for General Motor's A-Bodies
Converting to standard front
When swapping front disc brakes for your existing drums, the front brake assembly from any GM A-body from '67 through '72 will bolt right on to your '67. The following cars from 1964-1972 are classified as A-bodies:
However, the '67-'68 power brake setups utilize a four-piston caliper with a two-piece rotor and should be avoided. They are somewhat hard to find. You cannot find the 2-piece rotor new as they have not been manufactured for over 20 years due to a perceived safety hazard. There are one-piece rotor replacements available, but even these can be hard to find. The single-piston system used on '69-'72 cars is much more common and easier to locate. It is completely interchangeable with the earlier system (at the spindle level). (Read sidebar.) The disc brake rotors for these setups are 10" in diameter. ('73-77 A-body disc brake setups CAN be used, but since the ball joints are a different size and the spindles are taller, it requires some modifications. Another popular swap is to use the taller '73-up B-body spindles which allow the use of 11" or 12" disc brakes, but this requires the use of custom upper control arms. More on both of these swaps are discussed below.)
Other suitable donors include:
When you find an appropriate donor car, you'll need to get everything from the steering knuckle (spindle) out, including:
NOTE 1: If you're planning to convert a to a stock 10" rotor setup, your 14" SSIIs might not fit - even though they came that way from the factory. SSI rims will definitely NOT fit. (Be sure to read Identifying Oldsmobile Super Stock Wheels for confirmation on whether you can use current Rally rims.)
2: If the components you're purchasing are at a local swap meet,
and you want to verify the year of the parts, look at the steering knuckle.
'72-and-earlier had a two-piece unit (the steering arm bolts onto the knuckle), while the
'73 and later one-piece units had the steering arm cast into the knuckle. Make sure the
master cylinder was from a disc-brake-equipped vehicle. They are different. The
front reservoir of a disc-brake master cylinder is larger than the rear reservoir (see
photo above). The reservoirs on a drum-brake master cylinder are the same size.
NOTE 4: Read the Oldsmobile Chassis Service manual closely regarding torque specs. Some of the bolt torque specs require that the full weight of the car be on the wheels when the bolts are torqued. The upper and lower control arm bolts are two of them but there are others. If you tighten them with the wheels hanging in the air, the bushings will be squished tight (pre-loaded) so that when you let the car down, the control arms won't move to their natural position. It may sit too high as a result, not to mention adversely affecting the front-end alignment.
Converting drum brake spindles
to accept disc brakes
You might have heard that drum spindles can be modified for disc use. While this has been done by many people successfully, spending the $200-$400 on getting the correct parts from a donor car instead is still the best route. However, just for general knowledge I'm including the information you need to do this. I should also mention that I've not tried this, so proceed at your own risk.
Supposedly all that's involved is milling .750 off the pad at the top of the spindle near the upper ball joint where the spring anchor was bolted into. You'll also need to tap out the hole (the spring anchor hole becomes the caliper bracket hole) to full depth.
Swapping B-body brakes onto
While it is physically possible to put the '73-'79 A-body spindles on the '64-'72 A-body cars, this is NOT a bolt-in swap. The ball joint size and taper was changed, which means that you must use the '73-up ball joints. This will require machining the body of the lower ball joints to fit into the early control arms. Since the '73-'79 spindles are also taller than the early spindles it will require custom fabricated arms sold by Hotchkis or Global West. (See picture below.) Finally, the '73-'79 spindles will also require the later outer tie rod ends, again to match the different taper.
The bottom line is that after all this work, you will still only end up with the same size discs as if you had used the '67-'72 brakes. It would make more sense to get your hands on a set of B-body spindles with the 11" or 12" rotors. The work to install them is the same, but the brakes are bigger. (You will still need to get the custom upper a-arms mentioned above.)
Using stock A-body upper control arms with the taller '73-up B-body spindles will not work properly. Suspension geometry will be off and alignment will require over 1-1/4 inches of shims (if you're lucky) with probable steering column or exhaust interference.
However, in addition to the larger brakes, there are some advantages:
The following donor cars provide 11-inch disc brake spindles:
The following donor cars provide 12-inch disc brake spindles:
Important: There are two different types of 12-inch disc brake spindles. One
version uses a small outer bearing measuring .750. The second type uses a larger outer
bearing measuring .850. Use the large diameter outer bearing spindle.
Other Brake-related Information
|Should You Convert to
Rear Disc Brakes?
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