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Air in brake system


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20 replies to this topic

#1 rward

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Posted 18 January 2004 - 01:14 PM

'91 Loyale 4x4 wagon

I just did a bunch of front-end work that required removing the brake calipers. After hooking everything back up, I keep getting air in the brake system when I bleed the front brakes. I bleed them until there's no air, then come back a couple of minutes later and there's air again.

It seems to me air is getting in at the calipers. The only things I can think of are: 1) I didn't replace the sealing washers on the banjo bolts, as suggested by the shop manual; 2) There are two sealing washers per banjo bolt. I put one on either side of the banjo bolt assuming that's how it was before, but I don't remember for sure. Maybe one of these is allowing air to get in?

I'm getting air at both calipers so I'm doubtful that the sealing washers are bad. I'd think that at least one of them would seal up.

Any thoughts out there? Thanks in advance.

#2 Supaglu

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Posted 18 January 2004 - 02:24 PM

Hi,
Did you lose much brake fluid from the reservoir ? try bleeding all four brakes and see how that works - also keep making sure that the reservoir pot is constantly topped up !.

Regards
DaveH

#3 Setright

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Posted 18 January 2004 - 05:03 PM

A full flush, Setright style, requires one liter of brake fluid. I would try this first, before re-doing the banjo bolts.

#4 beauregaardhooligan

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Posted 18 January 2004 - 05:45 PM

I don't know about Subaru banjo bolt washers, but on my Valiant, they are only good for one tightening since they are made of copper. They must be replaced.
You should bleed all four wheels and also at the points where you opened the system.
Do *not* pump the brakes at any time when bleeding, this can cause micro-bubbles that come out later. Push the pedal down slowly and let it up slowly. Also be sure not to shake the brake fluid can.
Sometimes it just takes lot and lots of bleeding to get all the air out, be patient.
I use one of the cheap ($7) one-man bottle bleeders with very good results.
If there is a leak, you should be able to see it.

#5 Snowman

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Posted 18 January 2004 - 06:46 PM

You might also try gravity-bleeding the entire system. Open all the bleeder screws and just let it sit for a while (at least ten or fifteen minutes) while making sure that the reservoir is full.

This technique is often used on really stubborn systems that can't get all the bubbles out using normal procedures. It is slow, but works 99.9% of the time.

#6 rward

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Posted 19 January 2004 - 12:37 AM

I replaced the banjo bolt washers and did the gravity feed on all four wheels (for at least 1/2 hour) as suggested by Snowman. Still no joy. I'm still getting bubbles at both front calipers. It seems to me that air must be getting into the system. I've run about 3 pints of fluid through the system (mostly the front) so far. Even if air got in through the master cylinder initially, I shouldn't still be seeing that many bubbles should I?

Can anyone verify that the washers on the banjo bolt go one on either side of the brake line donut? I just want to make sure the thing is put together right.

Also, one of my shop manuals (but not the other one) says that the engine must be running when bleeding or the brake booster WILL be damaged. I went ahead and ran the motor when bleeding, but I've never heard of this. Has anyone else?

Anyway, I'll let it sit overnight and see if any leaks are visible by morning.

#7 Setright

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Posted 19 January 2004 - 02:25 AM

CRIKEY! With the engine on and full vacuum assistance on the brake the fluid must shoot out at the bleeders.

I have never heard it done this way. Maybe that's your trouble?


It sounds like baloney that the master cylinder should be damaged. It's designed to work with the engine stalled. You dont' want to lose braking because the engine goes out!

#8 calebz

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Posted 19 January 2004 - 02:57 AM

I just did a bunch of front-end work that required removing the brake calipers. After hooking everything back up, I keep getting air in the brake system when I bleed the front brakes. I bleed them until there's no air, then come back a couple of minutes later and there's air again.



Subaru brakes are plumbed diagonally..they need to be bled diagonally as well.. just bleeding the fronts won't do it.. do front left.. then right rear..
front right.. then left rear.. back and forth a couple of times.. see if that helps.

#9 NV Zeno

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Posted 19 January 2004 - 11:53 AM

All four corners should be bled whenever the system is opened. If you still get air after a couple or three "go-arounds", you may have to bleed the master cylinder. That's what worked for me.

#10 rward

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Posted 20 January 2004 - 12:56 AM

Ok, here's the deal. I bled all four wheels diagonally and got air at all four wheels, twice. I haven't bled the master cylinder yet because the bolts on the brake lines are a major PITA to get loose and, more importantly, the more I work on this, the more convinved I am that air is getting in.

The thing that has me thinking this is that I have bled enough air out of the system over the last three days to fill the entire system at least once, no kidding, not to mention the quart of fluid I have put through it. I can't imagine that much air could be trapped in there. My understanding of hydraulic systems is that air can get trapped and compromise the system, but I have a continuous supply of air bleeding out. At some point the air has to stop coming out if air is not getting in, even if an air pocket remains trapped in the system.

So, I'm thinking that maybe it's just a strange coincidence and the master cylinder has a leak. Any thoughts or, better yet, does anyone know how to test this? I'm curious to know what other people think.

NV Zeno - Did you have continuous air bleeding out of the system before you bled the master cylinder?

Thanks all.

#11 beauregaardhooligan

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Posted 20 January 2004 - 06:08 AM

Air pockets are possible.
Make sure the master cylinder reservoir stays full.
You *do* need to bleed the master.
There are special wrenchs for opening brake lines, look like a box end wrench with one side cut out. Be sure to use two wrenches, one on the fitting and one on the hose nut so you don't twist the brake line.
You *can* bleed the system from any point with a connection.
Usuing a quart, or more, is not unusual.

#12 NV Zeno

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Posted 20 January 2004 - 10:30 AM

The last time we bled my brakes, we used some sort of continuous feed contraption and still got a soft pedal. I figured my bud couldn't figure out how to use his new contraption, and went back to our usual method of one of us in the car on the pedal and the other under, doing the actual bleeding.

We went through a LOT of fluid, but after three or four times around, there was still air somewhere.

That's when we decided to bleed the master cylinder. Two or three "bleeds" later, voila..nice hard pedal.

BTW, no leaks were found.

#13 Setright

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Posted 20 January 2004 - 12:05 PM

I just bled my brakes, at each wheel. Haynes is a bit vague on the MC. Any pointers??


(I do not have air in the system, though)

#14 rward

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Posted 20 January 2004 - 02:23 PM

The problem here is not spongy brakes (although I have that too), which indicates that air is trapped in the system, but air bleeding out of the system. No matter how much I bleed the system, AIR COMES OUT at all four wheels when bleeding. I'll bleed each wheel (diagonally) until no air comes out, then start over and get air again and again and again.

Does anyone know how to test for air leaks at the master cylinder?

Thanks

#15 Supaglu

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Posted 20 January 2004 - 04:46 PM

Hi,
Assuming the car hasn't got A.B.S (if it has bleed the brakes with the ignition on) - try this :-
Starting at the master cylinder - with the reservoir full - you've got 4 brake lines leaving the MC - have someone press the pedal to the floor- open one of the lines and then close it, release the pedal and push it to the floor again - open the same line again and then close it. Do this half a dozen times or more to each line in turn until you get a jet of fluid shooting out of the line from the MC. (use a cloth to prevent the brake fluid from shooting over paintwork)
Once you have done this - bleed each brake in turn - starting with the brake farthest away from the MC - working your way round until you get to the brake nearest to the MC.
This should sort out any bleeding problems - as long as the MC is ok.
You could also clamp off each brake hose and try the brake pedal - if it's a good pedal then undo each clamp in turn with someone holding the pedal down - until you feel which one makes the most difference - the one that either sinks to the floor or drops the most is the line you need to concentrate on.
The only other thing that hasn't been mentioned here is the clutch hill holder !
Regards
DaveH

ps
to check if the MC is leaking - pull it off the servo and look at the seal - if its wet with brake fluid - replace it !

#16 NV Zeno

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Posted 20 January 2004 - 04:53 PM

In the case when my master was found to have air, there was no leak. That was caused by another problem that was found and repaired earlier.

Umm, I believe there are only two bleeders along the side of the master cylinder.

#17 rallyruss

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Posted 20 January 2004 - 05:40 PM

I would be verry suspicious of the master cyl.

I have had cars with old master cylinders get brake work done and then not bleed out the air properly before as well. most of the time it is the master cyl. that is at fault.

now you may be thinking but it worked before why not now?

think about this. you might not have changed the fluid verry often like most people forget to do. it absorbed moisture and started corroding the inside of the cyl. bore. not the part used everyday but the front portion. so when you went to bleed the brakes you pump the piston into the portion of the cyl. bore that it normally does not visit. In doing so the seals are damaged allowing air to get pulled into the cyl. when pumping the brake.

this may not be the case. the hill hoder could be at fault or something else as well but a new master cyl. is cheap and easy to install. oh yeah dont buy any reman master cyl. they just don't last trust me.

oh yeah to prevent this from hapening dont pump n bleed. use the gravity method as snowman said or use a suction device if you cannot get it to flow. if you really want to pump it use hooligans advice and pump slow and steady. one pump one bleed.

as for copper washers we reuse them all the time at work because on lots of vehicles the old ones seal better than the new ones. might not be text book but it work for us.

good luck

#18 beauregaardhooligan

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Posted 20 January 2004 - 05:58 PM

You say the problem is air bleeding out of the system. It has to come in somewhere.
If there is a leak in the system, fluid would also leak out, except for an internal leak in the master.
1 Are you keeping the master cylinder full?
2 Do you keep the pedal all the way down when the bleeder is opened *and* untill it is closed again?
3 Have you bled the MC?
4 Does the pedal slowly sink or does it stay where it bottoms out?
Once you get some pedal, go over everything and look for wetness while someone holds the pedal down.
Be patient, it can take a loooong time and much fluid to get it right.

#19 rallyruss

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Posted 20 January 2004 - 10:12 PM

Ed, not always.

I got totally confused working on a vw jetta with a air in system problem. it turned out to be the height sensing valve in the rear sucking in air but not the slightest indication of a leak.

:banghead:

#20 beauregaardhooligan

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Posted 20 January 2004 - 10:56 PM

Hmm. Well, learn something new every day, hopefully!
That wouldn't apply here, though, would it?
rward, you say you're getting air at all 4 wheels? I'd have to go with Russ on suspecting the MC.

#21 beachbum

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Posted 21 January 2004 - 06:30 PM

agree with snowman,i just had the same problem on my mustang,no matter how much i bled i kept getting air,so i gravity bled them and they work great now!just be sure and open all 4 and keep the mastercylinder full,i`d fill it 2 or 3 times just to make sure.gluck




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