Silicone brake fluid leakage

V

van Dyck

Senior Member
Hello - I've been away from here for more than a year having had brain surgery to correct an aneurysm problem. I am recovering. It is slow. When I came home from the hospital, I was itchen to drive my roadster, took it out of cold storage and noticed a wet area in the vicinity the of the left front tire. And the brakes pulled hard to the right!
Background: 1939 Ford brakes on the front wheels with the Buick aluminum drum adaption. Runs silicone brake fluid because it is supposed to be nonhydroscopic . Car has been stopping good since completion in 2004, that is until last spring. I installed new stainless steel lined cylinders in '03. But they leaked. I inspected the rubber cups and I noticed a circumferential groove around the leading edge, instead of a sharp edge! So I replaced them with correct size sharp edged cups, and everything worked until 2017 when the leakage started. That silicone fluid gets on the linings and the drums and erases all friction - not good. I've had it apart several times, cleaned up the mess and it is then only good for a few, only a few (maybe two or three days). Any suggestions to correct this would be welcomed.
 
Silicone will find any potential leak in the system. IMHO go back to DOT 4 and flush the system every 2 to 3 years.
 
Before going back to DOT 4 dismantle all brake components and thoroughly clean with brake cleaner. Absolutely ESSENTIAL !
 
I have used silicone brake fluid in verious cars for twenty years with no problems. I would suggest the fault is in those relined cylinders, are they the correct bore for the seals? They will still leak with dot 4.
 
As previously stated, faulty components are the cause of leaks, and will leak even when using standard DOT3.
 
Leaks are way easier to fix than corroded parts. You either need new wheel cylinders or closely inspect what you have to figure out why they are leaking.
 
I was researching having wheel cylinders lined with stainless. In my reading I found that a common problem is leaking past the outside of the liner from the bleader hole in the liner.
This could be a cause of your problem.
John
 
I have used DOT 5 for ovr 30 years. Only leaks that I have is when I need to snug up the fittings more. DOT 5 will find leaks that Dot 3 & 4 don't. In the long run DOT 5 is the way to go.
 
I had this problem with the 39, and the 46 I had, went for the permanent cure, sold them, now have the A, and a 36 because they have non leaking reliable mechanical brakes

The pistons should have less than .005 clearance
If you clamp the pistons in and apply air use soapy water to check for sleeve to original metal leaks
If you buy new production wheel cylinders take them apart to see if holes drilled properly, and for metal shavings
 
Dot 3, 4 and 5.1 is synthetic glycol based, and is NOT silicone based.


Glycol based should NEVER be mixed with silicone based.








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Most drum brake master cylinders have a residual check valve built into them. It holds a slight amount of pressure in the system at all times so the rubber cups are always being pushed tight against the cylinders when the vehicle is not in use. Otherwise they might leak. The pressure is too low to activate the brakes. Maybe your vehicle set so long that it lost its residual pressure? In the cutaway drawing the part they are calling the "inlet valve" is the residual pressure valve. It allows the fluid to return to the reservoir until the pressure drops enough for the valve to close. Which still leaves a little pressure between the residual check valve and the wheel cylinders.


I have some cars I never drive because they are not finished. One is a real Shelby '66 GT-350. It has had the same silicone brake fluid in it for over 30-years. Every once in awhile I get in it and stomp on the brakes a few times to make sure the residual pressure continues to do its job.


I went to a Bendix brake school. They said that if you flushed your brake fluid every two-year's the system would virtually last forever. Because the regular Dot 3, Dot 4 brake fluid adsorbs water, somewhere around 3% a year. The moisture tends to settle in the lowest point of the system which is the wheel cylinders. That's why they get pitted. If your fluid is brown that is the rust caused by moisture in your system. Sucking the fluid out of the master and putting new fluid in is not going to remove the moisture down in the wheel cylinders. That is why you should do a complete flush
 

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Thanks for all the various responses ! I am going to try a new pair of non-stainless steel cylinders when I take the car out of storage next spring. And probably do some bubble testing on the S-S lined cylinders. Happy Christmas Fordbarn residents. John
 
Different owners of vehicles here have had there wheel cylinders lined with stainless steel liners and have found after the time using aluminium pistons that the pistons start corroding and they seize up, it is a well known fact that aluminium and stainless steel do not mix, so you can either use cast iron or steel or brass pistons which would have to be made with stainless steel lined wheel cylinders.
 
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