Problem with brakes, One Bleeder Won't Pass Anything!

One relatively easy thing to do is to remove the inboard bleed screw completely and see if the hole exiting the caliper (or the bleed screw itself) is rusted/crusted shut.

 

If it's just the bleed screw, a piece of wire (hypodermic needle perhaps) should poke out the trouble. New bleeders are cheap.

 

Failed hose? They tend to swell closed, even though they look okay on the outside. They can act like a check valve, passing small amounts of fluid in one direction.

 

Often the 2nd and 3rd bleeder are for convenience and overkill. In 40 years of auto repair on claipers with more than 1 bleeder I have nver had to bleed with anything but the most convenient to reach outboard bleeder. That is why the inboard ones are always crusted up because no one uses them or really needs them. Even if I rebuild a caliper with dry insides I never have to bleed from more than 1 bleeder. Try it before you sweat it.

 

I take it the old calipers were seized? Was the fluid black? Water contamination can gunk up lines, maybe gunk from the master cylinder has been trapped in the inboard piston? I would try pushing fluid from the front piston backward through the inner bleed nipple;
1.remove pads.
2.put a g-clamp on the inner piston to prevent it moving.
3.with the bleeds closed gently depress pedal so only outer cylinder moves(not too far!)
4.clamp off the flexi-hose.
5.crack open the inner bleed.
6.take some water pump pliers and gently squeeze the outer protruding piston back into the caliper. This should clear any blockage between the two sides of the caliper/localised blockage behind the piston.
7.bleed system as normal.

 

Your "day job" is permeating your weekend hobby, Doc ....sounds like a clinical assessment for your patient who may have a urinary tract obstruction.

As for the actual caliper problem.... It is also possible that although the caliper is a fresh rebuild, when it was put together the o-ring for the passage way to that bleed outlet got miss-aligned / slipped out of position, and it is pinched off intruding into / blocking off the passage ---- I've seen that happen before. Is the caliper leaking slightly anywhere under pressure ? If not, don't worry about it...not worth opening up and rebuilding again.....go with what it is as long as it is functioning correctly.

That looks like a nice bleed-kit setup , btw What brand / model is it ???

 

Cool. Another thought is that everything is as it should be and that the inboard bleed passage is only open / exposed when the piston is moved away from its "home" position. I assume you are doing a one-man-bleed operation where you simply pull vacuum while the system is NOT under pressure (and the piston is fully backed into its "home" seat) ?

If so, you may try opening that bleed screw very slightly and applying the brake pedal to get pressure against the piston in order to make it travel a bit ---- see if that opens the passage to that bleed and you get some fluid to flow out

 

Usually the power bleeder works the best, but it would be interesting to see if a vacuum bleeder (for instance MightyMite) would solve this problem.

 

I don't accept this. On those 4 piston calipers the 2 lower piston cavities are connected. In theory one should bleed the outer bleeder first, then the inner. The theory is that air in the system can get stuck in the inner cavity while the fluid is traveling to the outer. I've seen this happen. Also, I've seen old calipers where the bleeder hole was clogged and it took a probe to clear, pedal pressure was not enough.

Without seeing it it sure sounds like there's something obstructing your bleeder hole. The hose must be OK if you're getting fluid out of the outer lower bleeder.

TomB

Below is from a Volvo manual
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I would also replace them with Speed Bleeders........the cats PJ's.

 

It doesn't take very much air in the hole you can't bleed to make the system soft. If you want to locate the problem corner of the brake system it's OK to gently clamp each rubber hose one or two at a time with vise-grips. That will stop fluid from getting to the soft spot. Don't crush the hoses please, although I have yet to have seen that happen.

 

I have yet to see a design that really needs the 2nd or 3rd bleeder but I have never worked on a 2002. I'm rebuilding an E46 system right now. They are stupid simple. If you really have trouble pull the caliper and blow out the pistons and clear the offending bleeder passage. If you are careful you will not bung up a new seal. Worse case you buy a new piston seal. Personally Id rather not pull the offending bleder and push a paperclip in the hole because I don't want debris in the cylinder if I can bleed without that bleeder. If you are really mushy I bet you got air in the system in other places too. Driving a car around having to pump the brakes is not safe. Don't drive it until you fix it. Better yet if you are having problems and you don't understand why have a pro take over and do the job right. No one should die trying to save a hundred bucks.

 

Then you have no fluid to that point or it is blocked behind the nipple (maybe metal or dirt). Make sure the brake system including the master cylinder is full and try to bleed again. If that fails take the caliper apart and see what is blocking the flow.

To fatbillybob's point about extra nipples. Sometimes calipers are interchangeable side to side depending on the vehicle manufacturer, so there is an extra bleed port that will (sometimes) have a plug and not a nipple when new, and then when it's rebuilt gets a nipple so it can be sold as a left or right.

Sometimes I think the caliper design lends itself to creating air pockets in more than one (typically the highest) spot. This BMW 2002 design looks like you may need to use all three nipples when installing the rebuilt caliper.

 

They're dual hose 4 piston calipers that are split between the top pair of pistons and the lower pair. To get the air out of the the lower pair of pistons each needs it's own bleeder. The calipers are distinctly not interchangeable from side to side any more than the rears are.
Dr.Uro needs to figure out why the offending bleeder won't bleed.
This system was standard Volvo, BMW, and Benz for years until ABS appeared. With both ends of a tandem master going to each front caliper a circuit failure will only effect either the top or bottom half of each caliper rather than total loss at one corner at the front. The bleeding diagram I posted shows the each fluid circuit going to one rear and both front calipers. A much better arrangement than the diagonal system most manufactures used.

TomB
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As Tom has said the 2002 calipers have two circuits going to them. The metal brake pipes supply the inner pistons and then there are drillings through to the outside of the calipers between the bolts that hold the calipers together that supply the outside pistons. If there is fluid flow to the outside pistons, then the hoses are ok and the inner pistons are getting fluid as well. You can confirm that the lower inner piston is getting fluid by removing the brake pad and pumping the brake pedal to check piston movement.
The bleeder port has to be blocked by something. If you want a hard pedal you will have to bleed all three bleeders, ATE put them there for a reason. There is also a specific sequence/order that they should be bled in, read the workshop manual.