I am planning to drain out and replace all of the break fluid in my '74. I am a DIY-er and I was planning a gravity bleed. Below I have put together a list of steps as guidance. I did however, want to ask for any / all additional guidance from the community, for any tips, additional steps, and general guidance and things that I should consider.

The reason that I am doing this is that I am experiencing a soft break, and a loss in breaking power. I did check, and my break booster is operating correctly. Also, I opened up the master cylinder, and I do have a notice lack of breaking fluid. So, the goal here is two hold: trouble shot the leak, and also perform a full break fluid replacement.

I do know that I am loosing break fluid in the passenger front tire area. I will trouble shoot this and make any necessary repairs. I wold like this thread to focus more on the gravity break bleed process.

One note: I do want to try a gravity bleed first, in order to get the air out of, and to put fresh break fluid into my break lines, and also because of the ease that it can be done with (from what I have read up on. Also, I also like trying everything out once by myself. I can also consult additional professional help for bigger or reoccurring problems I can solve on my own.

Steps I am going to perform
0: order to check break lines: passenger back inside , passenger back outside, driver back inside, driver back outside, passenger front outside, driver front outside.
1: jack the car up and make sure the back end is lower then the front. (opposite when I replace the fluid in the front break lines)
2: remove the back tires
3: clean up the area (remove dirt, gunk, and what not), check for any damaged parts, and make any replacements as necessary.
4: loosen up bleed valve to make sure it not ceased /locked up.
5: open up master cylinder and monitor break fluid level
6: set up and attach drain basin and hose, attach hose to bleed valve, and slowly open up valve allowing the break fluid to drain out.
7: monitor break fluid drainage until fluid color changes to the new clear fluid, while at the same time adding fluid off master cylinder, so no air gets trapped in the line.
8: once the new break fluid is present, close off the bleed valve, detach the drain hose, and clean up area.
9: move on to next bleed value as note in step " 0 ", repeating steps 3 through 8.

In my mind, this would be a good way to make sure new break fluid is in the lines, and is something only a single person can accomplish.

I appreciate any thoughts and insights.

Lou

 

FWIW: before you bleed anything, you need to find the source of the leak in the system. If the brake calipers are original, it's probably time to rebuild/replace all four.

 

As far as a gravity bleed, I believe that is the correct procedure. However, gravity bleeding is a very slow process! If you are waiting for new fluid to make it from the master cylinder to the rear passenger side, you will be there a while, but it should work. Much faster is to have someone pump the pedal while you open/close the bleeder valve.

I just went through this on mine a couple days ago. I started with a gravity bleed and got impatient. I have a Motive power bleeder which I had used unsuccessfully before. I used clamps this time on the master cyl and it worked like a champ.

 

I have never used uneven jacking of the vehicle when bleeding brakes and have good results without doing so. After gravity bleeding, you will still need to bleed the brake lines/calipers of air. Have 2 or 3 quarts on hand to do the job. Any unused fluid can be returned for refund.

 

Gravity bleeding done properly will leave no air in the system. I've done it on multiple Vettes ending up with rock hard brakes. It is slow to be sure, but if you're patient, it will get the job done.

Mike

 

Been doing it this way since the early '70,s! It works!

 

Not disputing your results but I still had air after gravity bleeding.

 

Easy Mike: I have narrowed down the leak in the system to the front passenger side tire. I can visually see brake fluid on my garage floor. Once I get the front tire off, I can get a better idea of the specific issue. Also, my master cylinder has two reservoirs; one for the rear brakes, and one for the front brakes. The rear break reservoir still is holding brake fluid, which reinforces the belief that my leak is in the front.

Jim-81: I am not worried about the time as long as the gravity bleed is done correctly. Pumping the pedal break is something I will take into consideration. I can see this helping. In this instance, does the master cylinder top cover have to be “installed” or just “covering” the master cylinder reservoirs? I can see leaking of the fluid out of the top of the master cylinder being a possible issue here when applying the brake pedal pressure.

For right now, the next step is to set aside some time to take off the front passenger tire and see what the immediate leak issue is. Second next step is to figure out is which (or all) calipers and break lines need replacing. This is part of making sure all components are in proper working order.

With that said, I do have a feeling that the calipers need to be replaced, and should be replaced. Most of the parts of the car are in bad enough shape, and that replacing them has been my best option. However, money becomes an issue here, since I am working on a budget.
Question 1: Can I get away with buying calipers from a local auto dealer (Autozone, O’Reily, or Napa Auto type places) or should I buy from a corvette specific dealer like (Ecklers, or Paragon)? There is a noticeable price difference here? I am looking for a healthy balance between quality, price, and functionality.
Question 2: Obviously other than buying calipers appropriate for my car, is there any sizing I need to take into account? I.E. rotor thicknesses, or are they all mostly a standard size? Is the caliper replacement more of removing the old one, and installing the new one, install the brake pads and I am good to go?

 

I'd say you have found your problem.

 

another thing to add to your procedure is to tap each caliper with a rubber mallet as it is bleeding to dislodge any air bubbles. I also have always had success with gravity bleeding. You make no mention as to whether your master has bleed screws.

 

And flick the rubber brake lines too. Also pour the fluid into the master cylinder slowly so as not to make any bubbles in the fluid. This is especially important if you are using DOT 5 fluid.

Mike

 

He shouldn't be using Dot 5.

 

Gravity bleed works. I have used the mityvac hand vacuum pump to bleed my brakes. It is faster and you get all the air out.
If you do use gravity, don't forget you will have two bleeders on each rear caliper.

 

Not when he's just flushing the system with brake fluid and refilling with fresh fluid. DOT5 should only be used on a completely new or a system totally devoid of any old DOT3 fluid.

Mike

 

My OCD is killing me reading this. It's brake, not break. You're working on the brakes, not trying to break something. Jeesh! Where did you go to school? Remind me not to hire anyone from there. How hard is it to get everyone on the same page here? I learned this stuff in grade school.

 

I second the vac pump idea. $20 well spent; same general idea, but makes the job go much quicker.

Additionally, there are several vacuum operated accessories that may eventually need troubleshooting, and the vac pump comes in handy to test with.

 

I wanted to provide an update to final status to the brake fluid gravity bleed.

To start off, I found out where I was leaking brake fluid. I took off the front passenger tire. I first performed a visual inspection of the line, tracing the line back from the caliper, into the engine bay. The break was in the actual solid metal line, close to the connection between the flexible brake line and the solid tube. After a few choice words, I disconnected the brake line from the caliper, and let whatever remaining fluid drain out. Then I pulled the retaining clip and the flex line and part of my solid brake tube fell to the floor.

At this point, I went over to my local auto body shop, who also restores corvettes. He knows what he is doing. He ended up having a complete brake line replacement set for a ‘74. (Small miracle there.) At this point, I have decided to replace the entire front set of brake fluid lines including the flex lines and calipers. He then directed me to a parts place a block away. They set me up with new flex tubes and calipers, new brake pads, some brake fluid and provided some guidance on what to and not to do.

So back at my garage with my father and brother helping out, we ended up removing the crossover line to the passenger side, and also the driver’s side brake line. We had some fun and a few choice words when we were installing the new crossover line. Snaking that sucker through the engine bay components was fun. We took out time and were able to get it softly in place in about 30 minutes. We all were being overly cautious. We did not want to snap that line. After having the brake lines fastener to the manifold and secured in place, we installed the calipers and attached the flex brake lines. Everything went together smoothly.

Instead of gravity bleeding the brakes, which would have taken a while, we did decide to pump on the brakes to get the brake fluid moving through the lines that much quicker. At this point we realized that since the brake pads were installed, but we did not push in the pistons for the calibers, before doing so. This issues turned out to our benefit though. After getting the brake fluid into the lines, we button up the brake fluid master cylinder, as to not have an open system line. Starting with the passenger side, we then opened up the bleed value, removed the pads, and pushed in the pistons. This allowed for any remaining air to be pushed out of the calibers, along with brake fluid, thus giving us a fully fluid pressurized brake line. We closed up the valve and reinstalled the pads. We repeated this for the driver side as well. This was probably not the most efficient method, but the end result is what counts. And, I am sure some of the auto shop mechanics would have had a great laugh at us three trying to get the lines and calipers working properly.

With the brake lines full of fluid, and holding fluid (aka no leaking which is always a plus), we took it out of a drive. The brakes are definitely back. I feel comfortable driving the car again. All in all, we took our time and spent about 6 hours, working on the car. It helping having the parts readily available, and the advice we received definitely was a bonus.

I will probably check the master cylinder in a few day to see if any additional air pockets were removed from the lines, and to top off the brake fluid.

… on to the next project…..

 

Thank you!

 

gravity bleeding, that is

 

Glad to read you got that sorted out. When I first started to drive, I was told to first make sure to have good brakes and steering before anything else.