MotorTraxx Techline

(HMCC Web Editor's note: One of the best things about the Web is it allows people to work together across time and geography. Dan Stern wrote to add some details to Bob's original article. I've included Dan's comments using a round symbol and italic text. You may reach Dan Stern via The Internet Slant Six Club)


For the A-body cars, I will deal with the 1963 model years and newer.
  • The '62 is exactly the same car, suspensionwise, as the '63-'72. The '60-'61 differs.
    The 1963 and 1964 models were only offered with drum brakes in the 9x2 1/2" configuration. The 1965 through 1969 models were offered with both 9x2 l/2" and lOx2 l/4" drums.
  • The '65 through *seventy-five* models were offered with both 9 x 2.5 front/9 x 2 rear and 10 x 2.25 front and 10 x 1.75 rear drums. There are '73, '74 and '75 A-body cars with 10" brakes with small bolt pattern from the factory.
    This is a simple upgrade if your car does not have the 10" brakes. The ball joints are the same, just swap the complete assembly.

    The next A-body configuration is the disc-brakes. These were available 1965-1970 as the same interchange.

  • Actually mid '65 through '72 used the same small-bolt 4-piston Kelsey-hayes disc brakes, with the *only* difference being that the '71-'72 cars used RH threads on the lugs on both sides of the car.
    The 1971 and 1972 cars are the same part with the 1973 and up the 4 1/2", bolt pattern.
  • This is a completely different, single-piston setup which also is used on the F-bodies (Aspen, Volare). There are quite a number of swaps and parts optimizations possible within the '73 and up disc brakes.
    It is possible to swap any of the A-bodies to disc brakes by using everything between the upper and lower control arms. When going from a drum to disc front brake setup, it is easier to buy the Mopar performance proportioning valve, than to change the master cylinder.
  • This is partly correct. Disc brake master cylinders differ from drum brake items in several respects. One such respect is that it is ESSENTIAL that a master cylinder (or section of a master cylinder) used with disc brakes NOT HAVE A PRESSURE RESIDUAL VALVE!! This is a small rubber flapper valve located behind the tube seat. Its function is to keep small ("residual") pressure on a drum brake system to avoid air being sucked in at the wheel cylinders. This does not create a problem with brake dragging, because drum brakes use strong springs to pull the shoes back. Discs rely on a complete lack of system pressure and the deformation of the piston seal to pull the piston and the shoe back ever so slightly from the disc. Residual pressure in a disc system will prevent this release and cause brake wear and heat buildup. Also, disc brake master cylinders have much larger reservoirs to cope with the fact that disc brakes have a much higher fluid carrying volume. This isn't so crucial as the PR valve above, if you keep careful watch over your fluid level.
    Plumb it accordingly and adjust your bias as needed.
  • Keeping in mind that A-body disc brake systems have had chronic problems with premature rear lockup, your advice to get the adjustable valve is quite excellent.

    For all of the bodies, the lower control arms are sometimes different part numbers, though the interchange is correct. In most cases this is because of the swaybar option. A swaybar lower will obviously work on a non-swaybar car. The reverse would work, but would require the mounts to be fabricated or welded on.

    The B-bodies show the same interchange for 1963 through 1970 for the drum brakes, There are again two basic sizes. The 10 x 2 1/2" and the 11 x 3". There are two other sizes of drum brakes used on the 1965 Super Stock and Hemi cars. The 11x2 3/4" and the 11x 3". The 11x 3" Super Stock brake is different from the 11 x 3" found on other B-bodies. The 11x 2 3/4" is an interesting upgrade for the average B-body, with 10" brakes. This interchange is found on the C-bodies through 1972.

    One other notation is the fact that the drums are same (for the body) with the exception of the earlier right hand and left hand lug nut studs. My recommendation is to go to the parts house, find the Dorman counter and replace any and all studs with right hand pieces. This is not nearly as confusing to anyone removing or replacing a wheel and tire.

    That interesting interchange above will allow you to put drum brakes from the C-body cars on the B-body cars, by again replacing the parts between the control arms. If you can disassemble and put your steering knuckle (B) on the C-body parts you may come out ahead. The biggest obstacle in any of the swaps is the fact that Mopar uses three (basic) different ball joint tapers and a combination of the three on these three bodies. This must be checked when attempting the swaps. The taper brakes are not the best. If you are not seeking that must match the steering knuckle.

    To correct this problem you may redrill and retaper the knuckle to match the ball joint, or, purchase a threaded ball joint ring and weld to your a-arm and screw in the proper ball joint. This is not nearly as complex as it sounds, and will allow you to put B-body brakes on the A-body. This is only worthwhile if you plan to keep front drum brakes.

    The B-bodies are showing the same disc brake interchange from 1965 through 1969, and again if you have the parts between the upper and lower control arms, it's a bolt in. I would be careful with this swap and make sure you have the right pieces. There was a change from leading edge calipers to trailing edge calipers. Going from leading to trailing will cause the calipers to hit the shock mount in full lock turns, and damage the shocks. Check your parts and your clearance.

    The C-bodies show a completely different part interchange, but if the ball joint size can be made the same, the C's will fit on the Bs. C-body cars show the first disc brakes in 1966. [editor's note: this is not correct. See corrections below for updated information.] The two drum brake sizes are the 11 x 2 3/4" and the 11 x 3". Both were in service through 1972.

    The disc brakes were the same in 1966-1968. There was a change in 1969 and they stayed the same until 1972 when they are designated early and late. The 1973 and up are basically the same.

    I did not forget the E-body cars. Most everyone is aware that the front end of an E-body is the same as the B.

    One last message is the fact that Mopar drum brakes are not the best. If you are not seeking that concourse restoration, and you want to switch - go disc. Please be aware that when you go to swapping brakes from body to body, carefully check your ball joint taper - and your bump-steer when the swap is completed. Bump-steer can most easily be explained by having someone jump up and down on your front bumper. If the front wheels turn in and out during this process, you have created a geometry problem and it must be connected before driving. (Much more common on rack and pinion cars.)

    To sum up this column, there is an advantage to putting B-body drum brakes on a high performance A-body. But is it worth the trouble and the expense? Probably not. The good swap is the disc brake set up from the 1973 and up.

    It does not appear that the B to C swap is much of an advantage unless you are going from the 10" to the 11", and you can do that with B-body to B-body. The real value of the information is what part will fit what car and how easy will the part be to obtain. For stopping power put the discs on the early B-bodies. The last note is that the finned drums first showed up on the C-body cars in 1969. They are interchangeable.

    Bob Doty

    July, 2000 UPDATE -- Corrections on C Body data.

    Hi! My name is Barry Richard and I'm a member of the Mid-South Mopars in Memphis, TN. I recently ran across your web site and was reading the various articles on brakes and engine swaps when I ran across some incorrect data. Since I'm currently building a 65 Sport Fury convertible and just put power discs on it, I thought I'd share some things I found out.

    The 65 C-bodies first offered disc brakes, not 1966's. These were the 4-piston Lockeed, non-floating brakes, like Corvettes. 1969-1972 were single-piston floating caliper brakes and used both the one piece and two piece rotors. Most of the ones I've seen were two piece. The HOLLANDER manual cites the 1973 stuff as interchangable with the proper bearings. However, the 73 C-body rotor hub is different and no bearing we've been able to find will adapt the 73 rotor to a 69-72 spindle or vice versa. The 73 spindle and rotor will work with the existing C-body drum ball-joints and the 69-73 brackets and caliper. The 73 spindle/rotor combo allows you to find junkyard rotrs off D-100 pickups up thru 78. 69-72 rotor/spindle combo is just that. NAPA wanted $180 for a new 69-72 rotor (each). Therefore, my recomendation for 65-73 C-body folks is a 73 model year C-body disc brake setup. I also recommend the disc brake master cylinder. Most C-bodies had 11x 2 1/2-inch rear brakes and these just need rebuilt. HOLLANDER calls out late 72, 1973 disc brake spindles, but this interprets to 1973 model year. If you want power, you can use the 65-73 booster. Of note is the fact that my 65 Fury had non-power brakes with a 4-speed. The centerhole on the pedal assembly was too small for the boot on the power booster as-is. I had to enlrge it to allow the booster boot to come thru the firewall. I used a 1980 disc/drum 4-way safety valve from a Mirada and plumbed the rest. Everything in the rear is 65 Fury.

    Hope some of your members can find this useful.


    Thanks, Barry! We appreciate the help! Nice Plymouth you have there too!

    Original Posting: July 12, 1997
    Page updated November 11, 1997; July 19, 2000

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