so im ready to struggle with my breaks again soon so was going to see what I should tackle first... here goes the description.

 

ive got an carbed ea82 87 gl wagon..ive done the 4wheel disc brake conversion..its got all brand new rotors and pads and has been bled. My problem is this... sometimes the brakes seem to be working great and other times I apply the pedal and it gets to a point and feels solid and wont really depress anymore, the brakes are applied and the vehicle starts to slow down but not nearly as well as they should be. so I was thinking a couple of things... could it be a piston on one of the calipers sticking? could it be that I need to install the proportioning valve from a vehicle that came with 4 wheel disc brakes to begin with? when I did the swap everyone seemed to think that you dont have to replace the proportioning valve or master cylinder or anything but I know from working on brakes that disc brakes require a higher pressure than drums so wouldn't you have to have the proportioning valve or master cylinder from a vehicle that originally came with one for the brakes to funcion right? but was also thinking it probably wouldnt be the valve or master cylinder because like i stated before...sometimes the brakes seem to work perfectly fine...anyways...suggestions!?

If it has power breaks you might have a leak in the vacuum diaphram in the booster. Have you noticed it being stiffer right after you were heavy on the throttle? Does it have the hill holder and if it does maybe it needs adjustment.

Let me put it this way:

 

_I_ might consider disassembling and examining my master cylinder first, then if it seems fine I would try a proportioning valve off a 4wheel disc vehicle.

 

I say it like that, because i've worked on many different hydraulic systems (repair and diagnosis) so i would be perfectly comfortable taking my MC apart and (providing it passes inspection) putting it back together functioning as well as it did before i took it apart. You may feel otherwise, but thats my two bits.

hmmm thinking about it more while im not as tired...would probably have to be something to do with the brake booster...whats the best way to check it for proper functionallity?