Using the wrong hydraulic brake fluid

[Nelson Howe]

Not knowing any better, I used Aeroshell 4 when I bled and topped up the hydraulic brake system in my Discus 2b. Initially it got the sponginess out of the brake. After working on it some more about a week later, I found it impossible to bleed the system further ( I thought I might still have a little air in the line) as the piston was very very slow to return after squeezing the handle. I also noticed that the rubber gasket membrane thing in the lid was deformed. After reading up on things a bit, I realize this (Tost) system calls for Dot 3-5 fluid and not the red stuff.

So how much damage have I done? What do I need to replace?

[Charlie M. (UH & 002 owner/pilot)]

In general (I have to update a correction on an earlier post here...), DOT 2, 3, 4, 5.5 are interchangeable, period.
DOT 5 is silicon based, while it "may work" it does NOT absorb water (part of my correction earlier), thus, any water in the hydraulic fluid settles to the low spot (part of that specific density bit.....now you know why you needed to pay attention to chemistry and physics in school.......
"Fluid compressibility" remains the same, just what it does with water since NO brake system it totally closed. They all have brake vents for the reservoir. Thus, they ALL allow some tiny bit of water in......

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On Sunday, May 5, 2019 at 6:26:52 PM UTC-7, Nelson Howe wrote:
> Not knowing any better, I used Aeroshell 4 when I bled and topped up the hydraulic brake system in my Discus 2b. Initially it got the sponginess out of the brake. After working on it some more about a week later, I found it impossible to bleed the system further ( I thought I might still have a little air in the line) as the piston was very very slow to return after squeezing the handle. I also noticed that the rubber gasket membrane thing in the lid was deformed. After reading up on things a bit, I realize this (Tost) system calls for Dot 3-5 fluid and not the red stuff.
>
> So how much damage have I done? What do I need to replace?

I believe the rubber components have to be a different type of rubber for each hydraulic fluid. So you probably need to replace all the rubber components.

[Charlie M. (UH & 002 owner/pilot)]

Note, I believe some brake systems use something other than a DOT rated brake fluid, so my earlier comment may be invalid.
If this is the case, then likely all the seals (piston, shaft seal, etc.) should be replaced.

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Check the color guys! 5606 is RED and Dot fluid is CLEAR. Don’t just grab any pressure pot and hook it up, it may have the wrong stuff in it. If in doubt, dip your little finger in the reservoir!
JJ

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On Sunday, May 5, 2019 at 6:26:52 PM UTC-7, Nelson Howe wrote:
> Not knowing any better, I used Aeroshell 4 when I bled and topped up the hydraulic brake system in my Discus 2b. Initially it got the sponginess out of the brake. After working on it some more about a week later, I found it impossible to bleed the system further ( I thought I might still have a little air in the line) as the piston was very very slow to return after squeezing the handle. I also noticed that the rubber gasket membrane thing in the lid was deformed. After reading up on things a bit, I realize this (Tost) system calls for Dot 3-5 fluid and not the red stuff.
>
> So how much damage have I done? What do I need to replace?

Hi Nelson,
My local club has three G103's that use DOT brake fluid. Every few years a new person comes along and grabs the 'red stuff' that is intended for the tow plane and carefully tops off a glider or two. When that happens, all the rubber bits like the O rings deteriorate and become useless. Based on this experience you will need to replace the master and slave cylinder O rings, and possibly the brake hose as well. A real pain in the hinder.

Oy!
Brian

[Craig Reinholt]

Perhaps use a label gun, then adhere a label in your G103's indicating DOT 2 or 3 (NOT 5606) would be appropriate?

[Dave Nadler]

On Tuesday, May 7, 2019 at 6:57:58 PM UTC-4, Craig Reinholt wrote:
> Perhaps use a label gun, then adhere a label in your G103's
> indicating DOT 2 or 3 (NOT 5606) would be appropriate?

You're assuming reading.
He's talking about club members.
Just use barbed wire.