Master Cylinder Failure

[RKplus10]

The rear master cylinder went bad on my 2015 Freewheeler this week. Pedal just dropped to the “bottom of the barrel”. Pumping did nothing and there are no leaks. I stopped and let the pedal “pop” upwards a couple of times while gently tapping on the master cylinder. I got a little bit of pedal, but not much. I took it to a mechanic who checked it out and he says m.c. is bad. I called around and apparently there are none in Texas. On back order but due next week. Strange, but TriGlide 2015 had a recall and they use the same part. Go figure.

[RKplus10]

Oh yeah, before anyone asks, no it had never been flushed with 18,000 miles. The fluid actually looked good but I guess I learned my lesson.

[Blueraven]

The rear master cylinder went bad on my 2015 Freewheeler this week.

I’m not aware of the reliability of Harley master cylinders however I don’t think failure is a common issue.

I think it’s highly likely you just happen to have a rare failure.

As far as doing a fluid flush; it’s not a mileage thing it’s a time thing.

Per The owners manual it should be flushed every two years.

This thread reminds me I need to flush the fluid on my Freewheeler as it’s been more than two years since it’s been flushed.

[Old Road Dog]

Every two years is what HD recomends. Investing in a brake fluid tester is worthwhile as they are so inexpensive now. I test the brake fluid once per month. Regardless, I flush the brake system every spring and again in the fall. I dont use any of the commercial flushing agents- I think they lead to trouble IMO. Just flush with brake fluid.

[Jack Klarich]

Roy, IMO HD created their own bad JUJU on the early models of the Freewheeler

Take a look at how the front brake lines run, look to see where the front brake light switch is.

Running brake lines and master cylinders too close to hot exhaust parts is never a good idea IMO

The brakes when applied cause a rise in fluid temps, now add the extra heat from the exhaust and engine crank case and you will see the need for replacing the brake fluid sooner than waiting for a part failure. JMO

As brake fluid heats up it reaches boiling point and produces gasses

In turn the gas does not like to compress as good as clean fluid, thus forcing you to pump the brakes and or stand on the pedal harder to stop

This causes the piston and seal in the master cylinder to travel further in a probably already scored cylinder, now you are losing pressure also ( you have an internal leak of the primary seal)

The scoring comes from the moisture absorbed in the brake fluid. Now you can easier understand how and why changing fluid and flushing is so important

This is also true of hydraulic clutch components , the only saving grace I see on modern Harley's is the use of better brake line materials ( IE plastics and stainless components) less prone to the moisture content of failing brake fluid

[RKplus10]

Thank you, guys. I learned my lesson (the hard way). I’ll definitely take care of all three systems.