ABS Failure (wear out after 9 years)

[glenncof]

1991 Range Rover (Classic) with 135K miles

This was tricky since it involved two components with inter-related failure.

First, the relay controlling the ABS pump stuck “on”. Since this ABS circuit is not controlled by the ignition switch the pump runs and runs. (Wife called and said there was animal under hood.) It is located under driver seat with a fuse for the circuit. Replaced it and thought I was done.

Second, the ABS Accumulator had gone bad. My manual says to replace it every 5 years (I ignored this as I didn’t know what was.) and my RR had 9 years on it.

The Accumulator is a high pressure steel ball with a nitrogen filled bladder. The ABS pump builds pressure in the bladder which provides the power assist to the master cylinder. Feels like ‘almost like’ no brakes when system fails.

The nitrogen in the Bladder leaks out over time so it can’t hold much pressure. This will cause fast cycling of the relay (this accelerated the relay failure above) and eventually the pump stayed intermittently “on” since it can not build sufficient pressure to trip the shut-off pressure sensor. Seems worse in cold weather. Pump gets very noisy (dry running?).

At the time I was using a British repair shop. They burnt out 3 new ABS pumps (finding metal particles) and tried replacing the master cylinder/bleeding whole system. Finally they gave up so I had them put in the old pump and did my homework to fix it myself.

Caution: This Bladder is very high pressure brake fluid when pumped. Pressure can be relived by pumping brake peddle. I remember it required a bleeding operation before connecting it, with bleed hose just turn on ignition for very short time. It was gradual, not high volume.

Normal operation; Turn on ignition and a werrring can be heard under hood. Red “Brake” light on dash is illuminated (just like when parking brake is set). Once the pressure reaches the set point on sensor; pump goes off and light goes out.

If brake pedal is repeatedly pushed you can here the pump start again and shut off.

I see www.AtlanticBritish.com sells ABS Accumulator for $249. My records show $262 which would have included shipping.

I have added 34K miles without a problem.