The Stovebolt Site Forums The Shop Area Engine Shop Flushing DOT 5 brake fluid

Put in a complete brand new brakes system, and filled it with DOT 5 silicone brake fluid because I thought it was the best. Now brakes feel spongy and I've learned that this is typical of DOT 5. So, how do you properly flush out the silicone to replace it with DOT 4?

AVE,

The brakes should work perfectly with DOT 5 fluid. If they don't it is probably the bleeding or adjusting procedure. The experts say that you cannot flush the system and get rid of all the traces of silicone...some will always remain and screw up any attempt to switch to DOT3/4.

These experts also say that if contamination of the system is suspected, you should flush the system a bit periodically with more DOT 5 until it flows clean.

I haven't had a hands on with DOT 5 so this is only 'book learning'...maybe there is a secret way to flush it out.

Having said that, the brakes should still work perfectly with the silicone, unless the system was dirty from DOT 3/4 and things are getting plugged.

Stuart

It is also possible that you have some parts with rubber that is not compatible with DOT 5 fluid. When I bought all new parts for my 1954 Suburban's brake system (2002), I traced parts back to the manufacturers and some of them would not certify that their parts would work with DOT 5 fluid, and some simply said their parts were not compatible. Eventually, I found parts that are compatible with DOT 5 fluid and I have a hard pedal and no problems.

I had a problem with DOT causing my master cylinder and front wheel cylinders to leak slightly (incompatibility of the rubber), I contacted Wagner Brakes on how to flush the system to remove it, they suggested using isopropyl alcohol to flush, then a thorough flush with DOT 3/4 to clean it out. They did say that a small amount of DOT 5 will not hurt anything as it is similar to the assembly lube used to put the whaeel cylinders and master cylinders together. After swapping back to DOT 4, I had no futher leakage issues.

thanks guys, anymore opinions out there?

I have run Dot 5 in my 37 truck for 20 years and have never had a problem. This past fall, I reworked the brakes just because it had been 20 years. I ran some new lines and upgraded to a dual master cylinder. Refilled the system, bleed the brakes and have a good hard, tire squeeling pedal. I think Dot 5 is the best stuff out there and you probably just need to bleed the system some more. Somtimes it takes more bleeding than what you might think. The great thing is that doesn't eat up the paint and the silicone kind of gives you a chance to clean up the under side of the truck. BTW, a good place to buy Dot 5 is a Harley store. They use that stuff all the time!
Joe

If your brakes are spongy on Dot 5, then you have a compatibility issue with some of the rubber parts in your system. No amount of flushing will "restore" damaged parts. My suggestion is to replace the seals and o-rings and use DOT 3 unless you have components that are rated for DOT 5.

The headaches associated with DOT 5 incompatibility far outweigh any performance values on a vehicle that does not see high brake temperatures. Plus, the counter at the Podunk Parts store doesnt carry DOT 5 if you ever have a need to pick up brake fluid on the road.

You might want to careful getting the silicone on any surface that you intend to paint in the future. You will have to remove all traces of the silicone or it will it very hard to apply non-contaminated over coats.

The alcohol flush is what my local mechanic said shows up on his books. Just my .02.

i have used dot5 in my mga for the past 20 years and the spongy pedal is typical to it. in the past the only restriction i have been able to find that it is not recommended for corvettes. that may have changed but years ago it was not recommended. Ron

So I'll try flushing with isopropyl alcohol. Being that all the parts were new (master, capilers, rear cylinders and brake lines)would any "damage" to incompatible rubber parts be that instantanious that they should have to be replaced?

Abe

Beware, the isopropyl alcohol you find in the drug store contains 30% water.

Sorry guys, I just can't buy that spongy myth. Whether it is DOT 1,2,3,4,5, Coca Cola or Budweiser, a hydraulic fluid is not compressible so if your pedal is spongy there is air in the line or something is bending or flexing.
Denny Graham
Sandwich, IL

A good reason for not using silicone DOT 5 is that water does not dissolve in the silicone, so any water that gets in will be there as little droplets. The boiling point of that droplet is 212 deg F so if that droplet gets to anyplace hot enough it will vaporize and cause brake fade.

I've had same problem with Dot 3, just need to do a better bleed of the system. I made a great pressure bleeder out of a small garden sprayer, no more spongy pedal.

Denny, where the issue with the spongy pedal with DOT5 is that it has a tendacy to hold on to any air that gets in it. I have experienced this with mine, It just takes a more digillent bleeding procedure so as not to cavitate the fluid. It mentions that on the bottle. Once bled thoroughly, I got a very firm pedal. However, I would suggest sticking with DOT3/4, leave the 5 for the Harley guys/

What I'm experiencing is a spongy feel at all times not just when it heats-up, so there can't be any boiling happening. And if it isn't boiling then it sounds from most of the posts that it must be a bleeding problem.

As far as bleeding, I've done it twice and there doesn't seem to be any trapped air, althought it is hard to tell because when I crack open the bleeder screws, it seems that air gets introduced into the discharge tube as the fluid is going out. I bought one of those vaccum bleeder pumps, and it too seems to suck air through the bleeder screw threads. Any suggestions?

If DOT 5 is not inherently defective, then I'm willing to stay with it, but I got to achieve a harder pedal.