All three brake systems offered on A-bodies from 1962-1972 used the exact same suspension geometry. The significant differences between the 9"x2½" and 10"x2¼" drums and the 11" Kelsey-Hayes discs were the spindle and lower ball joint. 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 upper ball joints. The difference between the lower ball joint on the disc brake cars and drum brakes cars were that the disc brake lower ball joint is a heavy duty version of the drum ball joint.
When rebuilding a drum front end, it is possible to use 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 a difference between the 1962-1969 drum and disc ball joints and the 1970-1972 drum and disc ball joints (need to check differences!).
9" Drum to 10" Drum Upgrade
To upgrade from 9"x2½" drums to 10"x2¼" drums, only the spindle and the hardware attached to it (backing plate to drum) need be swapped. To upgrade 9"x2½" 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). The 1960 to 1964 models were only offered with drum brakes in the 9"x2½" configuration. The 1965 through 1972 models were offered with both 9"x2½" and 10x2¼" drums.
9"/10" A-Body Drum to B-Body Drum Upgrade
It is possible to use the 11" drums from a B-Body car if the spindle and related brake hardware are used along with the B-Body lower ball joint. However, the larger B-Body upper ball must also be used, which requires the installation of the 1973-1976 upper control arm (UCA). Since B-Body disc brakes are easier to find nowadays than B-Body drum brakes, there really is no point to upgrade to these large drum brakes with the other disc brake options available.
For those interested in learning more about using B-Body drums (or even C-Body drums) in the A-Body vehicle, please visit the MotorTraxx Techline Brake Upgrade page.
Drum Brake to KH Disc Brake Upgrade
The Kelsey-Hayes disc brakes are an excellent braking upgrade to drum brakes. However, these parts are relatively hard to find and are quite expensive compared to the cost of upgrading to the slider brakes of the 1973-1976 cars or of the B-Body cars.
The KH brake system had differences in 2 areas. There is a difference in the ball joints from 1965-1969 and 1970-1972. In addition, there is difference in the calipers from 1965 to mid-1968 and from mid-1968 to 1972. The KH disc brakes used the same hubs with left and right-hand threads for 1965-1972 but the 1971-1972 used only RH threads.
Upgrading to KH disc brakes is relatively easy because the upper control arms can be reused and the original rear axle may be left in place unmodified. This upgrade requires the following items:
- K-H disc brake spindles
- K-H disc brake dust shields
- K-H disc brake lower ball joint
- K-H disc brake hub & rotor assemblies
- K-H disc brake calipers & hoses
- disc brake master cylinder (MC)
- disc brake distribution/proportioning valve
- new brake lines, including a new pair from the MC if you have a single reservoir MC
- 14" wheels
Kelsey-Hayes Brakes
While researching disc brake upgrades for KH disc brakes, I came across the following article: That’s The Brakes: Restoring and tweaking 4-piston disc brakes. Near the bottom of the page (Parts is Parts section), the author mentions Goodmark Industries as a source of unicast replacement rotors for Kelsey Hayes disc brakes. However, Goodmark never actually made this part but instead bought them from a supplier who has since discontinued production.
At some time, some companies may have carried a unicast B-Body rotor for 1966-1969 vehicles. According to Tom Condran, the rotor used on the 4-piston, 1966-1969 Kelsey-Hayes disc brakes are a bolt-on (but expensive) 4.5" replacement rotor for 1965-1972 A-Body vehicles. This possibility is completely wrong as the A-Body spindle is too short for this B-Body rotor. Furthermore, the B-body caliper does not fit the A-Body spindle. Only try this if you already have this rotor in your possession.
The only available option at this time is a direct replacement part for the 2-piece hub and rotor. There are no options for a bolt-on hub & rotor in a 4.5" BC unless you have it done for yourself at a machine shop. Replacement rotors and calipers are still available but do not include the hubs:
- Aimco 5384 (rotor)
- Bendix 141054
- NAPA 86739 / (caliper kit 518)
- Raybestos 76739
- Wagner BD60257
- Cardone 18-4406/18-4407 (R&L reman. calipers)
Replacement wheel studs are different than those found on drum brakes. The overall length of these studs is 2" and the shoulder length is 1-1/16". with a 7/16"-20 thread size.
- Dorman 610-130 (RH thread, use with 611-014 nut)
- Dorman 610-131 (LH thread, use with 611-015 nut)
- NAPA BK6413148 (RH thread, and head stamped 130)
- NAPA BK6414089 (LH thread, and head stamped 131).
Kelsey-Hayes 4-piston calipers are available either as rebuilds or brand new. Stainless Steel Brakes Corporation has brand new Kelsey-Hayes 4-piston calipers available as well as their own line of high performance aluminum calipers. However, this caliper did not interchange with Bendix-style 4-piston calipers.
Early Mustang (1965-1968) disc brakes are almost identical to Mopar K-H disc brakes but have a 4½" BC. As a last resort, you may consider modifying the rotors to suit the Mopar hub. Early Mustang calipers are similar to Mopar K-H calipers as well but may need some modification to fit properly. See Early Mustang Disc Brakes on Mopar K-H Spindles and Using mustang rotors for 4.5" bc.
Repairing Kelsey-Hayes 4-piston braking systems:
Because of the growing obsolescence of 14" tires, you might want to consider upgrading to 15" wheels or larger, which will allow you to upgrade to larger rotor disc brakes.
Early B&C-Body Brakes
According to Mike Martin (Mopar Suspensions, S-A Design Books, 1984, p. 66):
The A-body will accept various components from the B-body that will improve braking. First of all, the totally inadequate, 9-inch A-body brakes and spindles MUST be replaced with either 10-inch A-body pieces or, if the upper control arm is modified (to accept the larger ball joint used on the B-bodies), the B-body 10-inch, 11-inch, or disc spindles can be installed. In either case, the B-body backing plates and shoes will easily bolt on.
If the B-Body spindles (disc or drum) are installed, the lower control arm does not have to be modified to accept the larger B-body lower ball joint - the A-body tie-rod ends will also work without modification. The upper control arm can be modified to use the large disc brakes form the Road Runner and Charger R/T. However, if you prefer to use the 11-inch B-body drum brakes, the backing plates will not bolt onto the 10-inch spindles. In this case, the 11-inch B-body spindles must be installed along with a modified upper control arm.
The A-body spindle and lower ball joint are smaller than the B-body pieces. Because of these differences, both spindle and ball joint must be changed as an assembly. And since the caliper mounts are different, the B-body calipers must be used with the larger components.
The standard rotor and hub assembly used on 1965 to 1969 A- and B-body cars is the best choice for most disc brake applications. The long lugs [which also fasten the rotor to the hub] may interfere with some lug-nut lock sets, but they add an extra measure of insurance for high-performance and competition use.
[The book shows the photo of a] 1968 Bendix B-body disc brake assembly [that] has been installed on an early A-body. The massive caliper and 12-inch rotor (with a 4-1/2" bolt circle) make an enormous difference in braking, handling, and safety. Cool air, ducted from under the front bumper is directed at the caliper to aid cooling while road racing.
Brakes even larger than the 11" passenger-car brakes (such as those used on the C-body Fury or Monaco police cars) can be installed if the socket in the lower control arm is machined to accept the larger C-body lower ball joint.
Any modifications to the upper or lower control arms, ball joints, or sockets require precision machining. The upper control-arm bearing retainer must be cut out to install the larger ball joint and a new retainer carefully welded in and machined to size. When the lower control-arm socket requires reaming to accept the larger ball joint, the same precision machine requirements apply. These specialized modifications should be left to a machine shop with stock-car or road-racing experience. ...
Even though "Mopar Suspensions" was published in 1984, the information in the above passage seems to indicate that most of the A-body section was written in 1970 because Martin isn't aware that the Kelsey-Hayes A-Body disc brakes were produced until 1972 and that the 1973 to 1976 A-Body upper control arms obsolete his advice about modifying the upper control arm to take the B-body upper ball joint.
Although Martin mentions that B-Body and C-Body spindles are bigger than A-Body spindles, he doesn't mention anything about the mounting dimension differences, which implies that they can bolt-in without having any impact on handling. Richard Ehrenberg seems to confirm this in his Disc-O-Tech article. Because the 1974-1978 C-bodies used a different suspension design with unique C-body spindles, Martin must be referring to brakes used on 1966 to 1972 vehicles.
Because of the relative scarcity of these early brake components, the best braking option is to use the 1973 and later braking systems.
1973-1976 Slider Brake Upgrade
This is the most cost-effective upgrade using OEM parts for drum brake vehicles. While the 11" diameter of this rotor of this upgrade is the same as the earlier disc brake, KH disc brake vehicle owners may consider this upgrade to obtain the more common 4½" BC for a better selection of aftermarket wheels. The implementation of this upgrade also allows the further upgrade of the braking system to the 11¾" B-Body rotor.
Upgrading to 1973-1976 slider disc brakes is slightly more complicated because the upper control arms must also be replaced. Since the front wheels now will have a 4½" BC, the original rear axle must either be replaced or modified with a new bolt pattern. This upgrade requires the following items:
- 1973-1976 slider disc brake spindles
- 1973-1976 slider disc brake dust shields
- 1973-1976 slider disc brake lower ball joint
- 1973-1976 slider disc brake hub & rotor assemblies
- 1973-1976 slider disc brake calipers & hoses
- 1973-1976 A-Body upper control arm
- disc brake master cylinder (MC)
- disc brake distribution/proportioning valve if you have a single reservoir MC
- new brake lines, including a new pair from the MC if you have a single reservoir MC
- 14" wheels
Slider disc brake conversion information:
- http://www.moparaction.com/Tech/archive/disc-main.html
- http://www.bigblockdart.com/techpages/dbconversion.shtml
- http://www.rowand.net/Shop/Tech/EarlyMoparDiscBrakeSwap.htm
As an alternative to buying used parts, complete new kits are available for this conversion: