Brake pedal question (1 Viewer)

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95 80 series. Got a question on brake pedal sinking to floor. I have replaced master cylinder and all soft brake lines with OEM parts. New pads and rotors. Also deleted ABS and LSPV. Bench bled the master and bled the brakes using the two person method as well as using a power bleeder set to 10 PSI. I have gone through around a gallon of brake fluid and can see no bubbles while cracking a bleed valve. After pumping up the brakes with the engine running the pedal still sinks slowly almost all the way to the floor. It stops maybe an inch or two above the carpet. Rig stops fine and can lock up the tires. My question is, after researching on here it’s been mentioned a few times to stick a block of wood under the pedal to prevent the master from moving too far and blowing out a seal. I wasn’t aware of this when I bled the brakes the first time. Is this necessary on a brand new master as well? No mention of it in my FSM. Or could it possibly just be air is still stuck in the system?

Edit: brake booster was replaced last year with a Seiken one and tests OK.

Thanks
 
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it’s been mentioned a few times to stick a block of wood under the pedal to prevent the master from moving too far and blowing out a seal. I wasn’t aware of this when I bled the brakes the first time. Is this necessary on a brand new master as well? No mention of it in my FSM. Or could it possibly just be air is still stuck in the system
The block of wood is for an old master. After years of use, there can be corrosion on the unused sections of the piston. While bleeding the brakes if you go past the normal operating range, the seals can be damaged.
Not an issue for a new master, and would never really be an issue if people would change out brake fluid more often then they do. Brake fluid is supposed to be water clear.
 
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Thank you. That’s what I thought as well but just wanted to be sure. Will try driving it and bleeding a few more times before putting in for a warranty claim for a new master.
 
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So my problem continues. Front drivers side caliper. I’ve attached a YouTube vid to show what’s going on. Air is getting into the system somewhere but at this point I’m stumped. Constant stream of bubbles after leaving a power bleeder hooked up for three hours and going through more fluid than I want to think about. All three other calipers are perfect with no bubbles. There are no leaks anywhere that I can see. How would air be entering a pressurized system but no fluid leaking from anywhere?

 
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Figured I’d close this loop. Ended up being a bad master cylinder straight out of the box. It was leaking internally. When I opened it up I found a torn cup seal. Rebuilt it, bled the system again and I’ve got better brakes than I’ve ever had before. I also installed speed bleeders to eliminate the possibility of any air entering the system through the bleeders during the bleed process.
The bubbles from the above video I’d imagine were just simply air getting past the threads in the bleeder screw.
 
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Figured I’d close this loop. Ended up being a bad master cylinder straight out of the box. It was leaking internally. When I opened it up I found a torn cup seal. Rebuilt it, bled the system again and I’ve got better brakes than I’ve ever had before. I also installed speed bleeders to eliminate the possibility of any air entering the system through the bleeders during the bleed process.
The bubbles from the above video I’d imagine were just simply air getting past the threads in the bleeder screw.




Hi....I am also having a pedal goes to floor issue! 97 80 series
To sum up, pedal would slowly creep to the floor over about five seconds or so with engine running, solid without engine and stored vacuum depleted MOT test imminent..
Work done so far, new seals in all callipers, new pads front, all flexible hoses replaced, new master cylinder.... bled every way, pressure,vacuum, two man and several combinations.. no better..
Deleted ABS and LSPV bled again.. no better..
Dismantled new and old master cylinders and both looked perfect ( new one is non ABS) bench bled and plugged outlets then re fitted..solid pedal, re connected rear bled and pedal was better but still more slowly went to the floor, re connected front, bled and back to square one...
Have spent a lot of time searching through internet for inspiration and found a lot of threads but none had any real conclusion ....
 
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Pedal going to the floor indicates a leak or bad master cylinder. If there's no fluid coming out, I'd source a new master cylinder. Like the OP, I also received a bad master cylinder (Aisin/Advics).
 
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Pedal going to the floor indicates a leak or bad master cylinder. If there's no fluid coming out, I'd source a new master cylinder. Like the OP, I also received a bad master cylinder (Aisin/Advics).
Thanks for the advice.. perhaps I should try a third one ...
Just find it hard to believe that after all the testing that the master cylinder is the issue...
Incidentally I also have a 1996 3.0 surf and I noticed today that it does the same although much slower...
 

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