LexBrett2

Dear Friends,

This weekend I bled my rear brakes with a Mityvac, but couldn't get all the air out of the lines. I sucked out almost 1.5 liters of fluid, but a continuous flow of small air bubbles still remain.

Any thoughts on what I have had done wrong? I apologize in advance if I missed something obvious.

Tips or suggestions to other threads I may have missed would be much appreciated.

FYI, I did exhaustive internet research before I did the job, turned "off" SBC by allowing the car to sleep before doing the job, etc.

gafitanu

Sometimes when loosening the bleeder screw air gets sucked in between the screw and the caliper and it shows on your hose. One way to prevent that is to seal the bleeder at the caliper with grease, it will stop the air from being sucked in.
Which Mityvac are you using? The one that pressurizes the brake fluid reservoir or some other type? I flushed my brakes a while ago with a Mityvac and there was no air.

LexBrett2

Just checked and I am using an Actron, which I purchased at Advance Auto. It is a hand held reverse pump that sucks brake fluid directly out of the bleeder screw. Here it is:

https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds

I used Lucas heavy grease between the bleeder screw and hose. It seems air tight with the grease.

But perhaps the air is getting in between the caliper and bleeder screw, as you suggest? It's a steady small stream of bubbles and is just maddening.

I have also read that the "power bleeder" method (pump on reservoir pushing fluid through the system) is more effective in getting all the air out. I just bought one from ecs tuning and hope it works:

https://www.ecstuning.com/b-schwaben.../007237sch01a/

Thoughts?

gafitanu

My mistake as well, I have the exact Schwaben that you have and it will work very well, just follow the instructions. I don't think you have air in the system. Air moves quickly to the extremities of a hydraulic circuit and that's exactly where the bleeder screws are located. So when bleeding, the air gets out first. A steady stream of bubbles indicates a leak in the system sucking air but since the hydraulic pressure is way bigger the fluid would leak out quickly and you will see/feel that fast.

kajtek1

MB for years require pressure bleeding, meaning vacuum is not recommended.
Now we know why.

LexBrett2

My fluid level in the reservoir is constant, and I the brakes feel great, so it doesn't feel like a leak IMO.

But I do get some brake squeals first thing in the morning, but I was thinking that is just rust that goes away after pads rub on rotors after two or three stops. But then others have said the squealing is from the air in the brakes. Sigh...

I feel the bubbles MAY coming from the space BETWEEN the caliper and bleeding screw. Someone else suggested this, and I am going to put some heavy greases on it tonight to test.

Were you saying that you think the bubbles indicate a leak in the system?

mtrevelino

I would say is that you do not have a "sealed" connection with the bleeder hose on the nipple. When I do my motorcycle, it always shows bubbles.
Also with what Kajtek1 said, MB recommends power bleeding the system. I had a 1995 Volvo which required power bleeding. So this has been common practice for at least 20 years.
Mike T.

LexBrett2

Thanks for your suggestion. I'm going to the power bleeder this weekend. Have a great day!

LexBrett2

Turns out you were correct! I applied heavy grease and bubbles disappeared. Ironically the next morning my power bleeder came in the mail from ESC tuning, after I already completed the procedure with the suction method.