|
|
|
| Mopar A-Body cars often came equipped with 9" or 10" drum brakes. While these brakes might seem adequate for those people who have never driven a better-stopping vehicle before, there is much room for improvement. A-Body slant six cars produced from 1960 to 1972 were generally equipped with drum brakes along with 13" wheels with a 4" bolt circle (BC). Since the majority of A-Bodies were equipped with the slant six engine, the majority of A-Bodies until 1973 came equipped with 9" drums on all four wheels. All A-Body drum brake vehicles use the 4" BC. In 1973 and later, some A-Body cars were equipped with disc brakes which then included 14" wheels with a 4½" BC. The type of disc brakes on the earlier cars with the 4" BC was the Kelsey Hayes (KH) disc brake, which used a 4-piston caliper. In 1973, besides changing to the 4½" BC, Chrysler switched to the single piston, slider style of caliper on A-Body vehicles. The 1970-1974 E-Body and 1970-1972 B-Body vehicles used a similar single piston caliper that instead slid on pins. Chrysler made 3 different sets of front drum brakes for A-bodies: 9"x2½", 10"x2¼", and 10"x2½". The 9" drums were standard on all six cylinder cars from 1960-1973. The 10"x2¼" were standard on V8 cars from 1965-1972. Although Chrysler's press releases stated that 10" drums were standard equipment on all 1965 V8 Valiants and Darts, many 1965 V8's were delivered with 9" drums, The 10x2.5" brakes were standard on 1973-1975 V8 cars. Federal law mandated front disc brakes on all vehicles in 1976. Although it might logically seem that the 10" drum brakes were similar, early 10"x2¼" brakes and the later 10"x2½" brakes do not have any common hardware. The backing plates, drums, and spindles are different between these two brakes. Nothing interchanges between these two brake systems. Replacement parts for the early Mopar A-body cars can sometimes be hard to find. NAPA seems to have discontinued some parts, especially parts for the Kelsey-Hayes disc brakes. Centric Parts still carries a complete line of replacement brake parts for the early Mopar A-body cars. Other general Mopar braking system information sites:
While not specific to Mopars, the following sites have some excellent braking information:
1960 - 1961 A-Body BrakesThe 1960 to 1961 A-Bodies had unique suspensions and little is known about upgrading the brakes of these vehicles. The main difference with these early cars is that they had different pitman, idler, upper ball joints, and drag link, possibly also different tie rod ends. Torsion bars are same length but adjustors are located differently. Since the spindles and upper control arms are the same as the 1962-1972 vehicles, it may be possible to do the upgrades relevant to those later vehicles. 1962 - 1972 A-Body BrakesAll 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 UpgradeTo 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 UpgradeIt 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 UpgradeThe 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:
Kelsey-Hayes BrakesWhile researching disc brake upgrades for KH disc brakes, I came across the following article: http://www.allpar.com/history/mopar/disc-brakes.html. 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. Layson's Restorations, the Paddock, (and possibly others) carry 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. Unfortunately, the B-body caliper does not fit the A-Body spindle. 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:
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.
Kelsey-Hayes 4-piston calipers are still 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 will not interchange with Bendix-style 4-piston calipers. Early Mustang (1965-1968) disc brakes are almost identical to Mopar K-H disc brakes. As a last resort, you may consider redrilling 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. Repairing Kelsey-Hayes 4-piston braking systems:
Early B&C-Body BrakesAccording to Mike Martin (Mopar Suspensions, S-A Design Books, 1984, p. 66):
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 UpgradeThis 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:
Slider disc brake conversion information:
As an alternative to buying used parts, complete new kits are available for this conversion:
1973 - 1976 A-Body BrakesFrom 1960 to 1973, 9" drums were available as standard brakes for six cylinder cars. Although the 9" front drum had similar dimensions to the 1960-1972 models, the spindle was changed to be common with the new 10" drums of 1973. In 1973, the suspension was modified to use the B-Body ball joints, which were used on 1962-1972 B-bodies and 1970-1974 E-bodies, which included new spindles and a new common UCA and ball joints for all brake options. In addition, 10" drums were widened (2¼" to 2½") and the disc brake rotor was changed to a unicast design (integrated hub and rotor) although the 11" disc diameter remained the same. Because of the revised spindle design, the 11" A-Body rotors may be upgraded to 1973 and up B-, F-, J-, M-, and R-body 11¾" rotors. These larger rotors can be installed on any 1973 and later unicast rotor disc spindle if the proper caliper adapters need to be used along with 15" wheels. In addition, 1973 and later B-Body disc brake spindles may also be used to in place of A-Body spindles. Please refer to the Big Block Dart Spindle Comparison page for more information.
Drum to Disc Brake UpgradeIf you already have a 1973 and later A-Body, a disc brake upgrade is quite easy. The following parts will be required:
11¾" Disc Brake UpgradeIf you already have a 1973 and later A-Body, a 11¾" disc brake upgrade is also quite easy. Pin-type brakes may also be used but these items are less desirable to some because of the potential for flex in the pins under very heavy braking. However, the pin-type brakes may slide with slightly less friction. The following parts will be required:
Master Cylinder Considerationshttp://www.moparts.org/moparts/picture/print/pages/Points.html
Proportioning & Metering BlocksA-body disc brake systems have had chronic problems with premature rear lockup, in addition to getting an adjustable valve, it is a good idea to try smaller rear wheel cylinders. Brake linesFor RWD mopars, all brake lines from the distribution block should be of 3/16" steel or stainless steel brake tubing.
Autoparts DistributorsBrake Manufacturers
Print Resources
Brake Questions?While there are many Mopar forums, the following Mopar forums have specific brake system subforums for A-Body vehicles:
|
|
Send mail to webmaster (AT) rasoenterprises (DOT) com with
questions or comments about this web site.
|
