Bubbles with vaccum brake bleeder.

[02V70]

I replaced the brake hoses and flushed the brake fluid. I got a vacuum pump brake bleeder from harbor freight. Once I replaced the hoses and, I let it gravity bleed until there were no bubbles.

When using the vacuum pump bleeder, there were a ton of bubbles in the fluid in the hose. It seems that air was getting sucked in though the threads of the bleeder valve. I tried putting teflon tape on it, but it didn't work. I used the pump to flush all of the wheels with this happening. Once done with the vacuum pump, I let it gravity bleed for a minute or two. Could this have caused air to get into the braking system?

When test driving, the brake pedal seems a little easier to press, but seems to stop better than before.

[cn90]

This is why I never vacuum.
Best is to use compressor set at 10 psi.
I modified an ATE cap for air compressor, the DIY is in forum.

[MoVolvos]

.
Gravity was never meant as a method / tool for bleeding brakes. You need force to expel the air in the system. Gravity maybe helpful if the system is void of air initially so when you remove the brake lines air and contaminant will not go in from the opened area.

I have done brake work where there is air and corrosion in the caliper. Took several pumps to expel everything. So much so decided dissembled the caliper for inspection.

The bubble you are experiencing now is most likely from inside the system. The bleeder screw has fine and tight enough threads and brake fluid is thick so I doubt air is been pulled in and immediately cycled out.
.

[volvolugnut]

If you have opened the bleed valve more than half a turn, you MIGHT get air in at the bleeder valve. The bleeder valve should only open just a little to clear the seat.
If you replaced the hose, you will get air until you fill the hose with fluid.
Gravity will only work if there is enough height above the bleeder valve to the fluid tank and to overcome the restrictions in the lines. At best you may have two feet of height for about 1 PSI potential without restrictions. Any loop in the line above the the tank will stop the flow without added pressure or suction.
The vacuum pump can make about 14 PSI suction.
Perhaps you did not seat the hoses when they were replaced and have an air leak at the hose ends?
volvolugnut

Correction: If there is no air leak, you should be able to loop up above the fluid tank.

volvolugnut

[vtl]

This is why I never vacuum.
Best is to use compressor set at 10 psi.
I modified an ATE cap for air compressor, the DIY is in forum.

I had these tiny bubbles through screw threads even using Motiv pressure bleeder. No problem with the brakes after such flush, by the way.

[02V70]

I could hear hissing on the bleeder valve, so there was definitely air passing through the threads. There was no hissing or pressure loss with the bleeder valve closed so that rules out air leaking through the hose connected to the bleeder valve. I don’t think the bubbles were from inside the system as they never stopped and that many bubbles would result in non working brakes. There was also more air than brake fluid coming out most of the time.

[cn90]

The brake cap was modified for air compressor.
I wrote it up in 2010, 14 years ago

Here it is...

viewtopic.php?t=29243

And here on BMW forum...

https://www.bimmerfest.com/threads/diy- ... 7/#replies

[Blacklab467]

I’ve never had any success with vacuum brake bleeders, they always seem to pull air bubbles, likely through the bleed screw threads. Just bleed it in the conventional method with someone in the car working the brake pedal and push a clear tube over the bleed screw that drains into a water bottle. You’ll know if you have air or not this way and also clean fresh fluid.

[jonesg]

junk.

[volvolugnut]

I still disagree on vacuum pump bleaders. I have used them many times with success.
volvolugnut