Brake pedal barely working - goes to floor - master cylinder?

[Dev]

Bit of an update as I had to pop out in the 2 earlier briefly: The pedal goes solid when the car is off - it does not go to the floor at all. As soon as engine is on, the pedal goes to the floor (but still stops the car). Does this point to another issue other than the fluid?

 I would replace the fluid and see what it does before taking the next step in diagnosis if there are any internal leaks taking on air from bad seals.
 When the engine is off the vacuums assist boost of the diaphragm is no longer functioning and the pedal will be stiff due to over coming the spring in the master and the fluid. If there is a little air in the system it can be greatly appreciated once the car is on.

[MrChris]

@MrChris
Seldom, if ever mentioned on here is the tandem brake circuit and the vacuum assist.
My understanding and the implication of their malfunction is insufficient to say whether either of these could be your problem. But the vacuum assist only operates when the engine is on. The tandem system is designed to be fail safe but does alter the feel of the pedal.

Yeah a quick google lead me to articles/YouTube videos showing that something to do with the ABS could be at fault, or as I initially suggested: the master cylinder. It is very specific behaviour though which makes me think maybe ABS system. Engine off: Rock hard pedal, Engine On: all the way to the floor and brakes at the end of the travel.

I would replace the fluid and see what it does before taking the next step in diagnosis if there are any internal leaks taking on air from bad seals.
 When the engine is off the vacuums assist boost of the diaphragm is no longer functioning and the pedal will be stiff due to over coming the spring in the master and the fluid. If there is a little air in the system it can be greatly appreciated once the car is on.

Will bleed the system tomorrow and see what is what.

[Dev]

While this thread is about brake fluid and the pros and cons of grades that differ from that mentioned in the handbook and on the filler cap I wonder what consideration is given to those other fluids that may or may not be of some importance, such as:
Engine oil, how many Members use non synthetic (Toyota) SAE 5W-30 oil?
Gear oil, how many use (Toyota) SAE 75W-90 oil?
SMT oil- how many use Toyota Genuine Sequential M/T Fluid?
Coolant- how many use Toyota Genuine Long Life Coolant.
Also of note- Tyres- how many use 185/55R 15 81V front, 205/50R 15 85V rear or whatever the FL model is recommended?

Unrelated to brake fluid you might think, but these items were, around 20 years ago, what was recommended.

There is nothing set in stone when it comes to fluids recommendations and sometimes Toyota gets things wrong. There can be non Toyota parts that can exceed the manufactures but its hard to know so it depends.
Toyota fluids have been formulated specifically for Toyotas including engine oil and they have a very good track record of giving excellent service. There have been alternative fluids that have been in used in place of Toyota and they have also given great service however there are also fluids that had issues with their formulations even though they claim they have exceeded the manufactures fluid. Then we have those that take chances on using fluids that are not specified for the vehicle and it may return some initial benefit but there might also be a major trade off in longevity which take years to find out or you will never know because you cant say what caused the failure.

There have been many failures even beyond fluids with non OEM parts. One of the great things about Toyota is their stringent quality control that some third party manufactures cant match. 
Sometimes trying to get a benefit might actually be causing damage. One thing we can be assured of is if you go with OEM in a sea of unknowns you are at least guaranteed some peace of mind especially when there is not a substantial difference in price.
When you look further into it as I have you find out that there is specific reasoning to stick with some of the OEM fluids especially if it is a street car.

[Dev]

Yeah a quick google lead me to articles/YouTube videos showing that something to do with the ABS could be at fault, or as I initially suggested: the master cylinder. It is very specific behaviour though which makes me think maybe ABS system. Engine off: Rock hard pedal, Engine On: all the way to the floor and brakes at the end of the travel.

Will bleed the system tomorrow and see what is what.

Curious to know what happens and good luck. Hopefully it isn't the master or ABS unit as they rarely go bad.

[Ardent]

Not much to add, but as always on here. Lets start at the cheapest, easiest thing to try.
A good methodical bleed of the system seems the best place to start.

Have used the one man type bleed systems but still prefer having a second pair of hands or foot.
With 2 ops, you can do it as Mr T, describes.
Apply pressure to pedal. Open bleed valve. Pedal goes down. Fluid comes out. Close bleed valve. Release pedal. And repeat.
A small difference, but I do believe that to be the optimal method. Vs. Open press release close.

[Joesson]

I first used one of these in the '60's, after many years of company cars, when I didn't use it and 4 house moves I lost/ couldn't find it. I invested £2.80 in 2020 and got another, from Amazon.
Current price is £4.04 , such is inflation,  but available elsewhere for slightly less.
It can be used single handedly , but easier with a partner and it is not necessary to close the bleed valve between pumps of the pedal.
Copy and Search the following line and you will see various offers. Recommended.

Brake or Clutch Bleed Tube [PWN189] 25cm Long Rubber Bleeding tube.

[Dev]

 After trying many methods of bleeding I now switched to gravity bleeding which is the easiest method with the best results.
 Just need a clear tube over the bleeder nipple and cup to catch the fluid. Suck up the existing fluid in the reservoir and fill it with fresh fluid, open the bleeder and drain. Close the bleeder screw once fresh fluid comes out. If there are any bubbles they find their way out since the force of gravity pushes it out the line.

[MrChris]

Small update: the dot 3 hasn't arrived. Ran through some fresh rbf600. Braking has improved but the pedal is still super spongy and goes down way too far. There did appear to be a fair bit of air in the lines. The ABS did engage when I took it for a drive when I pressed really hard. I guess next thing is to wait for the dot 3 and run that through.

[Iain]

Regardless of what DOT rated fluid you have just put in, its fresh fluid so that wont be the issue. If you're still not getting a firm pedal there has to be another issue somewhere.

Any signs of leaks around the master cylinder or calipers?

I ran the rbf600 for a bit on track but it just didnt last long before it needed changing, i have sinced swapped to using Gulf rf1000 which seems to be holding up better.

[Alex Knight]

Braided or stock brake lines?

My money is on a leak. You clearly have a problem, as this is not normal.

[MrChris]

Braided or stock brake lines?

My money is on a leak. You clearly have a problem, as this is not normal.

Braided lines. Just did another bleed, was slightly better after. Pumping the brakes helps while driving. Can't see a leak as the fluid has not gone down and I can't see an issue with the lines or at the master cylinder.

[Dev]

You probably still have air in the system if you gained a sight improvement especially if it doesn't get worse. Sometimes air can get trapped under the master piston which is hard to get out. It can also get trapped in the ABS unit on a lot of cars where the dealer uses Techstreem to initiate the ABS while bleeding. Our cars generally do not have this issue with trapped air in the ABS module but its possible especially if you boiled the fluid. If there is trapped air it has to make its way back to the master or it ends up at the caliper after multiple presses which is then relived once you crack open the bleeder.
I had a very hard time bleeding on a different car where the pedal just wouldn't get as tight as I remember. Eventually after multiple bleeds between drives had one of the calipers expel air and then everything was ok after that.

Another tip is to tap on the master housing using a tool and also the caliper before you bleed again to shake any trapped bubbles so they can find their way out.

[AJRFulton]

What are you using to bleed the system?

[MrChris]

What are you using to bleed the system?

Wife in car, tube on the nipples (ahem). Push brake pedal, open bleed screw, close bleed screw, release, repeat until no air bubbles. Next step is to try gravity bleeding, possible get a vacuum bleeder but have read this is not necessary.

[AJRFulton]

The air pump pressure bleeders make life easier as it makes it a 1 man job is. Mine was like 25 quid off eBay about 5yrs ago. however, you know how to bleed

RBF600 might not be the best fluid for your need, but it won't be going off that quickly. It's not long life and the type of thing if you don't need don't use, but I'd expect at least 12mths if everything was working correctly.

Worth giving JSpec a call, and asking for a master cylinder and ABS pump, explain the situation and I'd imagine they'll be ok with a return if you don't need the part. I'd change the master cylinder first. Relatively straight forward, and IMO the most likely culprit.

Unfortunately without an obvious cause and leak, it might be a bit of trial and error.

[Joesson]

Wife in car, tube on the nipples (ahem). Push brake pedal, open bleed screw, close bleed screw, release, repeat until no air bubbles. Next step is to try gravity bleeding, possible get a vacuum bleeder but have read this is not necessary.

The automatic bleed tube I suggested in post #30 costs very little but really does simplify things. There is no need to close the bleed valve between pumps, the tube has a longitudinal razor slit that effectively works as a one way valve. Keep pumping with the tube end and slit immersed in a clear container of brake fluid until no bubbles issue from the slit.
I have not previously heard of gravity bleeding so cannot comment other than  it apparently takes a while to do it and, as with any method, the master cylinder must be kept topped up during the process.