I'm in Costa Rica. Last year, drove up to over 10K feet to see a volcano. On the way down the mountain, the brakes got dangerously spongy. After a while, they resumed to normal brake feel and behavior. Contacted this site for help at that time. Was told that the likely culprit was old hydraulic fluid. Had the system evacuated and replaced by Toyota. Everything has been great. Yesterday, went to another Costa Rica volcano, Irazu, also over 10K feet. I was very careful of staying off the brakes, and there was absolutely no problem going up, but coming down the brakes became spongy. Got down to the bottom fine, and the brakes resumed normal operation. The brakes are in good shape; had them checked out last year when the hydraulic system was evacuated and replaced. Are these LC brake systems adversely affected by altitude? Again, I was very careful on the entire trip to stay off the brakes and used the transmission to control speed. I just can't believe the brakes overheated, given my driving slow and staying off the brakes.
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A system filled with an incompressible fluid shouldn't be impacted by air pressure. A vacuum operated brake booster might. I would still suspect brake fade however.
If the brake fluid got hot enough, it would boil sooner at higher altitude. It would have to be pretty hot, but descending a mountain might do it.
My bet is on 1 of 2 issues: 1) a small amount of air in the system which is expanding at elevation and the effects on your braking become noticeable (this implies then that your brake system is not sealed well); or 2) brake fade on the drive down the mountain.
If you are at the top of the mountain and the vehicle/brakes are cool, do you still have an issue? If so, its probably not fade.
If you are at the top of the mountain and the vehicle/brakes are cool, do you still have an issue? If so, its probably not fade.
Rivman1243
SILVER Star
The air is also thinner at 10K and doesn't cool the brakes as well
Does your truck have ABS? If yes, it's possible you have air trapped in the ABS module that wasn't flushed out when you had the fluid changed. I'm also going to say this sounds like brake fade though. What year/model is your 80?
SmokingRocks
hopelessly addicted to Cruisers
This ^
- Thread starter
- #8
The year of the vehicle is 1994. Given that I used the brakes so sparingly when I headed down the mountain, I don't think the brakes overheated. However, my first thought was that it might have air in the system resulting from the bleed when the fluid was replaced. The brakes have worked stellar since I had the fluid replaced last year, but this is the first time I've been at altitude since the work was done. The symptoms are very similar to the volcano visit before the fluid was replaced. I guess one way to avoid this problem is to stop visiting volcanoes.
- Thread starter
- #9
Forgot to provide identification information as requested:
The stamping by the shock is: FZJ80 - 0062712.
The placard on the firewall reads:
Model: FZJ80L - GNMNU
Engine: FZ-F 4477 CC
Frame: FZJ80 - 0062712
Color: 181 Trim: FD10
Trans/Axle: H151F V292
Plant/Built: A11
The stamping by the shock is: FZJ80 - 0062712.
The placard on the firewall reads:
Model: FZJ80L - GNMNU
Engine: FZ-F 4477 CC
Frame: FZJ80 - 0062712
Color: 181 Trim: FD10
Trans/Axle: H151F V292
Plant/Built: A11
Vacuum brake boosters don't work as well at high altitude. The booster has atmospheric pressure on one side of the diaphragm and vacuum (generated from the engine) on the other side, the difference in pressure across the diaphragm produces a force that then pushes on the master cylinder thereby activating the brakes. At high altitude atmospheric pressure is less so the pressure difference across the diaphragm is less therefore producing less force, possibly resulting in less effective brakes. Vehicles designed to operate a very high altitude will frequently have a vacuum pump specifically to generate more vacuum for the brake booster.
- Thread starter
- #11
Wow, SilverStar, that sure sounds like a viable answer to my problem. Thank you so much for your insight.
TO SOLVE YOUR PROBLEM.
PURCHASE DOT 5.1 BRAKE FLUID AND FLUSH OUT ALL YOUR OLD BRAKE FLUID
FIT YELLOW STUFF FRONT PADS
CHECK THE FRONT RUBBER BRAKE HOSES, IF ORIGINAL , REPLACE WITH A QUALITY STAINLESS BRAIDED HIGH PERFORMANCE TYPE BRAKE LINES-HOSES,
I HAD SIMILAR ISSUES WITH MY 80 SERIES AND AFTER FITTING THE ABOVE PARTS HAVE NEVER HAD PROBLEMS AGAIN, EVEN TOWING HEAVY LOADS AND FULLY LADEN , AND ON THE PLUS SIDE THE BRAKES ARE FAR MORE RESPONSIVE.
PURCHASE DOT 5.1 BRAKE FLUID AND FLUSH OUT ALL YOUR OLD BRAKE FLUID
FIT YELLOW STUFF FRONT PADS
CHECK THE FRONT RUBBER BRAKE HOSES, IF ORIGINAL , REPLACE WITH A QUALITY STAINLESS BRAIDED HIGH PERFORMANCE TYPE BRAKE LINES-HOSES,
I HAD SIMILAR ISSUES WITH MY 80 SERIES AND AFTER FITTING THE ABOVE PARTS HAVE NEVER HAD PROBLEMS AGAIN, EVEN TOWING HEAVY LOADS AND FULLY LADEN , AND ON THE PLUS SIDE THE BRAKES ARE FAR MORE RESPONSIVE.
- Thread starter
- #13
I will definitely have your suggestion checked out. Thank you.
