brake pedal to the floor and reservoir overflowing (6 Viewers)

[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!