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Strange Brake Problem

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Old Jan 3, 2017 | 08:25 AM
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Strange Brake Problem

I'm normally pretty good about diagnosing problems but this one has me stumped. I drove my truck the other day to pick up a trailer. Brakes felt normal all the way there. As soon as I picked it up I felt a difference in braking, it was to be expected, as the trailer did not have it's own brakes and is a PIG. However, I expected to need more braking, not for the pedal to feel spongy suddenly. Got the trailer home and took the truck for a drive to see if it was just because of the trailer or not, and it is not. The brakes were just fine, and now they are spongy. I checked for leaks and cannot see any leaks anywhere. Pads and shoes still look good as well.

Any thoughts?
 
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Old Jan 3, 2017 | 08:46 AM
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"Spongy" is almost always air in the lines.
 
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Old Jan 3, 2017 | 08:57 AM
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Did you by chance get the brakes hot???
 
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Old Jan 3, 2017 | 12:58 PM
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Originally Posted by F250_Super_4X4
"Spongy" is almost always air in the lines.
I agree but how would it get in there when I cant find a leak. And how would it happen so suddenly?

Originally Posted by 78 PEB
Did you by chance get the brakes hot???
No. Normal driving and it was literally hard one minute and spongy the next.
 
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Old Jan 4, 2017 | 08:39 AM
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Bueller, Bueller?
 
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Old Jan 4, 2017 | 09:07 AM
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The situation could depend on how long it's been since the brake fluid has been flushed out for new fluid and how hot the brakes got with the fluid that's currently in the brake system.

If the fluid is old, it's likely accumulated moisture. Moisture is water. If water gets hot enough from the brakes, it'll boil and turn into a gas inside the brake system. Gas is compressible and the only way to get it out, to get rid of the sponginess (if this is what happened), is to bleed the brake system out with fresh brake fluid.

Brake fluid should be changed every 18 to 24 months (max) to minimize moisture accumulation.
 
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Old Jan 4, 2017 | 01:23 PM
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I would bet on it being a brake hose. If they swell they feel spongy which would make sense that it came all of the sudden.

Get someone to press the pedal and look at each hose.
 
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Old Jan 4, 2017 | 03:03 PM
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Originally Posted by ultraranger
The situation could depend on how long it's been since the brake fluid has been flushed out for new fluid and how hot the brakes got with the fluid that's currently in the brake system.

If the fluid is old, it's likely accumulated moisture. Moisture is water. If water gets hot enough from the brakes, it'll boil and turn into a gas inside the brake system. Gas is compressible and the only way to get it out, to get rid of the sponginess (if this is what happened), is to bleed the brake system out with fresh brake fluid.

Brake fluid should be changed every 18 to 24 months (max) to minimize moisture accumulation.
Brake fluid is fresh as of 4 months ago.

Originally Posted by PA74F250
I would bet on it being a brake hose. If they swell they feel spongy which would make sense that it came all of the sudden.

Get someone to press the pedal and look at each hose.
That makes sense. I'll check that out this weekend when I have some help.
 
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Old Jan 9, 2017 | 11:09 AM
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Turns out I forgot to look at the Proportioning valve. Its leaking bad. Bad enough that the front of the master cylinder is empty. Looks like its time for some brake work.
 
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Old Jan 9, 2017 | 11:11 AM
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Anything special I need to do for the Master Cylinder since the front is empty, or just a standard bleed after I replace the PV?
 
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