brake bleeding

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budgerian

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I have just overhauled all 4 calipers, replaced all 4 disks and pads, brake hoses AND hard lines (because the hoses refused to let go, I did not replace the long one to the rear).

All that was left to do was bleed the system, and here begins my problem:

Bleeding was done the oldfashioned way, one in the car, one at the bleed nipples. I started by bleeding the hard lines at the master cylinder to get fluid into the cilinder. Started with the side outlet closest to the servo, half a turn open, pedal in, fluid comes out, close, release pedal. So far so good. But both the bottom one closest to the servo and the front side connector don't release any fluid while following the exact same procedure.
No point in bleeding from the nipples since fluid isn't even getting into the lines.
And this was supposed to be the easy part of the job :-?

What could be the problem? I am clueless and any help will be appreciated, so i can finaly start driving again..
 
budgerian said:
I have just overhauled all four calipers, replaced all four disks and pads, brake hoses AND hard lines (because the hoses refused to let go, I did not replace the long one to the rear).

All that was left to do was bleed the system, and here begins my problem:

Bleeding was done the old-fashioned way, one in the car, one at the bleed nipples. I started by bleeding the hard lines at the master cylinder to get fluid into the cylinder. Started with the side outlet closest to the servo, half a turn open, pedal in, fluid comes out, close, release pedal. So far so good. But both the bottom one closest to the servo and the front side connector don't release any fluid while following the exact same procedure.
No point in bleeding from the nipples since fluid isn't even getting into the lines.
And this was supposed to be the easy part of the job
What could be the problem? I am clueless and any help will be appreciated, so i can finally start driving again.
Click to expand...

Believe it or not, BMW's recommended version of brake bleeding is to pressurize the brake fluid reservoir and then individually tap all of the bleeder screws/nipples beginning with the farthest caliper from the master cylinder. So, if you have a left hand drive vehicle, you would bleed in the following order: Right rear; left (driver) rear; passenger front and then finally the left front. If memory serves me, the front four-piston calipers are bled Top bleeder, then inside bleeder finished by outside bleeder.

Despite the above, I too have used the foot pumping method successfully for many years. I am told that by using the foot pumping method on a less-than-perfect rebuilt or worn master cylinder you run the risk of eating an internal seal. The theory being that a used or poorly rebuilt cylinder barrel may have irregular wear since the piston seals rarely sweep some parts of the cylinder. Same argument applies to clutch hydraulics.

I must apologize but your post is somewhat confusing. Apparently you attempted to bleed the master cylinder but you are unable to get fluid flowing from some of the master cylinder ports. You do not mention if you replaced or rebuilt the master cylinder or you are using the one that may have previously worked well. I cannot tell if you are cracking the retaining nut on a line and you just fail to see dripping fluid. If this is the case, maybe you have not cracked the nut enough? In fact, I would pull the line completely from the cylinder to remove all doubt. If this does not provide any success, continue reading.

Is it possible that you never fully primed the pump? This is not usually necessary, but I have actually witnessed a mechanic immerse the entire assembly in brake fluid to force all air out of the system and prime a troublesome master cylinder. Again, this is not my practice, nor is it my suggestion, but I bet it’s effective.

In any event, if you cannot prime/bleed your master cylinder it is dry and the question is why. Could it be that although you have the reservoir hooked up feeding fluid to the master cylinder, the fluid is being restricted to one area of the master cylinder? I recall having a similar problem with an entirely different car. It turned out that a small brass washer was improperly fitted under one of the rubber grommets designed to cradle the rubber feed tubes. The washer obscured the inlet hole in one of the master cylinder ports so that the master might have become “moist” rather than full of fluid. There is a washer used in your master cylinder "no 9", and if it is the correct size, this is a non-issue. However, it is not that hard to look to make sure the port is not covered by pulling the feed hose. It is possible that the wrong washer or just some debris is blocking the inlet orifice.
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If your master cylinder is partially dry and if it is not a restriction of fluid to the master cylinder, the only thing left is a piston seal is not sealing due to a defect in design or installation or cylinder wall irregularity - any of which means removal and replacement. It may not happen often, yet it happens. I recently had to install two new master cylinders for a well-known Japanese because neither master cylinder held pressure. The third part we tried worth perfectly.
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One more thought. If you were describing no fluid from a caliper nipple, my first suggestion would be to examine the nipple for blockage or even distortion. They are easily distorted and get plugged. Then I would see if there is fluid getting to the caliper. If that did not work, I am afraid I would have to pull the caliper and mechanically fish out any blockage or make sure the caliper is not frozen. The master cylinder is not much different in that there may be an internal defect or you have got something pinched or restricted in the inlet or outlet.

Sounds simple enough, unless you are stuck on the side of the road covered in brake fluid. :wink:

Hope this helps.
 
I'll run what i did by your suggestions:

I did start at the right rear, but could get no fluid out at all, so that's why I started to bleed the lines at the master cylinder (Which was not opened or removed, it has been without fluid though, I used it up while forcing the pistons out for the caliper overhaul. The master worked well before work began).

I did take the nuts of the "dry" ports out of the master completely to be sure, but this should not be necessairy, the one that did give up fluid, did so after turning the nut just one revolution.
I did not "prime" the pump, as it has not been off the car.
Therefore the connections to the reservoir have also not been altered and the reservoir and it's lines where blown clean with compressed air before filling up. Besides, fluid is getting to one of the ports.

There is no apparant leak in the master cilinder as the fluid level in the reservoir does not drop visibly, no matter how often we depress the pedal, it's confusing for sure!

If the rear connections at the master could be bled, but not the front ones, than that might be a clue, but I can get the rear side one to spill fluid, but not the rear bottom one, although they use the same part of the cilinder..

I really do appreciate youre extensive reply on the matter though, as it helps me to eliminate possible causes, but I fear the solution is not yet found.
I will attempt to bleed with a borrowed compressed air bleeder tomorrow, I'll post an update after that, in the meantime, just keep the suggestions coming. It's costing me sleep!

Roger
 
budgerian said:
fluid is getting to one of the ports.

There is no apparant leak in the master cilinder as the fluid level in the reservoir does not drop visibly, no matter how often we depress the pedal, it's confusing for sure!
Click to expand...

If I read you correctly, you replaced virtually everything, except the master cylinder. Forgive me, but if everything else was in need of replacement, what makes you so sure the master was still in tip top shape? I previously gave you an example of how two out of three Honda master cylinders were dead on arrival. Unfortunately master cylinders are like Verhoven-Hauer collaborations and not every effort is as good as Soldaat van Oranje. Master cylinders fail, sometimes without warning and it sounds like yours has failed. The master cylinder is a dual system as a safeguard in case one area of the braking system gets compromised. Obviously only part of it is working and when it comes to brakes ½ a system is not acceptable. I hope I am wrong, but I have run out of other reasonable possibilities. :cry:

Let us assume your MC was in good condition when it was permitted to go dry. It is quite possible that pumping the dry master cylinder caused damage to one or more seals. After all, rubber scraping against dry metal does not make for a happy mix. Besides, have you ever wondered why brake fluid tends to turn dark gray or even black after a while? It is the residue of those internal rubber seals. Like brake dust on wheels. To reiterate, chances are, when the helper pumping the brake pedal the pumping action involved moving the piston far more than it normally travels when the system is pressurized. Couple this additional movement with a partially dry master cylinder and it is easy to see how a seal could be compromised so that it no longer seals.

You state there is no apparent leak in the master cylinder. There doesn’t have to be an external leak for the system not to pressurize. Put it this way, if you had a single cylinder engine and the piston did not have rings, the piston would move up and down without creating much compression. If the master cylinder has one or more compromised seals or has an irregular internal barrel due to rust corrosion or wear, the same thing would happen. The piston would move without displacing much, if any fluid. Sort of like mixing paint, you are moving the stirring stick but you are not losing any of the paint. The fluid level in the reservoir does not change, but you still have an internal leak.

I know that saying this is easy, but if it were me I would pull the master cylinder and either rebuild it, or replace it with a known good used part or a new one. At some point your time and peace of mind outweigh trying to salvage the part. Droevig over het slechte nieuws
 
Well, I did not replace it, because I saw no need. Judging from how good it looked paintwise compared to the rusty servo, and the way the nuts came off compared to the nuts on the brake lines, I figured it was a fairly new master already, certainly not the original.

I only set out to change the fluid, the hoses and change the front discs because of shuddering in the steering wheel under braking. Decided to do the calipers while they were off anyway, and had no intention whatsoever to replace the brake lines, they looked just fine. It's just that I could not get them separated from the hoses, no matter what combination of heat, wd 40 and violence I tried. So I had to cut them off at the connectors to the hoses.

I will try the one man bleeding tool today, but I suspect I'll be driving up to W&N (aren't I lucky they are reasonably close me..?) again to get a master cilinder overhaul kit. :cry:
 
Not sure what you mean, what lines are you referring to?
And why would that be mandatory?

To explain once more: the hard lines were all in good condition, as was the master. I felt movement in the steering under braking, so I replaced the discs/pads and decided to replace ALL flexible hoses as they might also be causing this problem.
It's merely because the flexible lines could not be separated from the hard lines that I sacrificed these and replaced the ones that end at a flexible hose.
 
Hello again ,

I 'm talking about the flexible tubes or hoses that goes from the hard alu pipes (ex- master cylinder) and connect to the alu pipes (connected to the calipers).(Shown on diagram of previous posts.)
The problem of those pipes is at the connection of the metallic part on the rubber tube.
With age and the "attack" of fluid, the rubber tube inflates at the insert, and obstructs internally the flow of liquid.
They might look ok externally, but changing them is a must.
I understand this has nothing to do with your Master cylinder problem, but I have overhauled numerous E9 brake system, and these are an item frequently disregarded by repairers .
Since I could not make out if these were the "hoses" you were talking of, I just wanted to point it out .
Good luck on your repair.
 
As announced I bled the system today with an Eezibleed system that uses the spare tyres pressure to force the fluid into the system and the air out.

Low and behold, I managed to get fresh, clean fluid at all four ends! It took me three liters of fluid and the pressure of an entire set of wheels I had lying about to get all the air out, but the master cilinder seems to have survived the overhaul program (let's not shout it out too loud though..)

So, I am clueless as to what was my problem, but I'm sure glad I can brake again!
Let's just file this one under X...

Roger
 
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