Why did my 1st gen clutch pedal get mushy?

Background:
- 2000 Tacoma, V6, supercharger
- 80-ish degree outdoor temperature
- pulling a 3500 pound trailer up a few high mountain grades (7,000 to 11,000 feet).
While climbing a grade, I attempted to downshift. The clutch pedal went halfway to the floor before I felt any resistance. It continued to feel that way until after I crested the pass. I was able to pump up the pedal during the climb, but it would go mushy again. On the way down, the clutch began to feel normal. My theory is that the engine generates so much heat when climbing that it boils the fluid in the line. Once I was descending, less heat was being generated and the fluid was able to cool.
Here's why it's weird -
It's never happened to me before and it happened repeatedly over the weekend, both outbound and on the return trip.
I have owned the truck 10 years.
I have owned the trailer six years.
I installed the supercharger four years ago.
I've pulled numerous mountain passes with this setup without incident.

One possible explanation is moisture contamination, though I don't know how it would have happened. I know "dry" fluid doesn't boil until roughly 400 degrees, where "wet" fluid will boil at under 300 degrees. Regardless, I'm going to flush the system.

Have any of you ever experienced this problem?

 

Almost sounds like air in the line? A bubble could expand at high elevations like that which could then make a bit of mushiness that you’ve been slowly getting used to suddenly noticeable....

I’m no expert here but that’d be my guess based on the dead space in the pedal

 

When was the Hydraulic fluid last changed??

I have had some so bad with moisture it freezes in the winter

Might be moisture boiling creating air pockets .

See how changing the fluid works out .

 

boiling point also decreases with altitude

 

Check the fluid, or just go ahead and bleed it and put new fluid in if it's been a long time

 

Bleed it and replace the fluid. Easy and not expensive. I’m pretty sure that’ll fix it unless there is a leak.

 

Any updates did you figure this out ??

 

Your master is taking a shit

 

I replaced the brake fluid, but it'll have to wait until I hook up my trailer and pull a long grade in order for me to test it.

 

Update: I mentioned in August that I replaced the clutch fluid. I also split a 10-inch length of rubber line lengthwise and slipped it over the hydraulic line where it is closest to the left exhaust manifold. I had NO ISSUES with the pedal getting mushy last weekend when I pulled my trailer up a fairly steep grade to 9000 feet, so I'm happy about that. Thanks to all of you for your suggestions!

 

Glad you seem to have it figured out .