Brake pedal sinking at stop light. no leaks in system! looks like elec. master cyl.

Hi,... as for the popping sound,need more diagnostic input,like >>>what are you driving>>> given what you have on brakes ...1- check your master cyl. under the hood for fluid level , if ok, 2-with the vehicle in park & running,step on the brake about half way down rapidly about 10 times , done pumping the pedal up, stand on it and hold a great deal of pressure on it , does it slowly sink to the floor ??? if so,replace master cyl.if it holds , you have air in the system from a leaking wheel cyl./brake line/caliper ??? good luck !!!

master cyl

I would look for any leaks at each wheel and if no leaks master cylinder is no good.

Losing fluid somewhere or losing pressure in the master. Will need to be serviced by a shop. Can't drive it this way.

Not likely that the booster is an issue. The booster would not be able to overcome the brake fluid compression.
First open and inspect all brakes for leaks, adjustment, etc. Check all brake lines.
So if no leaks, did the fluid go low in the MC? If so, pad consumption would eat more than a MC reservoir of fluid, and not require MC replacement, but rebleeding and top up of fluid. If the pads are worn, and you replace them, often this will expel air back through the MC.

If you determine the MC is faulty, bench bleed the new one before install, or you will have lots of problems getting air out....

It sounds like master cyl. is drawing in air causing prob. also another test would bee too bleed out and get pedal back, now step on pedal and hold firmly and see if pedal creeps near floor indicating innternal leaking in master cyl. also have some one pump bakes slowly aand look for air bubbles in brake res. after bleed out indicating master cyl. is drawing air upon release of pedal.

Check the rear brakes are not leaking, or have air in the fluid feed line.
If above OK, it's probably caused by a faulty master cylinder.
(To check :- Slacken off the master cyl feed to the front (then rear) brakes, and observe if any fluid is being delivered - if not it is definitely a master cyl problem).

sounds like your master cylinder is beginning to internally bypass. By releasing and re-applying the pedal you are essentially "pumping" the pedal, to regain pressure. A quick check is to apply moderate pressure to the pedal and hold it. If the pedal begins to sink, replace the master.
Also check everything for small leaks that slowly bleed system of fluid and permit air to enter. (especially wheel cylinders and backside of master cyl.)

Sounds like your master cylinder is shot. Go to a parking lot, stop, and pump the pedal a bunch of times. Then get out and see if there is any fluid leaks by any of the wheels. That would indicate a brake line leak. My first guess, however, is your master cylinder.

1st need to know where the leak is? Is it a rusted line, or? To bleed after repairing leak, do the following: Have a helper start the Jeep, go to the wheel the greatest distance from the master cylinder, have helper pump brake pedal 3 times, pushing down about 1/2 way on pedal each time. 3rd time, he should hold pedal at 1/2 way down point while you open bleeder to let air/fluid out. As flow is about to stop, close bleeder. Repeat til all air removed. Check master cyl and refill often, because if you draw in air, you have to start all over. Go to the next wheel that's now the greatest distance from master cyl, repeat, til you get to wheel closest to master cyl. Done!!