1G No brake pressure after turning on car

[gusu]

Hey everyone,

I've never experience this and my friend who was an ASE certified Automotive Technician for 10+ years wasn't sure what would be causing this either. So a bit of backstory - I recently started having my front calipers stick after about 90,000 miles on both calipers. I have had 2g front calipers since I traded for my car in 2009 so no recent modifications of any kind, I was just replacing them because they were sticking. Other than the sticking occasionally the brakes worked fantastic and had zero issues.

After replacing the calipers and bleeding the brakes using a single person bleeder doing the standard procedure of rear passenger, rear driver, front passenger, front driver and bleeding until no air came out from 10 turns of the bleeder before going to the next caliper I noticed my car would lose 100% of the pedal the second you turned the car on. Thinking there must possibly be some air in the lines still I did the same thing with the same bottle but having my wife pump the brakes until firm then cracking the bleeder and doing the same thing of no air in the lines for 10 open/close of the bleeder before moving on. Still no pedal as soon as turning on the car, so we did the same procedure 3 more times and then tried again, and then no pedal once the car was on. So I got a good power bleeder and tried power bleeding.... same results...

Do any of you have any idea why this would be happening? The brake pedal is 100% normal until the car is on then it drops to the floor and all pressure is lost, however when you go to crack the bleeders open for the first time afterwards there is no air coming out of any of the bleeders. Just to rule this out, this has been happening over the course of a week and I have seen no stains or wet marks on the cardboard I put below each caliper.

 

[Chri_Evocoupe]

What year is your car?
The pedal stay in the floor?

 

[gusu]

Sorry, it is my current car in my profile, a 1990 Eagle Talon with no ABS. The pedal goes to the floor and returns with very little pedal pressure, before I turn the car on the pedal feels totally normal and hits full firmness after about 3 full pumps of the pedal.

 

[DSMPT]

Could be it's time to replace/rebuild master cylinder or/and booster.

 

[Dericsh]

Could be it's time to replace/rebuild master cylinder or/and booster.

I was going to suggest this too, I’ve been digging for threads to back me up without luck but it’s possible this was damaged during bleeding or was just ready to fail due to age.

 

[Chri_Evocoupe]

That the same im going to say, that sound more problem with the booster, maybe the diaphragm are bad
Also you can test the Master cylinder p
With your finguer on each output 1 at a time if you can hold the pressure with your finger the master are bad!!!

 

[gusu]

Hey everyone, I just got done replacing the master cylinder and bleeding the brakes. I bench bled the system as the manufacturer recommended and verified that I didn't see any bubbles coming through the clear nipples that connect to the hoses for the remote fluid reservoir.

At this point I am thinking it is the brake master, but can anyone explain why it would make sense that it loses pressure without any fluid level drop? I've gotten to the point that I taped I marked the master cylinder with the min/max fluid location with the pedal in/out. After starting the car the levels are the exact same even after pumping 20-30 times, if there would be a leak there would be fluid loss and 20-30 pumps should make a noticeable difference.

 

[pauleyman]

Hey everyone, I just got done replacing the master cylinder and bleeding the brakes. I bench bled the system as the manufacturer recommended and verified that I didn't see any bubbles coming through the clear nipples that connect to the hoses for the remote fluid reservoir.

At this point I am thinking it is the brake master, but can anyone explain why it would make sense that it loses pressure without any fluid level drop? I've gotten to the point that I taped I marked the master cylinder with the min/max fluid location with the pedal in/out. After starting the car the levels are the exact same even after pumping 20-30 times, if there would be a leak there would be fluid loss and 20-30 pumps should make a noticeable difference.

Bleed them again. You likely have bubbles upstream. Did you bleed enough for all the old fluid to come out?

 

[AWD-Tony]

Hey everyone, I just got done replacing the master cylinder and bleeding the brakes. I bench bled the system as the manufacturer recommended and verified that I didn't see any bubbles coming through the clear nipples that connect to the hoses for the remote fluid reservoir.

At this point I am thinking it is the brake master, but can anyone explain why it would make sense that it loses pressure without any fluid level drop? I've gotten to the point that I taped I marked the master cylinder with the min/max fluid location with the pedal in/out. After starting the car the levels are the exact same even after pumping 20-30 times, if there would be a leak there would be fluid loss and 20-30 pumps should make a noticeable difference.

Are you saying it’s fixed after replacing the master?
It’s a hydraulic system. If there’s an internal leak (most likely the seal(s) on the shaft), it will not force fluid to the calipers, hence no pedal pressure. It will just move fluid within the master. Also, when the engine is not on, there is no vacuum on the other side to assist the system. Once you start the car, there is vacuum so it’s easier to press the pedal.

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