Brake pedal that lessens when the brakes are applied

Hi and thanks for using 2CarPros.com.

A vacuum leak to the brake booster will not cause the brake pedal to reach the floor. In reality, it could make the brake pedal harder to press.

If your brake pedal goes to the floor, confirm the master cylinder is full and there are no leaks. Here is a link that discusses the pedal going to the floor:

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Now, if you find the brake fluid in the master cylinder is low, I suspect that the fluid is making its way into the brake booster. The master cylinder (MC) is mounted to the booster. What I have seen happen is this. The pistons in the MC begin to leak and allow fluid to bypass them. As a result, often times the fluid will leak from the rear of the MC where it mounts to the booster. The booster then begins to fill with fluid. If you find this is the issue, here are general directions for replacing the MC:

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Additionally, I have attached an exploded view of a MC for you to see. Look at numbers 10 and 11. They are the pistons I referred to earlier. If brake fluid bypasses them, that will allow the pedal to go to the floor and possibly leak fluid into the booster.

I hope this helps. Let me know what you find or if you have questions, and remember, brakes are not something to ignore. This needs be taken care of. I will be here to help if needed.

Take care,
Joe

Hi again:

The fluid should not be green. Can your mechanic flush the system and then properly bleed it when it is done? I have to be honest, maybe someone contaminated the fluid with another product.

Jeff, I need to know something. Are the rear braked drum brakes or disc brakes? Either one was an option. If they are drum brakes, they could be totally out of adjustment which will cause a low or soft pedal. The only other thing would be to have someone watch the rubber brake lines where they attach to the brake calipers. I have see situations where they have broken down and when the brakes are applies, have actually expanded like a balloon.

Again, if there are no leaks, the master cylinder is new, the wheel cylinders and calipers are not leaking, the rear brakes are properly adjusted, your mechanic properly bleed the brakes and the new master cylinder, and there is actually brake fluid in the system and not something other, they should work.

Let me know about the rear brake type. Additionally, check to make sure (if the rear are disc brakes) the pads are not frozen in the caliper mount and the brakes work when you apply the brake pedal.

I will watch for your reply,

Joe

Joe is one of our best! Use 2CarPros anytime, we are here to help. Please tell a friend.

Cheers, Ken