Brake Pedal Hitting Floor

Joined
Aug 8, 2013
Messages
134
Location
Weddington,NC
I have change some part on my 89 cruiser. Fj80 Booster fj62 M/C and all stock calipers and drums. I had the master cylinder leaking into the brake booster so I ordered new parts to do the work. I've bench bled the master cylinder and bled all the wheels and proportioning valve starting from the passenger rear and working my way up. If you pump the brake pedal with the car off it becomes hard. If the car is running. The brake pedal has continuous pressure but falls all the way to the floor. What other steps could I do to correct this problem of bled the whole vehicle twice and bench bled the master twice and I am lost for what's next. Thank you for your help.
 
Joined
Jan 2, 2014
Messages
339
Location
Seattle
Do you have vacuum to the booster and the push rod set to proper depth for MC? I’m guessing the pedal is connected properly to the booster because the pumping with engine off leads to hard pedal.
 
Joined
Aug 8, 2013
Messages
134
Location
Weddington,NC
I did some more brakes bleeding tonight and got all the air out. The brake booster I got is for a 96 fj80. I read that is was plug and play. The pedal is verm but still goes to floor. Could this booster be for ABS and I have gotten the wrong one. How can I identify it. Also if I hold gas and brake the brakes are non existent and pedal is hard like the car is off.
 
Joined
Jan 2, 2014
Messages
339
Location
Seattle
I have an 80 booster on my 60 and only recall one booster option but having an abs and non abs MC. I don’t remember if I chose a specific year, but usually search 80 parts with a 1997 model year. I don’t have an 80 yet.

There’s an adjustable push rod on the booster that applies pressure to the MC. If the push rod is set too short you’ll get little pressure from MC and set too long it won’t release pressure in MC. If you unbolt mc from the booster and pull it out of the way, you can measure the push rod length and the depth of the MC to verify they’re equal. I have an 80 non abs MC and had to shorten the push rod travel. Otherwise it was plug and play.
 
Joined
Aug 8, 2013
Messages
134
Location
Weddington,NC
I kept the 62 M/C and measured the push rob to the old booster to make sure they were the same. What would the reason for loosing all brakes if throttle is applied while braking?
 

2mbb

SILVER Star
Joined
Sep 1, 2003
Messages
5,428
Location
WC, CA
The brake booster only provides extra power to the brake pedal. Unless the master cylinder is leaking there is no brake fluid in the booster. It's a diaphragm with vacuum applied to one side to help you press the brake pedal.

If your drums are adjusted properly, and the pedal is going to the floor, brake fluid is leaking past the master cylinder or caliper/wheel cylinder seals, you have alot of air in your system, or your flexible lines could be damaged and bulging. This is happening whether the booster is helping or not (engine on or off), it's just probably too slow for you to notice when the engine is off.

This indicates a problem with your hydraulic system, not the booster.
 
Last edited:

2mbb

SILVER Star
Joined
Sep 1, 2003
Messages
5,428
Location
WC, CA
I kept the 62 M/C and measured the push rob to the old booster to make sure they were the same. What would the reason for loosing all brakes if throttle is applied while braking?
the booster works by having manifold vacuum applied to one side of a diaphragm to assist you when you push the brake pedal. manifold vacuum is highest when the throttle plate is closed and can be much lower under acceleration or power conditions. There should be a check valve at the booster in in the vacuum line between the manifold and the booster. This should help retain vacuum applied to the booster. You could have a vacuum leak, but this would present itself as a hard pedal.

I'm not sure what you mean by "loosing all brakes". Is this the condition when the pedal goes to the floor which you describe previously in this thread or is this a hard pedal that makes it harder to stop?
 
Joined
Aug 8, 2013
Messages
134
Location
Weddington,NC
the booster works by having manifold vacuum applied to one side of a diaphragm to assist you when you push the brake pedal. manifold vacuum is highest when the throttle plate is closed and can be much lower under acceleration or power conditions. There should be a check valve at the booster in in the vacuum line between the manifold and the booster. This should help retain vacuum applied to the booster. You could have a vacuum leak, but this would present itself as a hard pedal.

I'm not sure what you mean by "loosing all brakes". Is this the condition when the pedal goes to the floor which you describe previously in this thread or is this a hard pedal that makes it harder to stop?


This is a hard pedal that is making it unable to press hard enough to stop
 
Joined
Jul 8, 2012
Messages
355
Location
New Harmony, Utah
2nd on checking your rear brakes... If these are not adjusted right, even a little too much room between the brake drum and shoe can really make that peddle sink. Rear brakes can be such a pain.
 

Godwin

Resident Herpetologist
SILVER Star
Joined
Dec 4, 2004
Messages
5,981
Location
Alabama
This is a hard pedal that is making it unable to press hard enough to stop

If you have a hard pedal then that's an issue with the brake booster. Vacuum line to the booster is clogged; not sure how that would happen unless you left it open during warm months a dirt dauber built in it. The booster may be bad.
 

2mbb

SILVER Star
Joined
Sep 1, 2003
Messages
5,428
Location
WC, CA
This is a hard pedal that is making it unable to press hard enough to stop
If this is only happening when braking with the throttle open, then I would confirm the check valve is installed an working properly and/or check for leaks in the vacuum tube from the intake manifold to the booster. The check valve fits into a rubber grommet in the shell of the booster. It looks like a tubing fitting, but it keeps low pressure (vacuum) inside the booster so it will work properly. I suppose you could also have a leak in your booster diaphragm, but you say the booster is old and the pedal gets too hard to work only when braking with the throttle open.

You can download the FZJ80 or the FJ60 manual from the resources tab. Find the brake section and to the easy testing to determine if your booster is working properly. The tests are the same regardless which booster you have.
 
  • Like
Reactions: OSS
Joined
Sep 20, 2019
Messages
254
Location
Marquette Michigan
If it's still going to the floor pinch off the rear brake hose and try again, if it still goes to the floor then it's not the rear brakes, if now you have a firm high pedal now you know where to look. might help to narrow it down.
 
Joined
Aug 8, 2013
Messages
134
Location
Weddington,NC
Got a chance to work on the cruiser again. Still having the same issue of the pedal sinking to the floor. I have bled the brakes multiple times. I have bled the master cylinder multiple times also adjusted the brake booster push rod to the correct spec and overlooked for vacuum leaks, brake fluid leaks, and non-present. The booster I got is from a 1996 Land cruiser. The master cylinder is for an FJ62. I have also adjusted the rear drum brakes to the correct specs. I have tried two different master cylinders. I have also noticed that if I apply the brakes more rapidly while vehicle is moving, the pedal becomes hard as if there is no booster after the pedal becomes hard from rapidly breaking, it then begins to slowly sink to the floor. The only thing I have not tried is another booster. The reason I have tried the '96 booster is I've read that it was a direct replacement
 

Users who are viewing this thread

Top Bottom