Has anyone ever successfully used silicone fluid in a 69 SS with original master cylinder and brakes? My brakes worked OK before I took my car apart and had the original master and all wheel cylinders rebuilt. I flushed out all the lines and installed a new proportion valve below the master. I bench bled the master, gravity bled the system and still had a pedal that went to the floor. I just purchased a pressure bleeder that attaches to the master cyl and pushed a pint of fluid through each cylinder with no air bubbles. The pedal still went to the floor! Yesterday I installed a "replacement" master and re-bled the system, and still the pedal goes to the floor! Help!!
Where can the air be hiding? I used silicone fluid on a 65 Vette with 4wdb and had no problem bleeding!
Jim

Don't use a pressure bleeder. The more you disturb silicone fluids the more tiny bubbles (I think that a song) are formed. Silicone fluid is a pain in the A$$.

Regards,

I am using it without trouble. Whole new brake system so I didn't have to worry about it mixing with DOT3 in the lines.

Bench bled the master in the car, hooked up the lines and gravity bled it to the wheels. It was basically done at that point.

:confused:

Tim.

Pull the lines off the MC and install the bleeder kit lines that came with the rebuilt master and bleed it on the car. When finished,install a couple off those plastic block off plugs into the two outlet lines on the master tightly and step on the brake pedal! It should be rock hard and have no travel.
Now reconnect you brake lines and gravity bleed the pass rear and the pass front then the other rear and front. The gravity bleed method keeps air bubbles to a minimum and this method always works for me. I have been using silicone fluid and have had no problems.
Good luck.

graemlins/beers.gif

Ditto on success with Dot 5 silicone fluid, at least so far. I put a completely new brake system on Sherri's 59 Biscayne and the brakes work fine, with a firm pedal. I did the gravity bleed first, then the conventional pedal bleed. Sure glad I didn't use Dot 3, because I had numerous leaks that would have eaten a lot of new paint.

Thanks for the help. I really appreciate all the advice everyone is so willing to give on this web site! I just hope I can help someone out in the future!
Jim

I have Silicone DOT 5 in my 69 Chevelle with the stock front disc rear drum setup. No Problems, I used a homemade pressure bleeder that is just a flat metal plate and gasket that I clamp to the top of the Master cylinder and hook up 6 to 10psi of air. You just can't bleed too long at one time or the master cyl will run out of fluid.

One potential problem with DOT 5 silicone brake fluid that has NOT been mentioned is the fact that your brakes will get spongy with any major change (+/- 500 Feet) in elevation. Silicone brake fluid is VERY sensitive to barometric pressure.

Example, if you live in an area at 500 above sea level and drive to a location 1500 feet above see level, your brakes will be spongy and not work very well. This is caused by the change in size of the air bubbles that will STILL invariably be in your brake system after proper bleeding at home. They will be small and compressed at the lower altitude at which you bled your brakes. As you rise the barometric pressure becomes lower and the air bubbles get larger causing the spongy pedal and less braking capability. If you never leave your local area, no big deal. If you travel several 100 miles there is a good chance of a significant altitude change in most parts of the USA and therefore the potential for PROBLEMS! It is nearly impossible to get rid of all the air bubbles in a DOT 5 silicone system. You may think they are gone, but they are there in a small "compressed" bubble you cannot see.

The higher in altitude you go, the harder it is to bleed DOT 5 fluid. Ideally high altitude is the BEST place to bleed a system with DOT 5 fluid. If your brakes do get spongy at high altitude, just rebleed the system and you should be good to go. Your brakes will "really" be good when you get back home at the lower altitude.

Something to seriously consider if you plan to use DOT 5 fluid and doing a lot of traveling. You do not see any of the automobile manufacturers using DOT 5 fluid. Every wonder why???

Why do MOST motorcycle manufacturers use DOT 5?? :confused:
And have for years...

I use "5" in any of my vehicles that aren't driven often or on a daily basis.
Much more resistant to water absorbsion than DOT3.

Simple! Volume of fluid in the brake system is very small in a bike brake system in comparison to an automobile brake system.

I thought we were discussing brake systems in cars, not bikes?

Automobile manufacturers certainly do use Dot 5 fluid in all Military vehicles built (part of the Mil Spec). I worked for a worldwide manufacturer of forklifts and all we used was DOT 5 Silicone fluid and our brake systems were automotive type disc and drum brakes.

Aircraft use DOT 5 and the elevation difference doesn't seem to affect them.

I have never had a spongy pedal or problem with air bubbles, I have never even seen any tiny bubbles in my fluid while bleeding or any at work in the forklifts we designed and built.
As a matter of fact I climbed Mt. Washington in my van (about 8,000 ft change in elev) and never had a spongy pedal.

Originally posted by mjs13:
You do not see any of the automobile manufacturers using DOT 5 fluid. Every wonder why??? Maybe because it costs 10 times more. People seem to forget that cost is a huge factor in what a major manufacturer will use in production. DOT 3 is good enough and way cheaper. Think about having to put it in 500,000 vehicles a year.

Tim.

I am not a proponent of Dot 5 in a street driven application. In a seldom driven show vehicle that sits a lot, fine, but not in a vehicle that gets driven freqently or hard enough to get the brakes hot.

Here's my reasoning:

DOT 5 does have benefits for show car purposes-- it does not eat paint. That is the biggest advantage to using it. DOT 5 fluid is not hygroscopic-- it does not attract and absorb moisture as glycol based Dot 3 and Dot 4 fluids do. So, rather than water being evenly absorbed into the fluid as in a glycol based fluid (merely lowering the boiling point linearly as a simple function of how much moisture is in the fluid), in the hydrophobic DOT 5 any moisture in the system will form beads or "pockets" of moisture moving through the brake lines. Because of the difference in densities of the silicone fluid to the water, the water will migrate to the lowest point in the system-- typically collecting in the calipers. It is not uncommon to have caliper temperatures exceed 200° F, and at 212° F, this collected moisture will boil, leading to a steam pocket in the caliper causing vapor lock and you to lose your brakes. Additionally, DOT 5 fluid is much more compressible than glycol fluid due to aeration and foaming under normal braking conditions (small air bubbles are always present in the fluid), providing a spongier brake feel compared to glycol based fluids.

DOT 5 fluid is best suited for show car applications where its paint friendly characteristics are important. However, because any water in the system will collect in the lowest point, it's still a good idea to flush the system periodically to remove any pockets of moisture.

Also, silicone based DOT 5 is not to be confused with glycol based DOT 5.1; 5.1 being fairly common in high-end European applications.

The majority of the problems with going from a glycol based DOT 3/4 to silicone based DOT 5 is that the rubber seals in the calipers and the like which were previously exposed to DOT 3/4 will often swell immensely when you add DOT 5; that's why most manufacturers recommend either all new components or rebuilding your existing ones prior to switching to DOT 5; depending on what kind of material they used in the seals, they may swell up like a baloon after a change to DOT 5. Starting with DOT 5 initially on a fresh system shouldn't be a problem though.

Troy

I've had somewhat the same problem but while bleeding the brakes. The pedal would go down and push fluid out but when I closed the bleeder and then raised the pedal the fluid wouldn't go from the mster resevoir through the hole to the cylinder in the master. Then, there was no pedal at all. If I let it sit or pumped it a little a whole bunch it would eventually purge the air and begin to work again. The hole in the bottom of the disk side of the master basically seemed too small for the fluid to pass through. I finally enlarged that hole just a bit and it began working good.

If it can be spilled I will find a way so I really wanted to stick to the dot 5 that won't hurt the paint.

I did use it in an all drum car and it worked great there with no problems.

Peter

Originally posted by BillsCamino:
[QB] Why do ALL motorcycle manufacturers use DOT 5?? :confused: And have for years...
Sorry,that's just not true,Bill. Harley Davidson uses it and they have terrible braking performance. My Honda Valkyrie uses DOT 4 and my H-D Road King uses DOT 5.

Originally posted by mjs13:
One potential problem with DOT 5 silicone brake fluid that has NOT been mentioned is the fact that your brakes will get spongy with any major change (+/- 500 Feet) in elevation. Silicone brake fluid is VERY sensitive to barometric pressure.

Example, if you live in an area at 500 above sea level and drive to a location 1500 feet above see level, your brakes will be spongy and not work very well. This is caused by the change in size of the air bubbles that will STILL invariably be in your brake system after proper bleeding at home. They will be small and compressed at the lower altitude at which you bled your brakes. As you rise the barometric pressure becomes lower and the air bubbles get larger causing the spongy pedal and less braking capability. If you never leave your local area, no big deal. If you travel several 100 miles there is a good chance of a significant altitude change in most parts of the USA and therefore the potential for PROBLEMS! It is nearly impossible to get rid of all the air bubbles in a DOT 5 silicone system. You may think they are gone, but they are there in a small "compressed" bubble you cannot see.

The higher in altitude you go, the harder it is to bleed DOT 5 fluid. Ideally high altitude is the BEST place to bleed a system with DOT 5 fluid. If your brakes do get spongy at high altitude, just rebleed the system and you should be good to go. Your brakes will "really" be good when you get back home at the lower altitude.

Something to seriously consider if you plan to use DOT 5 fluid and doing a lot of traveling. You do not see any of the automobile manufacturers using DOT 5 fluid. Every wonder why??? I've heard this aurgument time after time and have never experienced it.

I am running DOT 5 Silicone in my '69 Corvette.
It is driven the Blue ridge mountains at least 4-5 times a year. It has NEVER EVER experienced any of the "high altitude" problems that other people claim will happen. In fact, the brakes have never performed better that when I swapped to the silicone fluid. I can lock em down at will at any altitude with no fading what so ever, and I don't exactly baby her on the twistys either ;)

You just have to be sure that you have removed all traces of the glycol based fluid before swapping to the silicone stuff.

and I bet the reason the Auto makers don't use is is because of the price.

Dwayne

I have been using DOT5 in my collector vehicles, 4-wheel drives and motorcycles for almost 30 years with no problems other than it is a pain in the a$$ to bleed. Once you have all the little, tiny air bubbles out the pedal should remain hard and no difference noted with altitude changes or in hard repetitive braking in my experience. If you do not get the air bubbles out then you may experience soft pedal and changes with altitude and hard usage. The trick to bleeding is to do it once and let it sit for a day or two so the little bubbles will collect in one or two areas and then bleed it again slowly and carefully so as not to "foam" it up again. Once you have the air out your pedal should remain consistently hard.
graemlins/hurray.gif

Also some new vehicles (i.e. the new Corvette) do use DOT5 from the factory.