purchased at any late-model salvage yard. The parts that Imran or Andy purchased new were the wear items in the system- rotors, calipers, hoses, brake pads and the dust shields, which were available from their local dealer. When searching through your favorite salvage yard, look for Envoy, Jimmy, Blazer, or S-15 pickup trucks and SUVs between the years of 1998 and Rear disc brakes were available on some as an option and standard equipment on higher-end vehicles. "When Andy and I searched our yard we removed parts for his '65 GTO from a 1998 Envoy and I removed mine from a 1999 Jimmy SUV, Imran recalled. "The yard had already taken off the rotors and 48 Page

4 calipers." Once you've found the appropriate donor vehicle, the first thing is to remove the rear-axle cover to drain the fluid, as you need to slide out the axles. Keep in mind that these rear ends have C-clips, so you must remove the small bolt holding the axle pin. Once the pin is out, rotate the carrier until you can get at the C-clips. Push the axles in remove the C-clips. This will allow you to remove the four studs on the end of the flange and take off the backing plates and disc-brake dust shields. The backing plates are the most important pieces in the conversion because though everything else can be purchased fairly inexpensively from your local GM dealer or parts retailer, the plates are quite expensive new, listing at $ each. And it s one of those situations where used versions for $50.00 or less per pair at your favorite salvage yard will work just as well. These backing plates have an integrated parking brake in them. Andy added that, Our dust shields were almost toast, so we opted to get new ones from our local GM dealer parts department ($19.70). Keep the old dust shields you get from the yard to match them up with the new ones from GM. Why? They made two different versions- on the S-15 the calipers will be at the 2:00 position and on the Jimmy and Envoy they will be at the 11:00 position. They work equally well, so there really isn t a more desirable location, though aesthetically one may ap- Prior to installing the backing plate, inspect and regrease the cam for the parking-brake mechanism (rubber piece on the bottom of the plate). Line up the dust shield and backing plate and bolt up to the rearend. Place a new parking brake shoe- also available at your local parts store or dealerover the backing plate, ensuring that the open end lines up properly with the piston mechanism on the bottom of the mounting bracket. This is how the backing plate and the dust shield should be oriented to mount on the righthand axle. (Parts shown from the axle side.) Page 49

5 After disassembling your current drum brake setup, the previously pictured parts will simply bolt onto any 65-and-newer 8.2-inch, 8.5-inch 10- bolt, as well as 12-bolt rearends. This setup will also work on a 64 rearend, but some of the steps are different (see sidebar). A mockup of the installation shows how it is done. Start by removing the axles and replacing the current wheel studs with new ones at least 1-inch longer. Next, slide the bearing retainer, backing plate, and dust shield onto the axle as shown here for the driver side (left), and slide the axle into the rearend. Use stainless-steel Grade-8 bolts with lock washers, and bolt the axle to the axle flange. Shim as necessary to center the caliper and torque the axle flange bolts to 35 ft-lb. After you have slid the rotor onto the wheel studs, mount the brake pads into their retaining cage and place them over the rotor. Bolt the retainer bracket to the backing plate using lock washers. pear better than the other, depending on the owner s preference. The rotors are a really nice design, measuring inches in overall diameter. They also feature an integral drum-style parking brake that lends itself well to adaptation to earlier cars. The calipers are a fairly conventional full-floating, single-piston design that may not be as exotic as some aftermarket units, but are very effective and light-years ahead of the drums you re replacing. Slide the new caliper over the pads and bolt it to the retainer plate. At this point, you are ready to install new brake lines, an adjustable proportioning valve, and if needed, a new master cylinder. Master Cylinders, Proportioning Valves and Lines As the scope of this article is limited to getting the brakes on the rearend of your choice, you are left to sort out the many options in the 50 Page

6 The dust shields, calipers, rotors, and pads can be purchased from your local dealer or parts supplier, and we strongly recommend that these particular parts be new items only. areas of master cylinders, proportioning valves and brake lines. Every case is likely to have unique requirements that are beyond the scope of a single magazine article. Depending on the year of your particular Pontiac and the configuration of the front brakes, you may be able to work with what you have or you may have to upgrade. In either scenario, it is imperative that the front and rear brakes work efficiently and in harmony with one another and it s your job to make sure that happens. For safety s sake, make sure that your brake lines are in good condition. Replace whatever is needed to ensure they are all up to snuff. A modern master cylinder should be used. If your car came from the factory with a disc/drum setup, The caliper we purchased at our local dealer was a remanufactured unit that set us back $36. It is a full-floating single-piston unit that will be a huge improvement over the factory-installed drums. Page 51

7 Diagram of the entire S-based truck rearend shows a partial view of the braking system. From here, one can see how easily the backing plate can be adapted to an older rearend, as the mounting flanges are the same. This simple point is what makes the entire swap so straightforward. 52 Page

8 you ll be able to re-use the stock unit, provided that the egg-shaped pressure-booster in the rear lines is removed. Its job is to increase the line pressure to the drums, as they require more pressure to use than the discs. It is not required with rear discs. From there, installing an adjustable proportioning valve will help you tune the proper front-torear balance. You won t need to remove the proportioning valve at the master cylinder, though an adjustable proportioning valve will need to be downstream of the distribution block. A Wilwood unit will cost between $41-$83, depending on whether you want a lever (PN ) or more economical knob style ( ). Andy s is mounted on the frame, near the front of the side rail. If you have a four-wheel drum system and are upgrading to discs up front as well and would like to go the aftermarket route, Stainless Steel Brakes, Wilwood, Baer Racing and countless others market affordable, high-quality master cylinders that will work in your particular application and generally run around $200. In Imran s case, he used a 1976 Corvette master cylinder because Corvettes came with four-wheel discs and it looked stock at a casual glance. The system has proven to be completely effective and reliable. Follow along with the photos and captions to guide you along with this clever mixing of old and new. This exploded view of the S-based truck caliper shows the single piston, O-rings, pads, retaining cage, and various fittings and fasteners. These are available new from GM or remanufactured elsewhere, and the price difference is substantial. Though the design of this last exploded view is slightly different, it shows what you will see after removing the rotor. The rotor s integral parking brake drum hides the shoe. GM sells all of these pieces as a kit for $ per side. Page 53

9 A, B and F-body Rear Disc Conversion Parts and Prices TrailBlazer, Envoy, Jimmy, Blazer, S-15 trucks and SUVs LH Caliper $ RH Caliper $ Rotor (2 Required) $ each GM DuraStop (Replacement Series) $ Note: This part number is no longer available from GM. Brake Pad Cage (2 Required) $ Brake Pads (Pair) $86.00 LH Backing Plate $ RH Backing Plate $ Shoe Kit (2 Required) $44.00 LH Backing Plate Kit* $ RH Backing Plate Kit* $ Brake Fluid $9.00 Miscellaneous Flexible brake line Wheel studs 1-inch longer Axle studs 1-inch longer * Includes all components shown in diagram 14 By contrast, at our local parts store we paid $36 each for calipers, $36 each for rotors and $19 for a pair of brake pads. True, they weren t genuine GM parts, but that is a huge premium to pay at the dealer. Conclusion Once everything is actually bolted to the rearend, there are still a few things to do. To finish up, cut the existing brake line, install a threaded coupler and flare the line. Attach flexible brake line to the coupler. Here you may want to fabricate a bracket to hold the flex line to the rear end. Next you can set up the parking brake. Imran was able to retain the factory cable. With this rear-disc conversion completed and installed, your Pontiac will enjoy the braking improvements of a modern, rear-disc design that uses inexpensive, readily available parts available at most auto-parts stores. There s nothing quite like taking all of the R&D used on late-model GM vehicles and applying it so directly to an earlier Pontiac. PP 1964-and-Older Rearends Andy Pooni used a bolt rear in his car, so he had some additional issues to overcome. Since these have pressed bearings, some more steps are required. The pressed bearings are sealed and there is no separate retainer plate to hold the bearings in the rear. So he needed to take the old drum-brake backing plate and cut out the material that mounted up against the axle. Slide all the parts over the axle in reverse order of final assembly and then press on the bearing. Other than this particular bit of cutting, all else is the same. 54 Page

10 Classic Pontiac Rescue It s Not Just Any Old Car, It s Your Pontiac... Classic Pontiac Rescue, LLC 730 N. Main St. Honea Path, SC Find Us on Facebook Imran used a brake-line bracket from the front of a Chevy 3/4-ton truck. He slid the line through the hole in the bracket and used a retainer clip at the coupler to hold it to the bracket, just like the factory does for front brake lines. He then drilled holes and bolted the bracket to the shock mounts on the rearend. He then hooked up the lines and bled the brakes. Next he attached the original parking-brake cable to the parking-brake cable on the backing plate and checked for proper operation. Page 55