80 series spongy brakes

sounds like you have covered everything.
try vise gripping each individual caliper hose one at a time and see if it gets better when example you clamp of right rear pedal gets hard you will then know at least what part of the system is playing up.
but it does sound to me like master cylinder

I am with Jim . Sound like pedal retension to me . Pads can make a huge diffrence in cruisers . You haven't overhauled your calipers I see . As jim said , make sure you clamp off each caliper to see if it helps the pedal , if not , then you have a stuffed master . It was overhauled I know , but dosn't say they didnt stuff up a seal during assembly . Also try gravety bleeding instead of pressure bleeding .

Clamping each brake hose is a good idea and won't do any harm to the hose as long as you don't crush it too tight - it's a "touchy feely" thing. I've done it for years on various vehicles when changing wheel cylinders. Nothing's ever burst yet. Most mechanics do it.

Alternatively, buy some suitable brake pipe fittings with a short length of brake pipe flared into 'em and seal off the open end - bend it over, flatten it with a hammer - add solder if you want to. Screw in this temporary fitting where required for each test. The temp fitting won't be expensive and any good workshop or supplier will do 'em for you.

Whilst "individual isolation" is one approach that you could take, I don't think the problem lies there. It sounds more like the Master Cylinder. Did you fit all new seals AND Master Cylinder check valve? I've known new check valves be faulty and this allows the brake system system hydraulic pressure (i.e. fluid) to leak slowly back into the master cylinder - that's what the check valve is designeed to prevent. It stops it brake fluid that is under pressure from flowing back into the master cylinder bore and collapsing the cylinders rubbers thus allowing the brake fluid to flow back into the master cylinder's reservoir.

Another oddity, I've experienced is the method or "rotation" of the brake bleeding. There's often a peculiar and particlar way to bleed brakes on some models. The best way to start is to do the wheel that is furthest from the master cylinder and then progressively bleed each wheel individually until you get to the one closest to the master cylinder. e.g If your master cylinder is on the driver's side firewall, then you would bleed the passenge side rear wheel first, followed by driver's side rear, followed by passenge side front and finally driver's side front.

The reason for this, particularly if you've just flushed and refilled the whole system, is that air hangs around in odd "corners" of the system. By doing the longest brake pipe run first, you are doing everything possible to flush out these air pockets. I learned this trick from an old mechnanic, when as an apprentice, I couldn't "get a pedal" on a brake system that I'd just fixed.

Also, check the brake booster vacuum diaphragm - big, round thing at the back of master cylinder. If it's got a slight leak, gone "snotty" or small hole in it, it can allow the pressure in the hydraulic system to back flow as if the check valve was leaking - see above. The diaphragms are designed to have atmospheric pressure on one side and a vacuum on the other - supplied by the inlet manifold or a vacuum pump if it's a diesel . If the diaphragm is leaking it allows the pressure in the brake sysetm to overcome the pressure you've applied with yer foot - fluid then leaks back into the master cylinder as the pedal slowly falls..

Bilbo

MikeV,
has this fault just started?, when did you notice this fault? , what were you doing when it occured? does brakes/pedal work normally while driving & brake pedal slowly sink to the floor only while stationary-i think you will find this is normal for ABS sytems. You could take the vehicle to TOYOTA dealer for expert advice-even if its only for a test drive with the foreman.

crazy

Hi Mike:

I have '91 80 Series GXL with the same problem. I got best results by changing the brake fluid. Seems over a period of time water gets in and can turn to steam under braking.

However - I put this same question to the guy in my 4WD club who is/was a Toyota engineer and he advised me that it was common to 80 Series. He further stated that the later models had larger brakes, but then it becomes a matter of how much money one wants to throw at the problem if you want to upgrade. If you have a fax number I can fax you the reply I received.

My email is jeller@bigpond.net.au

Cheers
Jack

I know what i'm about to say might sound strange but have you tried reverse filling, i had the same problem once, difference was it was a motorcycle, what we did was force brake fluid though the caliper to the master cylinder instead of through the master cylinder to the calipers, just another idea to think about, amazing how air can sit in a system and be hard to get out.

Baz.

Mike,

IF IT HAS A CHECK VALVE - not all do, it's located at the end of the MC piston, inside the MC. Sometimes has one for each system. So you could have 2 on split braking system. First you have the big rubber boot seals, they do main pushing of the fluid, then you have another smaller rubber/steel check valve. You'll need to pull the guts out of the MC to see it - if it has one.

Bilbo