Always air in the brake fluid - John Deere Gator Forums
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post #1 of 3 Old 09-19-2019, 06:45 PM Thread Starter
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Join Date: Sep 2019
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Always air in the brake fluid

We have a 2018 Gator 855D and apart from wallowing around in cow shit (she works on a dairy farm) and being driven by hooligans she has a relatively easy life. No high speeds, a wash before she goes to bed and very regular servicing by yours truly.
However recently the brakes have started to suffer. I know it’s air because I can bleed a heap of bubbles out of each calliper but there’s no evidence of fluid loss nor damage to the flexi or hard pipes. Once bled, the brakes are okay for a few days and then start to deteriorate again.
Has anyone come across this before and can provide some insight?
My only recourse is to swap out the master cylinder but that seems quite an expensive option on the off chance it might fix it.
Many thanks in advance and I’ll provide whatever extra detail I can but please remember I live in the future so there might be some delay between our replies.
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post #2 of 3 Old 09-20-2019, 10:57 AM
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Perhaps you can apply vacuum to the master cylinder lid and check for bubbles continuing to peculate through the fluid. Then apply vacuum grease (dielectric grease) at various points to see if it slows the bubble stream. I'm thinking at the brake bleeder threads and opening, line fittings, etc...

Some seals are made to retain more pressure in one direction than the other or the pressure assists in the sealing force. Think of a u-cup seal, where the open end of the U-cup is facing brake pressure. The seal holds while putting on the brakes, but leaks air when released.

2012 JD855D OPS Black Poly Roof, Deluxe Cargo Box, Front and Rear Protection, Power Lift, Front Hood Rack, Rear Screen (homemade), 800 Watt Inverter, 2500lb Winch installed in cargo bed, Front and Rear LED auxiliary lighting (4" square 27 watt), Front and Rear CV Guards, Koplin Side Mirrors
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post #3 of 3 Old 09-20-2019, 11:56 AM
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Firstly ill tell you a safety first horror story which i need to remind me of from time to time:
Never ever feel for leaks on high pressure hoses.
High pressure oil injecting in the skin can cause tissue loss, serious illnesses and death.

That being said the hoses could possibly be porous enough to let air in and not oil out.

What could also be is that the brake master cyllinder is not holding pressure.
I had the same experience a month ago with a new mechanic that kept saying air was coming out while in fact he just saw brake fluid squirting out with high pressure.
The culprit turned out to be the brake master cyllinder.which lost pressure due to a bad seal

If you keep the pedal pressed does it lose pressure over time?
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