Vacum Brake booster ?

[Eduardo96FZJ80]

Vechicle : 95 FZJ80 160k (Son's)

While driving down mountain, heavy use on brakes, (stop and go all the way down)
his brake pedal went floorboard ("lost about 80% of brakes" ) They pulled over, shut down vechicle and inspected system for fluid leaks and or vacuum leaks. They found nothing abnormal. They restarted the vechicle, test drove in a safe area, brake pedal normal again.

I searched and found little or no similar situation. Could the vaccum booster be failing?

I will try again

 

[Jim_Chow]

I would have thought that if the booster fails, you'd feel like you have no brakes, but the pedal should stop in about the same spot since the booster merely applies more pressure to the master. If the master cylinder is leaking internally, the pedal might go to the floor.

 

[Owyhee Jackass]

Sure it wasn't the ABS kicking in?

 

[Eduardo96FZJ80]

I would have thought that if the booster fails, you'd feel like you have no brakes, but the pedal should stop in about the same spot since the booster merely applies more pressure to the master. If the master cylinder is leaking internally, the pedal might go to the floor.

Good point, any idea as to why when they shut down and restarted brakes returned to normal?

 

[Landpimp]

bad booster will give you a high and hard pedal, not low and soft

 

[Eduardo96FZJ80]

bad booster will give you a high and hard pedal, not low and soft

Thanks,
So more than likely high heat in brake system caused some type of failure.

 

[Landpimp]

brake fuild might have just got too hot, flushing the brake system would make sense.

Thanks,
So more than likely high heat in brake system caused some type of failure.

 

[treerootCO]

Sounds to me like you boiled the brake fluid hot rod.

You want to brake before the turn, let off and power through the corner.

You can check the master by having someone press the brake and see if the fluid bubbles, rises, or swirls. I think my master is gone. If I press on the pedal, most of the fluid goes into the reservoir. I am going to NAPA today to see if the 170 is Aisin....I went to the dealer and they told me 258.00 and no one in the State carried the part. (12/78 FJ40) NAPA carries 3....one for 50, one for 100, and one for 180. I would call CDan but I'm not sure I have enough time. I want to make the snow run this weekend and I think brakes would help out.

 

[Landpimp]

Mike

I just got a Beck Arnly for my 82 fj40(same master up to 90) for $65, it was new(not reman) but not Aisin, it was made in the US. I called around and had some places check the boxs on other aftermarket brands and none were Aisins

I did find another brands(forget what) for $150.....but didn't check on the maker, figured if I was spending $150 I would spend an extra few bucks on OEM.

But it seem to work just fine, its very slighly different then the OEM one, but bolts up 100% like stock.

I got a EGR cooler tube, cooler nightmare going on........I hate old egr crap!

Sounds to me like you boiled the brake fluid hot rod.

You want to brake before the turn, let off and power through the corner.

You can check the master by having someone press the brake and see if the fluid bubbles, rises, or swirls. I think my master is gone. If I press on the pedal, most of the fluid goes into the reservoir. I am going to NAPA today to see if the 170 is Aisin....I went to the dealer and they told me 258.00 and no one in the State carried the part. (12/78 FJ40) NAPA carries 3....one for 50, one for 100, and one for 180. I would call CDan but I'm not sure I have enough time. I want to make the snow run this weekend and I think brakes would help out.

 

[Rich]

Ed,

The problem you described sounds very simple. Heavy use of brakes on a long downhill descent can overheat the pads and the brake fluid. If the fluid boils, then the master cylinder has to compress the brake vapor, which results in much longer peddle travel and much less braking.

What your son needs to do in similiar circumstances is to slow the truck down by driving in a lower gear so as to minimize the use of brakes.

New brake fluid would help, but is no guarantee against the problem happending again.

 

[Gold Finger]

Boiling brake fluid is what it sounds like, I have experienced the same on other vehicles when driving very hard. Brake fluid will boil easier the older it gets as it is hygroscopic and the water boils at a lower temp. That is unless it is silicone based

 

[Jim_Chow]

Sounds to me like you boiled the brake fluid hot rod.

You want to brake before the turn, let off and power through the corner.

You can check the master by having someone press the brake and see if the fluid bubbles, rises, or swirls. I think my master is gone. If I press on the pedal, most of the fluid goes into the reservoir. I am going to NAPA today to see if the 170 is Aisin....I went to the dealer and they told me 258.00 and no one in the State carried the part. (12/78 FJ40) NAPA carries 3....one for 50, one for 100, and one for 180. I would call CDan but I'm not sure I have enough time. I want to make the snow run this weekend and I think brakes would help out.

I got my Aisin (made in japan) FJ80 Master from a cruiser shop in NC for around $130 a couple of years ago. They originally sent me a FZJ80 MC, which would have worked, but I would have had to bend some hard lines. I think Man-a-fre has them for around $130, too.

Is your brake fluid brown/tan? If so, it's long gone. Better flush it out before everything rusts internally.

 

[Eduardo96FZJ80]

Thanks for all the input. Sounds like I should flush and bleed my brakes also.