Silicone Brake Fluid

J

Jim Griffith

Junior Member
Hey Guys,

The brake master cylinder on my '53 Sunliner is leaking and the DOT 3 brake fluid has damaged some of the paint on the firewall. I am planning to replace the master cylinder and repaint a portion of the firewall. I plan to replace the DOT 3 brake fluid with DOT 5 (silicone) brake fluid. Do I need to disassemble the wheel cylinders and clean them or can I just flush them with the new silicone fluid? All feedback appreciated.

Jim Griffith
 
Replace everything. Master cylinder, wheel cylinders, and flex lines. If you keep the hard lines flush real good with acetone than denatured alcohol and blow the lines dry.
 
I flushed my '52 F-7 truck with denatured alcohol, including the booster, after replacing the wheel cylinders about 5 years ago and it has been fine. I never replaced the master cyl. or booster, just flushed them out.
 
Common practice is to thoroughly clean all metal parts and replace all rubber including hoses. Flushing with a dissimilar fluid will not clean anything, you must use a strong cleaner capable of breaking down the old fluid type. This is especially important when changing from Silicone to DOT 3/4.

Sometimes you can simply flush the old Glycol fluid and refill with Silicone and suffer no ill effects, but it's a game of chance and considering the fact that this is a safety critical system I prefer to take no chances at all. Glycol fluid usually has the same amount of seal swelling properties from brand to brand, but silicon is not so closely regulated (based on what I learned several years ago, may be different now). This is one possible reason why some people have no problems switching with only a simple flush while others suffer sudden and massive brake seal failure.

My advise is always to play it safe and clean all metal parts including hard lines with alcohol or brake spray cleaner, allow to thoroughly dry, and then rebuild with new rubber all around.
 
What is brake fluid? Is that Dot 5 some kind of paint you put on the brake rods?


sorry i had to
Bill
 
Brake fluid is the the way the brake rods move,if they are adjusted right and smooth they are considered FLUID if not they are UNFLUID.I think this only applies to older cars ,on newer ones its just another name for paint stripper.
 
Cecil/WV said:
I flushed my '52 F-7 truck with denatured alcohol, including the booster, after replacing the wheel cylinders about 5 years ago and it has been fine. I never replaced the master cyl. or booster, just flushed them out.
Click to expand...

I forgot to say that I replaced the hoses, also.
 
I replaced everything on my '39 Hudson (Hard lines, hoses, wheel cylinders etc) and put DOT-5 fluid in about 20 years ago, then put the car away for storage and forgot I had it.

The storage building was put up for sale last year and mine was the last car in there. When I got it out the brakes were a little soft, I bled and adjusted them and they were great. I popped a couple wheel cylinders apart and inspected them; looked immaculate. Good stuff.

Yes, I had to pay a rather large past-due storage bill to get the car back. I figured they had sold the car long ago to cover the bill.
 
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Are there no issues with the DOT 5 not being compatible with the rubber seals? I wanted to use DOT 5 in my 40, all repro but original style brakes, but have been put off by reports of the fluid eating seals and leaking. is this not correct? I'd much rather use DOT 5
 
There were issues many years ago with some types of rubber but that is no longer the case. All modern rubber is required to be compatible with all standard fluid types. FWIW, I have a '67 MG that has used it since the early 90's with no issues.
 
I have never had problem #1 using it in any of my vintage vehicles...older seals or not. The problem isn't so much the material used in the seals, as is the condition of the brake system components. If the Master cylinder seals are worn out, or the bore is pitted, silicone will leak worse than Dot 3/4...same with the wheel cylinders. If silicone brake fluid caused seals to swell, then it would have been touted as a "seal reconditioner" years ago for worn seals..which it hasn't been. I, PERSONALLY, have never had any problems using it, and I would be willing to bet that all the stories about non compatability with seals, etc. are hearsay. Refer back to Post #9 by 46FORD. One other thing about using Silicone DOT #5 fluid...when bleeding the brakes, DO NOT pump on the brake pedal like a mad man. This puts small air bubbles in the fluid which do not quickly dissapear as they do with ordinary (DOT #3/4) fluid. I use a less disruptuve procedure to bleed the system...usually gravity or pressure bleed. Residual small air bubbles in the system are a major cause of spongy pedal when using silicone...
 
Ive had very good luck with Silicone Fluid in my '46. I did change over when I went with a new master cylinder and wheel cylinders as well as lines.
 
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