How many are driving around out there with no rear brakes?
And I should point out that ABS valves don't like water-filled (old) brake fluid.
This is a known and extremely common problem with 1-channel RABS. The reservoirs fill with rust, disabling the rear brakes with no "lights" or symptoms (aside from poor braking). Your 3-channel ABS may be different, but I doubt it. Other hydraulic parts don't like it either, but they are a bit more obvious.
As MAKG points out, and has been well-documented throughout the many threads in "brakes" category, the ABS valve, or more technically correct, the ABS Hydraulic Unit mounted on the frame just below the driver's clutch foot is a real sleeper relative to operation, or lack thereof, of both rear brakes.
I recently started a repair project on my 92 2WD ranger, thinking I had a rear right bearing freeze up. Upon removing the brake drum, a number of metal pieces of the brake adjustment system fell out on the garage floor. They were well worn at whatever place they were dragging on the drum, and were the obvious cause of the overheating (smoking) drum/axle on the right side, rather than the bearings.
Well, as I put everything back together with a new wheel cylinder, new brake shoes, new parts kit, and new drums, I wasn't able to get any brake fluid out of the bleeder valves on either rear wheel. Lots of research on this forum resulted in identification of the ABS Hydraulic Unit to be the likely culprit, seizing up over time, probably from moisture in the brake fluid, and preventing brake fluid from flowing past the unit to the rear brakes. Obviously, the front discs were the only stopping power for the truck for a good long time.
I would think that if no one hardly has the need to change fluid or bleed brakes, then a lot of Rangers are running around out there with no rear brakes, and they don't realize it.
Am I making more out of this "hidden" problem than I need to? It just scared me, apparantly getting little press unless you go hunting for it or have a specific need to be bleeding the rear brakes.
Hope this enlightens.
Regards,
Ron
92 Ranger
2WD
2.3L