Brake problem I've been unable to fix. (1 Viewer)

[Wayne]

My '96 has a brake issue I can't seem to fix. I've had it long enough I can't really remember when it started. With the engine running, after pumping, the brake pedal slowly goes down almost to the floor. With the engine off the brake pedal pumps up firm and stay firm. Making a panic stop is impossible. There are no leaks in the system. Only with the engine running do I have the problem. Three years ago I replaced all rubber hoses, the rear calipers, LSV, and booster. Thinking it had to be the booster or master cylinder I just replaced both, bled the system, and ABS actuator......I still have the issue. I'm considering taking it to Toyota and have them exchange the fluid and bleed the system with their machine. I honestly don't know what to do next. HELP!

O'Rilley's - Booster (Bendix) rebuilt, and front calipers (rebuilt) and ceramic pads (just purchased all three items)
Toyota - Rear calipers and pads, hoses, LSV (purchased all three items three years ago)
Amazon - Master cylinder (Aisin, new), Powerstop front rotors (just purchased both items)

PS The ABS system is not working, no light on the dash and fails functioning test. I haven't attempted to work on this issue yet.

 

[Sc0-]

Moisture in the hydraulic system? I guess moisture resembles a wax substance but when heated it turns back into a vapor? Only way to get it out is to get the brake system hot and bleed. Ran into this problem years back with a 993 Porsche, and recently my FJ80 after rebuilding the calipers. Pedal will be spongy until the moisture is out of the system.

Wouldn't really take it anywhere and expect them to fix it, unless they are Cruiserheads. Typical shop will do a service and charge you for it, whether it fixes the problem or most of the times it doesn't.

 

[Pin_Head]

If the pedal goes to the floor, the fluid in the master has to go somewhere. If it isn’t leaking to the outside, then the master is leaking internally. Sometimes ou can see it as turbulence in the reservoir. Probably another bad master.

 

[Wayne]

If the pedal goes to the floor, the fluid in the master has to go somewhere. If it isn’t leaking to the outside, then the master is leaking internally. Sometimes ou can see it as turbulence in the reservoir. Probably another bad master.

The really confusing part of this is the pedal pumps up hard and stays in position with the engine off, but pumps up softer and slowly goes down when the engine is running. Wouldn't the master cylinder leak pass the seals with the engine off also, if that's the problem? I'm on my second master cylinder trying to fix this with the same result.

 

[Bigwilly80s96]

test your ABS out on a gravel road, go fast, stop fast, see if it kicks in.

 

[sea bass]

I think your master cylinder is bad the reason it goes to the floor with the engine running is because it has the power of the booster Pinhead is right if it's going to the floor it's either leaking or Blowing by the master cylinder seals in which it's bad the asin Products off of Amazon are sometimes rebuilt with just a asin label on it I found that you have to watch products on Amazon a lot of it is China junk

 

[MoJ]

If the pedal goes to the floor, the fluid in the master has to go somewhere. If it isn’t leaking to the outside, then the master is leaking internally. Sometimes ou can see it as turbulence in the reservoir. Probably another bad master.

This.

I fought this issue a few months ago. I bled the system. No change. Had two separate mechanics bleed it. No change. Nothing worked until I replaced the new aftermarket master cylinder. I went with a new Toyota mc. All is well.

 

[Pin_Head]

The really confusing part of this is the pedal pumps up hard and stays in position with the engine off, but pumps up softer and slowly goes down when the engine is running. Wouldn't the master cylinder leak pass the seals with the engine off also, if that's the problem? I'm on my second master cylinder trying to fix this with the same result.

Yes, it would eventually drop to the floor, but it would take considerably more effort because the booster isn't assisting.

I guess it could also be a brake line ballooning, but it would probably do it all the time.

 

[jvazquez53]

Air is your worst enemy, here's a couple of things you can try...


I made one of these and solved my problems.

 

[Tedward]

Use to work on Forklifts and got many a bad master new in the box.
Just because it's new doesn't mean...

 

[jvazquez53]

Very important, do the master cylinder bench bleeding.

 

[Saito]

My MC was sh*t when I bought my land cruiser 3 years ago. Brakes were shot too. It would hobble when the pedal was pushed. New rotors, pads and calipers all the way around fixed that issue. Then my front brakes started engaging on their own. Had a very inconsistent pedal feel as well. Firm at times and then close to nothing at others. Really unpredictable. It would do as you’re describing and pump up fine w/ the engine off and seem to hold. I thought booster as well but replacing the MC solved the issues I had. I’ve also had lots of trouble with Toyota MCs over the years too for some strange reason.

 

[Wayne]

Okay, team, I'm going to attempt to bleed the entire brake system ONE MORE TIME. If that doesn't fix it I'll put a Toyota master cylinder in it. Thanks for all the recommendations. I'll post the outcome.

 

[jvazquez53]

Okay, team, I'm going to attempt to bleed the entire brake system ONE MORE TIME. If that doesn't fix it I'll put a Toyota master cylinder in it. Thanks for all the recommendations. I'll post the outcome.

I could not get a hold of a Land Cruiser MC, so, mine is running with a (Aisin) 4 Runner MC, Dont know what year. but runs just fine.

 

[pedwards]

My 1996 has the exact same issue. Please update and let us know how it went.
symptoms started after I replaced my failed booster. I've since replaced my MC (bench bled) and bled the whole system. Im considering replacing my brake hoses next.

 

[jvazquez53]

My 1996 has the exact same issue. Please update and let us know how it went.
symptoms started after I replaced my failed booster. I've since replaced my MC (bench bled) and bled the whole system. Im considering replacing my brake hoses next.

I have found that these trucks need to be bled really good in order to perform correctly.

 

[HRTROB]

Do you have decent stopping power when braking after pumping the pedal first to get it to firm up?

I had the same symptoms and it turned out to be the brake booster. If I pump the pedal it will be firm then slowly sink. I can pump it with the engine off and it will remain firm. Then I noticed that I had very little stopping power if I pump the pedal first to get it to firm up.

 

[zachwalker18]

I just fixed a similar problem. Mine would brake well initially and then the pedal would harden up and brakes would fade away. If I gave it 5 to 10 seconds, they would work again for a short while. I checked all the hoses, vacuum lines, etc. and finally decided on a new booster. I couldn't get the Seiken one recommended on here (sold out everywhere) and I didn't want to pay $600 plus for a new Toyota one so I ended up with the Cardone one off of Amazon. Good price, fit well, works well out of the box, but time will tell I guess. The brakes now work exactly as they did before. It took a little coaxing and I did end up lifting the engine just a bit to clear to intake manifold, but I eventually got it out and back in was much easier!

 

[Wayne]

Okay, another update. I had a friend help be bleed the entire brake system after installing a new rebuilt booster and master cylinder. I still have the exact same problem and have changed every part in the system, some twice.

QUESTION: The ABS system is not working. The light is out on the instrument meter at start up and a brake test indicates the system is inoperative. Could an ABS actuator failure (internally) cause or potentially cause this problem? (brakes pump up hard with engine off, and are soft and pedal sinks with engine running) Any help will be appreciated.

 

[BILT4ME]

Okay, another update. I had a friend help be bleed the entire brake system after installing a new rebuilt booster and master cylinder. I still have the exact same problem and have changed every part in the system, some twice.

QUESTION: The ABS system is not working. The light is out on the instrument meter at start up and a brake test indicates the system is inoperative. Could an ABS actuator failure (internally) cause or potentially cause this problem? (brakes pump up hard with engine off, and are soft and pedal sinks with engine running) Any help will be appreciated.

This could be trapping air in the system.

When bleeding, it is most beneficial to bleed it, then acivate the ABS (usually by driving it on gravel/dirt road and activating the ABS) then bleeding again and possibly do it a thrid time after activation.

If your ABS system is inoperable, then you MAY have air stuck in the ABS pump part of the system and it is bleeding air through.

Usually the symptoms described are determined as MC first, then booster problem. Again, just because they are "new" doesn't mean they work.