04 dodge 3500 dually , while setting at a stoplight with the brake applied the brake peddle starts to pulsate like its trying to throw up, then the peddle goes down. Only did it a few times, other wise the brakes work ok. The front pads are in good condition, the rears are new . Whats up?

If it were mine, I'd run to the dealer and have the ABS system scanned. 2¢

Robert

You do have an ABS problem there. Probably the unit, take it to the dealership and have it diagnosed. Those trucks use the ABS for the vehicle speed so you do need it.

I dunno. How does the ABS make the pedal drop? More like a MC bypassing internally.

By releasing pressure as it pulsates.

The interesting thing is that while slight pressure is applied , just what you need to hold the truck at the stop light , the peddle starts to push back up and then pulsates as I said like it's going to throw up , then the peddle sinks down . How does the ABS work with vehicle speed?

The abs module uses the wheel speed sensors and then broadcasts that info to the pcm and cluster.

I have replaced a lot of abs units in the early Genesis cars for that very condition. You would think it's a master cylinder but it's not.

Sounds like your hydroboost is suspect. Look at the ps pump pressures and or the booster

Mentioning power steering is interesting. When my rack developed a seal leak the power steering fluid went low. When the brakes were applied the pump would wine. Wondered why the brakes would be somehow connected to power steering.

They absolutely are connected. The power steering pump operates both.

Pressure comes out of pump and goes to hydroboost on the firewall. From there it goes through the booster and down to the steering box.

I don't see the hydro boost unit causing the pedal to push back like that. That is something an ABS pump would do.

Also you say the pedal goes down after this happens but you didn't say if it goes down to the floor, lower than normal or just back down where it was.

What kind of noise does it make when this is happening?

it goes down more than normal , still have brakes. No noise or change on engine sound that i recall.

Guess it depends on what exactly it feels like, which we can't tell over the Internet.

I can say that mine was pulsing a bit. It's a lighter, but faster pulse than ABS. if and pulsing is like a runner breathing after a 100 yard sprint 'deep and heavy' then what I was feeling was like a dog panting--rapid and shallow.

Don't know how else to describe it, but it was absolutely due to a failing hydroboost and weak PS pump. My guess was the failing hydroboost put debris into the system and killed the pump. I replaced the pump, the steering gearbox, the hydroboost all at once, and flushed out the lines and PS Cooler. Pulsing pedal went away after that, never touched the ABS stuff