ronsc1985

Is there any reason why one cannot vacuum bleed or flush the brake fluid?

The reason I ask is there is a blurb in the MityVac instructions about how not all ABS systems can be vacuum bled on the rear brakes. I am considering this method since the Motive pressure bleeder didn't work out due to them providing a faulty pump and incorrect thickness gaskets.

I forgot I even had Mity vac metal pump and attachments. I had bought it a long time ago to preset waste gates on a turbo RX7 drag car.

Bill Dearborn

I checked several online MightyVac manuals and didn't see the comments about the rear brakes.

I usually do pressure bleeding but when I have tried vacuum bleeding haven't had any issues. If you think about it vacuum bleeding isn't any different than pressure bleeding. Either the pressure on the master cylinder is increased thus establishing a pressure difference between it and an open caliper bleed screw or a vacuum is applied to a caliper bleed screw thus creating a pressure difference between the master and the open bleed screw.

I have used a vacuum tool that uses compressed air to generate the vacuum. The biggest issue I had with that is the high vacuum generated by the tool can quickly suck all of the brake fluid out of the master cylinder reservoir so it behooves you to have somebody watching the reservoir to make sure it doesn't run dry.

Whether you do pressure or vacuum bleeding the big question is how much fluid is enough. I do that by estimating how fast the fluid is flowing through the brake line by watching how fast the initial bubbles flow through the bleeder hose after I open the bleeder screw. Then I interpolate that speed to how long it would take the bubble to travel from the master to that bleed screw. I wait that long and then close the bleed screw. The advantage of vacuum bleeding is you control the pressure differential while you are at the bleed screw so keep it constant. Using a pressure bleeder like the Motive the pressure level changes as you bleed the fluid.

Bill

ronsc1985

Using a Mity vac there is a cup you suck the fluid into so one can tell how much came out. A rough estimate of how much fluid is in the system is about 4 fl oz max per wheel plus whatever is in the calipers. Best guess is 8fl oz per wheel should more then cover the volume in the system. Even if it isn't all changed it should be sufficient since the car is not road raced and high brake fluid temp is not a great concern. Actually the bakes feel fine now for one stop from 150 or so. The reason I'm changing the fluid is it's almost 6 years old.

It may take longer to do it this way but considering the time to move stuff around my garage to make room, jacking the car, removing wheels, etc. the time differential is not a great concern.

Carnac

For a long time I used ATE Racing Brake Fluid (DOT 4) in both the standard amber color and also in blue.

By having two colors available, I would alternate the colors so that I could tell when the line had all new fluid --- i.e. - when the system had amber fluid, I would use a syringe to suck out as much old brake fluid as possible from the master, add blue fluid, then pressurize with my Motive bleeder. I then open the caliper bleeder until I see the color change from amber to blue. I did this at each caliper (had to fill the master a couple of times).

The next time I would go from blue to amber.

Worked really well.

I have heard that US, brake fluid has to be amber and that the German blue fluid is no longer available.

Jim

TJC333

I have a 2019 Z06 and I use a Craftsman hand vacuum pump to bleed my brakes without a problem. I don't do a complete flush. I just bleed about four ounces out of each bleeder therefore eight ounces per corner.

ronsc1985

I tried my 20+year old Mitivac. Apparently the pump seals were leaking a it took a lot of pumps to get much vacuum and even then the drain rate was pretty much forever. I went back to pressure tank to flush the system.