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First Generation Brake Fluid Debate and Advice Needed

Guest DLT

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Thanks to the help of Jim Cannon, Ed Raner, the chassis manual, ROA and parts suppliers, I'm in the process of converting the brake system on my 1963 Riviera to a Dual Master Cylinder. The old single MC system was working fine with the exception of a small vacuum leak somewhere in/at the booster. I am making this change for safety reasons and to just go through the brakes from top to bottom since I don't really know the history and condition. When doing this, I will install the new dual MC matching the booster from a 67 drum/drum Riv, install a rebuilt booster from Booster Dewey (nice fellow), replace front lines from Inlinetube.com (back ones are in great shape), install a Tee for the brake switch, replace flex hoses, all wheel cylinders, pads, springs. <span style="font-weight: bold">But what about the type of brake fluid?</span> The previous owner claimed he had changed the system to Dot 5 when he replaced the MC (single) and rear brake lines. The stated advantage was to prevent rust in the system.

I've read through the brake topics on ROA. I spoke to the fellow at White Post who advises against silicone ("silicone has been the best thing for my business due to the failure of parts from it's use").

I would like the forum's advice on this topic. <span style="font-weight: bold">What are the pros/cons of DOT 3 or 4 vs Silicone Dot 5?</span> What would you recommend for my 63 Riviera?

Thanks in advance, Dalton.

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Guest simplyconnected

I do NOT recommend DOT-5 unless your brakes are subjected to very high heat (like a race car).

I recommend you use DOT-3 and CHANGE IT every 24,000 miles. Changing will keep the water concentration within acceptable limits, the rust inhibitor fresh, and your bleeder valves won't have a chance to seize. Master cylinder and wheel seals are made for DOT-3, DOT-3 is cheap, and available everywhere.

Your brake pedal will never be more responsive than with fresh DOT-3. The biggest mistake made, is when car owners leave the same brake fluid in the system for many years.

GM made NO mistake by delivering your Buick with DOT-3, and that is exactly what they still recommend. Remember to keep ALL petroleum-based products far away from your brake system because they will swell the seals. The first time you apply brakes, they will never let go. Keep water away, too. (I never take the reservoir cover off when it's raining.) DOT-3 is glycol-based, and it sucks up water faster than scotch. Wrap your bleeder screw threads in teflon tape when re-installing. Teflon always stays soft, is impervious to brake fluid, and will help keep your bleeder screws from rusting shut.

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What is it about DOT 5 that is bad? This is the first I have heard of it causing problems. I thought silicon was good for rubber.

I will drain and flush the DOT 5 out of my system and replace it with fresh DOT 3 if it is really bad for the car.

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Guest simplyconnected

Silicone fluid is slightly more compressible than glycol fluid. It neither accepts or disperses moisture, making it more corrosion-prone, and it doesn't change color to give the user an idea of its moisture content. Silicone brake fluid lacks glycol fluid's naturally occuring lubricity, making it incompatible with the mechanical valving in some ABS systems. DOT-3 absorbs and evenly distributes water, up to a saturation point. Changing DOT-3 (much like changing engine oil), when done at regular intervals, keeps the brake system healthy and rust-free. All DOT-3 is clear when new. That tell-tale orange/brown color coming out when you bleed, is rust (from moisture).

Be very careful when changing different types of fluid to or from DOT-5. Flush real well without using petroleum-base products. (I like to use alcohol).

The only advantage in using DOT-5 (in my estimation) is if you have a lot of cars that never move for many years in your barn.

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When this question comes up relative to collector/show cars, my recommendation is if you are in the process of rebuilding your brake system, change it to DOT 5. Going through the process of converting "just to convert" is not worth it unless you have the system dismanteled for other reasons.

I researched the topic extensively several years ago when I did a Tech Tip on it. I have not seen facts to date that suggest DOT 5 is not hands down the best fluid for collector/show cars. This is all based on the simple fact that DOT 3 fluid absorbs moisture and DOT 5 does not. Moisture is the number one enemy of brake systems on collector cars. It is absorbed through microscopic holes in the rubber seals in the wheel cylinders and around the master cylinder cover. Moisture changes the fluid properties in other ways but those are less likely to cause a problem in a collector car. With moisture trapped in the fluid, internal rusting will begin in the bottoms of the wheel cylinder and master cylinder bores which lead to leaks or other braking failures.

While it is true if DOT 3/4 fluid is flushed every couple years, you can avoid moisture related failures. I don't know anyone including myself who likes to bleed brakes, especailly on a car with a detailed engine compartment where one splash of fluid gone undetected will eat the paint. Its just not practical and easily stays at the bottom of the long "Things To Do" list nearly every car has.

Lastly, the environment in which the car is stored plays an important role as well. If your car is stored in an area that is climate controlled year round, or in a very arid climate, the effects of moisture on DOT 3 fluid will be much less therefore not be as big a concern. Owners of cars located in areas that have high humidity and large and or/rapid temperature swings should give converting to DOT 5 and/or DOT 3/4 maintenance a higher priority.

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DOT 5 is used in race cars because of its ability to absorb higher temperatures than DOT 3 or 4. It does also have the property of not damaging paint if it is spilled on a painted surface.

DOT 3 is hygroscpic, which means it absorbs the moisture in the brake system. It is FORMULATED to do this. As it absorbs water, it changes to a darker color, giving the owner an indication that the fluid is doing its job. When it is brown, change it out!

DOT 5 has a lot of trapped air in it, which is why none of the OEM's use it in cars equipped with ABS, it foams when the solenoids cycle in the hydraulic brake controller. This foaming causes the brake pedal travel to increase and makes for a spongy pedal. The same thing happens at high altitude. A friend of mine drove west in a 32 Ford with DOT 5 fluid and on the way up Eisenhower pass, had his brake pedal drop nearly to the floor!

All that being said use DOT 5 if you must, but DOT 3 and a good maintenance routine is all you really need.

My 2 cents! Happy New Year!


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Dear all, thanks so much for the advice.

Looks as if the previous owner had replaced the single MC and rear wheel cylinders and rear lines in recent years as the paint is still glossy on the parts. Lots of fluid was found in the Booster and Vac Reserve tank so I assumed the old master cylinder failed. He told me he used Dot 5 due to long storage periods. He did also state that the brake switch needed to be replaced after storage every winter. But I did not ask him if that was related to DOT 5 or just sitting.

Based on all the comments, I'm going to opt for Dot 3 and commit to a service schedule.

ANOTHER QUESTION - For flushing and cleaning out the lines prior to filling with DOT 3, I've seen reference to alcohol but what type of alcohol? Isopropyl, Ethanol, other? And is there a good "tool" to flush lines? A syringe or something similar? Do you recommend flushing the new lines as well?

PS - ran into a snag that has been frustrating. While the car is up in jacks, I am replacing the rear coils and all shocks as well as cleaning the under carriage. The lower bolt/nut securing the passengers rear coil spring clamp is rounded out (my fault). Tried for hours to cold chisel it off. It might work but it's slow going ... Plan to try a Dremel tool this weekend to see if I can cut it off. But if you've been down under there you know it's hard reach the head of the bolt and the nut and with only jack stand height, not much room to swing a hammer.

Also the lower coil clamps don't look so good anymore and I would like to replace them. Did not find a listing for a part in Old Buick, Clarks, or Classic Buick. I have a call into WheatBelt but if he can't help, any other suggestions? I have not yet tried the auto parts store with an example part in hand.

Again, may thanks for the advice.

Happy New Year to ALL!!!

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Guest simplyconnected

If you had DOT-5 in your wheel cylinders, completely disassemble the moving parts, then all the DOT-5 will be removed in the process. I always wash everything with new DOT-3 before assembly.

I understand you will replace your wheel cylinders, but you don't need to if the old ones have smooth bores. You can use "rebuild kits" for a few bucks per wheel. They are available at just about every auto parts store, and on-line.

Rockauto.com wants:

RAYBESTOS Part # WK13 {Professional Grade}

Rear; 15/16" Bore $3.10

RAYBESTOS Part # WK36 {Professional Grade}

Front $3.07

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