Help - Rear drum brake cynlinder piston poped out

I don't think you broke anything. Lost a lot of brake fluid, but that's about it. You should be able to push it back together if you open the bleed valve. Getting all the air out of the system is going to require Techstream, a MasterTech scantool, or something similar.

 

I also feel that nothing is broken. All that happened was the piston was over extended because the drum was not on. You should be able to reassemble using the parts you have.

 

If the piston did'nt come out all the way,you might not have taken in air.You have to put the drums on anyway to bleed it,so why not top off the resevoir and check for spongy pedal?

 

If no fluid leaked out, I would still try to push it back without opening the bleeder valve. Doing so, would not allow air to get in the line, and a very good chance that you would not need to bleed the brake line. When I do brakes, (95% front disk), I use a C clamp to push the caliper piston back, and I have yet had a need to bleed the brakes afterwords, because no air enters the system. Perhaps something similar could be done with the rear, by attaching the shoes, and carefully use a large C type clamp (possibly a padded wood workers clamp) on the shoes to push the piston back.

By opening the bleeder valve, there is a risk if allowing air into the system, that would require you to bleed the brakes.

Let us know how it went.

 

It may not be necessary to use a scantool to bleed the Prius brakes. Certainly any time-is-money mechanic would use a scantool. But if you'd rather spend time than money, all the scan tools do is operate solenoids. It can't be that difficult to unplug the solenoids, and hook up your own wiring to power the solenoids.

 

I would try a compromise between the "open" or "not open" school of thought. First, place pressure on the piston to push it back into the cylinder. Next, while holding the pressure, slowly open the bleed screw until it starts to let fluid out. Continue to press the piston as it moves in. Keep more pressure on it than is necessary to get it to move so that it does not have a chance to move back and suck in air. As the piston returns to the "in" position, tighten the bleed screw while still pushing in on the piston. This method should ensure it does not aspirate some air through the bleed screw as you are moving the piston back in. Trying to push the fluid all the way to the master cylinder may or may not work.

NOTE: if you have the drum off the other side, make sure to put it back on before doing all this. You don't want to accidently push fluid all the way back to the master cylinder, and back out to the other rear brake.

 

Sorry but your done. You opened the hydraulic system with the loss of fluid. The car's skid cpu will detect that loss of pressure and possibly immobilize the car. You may be unable to move the car.

There's no way to bleed the brakes without the proper software.

Check it by going into Ready and check the codes it will throw with your laptop.

BTW, here's a link from another poster with similiar issues:
http://priuschat.com/forums/gen-ii-...em-rear-brakes-no-pressure-when-bleeding.html

 

Meep, that's a bit of an oops. Did you rip the boot, or did it
just pop off the end of the cylinder intact? Was the car
powered up or down at the time? How much fluid escaped?
.
If you are very sure you didn't get air back up the rear line far
enough to land in the actuator, and didn't wind up draining out
enough fluid to empty the reservoir, there's a good chance that
you *can* recover gracefully from this. Please see the brake
section in my 100K maintenance pages, where I do a very brief rear
bleed to pull a little fluid sample. The other referenced thread
above is slightly wrong about not being able to bleed the rears --
but you have to do it with the car *powered up* because of the way
the brake system works. And it does not work through pumping the
pedal, as the actuator valves and accumulator will continue sending
pressure to the rear lines until the pressure sensors show the
right feedback. That implies that a held pedal and a leak in
the rear system would cause the accumulator to happily pump the
reservoir dry all by itself, so be careful here.
.
Remove both shoes to get more working room. The main spring just
under the cylinder is a pain in the nice person to unhook; a small
screwdriver held in a pair of vice-grips or something helps. Keep
everything *religiously* clean, and make sure you didn't damage the
edge of the piston seal. You might want to bleed a little more fluid
[and keep an eye on the reservoir] with the thing still open just to
make sure there aren't a lot of air bubbles coming out of the line at
you. Reinsert the piston *really* carefully to avoid messing up the
edge of the seal lip. Hopefully there's enough up-and-down in the
line that no bubbles would have risen all the way back up to the
actuator in the time it took you to post and read all this stuff
in return, and you'll be able to reassemble things and keep a solid
column of fluid intact. And as someone already said, having the
bleeder open just a touch will allow the piston to displace fluid
as it goes back in.
.
Air remaining in the rear lines will likely *not* give a "spongy
pedal" feel, as your master cylinder is pretty much insulated from
it all the time under all operational modes. The only difference
air would make is that more fluid would have to be pumped in and
out to bring the rears to the requisite pressure, and the nagging
chance that the trapped air could eventually migrate back up to
where it would do more harm. So you want to make sure that line
is thoroughly bled, maybe doing it again after a couple of days
of driving around. The only hint that something's amiss might be
more accumulator running, and a very slightly different subtle
change in valve modulation as the brakes are applied.
.
_H*

 

Okay, well, now you've likely got a wheel cylinder full of air.
So more fluid is going to leave the reservoir as the system tries
to compress against that, and/or you bleed that line. Do you
have additional DOT 3 brake fluid available? You should likely
pick some up before proceeding, to make very sure you don't
empty the reservoir.
.
Refer to the hydraulic diagram, and note that the only way
pressure can reach the rear wheels is through the SLARx valves
which are normally closed and need power to operate and open. When
the car is powered off the brake ECU still gets more or less powered
on when the brake pedal is pressed, and will do sort of a rough
rear-wheel pressurization in response to pedal application, but
it's better to come to full READY where you have smoother overall
control in the braking systems. To send continuous pressure to
the rear wheels, wedge the pedal slightly applied like I did with
my special rock.
.
_H*

 

^ that will throw a few codes. I had this happen to me last week. What I did was clean off the piston, put it back in and I cracked the bleeder screw and let gravity take over. Then I tried to bleed the system that way, but after I was done I saw all the brake warning lights light up.

I cleared the codes by using a jumper wire between terminals 4 and 13, and I have problems since - but I'm going to be taking the car in for a proper brake flush.

 

Yep - all the codes were cleared and my parents said they didn't see the dash light up like a Christmas tree.

The system threw 3 codes - 1 for brake system leakage, and 2 for left rear hydraulic fault - a pressure drop when the bleeder was cracked. After I cleared the code, I took the car on a vigorous test run to ensure no problems will happen - the regen was working, and heard the brake pressure pump running normally.

 

,i just want to post a newbie question on how to clear those codes..

 

I also knocked the piston out but I had an added rip in the boot. At, first I didn't see the rip and started bleeding but to no avail. After another inspection I noticed the boot rip. Very small rip but is pumping air back into the system. I replaced the wheel cylinder. Been through all the steps.Filled reservoir twice after hitting the median between full and low. Just wondering roughly how long I'm supposed to sit pumping the brakes before I get any pressure. Could there be another issue or is there just that much air in the rear line? The fluid is dripping out and not really spraying.