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Author Topic: Brakes: 11.75" Disc Brake Upgrade  (Read 14592 times)

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Reggie

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Brakes: 11.75" Disc Brake Upgrade
« on: January 10, 2008, 19:02:32 »

Upgrade Your M-Body to 11.75" Disc Brakes

All M-bodies came with 10.87" (AKA 11" per the Factory Service manual) front disc brakes.  The size refers to the diameter of the cast iron hub and disk assemblies (rotors) which are mounted to the spindles. Each rotor has a caliper that straddles it. The caliper is a device that has a hydraulic piston, one inboard pad (or shoe) and one outboard pad. Each caliper is mounted on a sliding assemby called an adapter, so that it can freely move in and out.  As the brake pedal is depressed, brake fuid is forced into a cylinder in the caliper which causes the piston to move the inboard pad against the disc. As the force increases, the entire caliper assembly slides inboard and pulls the outer pad against the disc to provide a clamping force. When the pedal is released, the process is reversed.  The design is self-adjusting.

As far as it is known, no F/J/M-cars came from the factory with 11.75" rotors.  However, many earlier Chrysler products were built with 11.75" rotors. Because the factory bean counters dictated that things got changed only when necessary, it is pretty easy to upgrade an M-body to the 11.75" rotors by finding parts donors with 11.75" rotor caliper adapters. The 11.75" caliper adapters bolt right up to any M-body.

Types of 11.75" Disc Brake Assemblies

There are two types of 11.75" disc brake assemblies used by Chrysler, which require different caliper adapters:
 
  • Kelsey-Hayes Pin-type - With this design, the calipers slide on pins that are attached to the adapters. The adapters measure 3.5" from the center of the "pin" holes to the center of the mounting holes.  They were never used on M-bodies, but they can be adapted if a new 1973-up pin-type caliper is also used. This design is less likely to stick, but new pins may be harder to find. Member Reggie was able to order new pins (called Brake Caliper Housing Bolts) from NapaOnline.  The stock number for a pack of two pins is 82253W.  To do both front wheels, you can order two packs (four pins) for a 1976 Cordoba.
  • Slider-type - With this design, the calipers slide on a machined surfaces on the adapter that position and align them. With the slider side resting on a flat surface, the adapters measure 3.675" (3 5/8" from the center of the mounting hole to the surface. These were used on many 1973-up B-body cars. They are the same design as the 11" adapters on all M-bodies, and the existing M-body calipers can be used on them with no modifications. Allthough this design is more prone to sticking, it works well with regular brake maintenance. Parts for this design are also more plentiful.

There seems to have been no rhyme or reason to Chrysler's choice of using the pin-type or the slider-type design. Both types were used in many different applications, so it may have been a matter of parts availability among different suppliers. Member "Dr.Jass" recalled that both his 1977 400 HP Cordoba with S13 HD police suspension and his 1979 Chrysler 300 had 11.75" rotors with pin-type calipers. He also had a 1978 400HP Cordoba with 11.75" rotors and slider-type calipers.  Member Reggie bought a 1976 Cordoba 400 parts car that had pin-type calipers.

Either setup uses the same 11.75" rotor, but when swapping larger rotors to an M-body, it's much easier (and cheaper) to just use the slider-type adapters.

Advantages to using the slider-type calipers:

  • You can keep your original slider-type calipers which are no different than those used with the 11.75" rotors.
  • You won't even need to disconnect the brake hoses (unless they need to be replaced). Just remove the calipers from the old adapters and hang them securely out of the way so the hoses aren't stressed.
  • You can also use the same size brake pads. All slider-type pads are the same size regardless of the rotor diameter. If your existing pads are relatively new, there is no need to replace them.

Sources for 11.75" Caliper Adapters:

  • Junkyard Donor Vehicles
    • 79-81 R-Bodies including New Yorkers, Newports, Gran Furys, St.Regis
    • 73-79 B-bodies including Cordobas (especially 360s and 400s), Charger SEs, Furys, Monacos and Polaras.
    • Thunderstruck's Tip: "The dust shield is the same for both rotor sizes. In fact, that's a visual clue if you are junkyard hunting. If the rotor is a bit bigger than the dust shield, it's the 11.75" rotor, if the dust shield is a bit bigger than the rotor it's the 10.87" rotor."
    • Bill55az's Tip: "Be sure to take the bolts as well, don't leave them there.  The new adapters are thicker so the bolts are longer."
  • Cass Eslick (DoctorDiff) also sells the 11.75" caliper adapters

Additional Parts Needed:

  • 11.75" Rotors - You have two options
    • Order two new heavy duty rotors for a 1978 400HP Cordoba (most brake parts companies have superseded all their 11.75" rotors to the HD ribbed unicast piece anyway).
    • Bill55az's Tip: "If you have a self pull junkyard in your area, you can get them cheap. New or rebuilt rotors are available but they are expensive and do not come with new bearings.  I have found several sets of rotors in the junkyards that are essentially new.  All have come with good bearings.  Hint, when you pull the rotors, run a wire thru them with the bearings in place so they don't fall in the dirt or get mixed up.  Bearings wear to the cups, so keep the left side bearings in the left side rotor and vice-versa.  Carry plastic bags with you, and put all the parts into the bag immediately."
  • Wheel Bearings/Cups - Order two new Timken bearings for a 1978 400HP Cordoba
  • Grease Seals - Order two new grease seals for a 1978 400HP Cordoba
  • Wheel Bearing Grease - Use only MOPAR wheel bearing grease P/N 4318064 or 5083150AA. Also pack some grease inside the hub.
  • Brake Pads - Order new pads to fit your vehicle if needed
  • Calipers - Order two new calipers to fit your vehicle if needed
  • Front Hoses - Order two new front brake hoses to fit your vehicle if needed
  • Mopar P5249088 Proportioning Valve. This will allow you to fine tune your brake system between the front and rear. This unit should be plumbed into the rear brake line after it leaves the factory Combination Warning Switch/Hold Off Proportioning Valve Assembly. Do NOT eliminate the factory assembly.

Swap Procedure:

  • Unbolt the caliper and use a piece of stiff wire to tie it up out of the way.
  • Unbolt the stock caliper adapter.
  • Bolt on the 11.75" caliper adapter.
  • Install the 11.75" rotor. You will also need to install new cups and Timken bearings.  The bearings MUST be properly packed with grease or they will seize up.
  • If you are re-using your old caliper, you should use a fine wire brush to clean the sliders first. Home Depot or Lowes have these types of brushes in their Plumbing sections.
  • Also use a fine wire brush to clean the sliders on the caliper adapter.
  • Make sure that you carefully coat the slider "ways" with Nevr-Seez or some other type of anti-sieze compound. Don't slop it on - you don't want to get it on the pads or rotors.  Just make sure the slider channels are coated so the caliper can move easily through its travel. Carefully wipe off any excess before you drive it.
  • Bolt on the caliper.

Swap Considerations:

  • The 11.75" rotors are heavier. More weight does affect mileage and acceleration, so unless you have a high performance car, your stock units are fine.
  • If you swap to 11.75" rotors, you will NOT be able to use rims smaller than 15".

Sources:

Photos:
  • Sider-type caliper adapter installed on spindle (Courtesy of M_Body_Coupe)
  • Slider-type caliper installed on adapter( Courtesy of M_Body_Coupe)
  • Slider-type caliper adapters removed from car (Courtesy of Bill55AZ)
  • Replacement caliper pins - NAPA Stock # 82253W - Brake Caliper Housing Bolts (Courtesy of NapaOnline.com. Copyright¬© 1999 Genuine Parts Company. All Rights Reserved)
« Last Edit: May 26, 2009, 13:07:59 by Reggie »
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