Brake Bleeding Question

When bleeding my brakes:
I pump the actuator and fluid moves as you would expect through the lines.

But when I stop working the actuator, the fluid rushes back into the actuator. Think of putting a water hose in a bucket that is turned on all the way. Fluid rushes in like that and will overflow until (what I assume) the pressure in the system is gone.

Trailer wheels are off and both axles are up on stands. There is no pressure on the system other than what I manually put into it when pumping the actuator.


Any ideas why fluid would flow back into the actuator?
The only thing I can think of is that the backup solenoid isn't working and allowing "reverse pressure" back into master cylinder. But then again, if this didn't happen I would assume my brakes would be grabbing and not releasing.

I'm stumped right now and google isn't helping.

Does it rush back in after you release the actuator? or you holding it with pressure on it and the fluid rushes back in?

If your letting off the actuator then that is why the fluid is rushing back. When you hit the truck brakes it slows and the trailer pushes against the actuator forcing fluid into lines and into the caliper applying the brakes. when you take your foot off the brakes the actuator releases pressure allowing the fluid to flow from the calipers and lines back to the reservoir and releasing the brakes. If your trying to bleed them you need to pump and hold the actuator and someone else to release the bleed screw or some way for you to secure the actuator with pressure on it.

When bleeding brakes, just push the pedal down and hold it, no pumping. Then close the bleeder. Release the pedal, and the springs on the brakes will push the fluid back to the reservoir. Repeat till air is out of the system.

Yes, after I release the actuator, the fluid rushes back in.
This just has never happened for me before. I've never had the fluid rush back in, or at least at this volume and/or pressure.

The reason why I was pumping the actuator is that I have completely overhauled my brake system. New everything except the actuator. So I had to "pump" to fill the new lines.


Well, maybe this might be the 1st calipers that I have ever had that are working right by pushing that fluid back so that the brakes release?

You may have a lot of air in the system if it is "rushing" back. On disc brakes, only a small amount of fluid is used to actuate the brakes.
You should only push the pedal down with the bleeder open, close the bleeder, push pedal down, close the bleeder and continue till there is no air. NO PUMPING!!

with surge brakes the actuator is the pedal. With only 1 person you need a brake bleed kit or the vacuum hose and bottle method. When bleeding brakes if you do not have a person on the pedal and one on bleeder valve. You will suck air back in without a bleeder kit or a jar of fluid and a piece of vacuum tubing aubmersed in the fluid.

Thanks ChuChu and Stump.
I'll try a different method and see if this is a result of air in the system (which I think very well may be). I

Or you could rig something to hold the actuator in place while you go bleed them, gotta be creative, but there are ways.

Definitely air in the calipers. Look at the calipers and see if the bleeder is at the top? If not, you will have to swap sides so they are at the top. Also some calipers have a tapped hole at bothe ends, if this is the case than just relocate the lines to the bottom.

Shouldn't be a problem. I can push the actuator in all the way and it will no come back unless I release the safety lever that is under the tongue. Or whatever that thing is called.




Not sure if the image will show up. It's not when I preview the post.
Let's see...

OK. I'll try again.

My calipers have 2 bleeders. I might want to try using the one at the top.
I'll work on the pic.

Here we go....

I've been working with the lower bleeder just because it's easier. Maybe if I work with the top one it will be different?

Storage facility security guard.
I don't know if he's mean but he sure is loud

yes it should be bled from highest point on the wheel cylinders. i don't know the tilt of the trailer but if it's nose down you could have a heck of a time trying to pump bleed the wheel cylinders. a helpful hint would be to raise the tongue as high as you can, fill the reservoir and open one bleeder at a time till fluid starts to come out, monitoring the reservoir, do not let it go dry or more air will get into the line. then move to the next. then you can pump bleed them with ease till you get no air bubbles out of the cylinders

p.s. it's called gravity bleeding