No brakes. Bad Master cylinder?

[Lowside]

Hello folks. I have a question about the brake system on my 1994 FZJ-80. On my way home from work Friday I noticed the brake pedal traveling a bit farther toward the floor each time I'd use it, until it was actually bottoming out with no braking whatsoever! Luckily I was close to home so I used the e-brake and got it home. I was away for the weekend and got a chance to look at it again today. Strangely enough the brakes were fine this morning when I fired it up and drove it up and down the driveway. I'm not planning on driving it but found that to be a little strange. It was much cooler this morning then when the problem occurred on Friday. I checked the fluid reservoir and it's full. Does this sound like bad master cylinder?

I priced new master cylinders as well as master cylinder rebuild kits today and would like go the rebuild route. Does anyone know how involved installing a rebuild kit is? Any special tools required?

Many thanks for any help...

Ted

 

[Jim_Chow]

Just out of curiosity, when was the last time you flushed your brake fluid?

 

[Lowside]

Just out of curiosity, when was the last time you flushed your brake fluid?

I did a full system flush with a Mighty Vac in Sept of 2002. I got the truck in Feb of 2002 and don't know any history before that. It was a fairly neglected vehicle so I doubt it had been flushed very often in its life. Does flushing sometimes cause master cylinder failures??

Ted - Denver

 

[corbs]

I think he was going to suggest you flush it if you hadn't. You might want to check your slave cylinders or whatever they're called at the brakes. You may have a leak there. I had a leaky cylinder that would cause loss of pressure off and on.

 

[Kalawang]

When brakes fade, double pumping sometimes helps. Other times you just step harder instead of gently.


Were you using the brakes heavily when it began to fade ? I have experienced your symptoms but only when using the brakes heavily/frequently, as in driving down a mountain. In my case, a bit of rest for a meal brought my brakes back to normal.

I doubt a check up will find anything wrong if these symptoms came up only during heavy brake use. It might help to look for a different brake fluid, but the debate on that continues.


Kalawang

 

[turbocruiser]

When brakes fade, double pumping sometimes helps. Other times you just step harder instead of gently.

Were you using the brakes heavily when it began to fade ? I have experienced your symptoms but only when using the brakes heavily/frequently, as in driving down a mountain. In my case, a bit of rest for a meal brought my brakes back to normal.

Kalawang

Kalawang, I'm not any at all trying to sound motherly here ... I'm hoping it simply sounds friendly ... but if your brakes are behaving that way, they are running really really hot, so hot in fact immediate failure is possible.

When you are driving down mountains you need to rely on engine braking ( staying in lower gears without overdrive on ) much more than on brake braking. I drive up and down mountain passes all the time and honestly I almost always ONLY lightly touch or tap the brakes just prior to placing the rig into turns and the rest of the time I rely on the right gear and the right amount of acceleration.

To give you an example, whenever you drive down one of my favorite passes, Pike's Peak, 14K elevation, there are multiple checkpoints on the way down where local officials stop your vehicle, feel for excess heat from the brakes and FORCE you to stop driving if the brakes are too warm. While you are waiting for the brakes to cool, they basically provide the same advice as above. Again, not any at all to sound wrong, just hoping this helps keep you on the road - literally!!! Peace.

 

[Kalawang]

Kalawang, I'm not any at all trying to sound motherly here ... I'm hoping it simply sounds friendly ... but if your brakes are behaving that way, they are running really really hot, so hot in fact immediate failure is possible.

When you are driving down mountains you need to rely on engine braking ( staying in lower gears without overdrive on ) much more than on brake braking. I drive up and down mountain passes all the time and honestly I almost always ONLY lightly touch or tap the brakes just prior to placing the rig into turns and the rest of the time I rely on the right gear and the right amount of acceleration.

To give you an example, whenever you drive down one of my favorite passes, Pike's Peak, 14K elevation, there are multiple checkpoints on the way down where local officials stop your vehicle, feel for excess heat from the brakes and FORCE you to stop driving if the brakes are too warm. While you are waiting for the brakes to cool, they basically provide the same advice as above. Again, not any at all to sound wrong, just hoping this helps keep you on the road - literally!!! Peace.

Turbo,


Thank you for the advice. It is correct in most instances. However I was on a long downhill and already in low gear and still driving faster than I was comfortable with. Thus the brakeing. I've made that trip often enough and have tried to stay off the brakes, but no go. Given time and a bit more cash or a better income, I'll probably upgrade my entire brake system, or leave earlier so I can stop more often.


Kalawang

 

[Lowside]

Kalawang, thanks for the reply. No, this definitely wasn't brake fade, like you get from heated up brakes during heavy use. I was in stop and go traffic, going not more than 5 miles per hour. This was complete brake failure, pedal to the floor with no braking whatsoever. Pretty freaky. I just wonder what would cause that type of failure one day with brakes that are fine the next. I actually drove it around the neighborhood today trying to make if fail again and couldn't. The master cylinder reservoir is full and there are no apparent brake fluid leaks anywhere.

Were you using the brakes heavily when it began to fade ?

Kalawang

 

[Kalawang]

Lowside,

Try depressing the brakes gently with the engine on but not moving. If the pedal goes down, see if you can fix it with vigorous pumping.

Your last flush was in '02. I change my brake fluid much more often. It's cheap. Try that too.


Kalawang

 

[ElJefe]

Kalawang, thanks for the reply. No, this definitely wasn't brake fade, like you get from heated up brakes during heavy use. I was in stop and go traffic, going not more than 5 miles per hour. This was complete brake failure, pedal to the floor with no braking whatsoever. Pretty freaky. I just wonder what would cause that type of failure one day with brakes that are fine the next. I actually drove it around the neighborhood today trying to make if fail again and couldn't. The master cylinder reservoir is full and there are no apparent brake fluid leaks anywhere.

I had a similar problem with the clutch MC on my BMW. Very intermittent. Pedal to the floor, and I would pull it back with my toe, and it would work fine for another couple weeks/months. Rebuilt it and continued to have the same problem. Finally after about a year I got fed up and replaced it. It never happened again. FWIW, I disected the old MC and it looked to be in perfect condition... no rust, no scoring, still had factory hone marks, and cups looked perfect?!?