Brakes soft when car is running. Any ideas?
 

Hello, I have been having some trouble with my brakes lately. They were pretty soft while driving, so I bled them. After bleeding, they feel way better when the car is off, but when I start the car they go straight to the floor. I disconnected my brake booster, and with the booster disconnected the brakes feel 'normal' but when I hook it back up they get soft again. I bled the brakes with my brother many times over again (in the correct order), and even bled the master cylinder a bit. I am at a loss as to what is wrong and really want my car back on the road. Let me know what you think.
Thanks

Nobody has had this issue?

vacuum leak?

Wouldn't a vacuum leak make the brakes harder to press? I thought the brake booster needed vacuum to assist the pedal. Am I wrong in thinking this way?

Replaced the master cylinder yesterday and bled everything. Same problem. Am I missing something here?

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did you adjust the replacement part?

I did not. The brakes feel fine with the car off though. I think there is still air in the lines. I'll try adjusting it after I bleed some more

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buy the russell speed bleeders and never look back.

worth every penny.

also, make sure your master and booster are bolted down nicely.

Rebleed, bench bleed the master if need be. Go around the car twice. Its amazing how little air will give you a bad feeling.

Bled it again today twice. The pedal feels good with the car off, but still little feedback when it's running. I pulled off the calipers and noticed that my rotors are super worn out. Could this cause the weak pedal feeling? The car still stops OK, but the pedal just feels like it's so easy to press.

How are you bleeding the brakes?

I was doing the two man method with my brother. We did the master cylinder on it too, so we bled that from the bleeder valve on it. We also used a jar and ran a hose from the bleeder screw into it. That way we could check for bubbles. I also cracked the lines on the master cylinder when the brake pedal was being depressed to bleed air that way too. Another thing we did was run a hose from the front left bleeder valve into the brake fluid reservoir and pump the brakes.

Yeah you're doin' it how I've had the best luck. Its been a pita once on this car and the tiniest amount of air came out of my front drivers, amazing the difference it made. Keep at it I guess.....

I've been doing this for like two days lol. Thanks for the advice.

I did this yesterday and the brakes feel way better. The adjuster nut seemed pretty loose, but I'm just going to hope it doesn't move. :hs: So in case anyone reads this one day: adjusting the arm fixed the issue.