Brake problems - think I messed up

[StuP]

Sorry if this is long winded, but I'd appreciate peoples opinion.

Scenario: 2013 Santa Fe, ~ 95k miles. Brakes ok but the pedal slowly sinks under constant pressure, will pump up. Same behavior when engine running or off with brake booster drained.

Checked - fresh fluid, bled brakes, no discernible leaks from any of the wheel or master cylinders, no leak into the brake booster, fluid level constant in reservoir.

So... fitted a new master cylinder, problem much reduced HOWEVER, like a fool, I allowed the piston in the new master to get pulled out and I just reinserted it without thinking about the seals. I suspect I damaged the seals on the new piston doing this, (or just a poor quality aftermarket cylinder ?), hence I still have the same problem, just reduced.

Any thoughts of what else to look at before I try another new cylinder ?

 

[41mag]

If all you posted rings true to form, I would install new master. Bench bleed before hooking lines up. Then gravity bleed rest of the way, before pressure bleed.

If you are mechanical enough , you can try to bench bleed master but you may have damaged seals.
I would suggest above based off what you posted .

 

[Rolling_trip]

Are you sure you got all the air out? Vacuum pump bleed kits are cheap and work better than the pump brake method.

 

[basstracker89]

If you haven't, I'd bleed the entire brake system all the way to the calipers. If that doesn't do it, replace master cylinder. Then bleed entire system

 

[StuP]

Are you sure you got all the air out? Vacuum pump bleed kits are cheap and work better than the pump brake method.

Bled conventionally and with a vacuum. The brakes aren't soft on initial application, but the pedal sinks under constant pressure. They will pump up, but then sink again, not symptoms I've seen of air in the system, but leakage / seepage somewhere causing pressure loss after application.

 

[41mag]

Bled conventionally and with a vacuum. The brakes aren't soft on initial application, but the pedal sinks under constant pressure. They will pump up, but then sink again, not symptoms I've seen of air in the system, but leakage / seepage somewhere causing pressure loss after application.

Possible master bypassing too

 

[87KJH]

For some models you may need to bleed the brakes with a Diagnostics Scan tool that activates the ABS pump to get all of the air out.

 

[StuP]

For some models you may need to bleed the brakes with a Diagnostics Scan tool that activates the ABS pump to get all of the air out.

From what I've discovered not required for this model / year. I have decent scan tool, I'll double check if that's an option though. Just doesn't feel like air.

 

[41mag]

From your explanation, I will say again it sounds like the master is bypassing.
You say you can pump them up and get a strong pedal and hold it and it then it sinks under constant pressure ?? But you are NOT loosing fluid anywhere ?
Sounds like a bad master.
(Almost impossible to tell for sure without being there and seeing for myself - but that is my opinion as a master mechanic for more years than I got fingers and toes !! lol. )

 

[Realstudent368]

get a new master cylinder... you know that's what it neeeds