How to flush Dot 5 from C3 Brake System

[Ed D.]

After 40 years of using DOT 5 in my 72, I may find in necessary to switch to DOT 3. DOT 5 has preserved my brake system with no rust in brake lines, still have the original master cylinder with original piston part, calipers lasted form 1983 to 2022 with no leaks. I had my caliper rebuild last year and one at a time I am getting leakage with the DOT 5. It is a shame that no one including Raybestos can make a rubber that will not be deteriorated by DOT 5, as it is the best brake fluid to preserve a low use brake systems. I dont understand how all Federal Government Vehicles use DOT 5 with no rubber break down. It is a real shame that the Corvette caliper repairs community cannot use a rubber product that will tolerate and not break down under DOT 5, which is the best brake fluid for most of our cars.
Sorry for the rant, the question is how do I drain and flush my brake system to convert from DOT 5 to DOT 3?
Ed

[Richard F.]

[Owen L.]

Re: How to flush Dot 5 from C3 Brake System

They do not use D.O.T. 5 in the passenger vehicles for no particular reason.

More than likely because anti-lock brakes are pretty standard on all passenger cars and DOT 5 does not perform well with the anti-lock pulsing action.

If I were to ever change from 5 to 3/4, I'd likely use an alcohol flush.

[Harry S.]

Re: How to flush Dot 5 from C3 Brake System

Ed, when I went from DOT 5 back to DOT 4, I did a gravity alcohol bleed. This was on the 63 with drum brakes. When finished with alcohol, I changed all the rubber lines.

[Ed D.]

Re: How to flush Dot 5 from C3 Brake System

Here is what the local Post Office uses on their trucks. Thanks for the info.
Ed

dot 5.jpg

[David M.]

Re: How to flush Dot 5 from C3 Brake System

I just had Mike at Brakeboosters refurbish my booster & master. He recommended Synthetic Dot 4, Castrol brand in particular. Said Dot 5 would void the warranty. Dot 4 Synthetic wont eat the old-skool rubber.

This set up is for my 68 442 with front disc.

To flush I would invest in a "motive" pump style brake bleeder. Simplifies bleeding and makes you actually want to do it every few years as we should be doing.

He also mentioned when bench bleeding dont go into the master more than an inch or so with the piston. In other words don't bottom it out.

Another thing we Corvette owners forget to do is once a month go out and stand on the brake pedal a few times to keep the pistons from prematurely leaking due to lack of use.

[Ed D.]

Re: How to flush Dot 5 from C3 Brake System

Ed, when I went from DOT 5 back to DOT 4, I did a gravity alcohol bleed. This was on the 63 with drum brakes. When finished with alcohol, I changed all the rubber lines.

Harry, was there a specific type of alcohol that was used? Did you change the rubber in the wheel cylinders as well as the hoses? Did you do a flush with DOT3 after the alcohol flush?
Hope you are well
Ed

[Owen L.]

Re: How to flush Dot 5 from C3 Brake System

Said Dot 5 would void the warranty. Dot 4 Synthetic wont eat the old-skool rubber.

Old-school rubber is EPDM which DOT 5 will not affect – nor will 3, 4, 5.1, or synthetics. Practically all vehicle brake rubber seals used since the '50s was EPDM until the last 15 years or so. The remanufacturers are using a different (cheaper?) elastomer and blaming the fluid.

[Duke W.]

Re: How to flush Dot 5 from C3 Brake System

DOT 3/4 is not compatible/miscible with DOT 5 silicone, and I've seen plenty of conversations turn into disasters.

My recommendation when converting from DOT 3/4 to 5 is to start with everything dry and assemble with DOT 5, which would include wheel cylinders/calipers and the master cylinder. Brake pipes and hoses should be thoroughly flushed out with denatured alcohol and air dried.

I'm not sure how to go the other way because I don't know a good solvent to DOT 5.

There's been lots of discussions on this subject around the Web. Some say that Raybestos rebuilt calipers are okay with DOT 5. Have you contacted them with your problem? Are the calipers still on warranty?

There's also the lip seal vs. o-ring seal issue. I don't fully understand which is best and since my SWC is drum brakes I only follow it peripherally.

You should also search the DOT and NHTSA web sites and see if they have any useful information, and file a complaint against Raybestos and the DOT fluid marketer.

Duke

[Gary B.]

Re: How to flush Dot 5 from C3 Brake System


Duke,





Gary

[Harry S.]

Re: How to flush Dot 5 from C3 Brake System

Harry, was there a specific type of alcohol that was used? Did you change the rubber in the wheel cylinders as well as the hoses? Did you do a flush with DOT3 after the alcohol flush?
Hope you are well
Ed

Ed, I just used rubbing alcohol. I changed all the wheel cylinders at the same time, so all new rubber.

[Duke W.]

Re: How to flush Dot 5 from C3 Brake System

"Rubbing alcohol" is about 30 percent isopropyl alcohol and 30 percent water.

Denatured alcohol is primarily ethyl alcohol with some added methyl alcohol and other chemicals that will make you sick if you drink it. It' probably also has some water in it, but a lot less than drugstore isopropyl alcohol.

Neither denatured alcohol or traditional mineral spirits/paint thinner can be purchased in Southern California anymore.

Duke

[Duke W.]

Re: How to flush Dot 5 from C3 Brake System

I just had Mike at Brakeboosters refurbish my booster & master. He recommended Synthetic Dot 4, Castrol brand in particular. Dot 4 Synthetic wont eat the old-skool rubber.

Many think that "synthetic" brake fluid is better than... regular brake fluid?

The fact of the matter is that ALL brake fluid DOT 3, 4, 5, and 5.1 is synthetic because it's produced by a complex petrochemical process rather than being derived from crude oil by conventional distillation and catalytic cracking.

There's no generally accepted technical or legal definition for "synthetic", so don't assume that any product labeled "synthetic" has any real meaning.

I use DOT 4 in my modern ABS cars, but like engine oil, I don't pay attention to brand. I just buy the least expensive product that meets the DOT spec I want for brake fluid and the API spec I want for engine and gear oil.'

Duke

[Ed D.]

Re: How to flush Dot 5 from C3 Brake System

Just to reduce any confusion, all no potable alcohol is denatured. The reason is, to make it non drinkable so no US Tax is collected. The main denaturent is diethyl phthalate which will make you sick if you drink it.
Ed

[David M.]

Re: How to flush Dot 5 from C3 Brake System

Personally I would not introduce rubbing alcohol or another non brake fluid product to the system. Brake cleaner is about it. It evaporates quickly.

Simply flush about 1/2 to one gallon of what ever you plan to use and go. If your anal do it again after a cpuple 100 miles. The Motive or any power bleeder makes bleeding a simple job.