Toe brake master cylinders leak at the top

[BC0979]

Just filled my brake lines with Shimano brake fluid which is mineral based and was recommended by my dealer.

Got all the connector leaks stopped except for the very top of both cylinders.🤨

The bleed Allen screw is as tight as I can get it. It is so tight that it will rotate the top plate of the cylinder.

Maybe it takes time for the top seal to expand from the newly installed mineral oil?

 

[IBob]

I did not fill my cylinders to the very top. This is also the reservoir for each brake, and I assumed there should be an air gap.

I have not had an leakage there since new.

[facthunter]

Yes you need an air space and usually a diaphragm on the reservoir to allow it to  vary in volume. IF your "rubber" parts are not for Mineral oil, you wont have brakes for long.  Mineral based oil  doesn't attract water or ruin paint.   Nev

[onetrack]

Brake seals should not expand from contact with brake fluid. If they are expanding, I'd suggest it's a sign they're adversely reacting to the mineral-based brake fluid.

Did you actually check with the brake components manufacturer as to whether the seals and other rubberised braking components are compatible with mineral-based fluid?

[IBob]

BC0979 I just printed out the 06/23 version of the Savannah S Maintenance Manual....which has grown from just 16 pages in 2014 to 132 pages in this latest version. It includes a section on the brakes including bleeding that states the oil level should not be higher than half of the (upper) tank level, or approx 20mm down from the top.

 

Onetrack, unless there have been changes (I have yet to read all of this new manual) ICP specifically call for mineral based oil.......and that is what is in my S.

[IBob]

PS: If you register your build with ICP, you get access to Maintenance Manual updates etc

I reccomend it.

[BC0979]

Ahhh.. reservoir

This is the first time for me with his type of cylinder.

My other plane had closed, non reservoir cylinders with bleeders so you could pressure bleed from either end. I did not see any info on my construction manual on the air space and did not know about registration either.

Apparently there isn't any issue with our park brake located above the toe brake cylinders cuz I would think gravity would cause the fluid to drain down to the toe brakes and eventually empty out/bleed off.

I quess I should use a syringe and remove a few CC's and make a 20mm dip stick,LOL

 

Thank you all for the insight

 

 

Edited November 23, 2023 by BC0979

[IBob]

BC0979 nope, no problem with the park brake draining down. It could only do that if there is a leak up at the park brake letting air in to replace the the fluid as it drained down.

[facthunter]

I don't understand How that works IBob. Also a hydraulic Brake like that cannot be relied onto stay pressurised.  A slow leak with let it off., same as a foot brake will is left long enough in the same circumstances  Nev

Edited November 24, 2023 by facthunter
typo

[IBob]

Facthutnter, if BC0979 is referring to the standard Savannah park brake, it is simply a pair of ganged shutoff valves in circuit between the pedals and the wheels: the pilot closes the valves while standing on the brakes.
In the Savannah, these valves are situated just under the LH end of the instrument panel. So the brake lines go up from pedals to valves, then back down to the wheels. However, this will not result in fluid flowing back down to the pedals, unless an air leak at the valves allows air in there to replace the falling fluid.
And you are right, such a brake should not be relied on for any extended period. But it does allow time for the pilot to find a rock or chocks as required.

[BC0979]

I downloaded the maintenance manual as you suggested.

Thank you, thank you

Very difficult to find things on their website 😕

The person that made the construction manual must have done the website too LOL

I removed the 20mm long machine screw/dip stick and syringed the excess out

😁