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Most A-bodies came with slant six engines and as a result, most A-bodies came with the minimum requirement of brakes: 9" drums on all four wheels. These are barely adequate for slant six cars, but should be considered unacceptable for V8 cars (1964 V8 A-bodies, despite coming equipped from the factory with 9" drum brakes, should be outfitted with something beefier). There are a lot of possible swaps, below is a description of all of the factory A-body brake systems and their similarities in components (ball-joints, spindles, etc).
Chrysler made 3 different sets of front drum brakes for A-bodies: 9x2.5", 10x2.25", and 10x2.50". The 9" drums were standard on all six cylinder cars from 1963-1975 (see footnote #1). The 10x2.25" were standard on V8 cars from 1965-1972 (some 1965 model V8's came with 9" drums, although it was not Chrysler's original intention. It was stated in press releases that ALL 1965 V8 Valiants and Darts would be equipped with 10" drums, however some early year V8 cars came though with the 9" drums). The 10x2.50" brakes were standard on 1973-1975 V8 cars.
All A-body drum brake cars were small bolt pattern!. From 1973 to 1975, A-bodies with drums used the small bolt pattern (5x4"), while the disc brake cars used the large bolt pattern.
To make the distinction, early 10x2.25" brakes and the later 10x2.5" brakes do not share backing plates (see footnote #2), drums or shoes. You cannot mix and match parts between these brake systems. Note the photograph below and the different appearances of the two 10" drums.
All three brake systems offered on A-bodies from 1963-1972 used the exact same suspension geometry. The significant difference between the 9" drum, the 10x2.25" drum, and the 11" Kelsey-Hayes discs were the spindles. Otherwise, all three brake systems share the same suspension components including upper control arms (UCA), lower control arms, brake strut rods, tie-rods, shocks, and ball joints. The only exception is the lower ball joint on the disc brake cars. The disc brake lower ball joint is a heavy duty version of the drum ball joint.
When rebuilding a drum front end, with a rebuild kit from PST, for example, one can opt for the 1966-1972 disc brake rebuild kit. This kit is identical to the drum brake kit except that it comes with a heavy duty lower ball joint. There is an expection, there are two holes that accept the large bolts that fasten the ball joint to the spindle. On some ball joints, these holes are threaded and on some, they are not (the author can't remember which years are which..)
To upgrade from 9"s to 10x2.25"s only the spindle and all the brake hardware (backing plate to drum) need be swapped. To upgrade 9" (or 10x2.25" drums) to the KH 4-piston discs, you'll need spindles and the heavier duty lower ball joints (using the drum brake lower ball joint would probably lead to premature ball joint failure).
For 1973-1976, 9" drums were available as standard brakes for six cylinder cars. This front end (drums, ball jounts, spindles) was more or less the same that had been used from 1963.
In 1973, for 10" drum and disc brake A-bodies, the front suspension and brakes were changed considerably. The new 10x2.5" drum brake system was introduced as well as the new unicast 11" disc rotor system (this disc system was standardized across the board for all A,B,C and E bodies in 1973). The A-body 10x2.5" drum and the new unicast discs shared the same UCA, and upper and lower ball joints. These are the same ball joints used on 1962-1972 B-bodies and 1970-1974 E-bodies. The A-body UCA is not shared with the B-bodies or E-bodies. Although the suspension geometry is the same of 1973-1976 A-bodies and 1963-1972 A-bodies, since the upper ball joint changed, the 1973-1976 UCA for 10x2.5" drum and disc cars is different than the 1963-1972 A-body UCA.
The 10x2.5" brake system was actually adopted from the 1962-1972 B-body 10x2.5" drum system, however there were several running changes in bearing diameter, wheel cylinders, and hold down kits that make interchange non-existent between the B-body 10" drums and the 1973-1976 A-body 10" drums.
The 1973-1976 A-bodies disc brakes are significantly different than the early disc brakes. In 1973, Chrysler adopted the Chrysler built "unicast" rotor across the board on all A/B/C/E-body and D-100 truck applications. This marked the end of the the four piston calipers and two piece rotors used in previous years. The "unicast" rotors were so-named because they incorporated a single casting of the rotor and hub where previous disc setups used a separate hub and rotor design.
Later in the 1970s and early 1980s, some large C-body, B-body, and R-body cars came with 11.75" rotors. These can be installed on any 1973 and later unicast rotor disc spindle if the proper caliper adapters need to be used along with 15" rims (stock 14" rims don't fit!).
One Additional note: the 1973 A-body 10x2.50"s used a finned drum, that might not accept the early factory steel rims or aftermarket rims made prior to these brakes. My American Racing slot mags fell prey to this change and can only be used with 1964-1972 small bolt pattern hubs.
1966 and earlier cars were equipped with a single reservoir master cylinder (MC). A Federal mandate required all 1967 and later cars to have a dual circuit hydraulic brake system, so Chrysler began using a dual reservoir MC. Retrofitting 1966 and early cars with a dual reservoir MC and a dual circuit hydraulic brake system is a great safety improvement and is highly recommended. All that is needed to do this is a 1967-1975 (see footnote #1) drum brake master cylinder, brake lines, and a distribution block.
Up until the mid 1970s, drum brake wheel cylinders required a small amount of residual pressure to remain in the hydraulic circuit at all times to prevent leaks by keeping the wheel cylinder seals tight against the cylinder wall. During the mid 1970s, new wheel cylinder technonlogy was introduced that eliminated this "residual" pressure requirement. If your drum brake wheel cylinders are the older design, you'll need to make sure your drum brake circuit (rear for disc cars, both front and rear for drum cars) has a residual pressure valve. Until early 1968 models, residual pressure valves were external and were fitted between the brake line and the MC. Begining in 1968, residual pressure valves were internal to the MC. Drum brake MC's used two valves and disc brake MC's used only one valve for the rears.
The fact that power assisted MC's used a different diameter piston than manual brake MC's, coupled with the fact that disc and drum MC's are unique based on the use of residual pressure valves, makes it important that the correct MC is used for a given application. Power assisted disc brake cars should use a MC designated for a power assisted disc brake application. Manual disc brake cars should use a MC designated for a manual disc brake application. drum brake cars should use a MC specifically for either a power drum car or a power disc car.
Perhaps more importantly, the piston in a manual master cylinder has a relief it it's bore that accepts and holds the brake pedal rod with a small lock rubber bushing. power master cylinders often times, do not have this relief. If a power master cylinder is used in a manual brake arrangement, the pedal rod may very well not be secured in the back of the master cylinder,,,, and can fall out!
It is also very important that a FWD master cylinder is not used on a RWD car. On RWD cars, only use a master cylinder specified for a RWD car.
One can also use the modern aluminum RWD Mopar MC's (with a plastic reservoir container). This requires an adapter plate to be purchased or fabricated to allow the modern 2 bolt MC to adapter to the old style 4 bolt MC flange. There are at least four variations of the aluminum MC's each with different diameter piston bores.
Proportioning blocks and metering blocks are a good topic for a lengthly article. Without spending too much time on this subject, here is a cursory glance with a few important points. I'll refer to this class of component as a distribution block short for distribution block. Some blocks proportion, some meter, some provide a "hold-off" fucntionality, but to lump them together, I call them distribution block.
The brass distribution block used on four wheel drum brake cars are distribution blocks. There is no front/rear proportioning functionality, nor is there a "hold-off" or any special metering functionality. Starting in 1967 or so, these distribution block intregrated a pressure sensor for an instrument panel brake warning light. If converting a 1966 and earlier single circuit system to a dual circuit system, and four wheel drum brakes are being used, a 1967-1975 (see footnote #1) four wheel drum brake distribution blocks can be used.
The distribution block on disc brake cars are a little more complex intregating, not only a pressure sensor for an brake warning light, but front/rear proportioning functionality, and in some cases, a "hold-off" functionality. Since these disc brake distribution blocks sometimes serve several functions, they are more appropriately termed "combo-valves".
For the most part, early combo-valves were brass, later combo-valves were cast iron, except in the case of pickups, where a brass combo-valve was used for most, if not all, 1970s & 1980s model pickups. Front/rear proportioning varied platform to platform and year to year due to different braking characteristics of the different size cars.
For dual circuit RWD mopar brake systems, all original brake lines were 3/16" steel (this is a special thick wall "brake line tube" or "Bundy brake tube" that is capable of handling pressures in excess of 1000 PSI). Aftermarket suppliers also offer stainless steel. Stainless Steel lines are harder to flare correctly and are hard to secure a good seal. All brake line ends should be terminated with a correct 45° double flare backed up by a male threaded nut. Compression fittings should never be used, in fact no fitting other than the OEM style 45° double flare should be used unless you are working with a brake line vendor that has assured you otherwise and you will trust with your life! Fittings, both male and female, should never be anything but 45 degree double flare specification. Brake lines should not make use of unions simply to make a brake line longer. These are not only safety measures, many of them are federal auto safety requirements.
There are several vendors that sell reproduction brake lines pre-bent. all seem to produce quality products. There were various sized tube nuts used once the dual circuit brakes systems were adopted in 1967. Prior to this, all tube nuts were 3/8" hex on a 3/16" tube with the single exception of the single large master cylinder to distribution block line. The disc brake distribution block made use of different size thread tube nuts for all ports on the distribution block. This was an effort to prevent the brake system from being incorrectly plumbed by anyone assembling or servicing the brakes. The exception is the two front disc line ports are the same because swapping left and and right wouldn't matter.
The tube nuts going to the disc brake master cylinder are different as well. One is 9/16" thread & 3/8" tube while the other is 1/2" thread & 3/8" tube. Each tube's entry into the distribution block has different thread size tube nuts as well, so there are four sized tube nuts on those two lines.
Master cylinder feed lines make use of different diameter threaded tube nuts for all four ends of those two master cylinder feed lines. Keep this in mind when plumbing your system. If you are ordered all new lines, call the vendors and ask if the lines can be made with the correct tube nuts for your application. For example, if a stock replacement 1962-1966 rear brake line is ordered and you plan to use any 1967 and later combo valve you will almost certainly have the wrong tube nut to connect to the combo valve. Rather than use adapters, it is advised to cut the end off and use the correct tube nut.
