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Rear Brake Upgrades - Wheel Cylinders

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Mopar A-body disc brake systems have had chronic problems with premature rear lockup under heavy braking and there are two options for correction: proportioning valves and smaller rear wheel cylinders. Dan Stern is extremely knowledgeable about about Chrysler vehicles and he very kindly provided the following rear brake wheel cylinder information. The following wheel cylinders fit all Chrysler rear brakes:

 

Wheel Cylinder Bore Size

Part Numbers

 Typical Applications and Notes
15/16"  
  • Stock rear wheel cylinder bore is 15/16" wheel cylinder used on all A-Body 10", 11" and 12" drum brake vehicles applications.
7/8"
  • ACDelco 18E81
  • NAPA 37236
  • Raybestos WC37236
  • United 37236
  • Wagner PN ?????
  • "in betweener" bore in case you want a bit more rear braking force.
  • The 7/8" bore cylinders are found on the rears of '71-'77 B vans and D trucks.
13/16"
  • ACDelco 18E268
  • NAPA 37696
  • Raybestos WC37696
  • United 37696
  • Wagner F113704
  • Some '60s police vehicles, got a smaller 13/16" bore to prevent rear lockup under hard braking. These 13/16" rear wheel cylinders are an inexpensive, bolt-on magic bullet that eliminates the premature rear lockup for which disc brake A-bodies have been notorious ever since they were new.
  • Results are materially better than keeping the 15/16" cylinders and adding an adjustable proportioning valve.
  • The 13/16" rear wheel cylinders are such an easy find because they're factory equipment on '90s Dakotas w/10" rear brakes on the A-Body 9" drum applications.
3/4"
  • ACDelco 18E326
  • NAPA 37863
  • Raybestos WC37863
  • United 37863
  • Wagner F123412
  • Need 'em even smaller for some reason like extra-hard brake shoe compound, super-severe service, or extra-large rear brakes?
  • The 3/4" bore units still exist because they're on the rears of '91-'95 AWD minivans.

 

Upgrading 65-72 A-Body 8-3/4" axles to 4-1/2" BC

For high horsepower applications, it is difficult to find a stronger OEM axle than the 8-3/4" that came with the early A-Body cars. When the front end is upgraded to 4.5" BC disc brakes, it makes sense to change the axle's bolt pattern at the same time to avoid having two different sets of wheels on the car.

Although redrilling the axle flange and brake drum is one option, a better solution is to replace the axle shafts with a suitable 8-3/4" axle shaft from another body style. Since all rear drum brake backing plates from the other body styles all mount to the axle flange with the same bolt pattern, this would also be the ideal time to install the rear brake you require. OEM axle shafts would have to be cut down and resplined to fit the A-Body 8-3/4" axle but aftermarket axle shafts are available to fit a wide variety of axles and brakes.

Because of the relatively low demand for these custom axles, axle manufacturers haven't (yet) a set up standard off-the-shelf parts for this conversion. Most require detailed measurements of the axle and brakes to be able to fabricate the correct part. The following manufacturers can provide conversion kits that include axle shafts, bearings, and studs:

 

Disc Brakes

Although the 1974-1975 Imperials were equipped with rear disc brakes, the scarcity of these parts makes this option an unrecommended upgrade. Aftermarket disc brake conversions are a more realistic upgrade if rear disc brakes are desired but they provide minimal additional braking over the rear drum brakes.

http://www.markwilliams.com/detail.aspx?ID=1717

 

 

Still to be added:

  • ready-made axle shaft PNs for the various 8-3/4" axle and brake combinations (Moser, Strange, etc)
  • rear wheel disc brake upgrades
  • rear brake interchanges