Brake master cylinder too small for brakes?

[Quint]

Took the supra for a test drive finally. Brakes work barely.

I'm guessing the standard GA-70 brake master cylinder is too small to drive the JZA-70 pots i've put in (new hubs etc.)?

Cheers.

'Ohh, she goes quite well.'
...
'Ah oh, they don't.'

[RomanV]

You can get the standard master cyl bored out to a larger diameter, which makes it pump more fluid through.

Or find a master cyl with a factory larger bore that bolts to your booster, IIRC V6 camrys have got a fairly large dia bore in the master cyl.

[rollaholic]

whats the brake pedal doing?

[Quint]

Travelling to the floor and then feeling very soft when the brakes start to engage.

[Malcolm]

lots of travel and feeling soft could certainly mean the master cylinder is too small a diameter, but it could also be that your brakes are not properly bled. I'd suggest giving them another good bleeding before looking to solve a problem that may not exist. It may still be prudent to increase the size of your master cylinder if you have increased your piston area though

[rollaholic]

if you give the pedal a couple of pumps it should tell you whats going on, if you start to get a better pedal after a few pumps then you most likely have some air in there.

[allencr]

Travelling to the floor and then feeling very soft when the brakes start to engage.

Air and/or bad MC.
While a small dia. MC will feel a bit softer from its different mechanical/hydraulic advantage, you couldn't say that it feels very soft from that alone and it would not got to the floor, just about 2cm/1in travel difference.

[Quint]

Pots are the same size between the two, so that isn't the problem.

Bleed the callipers, no air there, noticed however that the air is bubbling up in the Master cyl. Continuous pumping, continuous air bubbles. If air is leaving the system (bubbles in the master cylinder) Then how is the pedal not coming up? Tryed to undo the line closer to the cylinder to bleed it there, but toyota never intended them to be undone (brass starts to strip)

Has me scratching my head.

[Flannelman]

Sounds like the master cylinder is poked. replace it and your brakes shall return.

Side note - to check if the booster is working have the engine off and pump the brakes till they are hard. Press on the pedal and start the engine. The brake pedal should sink if the booster is working.