I have a 94 Land Cruiser and last week after visiting one of Costa Rica's volcanoes, on the way down, near the bottom, the brake pedal started getting spongy. The brakes still worked but the pedal seemed to be getting lower, which I remedied by pumping. After a while the problem completed subsided and went back to normal pedal operation. The same thing happened a few days later, under the same circumstances, agaom coming down from the volcano. I did not think I was riding the brakes, but using lower gears, and tapping on the brakes as needed. Anyway, it did happen a second time, and I pulled over and the brake disks was very hot, not smoking, but hot...............burned my finger. I have never had first hand experience with over-heated brakes. I know that if it's too severe, the pads/disk will glaze over causing a loss of braking power. That did not happen; it was just spongy brakes for a period of time. My question: is it normal that a brake pedal gets spongy and seems to drop near the floor when the brakes get overheated, and then returns to normal with continued driving? It has not recurred at all after that second time. I'll be taking it to my Toyota mechanic soon, but I'd like to be able to suggest to him what caused the anomaly.
Brake Pedal Fade from Overheating?? (1 Viewer)
- Thread starter talegate
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When was the last time you flushed/changed your brake fluid? I was having the same problem and changed mine - problem solved. Something about overuse and heat get condensation in the system. I'm sure someone much smarter than me will chime in but changing the fluid solved this problem for me. Good luck!
-Rob
-Rob
Yes, you need to do a brake fluid flush and make sure you have removed all air. When the brakes get that hot, the brake fluid boils, causing gas bubbles. The gas is what causes the spongy pedal. As it cools down, it is back to a liquid and works fine. You were pushing your system hard and not far from failure. Part of that cause can be due to the LSPV lifting the rear, reducing brake pressure on e rear and forcing the front brakes to do all the work. (As the rear lifts, it reduces brake pressure to the rear in order to prevent rear wheel lock-up.)
Brake fluid is VERY hygroscopic (absorbs water) and it does need to be changed every so often to flush out the moisture-laden fluid. Fluid with water in it will boil at a lower temperature than fresh fluid. Only use fluid from a new, sealed container. Do NOT use synthetic unless you want to replace your entire braking system. (DOT 3 is what you need, NOT DOT 4)
Brake fluid is VERY hygroscopic (absorbs water) and it does need to be changed every so often to flush out the moisture-laden fluid. Fluid with water in it will boil at a lower temperature than fresh fluid. Only use fluid from a new, sealed container. Do NOT use synthetic unless you want to replace your entire braking system. (DOT 3 is what you need, NOT DOT 4)
Squash
SILVER Star
Sounds like you are generating excess heat because of constant brake application which in turn can cause brake fade/gassing at pads and rotor/drums, spongy pedal most likely from water contaminated brake fluid.
In the mean time gear down and let the engine control your desent.
Combine braking with engine braking, this will allow time for brake system to somewhat cool
Flush brake fluid, use new unopened fluid. Upgrade your components to incorporate the latest technolgy if you plan on future long decents...
We drive lots of -15% grades and yes the proper gear does wonders!
In the mean time gear down and let the engine control your desent.
Combine braking with engine braking, this will allow time for brake system to somewhat cool
Flush brake fluid, use new unopened fluid. Upgrade your components to incorporate the latest technolgy if you plan on future long decents...
We drive lots of -15% grades and yes the proper gear does wonders!
As others have said, fluid change will help. If the problem persists, your rubber brake lines might be getting fatigued and expanding under braking, in which case the solution would be new soft lines or braided steel lines. But change out the fluid and bleed the system first.
I have this same issue whenever I go to certain trails around here where there is a steep windy decline on the way back. I even have the powerstop 360 brake rotors and pads from duizer. Which havent really helped much btw. I have flushed my fluid and it's still a problem. The issue is that the pads generate so much heat that they sublimate and a gaseous buffer forms between the pad and rotor that your calipers have to overcome in order to regain grip. Not much you can do about it except use engine braking power and pull over and put it in park before you totally lose brakes. You can get some pretty great brake fluid like redline and stuff, that doesn't boil until ridiculously hot temps, but it will only give you a slightly better chance of overcoming the outgassing of your brake pads. I would make sure your parking brake is in top notch condition, might need it if you're going to do a lot of that type of driving.
I didn't think about the outgassing on the pads. Makes sense as well. That's some serious hard braking for that to occur, but it does happen.
Outgasing doesn't just occur during high speed short burst breaking like in racing... A lot of it has to do with the length of time and frequency of your braking and your overall driving habits as well as the weight of the vehicle. The 60/62 and 80 series land cruisers are far too heavy for the brakes they came with. Some people may argue that their cruiser will lock them up if need be. That doesn't mean that the brakes are adequate. Sure, at 35-45mph on a flat damp road your cruiser will lock its brakes no problem. Then again, the gripping force and available surface area of your pads against your rotors is substantially greater than the grip your damp rubber tire has against damp asphalt and your tire is certain to lose its bight long before the pad and rotor are too hot to outgas. But for dry pavement and tires that are wide enough, tall enough and have a substantially greater contact surface and ability to grip pavement, the pad and rotor lose the battle and are easily overheated to the point where outgasing is frequent on declined terrain. The only real solution is to realize that you're not driving a car, you're driving a large vehicle and with that change in vehicles has to come a change in driving habits, and even then, the 80 series will always be too heavy for constant consistently reliable breaking in hillie terrain.
System wide or just a quick temporary fix?
Cooling fins on the calipers over the pistons type thing or a windshield washer hooked up to spray alcohol on the calipers type thing?
Because both are doable with the correct rescouces, one is expensive and long term, the other is cheap and doable with junkyard parts.
Cooling fins on the calipers over the pistons type thing or a windshield washer hooked up to spray alcohol on the calipers type thing?
Because both are doable with the correct rescouces, one is expensive and long term, the other is cheap and doable with junkyard parts.
I’m in for something long term. In 4 low and 1st I still boil the brake fluid on a few trails I’ve found. Great rotirs, pads, new fluid. Still boils and lose brakes just about. Speed is slow so I’m not sure slotted or drilled makes a difference. So my thought is cool the fluid. Not sure that it’s really possible though.
Ducted air cooling is out then, because of the slow speed.
Forced air cooling over finned calipers would work with a high enough volume air compressor. The reworked Yorks run about 10CFM at 1000RPM.
And if combined with a misted coolant, like methanol/water mix you could potentially reach sub 30 F temps.
With a vortex cooler you'll hit sub Zero F temps. I'm looking at this type of cooling for the winch motor.
Interesting thoughts here.
Forced air cooling over finned calipers would work with a high enough volume air compressor. The reworked Yorks run about 10CFM at 1000RPM.
And if combined with a misted coolant, like methanol/water mix you could potentially reach sub 30 F temps.
With a vortex cooler you'll hit sub Zero F temps. I'm looking at this type of cooling for the winch motor.
Interesting thoughts here.
Then why would he get a low pedal?
Because any water absorbed into the brake fluid is boiling off creating steam, which is a gas, which is compressible.
Brake systems are dead headed at the caliper reservoir, there isn't any flow, so cooling the lines doesn't do anything.
Yes boiling fluid is compressible but how can outgassing pads cause a low pedal- ?
I’m not sure honestly. I know that on a recent trail, 4 lo, 1st gear, insane long decline. Engine bay at 165. 102 outside. Hard braking to avoid obstacles. No choice but to brake. Overheated. Stopped. This time I scanned the caliper, 290 degrees. Super hot. Bled off some fluid from right rear, super hot, nearly clear, no air. Added new fluid. Finally cooled it off with water on all 4. Made it down.
Brake rotors, calipers, pads, fluids, all less than 1K on them. Mostly OEM. New master cylinder, new booster both OEM. Great brakes the rest of the time. Pedal hit the floor on this hill, no stop. Luckily the parking brake is all new.
So, I blame hot calipers making the fluid boil, slight foaming.
Stumped me.
I could see where outgassing pads would create a boundry condition with a layer of gas between pad and rotor reducing/eliminating friction. But that wouldn't cause low peddle.
Good point.
