Abs light comes on at times and at times the

Sounds like the power brake unit has failed.

You have a abs problem. Most likely a wheel speed sensor. Have system scanned for codes. The reason the pedal pushing back is system detected a skid. Brakes should work fine though

that is abs,it will shutter when working hard

I think I would get the body computer scanned for trouble codes and find out why the ABS warning light is on first.
The hissing noise usually means the booster is leaking vac but if the booster was faulty the brake pedal would be hard to push.

If the ABS system were the problem, the ABS warning light should come on.
So I would say the problem is with the vac booster. The booster is between the pedal and the master cylinder. It uses vac to boost the pressure applied to the master cylinder by your foot.
You may have to leave the vehicle with a mechanic to drive until the problem occurs.

take it to an accredited brake specialist shop
I suspect that the brake booster is becoming defective and the small application to the pedal causes excessive booster reaction
the abs section only maintains applied brake fluid pressure as set by the position of the pedal
that is to maintain the pressure as the stopping and start movement of a skidding wheel opens and closes a valve to that wheel /s
if you are on ice that sudden hard braking will cause the wheels to lock and immediately the abs cuts in to allow the wheels to turn and then to allow brake action to be reapplied
if the abs is working under brakes you will get a pulsating feeling under your foot as the fluid pressure is alternation between full on and released by the abs valves

There's a service bulliten about that problem with rust build-up on the front hubs pushing the sensors out of posistion [ most common on the pickups in areas that use road salt ], it happens mostly at very low speed. The best way to find out the problem is to have the system scanned.

with the sound of air when applying the brakes, sounds like a bad power brake booster, located behind the master cylinder,large round peice

Its the abs sensor, if you encounter an ice patch or snow you won't even be able to stop because the pedal will will push back and make the rip grind noise. If you pull the ABS fuse out, you won't have ABS but you can stop and you won't have the grind noise and back pressure for now. Its safer to not have ABS when the sensor is faulty.

Simon Atari
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