Kelsey-Hayes / Hydromax engaging at slow speeds

[Dav L]

Symptom: Only when driving very slow (<5mph) and easing into the brakes, the pedal feels like antilock is engaging. Makes the antilock noise, pedal pulsates. Seem to be more common when the RV was started up and am making the first or second stop out of a parking lot.

Can be surprising and sometimes one wonders if the RV will stop in time. Brakes are functioning, just like if antilock was engaged on a loose surface.

Otherwise, brakes work fine. No issues when vehicle is faster than 5mph.

Some "normal" hydromax whistle when brakes are applied (even when stopped). Whistle changes pitch dependent on brake pedal pressure.

What I have done so far:

4 wheel rotors / pads replaced, new rear calipers, bled brakes, replaced rear diff speed sensor (had some metal on it), removed and cleaned front speed sensors (had lots of metal shavings on them), removed front hubs and cleaned front tone rings, disconnected and inspected antilock module connector and same wiring harness connectors aft of that (a foot further back from the module), disconnected front sensors (that turned the ABS light on - so I assume they were fine).

Topped up power steering fluid, inspected serpentine belt.

No dash lights on. Steering seems fine (shared power steering pump with hydromax).

I don't have a scan tool that will show sensor status real time, so not sure if a wheel / diff sensor is actually triggering the event. But no lights on so I assume no ABS codes are set. Issue isn't consistent, but does happen a couple of times with each camping trip.

My next steps were to find a real scan tool, and / or pull the ABS fuse to isolate that it is Kelsey-Hayes Vs. Hydromax related issue.

Any other ideas?

[mrt_1111]

I would change the brake fluid and disable the abs system and test drive it again.

[Dav L]

Brake fluid was swapped during the bleed.
Fuse is next.

Thanx