brake pedal to the floor and reservoir overflowing

[Brian Maenpaa]

So I'm running heavy on a steep downhill trail and my brake pedal goes to the floor. I pull the mostly ineffectual hand brake which slows me enough to drop the truck onto 1st/low and coast to a flat spot. When I get out, my reservoir is overflowing. I'm in the middle of the mountains far from assistance and no cell service, so I let the truck cool and draw all the extra fluid from the reservoir. I then pump the peddle with the key off a couple of dozen times and pressure restores to some degree. I turn the engine on and the brakes are a little soft but working again. After a mile or so, the brakes are good as new. In fact, I was able to drive all the way home without any issues at all. 30 years on track and trail and this has never happened.
Before I start replacing things, I thought I would post for feedback.
Thanks in advance.

 

[smritte]

Sounds like you boiled the fluid. Brake fluid absorbs moisture over time lowering the boiling point and forming acids.
When's the last time you changed it?

Slow downhills have very little airflow across the rotor. The rotor needs airflow to pull away heat. The heat buildup hot soaks the calipers and you get this. I would see this often at off road events with long slow downhill trails.

 

[Brian Maenpaa]

Couldn't tell you. 10 years ago maybe. I topped it off right before the trip. Sounds like it's time. I was running really heavy and had just descended probably 2000 feet in like 4 minutes.
The booster and cylinder are original and have never been a problem. Would you recommend proactive replacement?
Thanks Smritte.

 

[ZackR]

Switch to a two year interval for brake fluid and I bet this never happens again. It's often the most neglected but crucially important fluid to keep in good condition. With a one man bleeder (also known as the gatorade bottle method) it's easy to replace the fluid without introducing any air (the fluid drains into a container with the hose submerged so air cant be sucked back in). I have four vehicles and a motorcycle so I'm flushing brake fluid pretty regularly and this method works great.

 

[Brian Maenpaa]

Thanks Zack. I just found a video showing that exact process and will do ti this weekend.
Sooo many fluids!

 

[80serie]

I had the same issue. Pads, fluid, rotors are all in good working condition. Before I spent trying money trying to fix it, I checked my LSPV valve for adjustment. Although it was in the middle of range specs, I changed the adjustment to max spec for rear brake (but still within specs). I realized that I was braking only with the front brakes. It takes 15 minutes to adjust, cost nothing and my truck feels much safer now.

 

[jonheld]

Couldn't tell you. 10 years ago maybe.

Brake fluid should be almost water clear. The darker it gets, the more contaminated it is.
As previously stated, it is hygroscopic and does not "flow" through the brake system. So it just sits there and will corrode the hard brake lines and caliper pistons from the inside out.
It should be changed at least every 2 years or so, like EVERY other fluid in the vehicle. This is basic maintenance.

 

[smritte]

Replacing the rubber parts should probably be done soon. My Cruiser was almost 20 years old when I got it. Brake system "worked". When I replaced the flex hoses, you could bend them into curly "Q's" and push rubber chunks out of them with brake clean. I was able to chip pieces of the master cylinder seals away with my fingernail. This is the result of the acid breaking down the rubber. As the others have posted, the fluid should be clear with a very slight amber color. As acids form, it attacks the rubber turning it brown. As it gets worse it turns black from the acid attacking the aluminum. Now your pitting the master and caliper bore's. I've seen brake fluid look like adobe mud. Cast iron brake parts where the moisture was rusting the iron.

If you have ABS, there's seals inside the system. "If" those seals break down, you get a symptom exactly like a bypassing master cylinder, pedal slowly goes to the floor with no fluid loss. Some abs have a test port for this, ours doesn't. I have replaced a number of ABS units for this issue over the years and is the main reason my cruiser no longer has ABS.

 

[smritte]

It's often the most neglected but crucially important fluid to keep in good condition.

For some reason, no one ever changes brake fluid and power steering fluid

 

[COS80]

For some reason, no one ever changes brake fluid and power steering fluid

And its not even hard to do. I've never understood this.

 

[Brian Maenpaa]

Thanks All.
It's always something with an old truck.