OK, all you brake experts... I am replacing all of the brake hydraulics on my car trailer and going to silicone fluid because it sits idle for extended periods and I have had a problem with corrosion as the fluid seeps from the various cylinders. My question is, what should I flush the lines out with, if anything? Are trace amounts (residue) of glycol based fluid compatible with the silicone fluid, or do I need to get all of the lines spotlessly clean and dry?

D/W

_________________

If it ain't broke, fix it!

I've heard that silicone brake fluid can cause corrosion problems because it traps water in the lower portions of your brake system, instead of absorbing water like DOT-3 does.

_________________
82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Yea, that RUMOR has been going around in circles. Does anyone have EVIDENCE and PROOF of this phenomena? Come on, let's see it!!

The old DOT 3 fluid ABSORBS water right out of the air and saturates itself.

I dont' believe that DOT 5 Silicone does this so how's the water going to get in it? Leave it in the rain with the master cylinder cover off?

I put DOT 5 Silicone in my 1976 Valiant, must be 8 or so years ago along with all new master cylinder, hard lines, hoses, and wheel cylinders. The fluid in the mc is still as clear as the day I put it in there and I have never ever had to add any fluid ever. Someone reading this says my steel lines will burst at the low spot because there is water in there. Phoey!! The lines are stainless steel and there is no water in their either.

I'll go talk to the guys at the local airport hanger and see what they say. I know airplanes use Silicone brake fluid.

I dont' know what to tell you Dennis. If it were mine, I'd probably take apart the wheel cylinders and master cylinder and clean them out and rebuild them. Any old brake parts like this that I've ever had apart were all full of crud and rust. Many of those old trailer brake cylinders have a cap on the master cylinder that is open vented to the atmosphere. That will make sure that old DOT 3 brake fluid will absorb as much water out of the air as fast as possible. My dad had the brakes rebuilt on a car tow dolley he bought last year, everything was stuck solid. The new master cylinder had a modernized cap with a diaphagm in it similar to a car. This keeps the wet atmosphere away from the brake fluid.

Anyway, I think the Silicone brake fluid is a great way to go. You can report back to us with the results in 5 or 10 years !!!!!!

The problem I have with the trailer is that the seals seep a very small amount of fluid over the months/years it is not used, probably due to lack of residual pressure and continual heating and cooling caused by weather etc. The fluid that seeps out then combines with moisture in the air (trailer stays under covered storage) and corrodes the wheel cylinder pistons to the point of freezing them solid on occasion. I have to unstick one or both just about every time I drag out the trailer.

D/W

_________________

If it ain't broke, fix it!

I have new (aluminum) wheel cylinders and a fresh Master cyl (looks to be for a '48 shivvy ) to install.

You are correct about the cap. What's worse is that it has a screw on cap with vent holes so that rain could actually run in! I rectified that by fabricating a little rain cap for it, but you are right, it is vented to the atmosphere. I don't know of one with a modern diaphragm-type cap that will retrofit, though... It's a Balcrank activator with two thru-bolts that attach the master cylinder, if anyone knows.

My main concern was what little residue might remain in the lines once I blow them out.

D/W

_________________

If it ain't broke, fix it!

Dennis,
I'll take a look at that car tow dolly my dad has, IF he still has it, and see if that cover is screw in or not. I have an old Cushman Truckster with the same threaded cap with open vent pointing right up to the sky too, or is the hole drilled into the side of the hex?? MC is attached with two bolts, just like the trailer MC. Wonder if they are the same?

Some brake parts I've had in the past have some kind of clear slimy assembly fluid on them. Occasaionally a rebuild kit will come with a capsule of the same stuff. I wonder what that is and if it would help prevent your problem?

OK, you have a new MC and wheel cylinders to install? Are your steel lines still good? I would use some brake cleaner in a spray can and flush everywhich way you can, then blow out with dry air, install your new parts and put the Silicone in. As I said before, you can report back to us in 5 or 10 years. Obviously the DOT 3 stuff and an open vent is NOT going to eliminate your problem.

The ASE has some research papers published about silicone brake fluid.
i remember one mentioned that a little dot 3 fluid mixed with silicone
caused no problems. Also i read an article in one of the car magazines
to use silicone fluid to flush out the dot3 fluid, when converting to silicone.
I think popular mechanics website has an article about that.
also the ase website may have the paper , if not then your local library in the
reference section has the big book for ASE for each years worth of papers
published.

I would think that by the time you bleed the air out of the lines any residual DOT3/DOT4/alcohol/water/crud..... would be gone too...............

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

electric brakes....easy to bleed.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

...thanks, sandy, that's helpful. If I'd wanted electric brakes, I'd have equipped my trailer with them in the first place. Hydraulic brakes on a trailer have numerous advantages, not the least of which are you don't have to even think about them at all when you're pulling, and you can put the trailer behind multiple pull vehicles including rentals, none of which have to have an electric brake controller. I have experience with electric brakes in the past, and they have their problems as well.

D/W

_________________

If it ain't broke, fix it!

I used to have lots of brake corrosion problems with DOT3 up in the rust belt; the pistons would tend to sieze solidly in their bores due to rust. Sometimes, they got so stuck that I had to pound the piston out using a punch and 3lb ball peen hammer.

I switched to DOT5 starting about 19 years ago and have had no problems since. I have noticed no difference between brands. I also replaced or rebuilt the pistons, calipers, master cylinder, hoses, and replaced or flushed the hard lines carefully at the same time.

I use DOT5 in both my show car and my daily driver, but only covert another car over to it whenever I entirely overhaul a brake system.

I have never experienced outgassing problems, but I've never driven to very high altitudes either.

Yep, I've seen it. Nope, it's not a rumor. Yep, it's ugly, sudden, usually catastrophic and virtually impossible to predict/detect until it happens. Nope, don't have pictures.

Silicone fluid isn't necessarily better, and even if you believe it is, it's not a throw-it-in-and-forget-about-it-forever deal.

Here's the thing: no seal is perfect. Moisture can, does, and will get into the brake hydraulic system due to humidity gradients, temperature gradients and pressure gradients across the seals. How much moisture gets in is highly variable, depending on ambient moisture (more in Portland than in Phoenix!), system heat levels reached, duration of just sitting around, owner maintenance practices, and so forth.

When moisture enters a system filled with regular brake fluid (DOT 3, 4 or 5.1), the fluid absorbs the water. This disperses the water throughout a relatively large area of the system. It's never good to have moisture in the brake hydraulics, but this dispersal means that a relatively large amount of water has to accumulate in the system, and remain unflushed for a long time, before corrosive attack becomes a possibility worth worrying about.

When moisture enters a system filled with non-hygroscopic brake fluid (DOT 5 silicone), it is not dispersed or absorbed. It remains in a cohesive blob, which tends to get mechanically moved (swept by brake fluid motion, pulled by gravity) to the lowest points in the system. It remains there, highly localized and much more concentrated than if the brake fluid had dispersed it, and—depending on the materials it happens to be contacting—can begin to corrode important piece of your brake system from the inside out.

That's the way it works. Now, how much of a problem/risk is it? Totally depends on how you maintain the system. With any/all fluids, as long as the system is flushed and refilled every so often (every few years) you shouldn't have any brake hydraulic system problems.

The other nuisance with silicone fluid is that it is much, much more difficult to get a firm pedal with it, for its consistency is such that it traps air in tiny bubbles that are very slow to rise to the surface and pop. That's why the silicone fluid container warns you not to drop it, shake it, etc. Good practice is to pour the fluid against the sloping sidewall of a funnel rather than directly into the master cylinder—this gives the bubbles a good shot at popping.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

I can attest to the tiny bubbles............

My motorcycle uses DOT5, and it took 4 hours to bleed the front line when I changed to brake line to stainless steel braided (didn't bother with the rear). I ended up using a speed bleeder and routing the output back to the master cylinder for a continuous loop. (and I had temporarily hung the caliper above the master to help with the bubble flow)

_________________
Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

I agree that bubbles in DOT5 are much more problematic that DOT3, so I'm also careful to avoid creating them when filling the MC.

When I switch over to DOT5, a trick I'd heard about and use is to tap the wheel cylinder or caliper with a ball peen hammer while bleeding to dislodge any bubbles. I begin with just gravity bleeding (to slowly wet the system and avoid bubbles), then start tapping after fluid reaches the bleeder, then the usual with-an-assistant bleed cycles (tapping between cycles). I've installed the Russel bleed screws w/ check valves, but still find it goes much, much better with an assistant and the traditional method. That and patience seems to work fine for me; it takes longer than DOT3, but not all day.

I clean anything I dissassemble in the system and new lines very well, finish with a final ethanol rinse, let dry, then also use a thin film of silicone grease (from J.C.Whitney) on the cups and seals. I've never had to open up or replace any cylinder or caliper I've prepped that way and then put DOT5 in over the last ~20 years, so I haven't looked inside them since.

I don't flush my brake systems regularly; perhaps I should reconsider that based on Dan's discussion.

When I've taken systems apart after years with DOT3, pitting and corrosion are usually quite obvious. Also, in hydralic clutches (as in my Jeep), leaking DOT3 can dissolve plastic parts, such as the bulkhead connector... I've also seen a very tiny DOT3 leak dissolve the glue holding the liner to the brake shoe - the whole liner fell off all together; a very big surprise, very fortunately at low speed - a good argument to get glued and riveted shoes. One lives and learns (if you're lucky).