Changing brake fluid

[Karl K.]

I have a 65 Corvette with power brakes that I want to change
the brake fluid on. I think that gravity bleeding may
be easier on the master cylinder than the pumping the brake pedal
and opening the bleeder. Any thoughts or experience with this?
Thanks,
Karl

[Terry M.]

Re: Changing brake fluid

When you say: "Change the brake fluid." what exactly do you mean? Do you intend to change the DOT number, or replace like-for-like?

Different answer depending on your answer.

[Karl K.]

Re: Changing brake fluid

Hi Terry,
that's a good question. I hadn't gotten that far, I didn't
know I had choices. I would have gone with what was
compatible with what the repair manual recommended.
That raises another question, what's in here now.
What are my different options for brake fluid?
Thanks,
Karl

[Terry M.]

[Karl K.]

Re: Changing brake fluid

Thanks Terry,
That's a big help!
Karl

[Terry M.]

Re: Changing brake fluid

Karl I just noticed in your OP you said you have a 1965. I went on and on about newer systems, I am sorry for not paying attention.

In that case most folks will recommend you bleed the farthest wheel cylinder first (RR) then left rear, then right front and lastly left front. I can assure you there is no scientific or technical reason to do it that way, so long as you get fresh fluid at each bleeder. But you will see a fire storm of comments now because the believers are passionate. It simply doesn't matter, but do it your way.

There is information in other posts about the best fluid to use among the polyglycols. All will absorb moisture from the atmosphere. Some will do so more quickly than others. Generally the higher the number the better the fluid will be before absorbing moisture. After absorbing moisture it is all pretty much the same. Given the way most of us use our Corvettes a high-cost fluid is not necessary. You may feel more comfortable to know that Bowling Green installs DOT 3 in the new Corvette braking systems. They use DOT 4 in the hydraulic clutch systems -- more heat there.

Buy your new fluid from a high-volume FLAPS (Friendly Local Auto Parts Store). The fluid begins to absorb moisture while it sits on the shelf unopened. Good quality fluid comes in a metal can -- metal cans will not transmit moisture through the container, plastic does -- but you will generally pay out the wazoo for that kind of quality, which you will likely not need.

I would guess a quart of fluid will sufice for your fluid change, but you might want to have another pint on hand just in case.

[Paul S.]

Re: Changing brake fluid

When I replaced the MC on my 67 this Spring, I read all the posts about members' various methods, and issues with each, of flushing and bleeding the brake system.

I had used a Motive Power Bleeder on my 911's for years and was very comfortable with that; I bought the adapter and instead of using the chains I used a piece of wood and a C clamp to seal it tight against the MC; bled in the order Terry meantioned and before proceeding to the next caliper, tapped the caliper hard with a rubber mallet until there were no more air bubbles. When I was done I had all the air out the first time.

And I used ATE Type 200 DOT 4 fluid, again because I use the same in my 911's, and there's a local Porsche indy shop here that carries it.

I am a big fan of the motive power bleeder--you do not need to pressurize it a lot (10-15 psi) and it will flow fluid much faster than gravity bleeding and a lot easier than 2-man pump the brake pedal method. Easiest and most effective way of bleeding a brake system and doesn't require a helper.

[Terry M.]

Re: Changing brake fluid

We flushed new fluid into a long neglected 1979 Corvette brake system in school today. Gravity didn't work, but pump the pedal did. We made a huge improvement int he brake system, but there is still air in there. I think I will invest in a Motive bleeder over the winter and try again in spring.