Vintage Pontiac - Rear Disc Brakes On A Budget - Parts Bin Binder Bash
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 1967 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/G-Machine movement. Making an early GTO accelerate like a new one is not 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-one that many 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. Also, keep in mind that with this swap the rear track will increase approximately 11/44 inch on each side, so check your tire clearance.
Canadian GTO fan Imran Chaudary, president of the Classic GTO Club of Ontario, has developed an affordable and relatively simple rear disc brake conversion for '60s- and '70s-era GM cars that uses parts originally designed for '98-'02 two-wheel-drive compact GM pickups (Chevy S-10/GMC S-15) and SUVs (Chevy Blazer/GMC Jimmy and Envoy). The system works fo 8.2- and 8.5-inch 10-bolt and GM 12-bolt rearends. Imran has this system in his street-driven 11-second '69 GTO (a former HPP Shootout participant) and has racked up four 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 like these brake systems will be overtaxed with even the weight of a late-'60s Bonneville.
This setup is also going into club treasurer Andy Pooni's Pro Touring '65 GTO. Other club members have used this combo for their own cars and have recorded similar results. Best of all, the conversion won't break the bank and is fairly simple to accomplish.
"It's really amazing how well these new parts go together with the older rearends," Pooni says. "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 Caprice is an outgrowth of the '73-'77 A- and G-bodies, which were closely related to the '64-'72 A- and G-body platforms, you begin to see how that 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 Chaudary or Pooni 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 two-wheel-drive S-based compact pickup trucks and SUVs between the years of 1998 and 2001. Rear disc brakes were available on some as an option and as standard equipment on higher-end vehicles. "When Andy and I searched our yard, we removed parts for his '65 GTO from a '98 Envoy, and I removed mine from a '99 Jimmy SUV," Chaudary says. "The yard had already taken off the rotors and 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 rearends 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 to remove the C-clips.
This will allow you to remove the four nuts 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 even though everything else can be purchased fairly inexpensively from your local GM dealer or parts retailer, the plates are quite expensive new, listing at $74.06 each. And it's one of those situations where used versions for $50 or less per pair at your favorite salvage yard will work just as well. These backing plates also have an integrated parking brake in them.
"Our dust shields were almost toast," Pooni says, "so we opted to get new ones from our local GM dealer parts department ($19.70 U.S.). 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 appear better than the other, depending on the owner's preference.
The rotors are a really nice design, measuring 11.625 inches in overall diameter. They also feature an integral parking brake drum 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.
Master Cylinders, Proportioning Valves And LinesAs 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 areas of master cylinders, proportioning valves and brake lines. Every case is likely to have unique requirements that are beyond the scope of a sin-gle 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. Either way, 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 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, you'll be able to reuse 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-to-rear 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 $40-$80, depending on whether you want a lever (PN 260-8420) or more economical knob style (260-8419). Pooni'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 Chaudary's case, he used a '76 Corvette master cylinder because Vettes came with four-wheel discs that year, 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 learn more about this clever mixing of old and new.
Special thanks to Jason Walton at Randall Farnsworth Group for providing the GM part numbers and prices.
Once everything is 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.

Photo Gallery: Vintage Pontiac - Rear Disc Brakes - High Performance Pontiac Magazine

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