Lost brakes! Almost crashed.

[dmaddox]

On the way to work this morning in my 1980 FJ40 (100% stock), 52K original miles. I was coming down a hill to a red light went to step on brake and it wheeeeeeezed to the floor and when it reached the floor the front wheels locked and I started skidding sideways. I let off and pumped and turned into it and came to a stop in the next lane (LUCKILY no one was behind me or beside me.)

I turned off on a side road to evaluate. It sounds like wheezing air out of a ziploc bag when I push down on the pedal and if i pump it rapidly it sort-of builds up pressure, but then just wheezes out.

Booster? Check valve? M/C?

Thank you

 

[40's rock]

I blew a master on a downhill...lost most all of the pedal. I do not recall any air sounds, just could not build pressure when I tried to pump it up.

To my understanding, the best way to check if it is the booster is to try to pump it up with engine off / then start to see if the pedal gives or vice versa.

 

[firestopper]

Check master break fluid level, booster for vacuum leak. you should be able limp it home using e-brake and low gears.
Quick way to check booster is to place a "T" between manifold and booster and a vacuum gauge. Look for vacuum drop when you press the brakes with engine idling.
You stated "wheezing air" sound to me like a bad diaphragm in the booster. You should not loose brakes completely,only vacuum assist aka power brakes.
good luck and "test before you replace".
firestopper

 

[firestopper]

Check master break fluid level, booster for vacuum leak. you should be able limp it home using e-brake and low gears.
Quick way to check booster is to place a "T" between manifold and booster and a vacuum gauge. Look for vacuum drop when you press the brakes with engine idling.
You stated "wheezing air" sound to me like a bad diaphragm in the booster. You should not loose brakes completely,only vacuum assist aka power brakes.
good luck and "test before you replace".
firestopper

 

[dmaddox]

I'll have to go buy a "T" and a vacuum gauge. Not a big deal. In the meantime - are there any tests I can run out to the parking lot and try?

It was mentioned to try to pump it with the vehicle off and then on. What am I looking for? If I can build up pressure while OFF and then start it and the pedal goes to the floor - bad check valve? If I can't build up pressure either way - bad booster?

Thank you

 

[SteveH]

Here's a test - with the engine off, pump the brakes until the pedal is hard. Press fairly hard on the brake pedal and while holding it, then start the engine. The brake pedal should go down as the booster starts working. If there is no change when the engine starts, then the booster is probably bad.

If the pedal just flat goes all the way to the floor when pushing (over a relatively short period of time), then the master is shot. The pedal should never go to the floor with properly working brakes (obviously). Check brake fluid levels (as a matter of course) while you're under the hood and look at all 4 corners for obvious brake fluid leaks.

 

[firestopper]

Here's a test - with the engine off, pump the brakes until the pedal is hard. Press fairly hard on the brake pedal and while holding it, then start the engine. The brake pedal should go down as the booster starts working. If there is no change when the engine starts, then the booster is probably bad.

If the pedal just flat goes all the way to the floor when pushing (over a relatively short period of time), then the master is shot. The pedal should never go to the floor with properly working brakes (obviously). Check brake fluid levels (as a matter of course) while you're under the hood and look at all 4 corners for obvious brake fluid leaks.

Agree, but check all vacuum hoses for slits connections etc.

 

[Splangy]

If the pedal went to the floor, its not the booster. If the booster (or vacuum line) failed, the brake pedal would have gotten former, not softer.

Look for fluid loss in the master cylinder reservoirs. Are the reservoirs still full? Half full?
Also check for leaks at all four wheels and along the lines/hoses. Brake fluid leaks usually make a mess and are usually very easy to spot.

 

[Poser]

Do you have the sectioned single reservoir on the master or two individual reservoirs?

What is the fluid level to the rear circuit?

Are you leaking fluid anyplace under the truck?

 

[RicardoJM]

I experienced a similar failure and fortunately did not hit anything. I limped home with low gears and emergency brake. My failure component was a passenger front brake cylinder. It was an opportune time to convert to disc brakes up front. If you brake fluid is low in the master, a line or cylinder likely is leaking and there will be brake fluid at the failure point.

 

[lostmarbles]

Hi Dallas.

I'm with Poser et al.

Is there any loss of brake fluid?

I'm thinking perhaps the rear hydraulic circuit has blown a hole leaving just your front operational.



PS. I note from your signature line that you still have your BJ42. What's the story with it? As I recall your build thread sort of stopped dead in its tracks with many asking for updates but eliciting no reply from yourself.

 

[Coastline]

Lost brakes! Almost crashed.
On the way to work this morning in my 1980 FJ40 (100% stock), 52K original miles.

That is a 33 year old and VERY used truck, chronologically speaking. This is an excellent example of why anyone who wants to buy a Fj40 for just a few thousand $$ and expect it to be a daily driver right out of the car wash might be insane.

Time will take its toll on old rubber.

 

[Poser]

Do you have the sectioned single reservoir on the master or two individual reservoirs?

What is the fluid level to the rear circuit?

Are you leaking fluid anyplace under the truck?

What did you find out?

 

[dmaddox]

Sorry - it's been VERY cold and I haven't had an opportunity to dig into it.

With the engine off, I can build pressure (high pedal) - but when I come to a stop it just locks up the fronts, even after pumping.

When I got home - I noticed that yes, the rear brake fluid cup was empty.

I keep an eye on all fluids - this is not my first cruiser "out of the car wash". However - if this is negligence on my part - I need to learn what I did wrong, and how to fix it.

thank you!!

 

[dmaddox]

Hi Dallas.

I'm with Poser et al.

Is there any loss of brake fluid?

I'm thinking perhaps the rear hydraulic circuit has blown a hole leaving just your front operational.



PS. I note from your signature line that you still have your BJ42. What's the story with it? As I recall your build thread sort of stopped dead in its tracks with many asking for updates but eliciting no reply from yourself.

I am in the US Army and was gone all of last year, I returned home in late November. I plan on getting back into the BJ42 project when it warms up a bit!!

Thanks!

dallas

 

[Pearly]

Welcome home!

If your rear chamber is empty, I would suspect you have a leaking rear cylinder. Time to take of the rear drums and have a looksy! You could do the disk conversion while you're in there!

 

[ken_79-fj40]

My old master cylinder was actually leaking fluid out of the rear circuit right into the booster. Brakes worked fine, but if it went dry I would have brakes like you describe. If you don't see anything near the rear wheels or coming out of a line it wouldn't hurt to unbolt the master and see if it's doing what mine did. Of course now I have new master installed in mine and I can't seem to get it bled solo with my pressure bleeder so I have no brakes at all. I need to enlist a pedal pumper soon.

 

[PabloCruise]

Oh noes Dallas - that sounds like a bad morning!

Glad no one was injured.

Not much new to add here... Look for leaks at the rear cylinders, rear soft line and finally at the master.
the leak is one thing, but what about the wheezing noise you heard? I guess it could be possible your MC is leaking into the booster and damaged the rubber in there as well?
If your MC is bad you can bench bleed it first and then do a full system bleed. Easier than clamping the MC in a vice is to mount it on the vehicle and use bleeder nipples on the MC w/ that clear plastic aquarium tubing running back into the reservoirs. That way you can use the leverage of the pedal to bleed the master, and then hook up lines and bleed all 4 wheels.

Let us know what you find!

 

[lostmarbles]

I am in the US Army and was gone all of last year, I returned home in late November. I plan on getting back into the BJ42 project when it warms up a bit!!

Thanks!

dallas

There's a number of us on the diesel board that miss your posts there Dallas ... so it'll be great to have you back delving into the depths of Toyota's 1980's diesel-electrical mysteries (as you were before).

I'll use my mind-power to transfer some of our summer heat over your way.

 

[Tin basher]

Had my 76 do the same thing blew a front line
I did hit something 1800 bucks damage to a 95 dodge
Scratched the paint on bush bar on cruiser
Good was it happend pulling into my driveway
Bad I had two broken trucks