Hydraulic reservoir

[Lynn Eades]

Bruce, as an apprentice we were taught to use methalated spirits to clean brake components. This would be when you have them stripped. You would then lube components with the brake fluid that you intend to use, on assembly. The following, I ripped from the net:

Since DOT 4 fluids were developed, it was recognized that borate ester based fluids offered the potential for boiling points beyond the 446F requirement, thus came the Super DOT 4 fluids - some covered by the DOT 5.1 designation - which exhibit a minimum dry boiling point of 500F (same as silicone, but different chemistry).

You can go ahead and mix or flush (replace) any DOT 3, DOT 4, or DOT 5.1 brake fluids, no problem. So there are no special bleeding procedures and you don't need to run anything in the lines. The only one to watch out for is DOT 5 (silicone brake fluid).

DOT 5 does not damage paint like other brake fluids do, but is not recommended by AP Lockheed for use in their systems due to higher wear than with other type fluids.

Brake system contamination:

The single most common brake system failure caused by a contaminant is swelling of the rubber components (piston seals etc.) due to the introduction of petroleum based products (motor oil, power steering fluid, mineral oil, etc.) A small amount is enough to do major damage. Flushing with mineral spirits is enough to cause a complete system failure in a short time. I suspect this is what has happened when some owners change to DOT 5 (and then assumed that silicone caused the problem). Flushing with alcohol also causes problems. Brake systems should be flushed only with DOT 3 or 4.

If silicone is introduced into an older brake system, the silicone will latch unto the sludge generated by gradual component deterioration and create a gelatin like goop which will attract more crud and eventually plug up metering orifices or cause pistons to stick. If you have already changed to DOT 5, don't compound your initial mistake and change back. Silicone is very tenacious stuff and you will never get it all out of your system. Just change the fluid regularly. For those who race using silicone fluid, I recommend that you crack the bleed screws before each racing session to insure that there is no water in the calipers.

British Cycle Supply Company does not recommend use of DOT 5 silicone brake fluid on British motorcycles equipped with any AP Lockeed disc brake components.

Not exactly what you were asking, but should help.

[Lynn Eades]

Having had a quick read on the net, I think I would stick with dot 3 or dot 4. Silicone fluid (dot 5) is not recommended by Porsche for instance. Silicone has other problems. I think better the devil you know unless you were replacing all the components. Keep your fleet the same. My gut feeling.

[Bruce Parker (RIP)]

Originally Posted by Lynn Eades

Having had a quick read on the net, I think I would stick with dot 3 or dot 4. Silicone fluid (dot 5) is not recommended by Porsche for instance. Silicone has other problems. I think better the devil you know unless you were replacing all the components. Keep your fleet the same. My gut feeling.

Thanks Lynn, that's what I was tending towards. If I didgdo to Dot 5 I probably would have run new lines anyway so everything would be new, but the existing lines are great and would be a pain to re-run. The old fluid gave me 12 years and who knows how many more had I not gone all nervous (plus covid spare time). My only problem was fluid boiling in the accelerator slave which is located right below the manifold exhaust pipe. I have since installed a heat baffle that seems to have solved the problem.

[Barry Churcher]

I hate Dot-5 and dread working on the vehicles that the owner insists using it. The spongey pedals and soft brakes become my problem all of a sudden. We learned to say "no warranty on Dot-5 brake jobs" . Photos taken by CUCVRUS.
Cheers,
Barry

[John Mackie]

My comments to Lynn in post 12.
I grew up with the old brake fluid that was made from caster oil and metholated sprit, we used metho to wash up brake cylanders . then we got mew high temp fluids that had a higher boiling point but were water soluble, we used water to wash them up.
I restored a truck many years ago and used silicone fluid I think it was Ok.

Recently I bought a hydraulic stop light switch (13480) Marathon and in the packet it had a note NOT TO USE THE SWITCH WITH SILICON FLUID !!!

I an currently restoring a Ford truck (11T ) and will not be using silicon fluid in it.

[Harry Moon]

I used methyl hydrate to flush mine. I've been using silicone fluid for 40 years with never a problem but for the last few projects i use a pressure bleed system and fill the systems from the wheel cylinders or slaves. the pedals are hard right away and if replacing a brake sensor(too often grr) a quick push from the closest wheel cylinder clears any bubbles out of the system.the trick is not to create and bubble up the fluid.