Rear Disc ABS Options

[wish4hemi]

Were rear disc brakes on the 2001.5 and 2002 trucks only available with all-wheel anti-lock brakes? Or were there rear disc trucks made with rear wheel anti-lock (RWAL) only? I'm wondering how folks handle the drum to disc axle swap in regards to ABS as it seems like most of the rear disc trucks I've seen have all-wheel anti-lock. Is it prudent to run rear discs with rear wheel anti-lock only? This situation might exist if putting a rear disc axle in something like a 1999 truck with RWAL rear drums.

[Tractorman]

1 hour ago, wish4hemi said:

Were rear disc brakes on the 2001.5 and 2002 trucks only available with all-wheel anti-lock brakes? Or were there rear disc trucks made with rear wheel anti-lock (RWAL) only?

 

Here is what I recall.

 

All trucks from 1994 through 2002 have disc brakes on the front axles.

 

1994 - 2001   -  front disc brakes and rear drum brakes, rear axle anti-lock brakes only (not independent rear wheel anti-lock)

2001.5 - 2002 - front disc brakes and rear disc brakes, four wheel independent anti-lock brakes

 

2 hours ago, wish4hemi said:

Is it prudent to run rear discs with rear wheel anti-lock only? This situation might exist if putting a rear disc axle in something like a 1999 truck with RWAL rear drums.

 

I think the answer is yes.  I believe the RWAL system uses a single sensor at the ring gear location - not a sensor at each rear wheel.  It would seem that the ABS controller would not know whether or not the rear brakes are drum or disc.

 

- John

[Mopar1973Man]

@Tractorman is correct. Either RWAL or ABS will only have the single sensor on top of the rear diff to measure speed. Just a matter of hooking up brake lines and parking brake cables.

[wish4hemi]

I wonder if the RWAL module under hood is "calibrated" for drums in the way it modulates fluid to the rear when necessary. I might also wonder if the height sensing proportioning valve typical on drum-equipped 2500 8,800 GVW trucks would need to be removed with rear discs.

 

It looks like the master cylinders between drum and disc trucks are different as well according to the parts books. Raybestos lists MC390426 for the 1999 (rear drum, 1.250" bore) and MC390732 for the 2002 (rear disc, 1.313" bore). 

[Mopar1973Man]

I would upgrade the master cylinder for sure. 

 

I'm not sure about the ABS system.

Edited June 9, 2023 by Mopar1973Man