Technical Knacker Master Cylinder?

[chevychase]

I recently replaced my discs and pads. Nothing unusual in that activity, I've done my brakes on countless cars. But this time the brake feel is soft and the pedal when pushed slowly fails to the floor. I didn't break into the system so no way to get air in the pipes. This only showed itself after the brake changes and I've no leaks.

I've bleed the brakes on all corners a couple of times and pretty much replaced all the fluid but the issue still presents.

I've heard from somewhere that winding the rear calipers in can 'reverse the master cylinder seal'? Is this fixable, can it be un-reversed? Or is a replacement of the master cylinder the only remedy?

 

[jackwhoo]

Replace the master cylinder

 

[bugsymike]

Sometimes an indicator of master cylinder seal fault can be if you press pedal down once hard/quickly it feels OK , but if you press it gently it creeps down.
Another point in that direction is if you can look in the reservoir when someone presses the pedal the level will actually rise as the fluid in the master cylinder is displaced back into the reservoir due to the dodgy seals.
I am assuming all brake discs and pads new , not just pads as I have had some where worn discs but new pads resulted in a terrible pedal until driven a few miles to wear into the old discs and yes I know they should have been replaced , but some customers plead poverty

 

[chevychase]

Thanks for your input. Yep new pads and discs. It's been a while now and would say they are bedded in ok. When I'm driving it doesn't feel too bad, I can stamp the brakes and get the abs to activate, and normal driving is OK ish. It's just when holding at a stop or when testing the pedal just sinks slowly. It's got an MOT tomorrow so we'll see what the garage make of it. Just doesn't fill me with confidence that the MS won't suddenly fail whilst driving.

 

[jackwhoo]

Thanks for your input. Yep new pads and discs. It's been a while now and would say they are bedded in ok. When I'm driving it doesn't feel too bad, I can stamp the brakes and get the abs to activate, and normal driving is OK ish. It's just when holding at a stop or when testing the pedal just sinks slowly. It's got an MOT tomorrow so we'll see what the garage make of it. Just doesn't fill me with confidence that the MS won't suddenly fail whilst driving.

Typical master cylinder seals starting to fail.....fit new master cylinder.....currently car is not safe

 

[bugsymike]

Yes, as @jackwhoo says, points to master cylinder.