New Brake Master Cylinder Needed??, diagnosis inside Options

[BonzaiCelica]

I replaced my brake master cylinder with a new Raybesto unit as well as a new proportioning valve (OEM). My problem is I will get air pockets 5 min into driving, pedal sinks momentarily and then brake feel is back to normal

While bleeding brakes, once i crack a caliper open, air bubbles do not come out till about 10 seconds later.

-Booster Operating check OK
-Booster Air Tightness check – engine off OK
-Booster Air Tightness underload OK
-No Leaks at Banjo Bolts
-Soft Lines OK
-No rust between shims and pads
-Caliper Pistons Seals not torn or leaking
-Caliper Pistons move freely when pressed inward with bleeder valve open

[slavie]

Can you push pistons back in with bleeder closed? Roughly same amount of effort on both L and R sides? The fact that you can push the pistons in with bleeder open is great, means that the pistons are not stuck, but tells you nothing about the condition of the rubber lines, which I would suspect next. Soft lines can look fine on the outside but have inner lining swollen/collapsed, not allowing easy bleeding and potentially causing the caliper to drag. Pressurized fluid can push through with booster working, but not so much when bleeding brakes.

May as well go with SS lines. I think StopTech ones may be no longer available (I had a hard time finding a set in stock), but you can but the Toyota adapters and universal SS line of appropriate length and basically build your own a la carte for less than the cost of StopTech lines.