Hydrovac if you step the break and hold it for few mins. the break start to go down. i check the brake master there is no leak. any suggestions?

1-change brake master cylinder it has damage o rings that losses break due to its age

2-also try to check all hoses pipes for break oil leak include under car pipes that connect master cylinder to the rear wheels

3-check pressure pipes that connect master cylinder to cylinder head

regards

check the brake pads. When they start to wear down, they can have extra play in the pedal causing you to have to press further or pump them. If they are still loosing pressure, check the fluid levels and check again for leakage all through the lines, both front and back.

Try to check your HYDROVAC assembly.. remove assembly and detach brake master, see if there are fluids present on the accumulator tank of the hydrovac. replace brake master rubber caps or brake master assembly.

Hello and welcome to FixYa!

When you open be bleed valve, does the fluid flow solid when brakes are applied? If yes then the problem will be on the hydrovac. You can have a vacuum leak that's why the brake pedal stays on the floor. If the fluid is not solid then you'll need to bleed it out some more. You may need to replace the hydrovac to get your brakes working normally again.

Hope this helps and thank you for using FixYa! Have a good one!

your problem could be the Master Cylinder,first check the wheel cylinders for leaks if there are no leaks,then bleed the brakes.if that dosen't work replace the Master Cylinder there are steps to bleeding the Master Cylinder instructions come with it.

U are going to need a new brake master cylinder, the internal seals are leaking and allowing the fluid pressure to leak down, this why the sinking pedal

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!!

The fluid level will drop when the brake pads and or shoes wear thinner. A good way to check for a hydraulic fluid leak is Shut engine off step down on the brake pedal and hold it for 3 minutes. The pedal should not slowly drop. It will go down and hold.

Look for a valve in the hose connected from the brake master's hydrovac going to your engine's intake manifold . check if it is still working, the valve traps the vacuum from your manifold to the hydrovac. Replace valve if air passes it on both sides.

make sure no leaks are on the hydraulic lines. if there are no leaks, the prob is with the diaphragm of your hydrovac system, which needs to be replaced as an assembly along with your brake master cylinder.