1990 XJ ABS pump

Ok heres the deal... When I turn the jeep's key to the on position in the morning I can hear the bbbbbbbbb of the abs pump for a few seconds. Every time I step on the brakes, i hear bbbbbbbbbbbb. If i am applying steady braking pressure i hear a bbbbbb 5 seconds bbbbbb 5 seconds bbbbbb repeat... if i apply moke brake pressure there is a longer bbbbbbbbbbbbbbbbb. Brakes stop the vehicle just fine. It seems like the ABS pump is acting like a GM hydroboost system of sorts... Normal? oh yeah, please forgive my ignorance, I just had my virgin renix cherry popped when I bought this jeep last week.

Chris

Stats: 1990 XJ Laredo, 4.0 NP242 ABS AW4 Cruise control 207k on the clock :wantyou:

yes its normal for the pump to run. does it on my 1990 as well. your specs are exactly the same as mine haha

You should be able to apply brakes 3 to 5 times before the pump would start its cycle.

Based on your description, it definitely does not sound like a normal operation of the system. This is a typical symptom of a bad accumulator: the round/spherical tank next to the master.
In this present condition, your pump is working too often and may (will) also fail soon due to overheating.

To replace the accumulator: with the key in the OFF position, relieve ABS pressure by depressing the brake pedal about 50 times (just to be safe). Grab the accumulator with a big vicegrip or channelok or oil filter wrench or other suitable tool and unscrew. Replace with new/good unit. There should not be any brake fluid loss. Turn the key ON and wait for the pump to build-up pressure. Check for leaks. Wear safety glasses, just in case…2000+ PSI.

My final recommendation: do a search here on problems and replacement of the whole system (Bendix ABS) with a standard brake booster/master cylinder. I had my share of problems, fixes and money put into this horrific system. Over the years, I had multiple failures of the accumulators, wheel sensors & pumps. I kept it as long as I could but my last and final incident (strange modulator behavior/cycling which I couldn’t diagnose or reproduce) convinced me to install a system which is safer for me and for others on the road.