Soft brakes. Any advice?

[GR_CoB]

2009 Pontiac Vibe, base model with 2.4L engine option. Same vehicle as Toyota Matrix.
- Rear caliper seized up. Passenger side seized up, but to be safe I replaced both rears. New pads, rotors, hardware.
- I was alone, so tried gravity bleeding. Took forever, seemed to work. First drive proved it was a fail, tons of air in the system.
- Once wife got home I got her to pump the brakes. Bled them properly this time, starting from the farthest. Pedal feel improved dramatically, when car is off.
- Test drive went well, but when engine is running the first 60% of pedal travel is nothing, followed by last 40% being the engagement point. Again, once engine is off - 100% of the pedal travel provides proper resistance.
- Logic tells me there is air in the ABS module/pump. Can't find any specific bleeding procedures for that on my vehicle.
- How bad of an idea is it to try to bleed the brakes again, but with the engine running? Or are there any other tricks you'd try first? I know some ABS modules have a bleeder valve, mine doesn't seem to have it. Unless it is well hidden, which defeats the purpose...
I'm open to any and all suggestions.

 

[Donald]

Consult with your vehicles service manual to know if the engine should be running or not. Mine need to be *off*.

Also prefer a brake pedal depressor over speed bleeders, because it's not vehicle specific and you don't have to worry about a malfunctioning bleeder. What I do is set it up, lock it in place, then I move the seat forward a little at a time (assuming you have electronic seat adjusters). No second person needed, and just need one free hand to depress the brake further .

If you don't want to go the brake pedal depressor route, you can just get a Motive Power Bleeder. Those things are great. Just make sure you don't have any blocked brake nipples say if you're working on an old vehicle. The brake fluid reservoir will overflow without you knowing it. Ask me how I know . Should work flawlessly however on any well-maintained vehicle.

Speed bleeders especially the SS ones hopefully will not rust stuck and require a caliper replacement. So good for that even if you never use the one way bleeder function.

 

[GR_CoB]

The car is gone. But a few hours before it got totalled I did bleed the brakes with engine on. Lots of air came out, and brakes and pedal feel became better than it ever was in my ownership. That's just for anyone who comes across a similar issue in the future.