I have been having issues with my brake system over the last year. Started with the ABS and Brake light coming on in the dash display. I traced it to the drivers side front tone ring sensor and replaced it but all the lights came back on within a month. I think its the speed sensor in the rear diff this time but have not got to replacing it as there has been no performance issues with the brakes until now.

After sitting for a few months this spring the other day I noticed what I would describe as a rapid pulsing feel in the brake peddle under moderate to heavy braking with an electronic like buzz. Its almost like the pulsing/sound when the ABS is kicking in on low traction surfaces, except that it is happening on dry pavement with no loss of traction. It also feels and sounds different than normal ABS working...hard to describe.

So do you think this is an electrical issues related to the ABS lights and a failed sensor (either the one in the rear diff or the front tone ring sensors) or is this more likely to be a hydraulic issue such as failing hydro boost or air in the lines? The brake fluid has been changed within the last two years, new pads and rotors, rebuilt calipers pretty much everything serviced with no issues until now. I do not see any obvious fluid leaks anywhere but have not puller the rims off to look super close. Any ideas appreciated!

 

Hmm, sounds like you have a sensor reading incorrectly causing the ABS to engage. Will need to pull the codes for it if any. If no codes, the truck will need to be put on the scan tool and driven while watching the wheel speed sensor readouts. This will tell the tech which speed sensor has the issue and needs to be inspected/replaced.