Brake pedal slowly goes to floor while at light after 5 lug conversion

Are these parts new? Sounds like a bad booster.

Another vote for a master cylinder with an internal leak... Replace it.

Lawbreaker5.0 said:

Are these parts new? Sounds like a bad booster.

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I could be wrong here, but a bad booster gives you a very hard pedal.

Stever89 said:

I could be wrong here, but a bad booster gives you a very hard pedal.

Click to expand...

You're not wrong, the booster is how hard the pedal is to push, but hard or soft, it will still hit a point where you just can't push it down anymore. It sounds like you got a bad mc if it slowly goes down once you're stopped.

I used to work a a shop that dealt with s10 chassis and I remember test driving a vehicle with a mechanic. As we waited at the light he pedal kept dropping down and would allow the car to almost move forward. I ask the mechanic I was assisting and he said it's a bad booster. We changed it out and it stopped. I could be wrong but that's why I thought booster. When everyone is saying leaks, I guess you should be actually loosing fluid. That should be a quick diagnoses, are you is the reservior loosing fluid?

Let's kill or thrill the bad brake booster idea once and for all...

Borrow or buy a vacuum gauge & connect it to the vacuum tree where the booster connects. Start the engine and let it warm up. At idle speed, you should see 16"-19" of vacuum. Increase the engine speed to 1000 RPM and the vacuum will increase slightly, maybe to 18"-21" of vacuum. If you dont have at least 16" of vacuum or more, then you have vacuum problems. The booster needs a minimum of 12"-14" of vacuum or more to work properly.

To test the booster, start the car and let it idle for 2 minutes, then increase the engine speed up to 1000 RPM and hold it for 30 seconds. This gets your vacuum up to it's highest point.

Shut off the engine and press the brake pedal. You should feel some give in the pedal. Repeat the process 3 or 4 times. The pedal should get harder each time. If it does not, the booster is probably bad.

New or not...i'm betting it a bad master cylinder...but check for a fluid loss in the reservoir and make sure you bleed the brakes again...you start at the right rear, then left rear, right front then left front.,
Please let us know what your found.

A bad MC won't usually leak fluid, it's an internal leak allowing fluid to pass by the piston inside causing the pedal to drop without loosing any fluid. I'm 99.9% sure you got a bad MC.

plus one for MC leaks, if there is no leak in any in of the lines it has to be. booster usually out live vehicles and if they go bad you will get a hard pedal if anything and possibly brakes grabbing and not releasing. the reason it is stiff when off you dont have enough pressure to make it leak

its common, even if new for this to happen, the first MC i got was bad and i had the same issue

just replaced a PIA booster to solve the same problem, didnt work. Got a new MC and all is well.