Brake Pedal "feels odd"

About 4 months ago I had to have the master Cylinder replaced. I had the mechanic use the OEM master cylinder at an outrageous cost of nearly $400 plus labor.

I have noticed that the brake pedal is beginning to feel odd. After the car sits for a few hours, when I get in and step on the brake the pedal is rock hard and barely moves until I start the car. Then the assist comes back immediately and the pedal feels normal. Except that when the car is running and standing still, I can continue to apply pressure to the pedal and the pedal will continue to head to the floor slowly without a stopping point.

The mechanic that changed the master cylinder said that it is normal. I did not argue because I need input from some of you first to assist me or support him.

Does anyone have any information to assist me please?

I would be most appreciative.

Thank you!
Bob

I am not sure what is going on? maybe someone with more exp can help you but I can tell you I can not push the brake to the floor on any car that I have ever owned. Check fluid level?

If it truly sinks all the way to the floor, that is not normal. You either have a leak somewhere, a bad master cylinder, or a lot of air or contamination of the fluid.

-Rod

Sounds like I need a trip to the Dealer.

Thank you for your input.

I will let you know what I find out.

Rechecked the fluid and it is fine and clear and appears to be clean.

I think I need to head to the dealer.

Thanks for the input!

Why did you have to replace the original master cylinder? If the old one leaked brake fluid into the vacuum booster, it is likely ruined and will have to be replaced too.

It was leaking. I was told that at the time that the leak may or may not ruin the master cylinder. The mechanic had told me that there wasn't much fluid in the booster when he replaced the master cylinder.
I had forgotten about this-but now it make sense. What I am experiencing does sound like booster issues-doesn't it?

Any idea what that replacement could run?

Thanks for you help and response.

i would'nt think its a booster problem.when you push down on the pedal &
it feels like its going to the floor does the ''brake light'' come on??
if it does then maybe you have a leak or air in system.
if the light does'nt come on then it maybe normal.
how do the brakes feel while driving do they feel ok.
either way with the way you are discribing its not a booster problem

i would'nt think its a booster problem.when you push down on the pedal &
it feels like its going to the floor does the ''brake light'' come on??
if it does then maybe you have a leak or air in system.
if the light does'nt come on then it maybe normal.
how do the brakes feel while driving do they feel ok.
either way with the way you are discribing its not a booster problem

If it really goes all the way to the floor, then yes it is not a booster problem. However, if it's just that the pedal gets easier to press as constant pressure is applied (so that it sinks some) then it probably is the booster. The air (vacuum) valves inside the booster as well as the seals and the diaphragm itself are often damaged by brake fluid.

BTW, the brake light on the LS does not come on due to pressure differential or any other issue but for one. That one is low brake fluid level.

Don't be so quick to rule out things that you have seen. I am not ruling out that it could be something other than the vacuum booster. I'm just adding that possibility. If the brake fluid level isn't going down, then it pretty much has to be the booster or the master cylinder, (or less likely a bad installation where the air wasn't bled out or the push rod set right).