[AgnosticRaptor]

Hi all, hoping to gain some insight here as I'm at my wits' end with what should be a rather simple brake bleed job for my '08 Mazda3 hatch. I've tried a variety of methods (among other things that I'll mention) but none seem to be providing any results.

The Problem: The driver's rear wheel refuses to bleed. That is, when cracking open the bleeder screw and pumping, no fluid (or air) flows out of the line/caliper. There is no commensurate drop in pedal pressure and height once the bleeder screw is cracked open as well.

What I've tried and done so far: In attempting to fix this problem, I've replaced the rear flex hoses and rear calipers while also verifying that the master cylinder has no leaks and the brake booster builds + holds pressure. There is no blockage in the system, as the driver's rear wheel did bleed correctly a week ago with no issue...it simply refuses to let any air or fluid out now.

As mentioned before, I've also tried a variety of brake bleeding methodologies to fix this issue, including:
1. Standard recommended bleeding procedure by starting with the back wheels, then cross bleeding. I've also bled the rear wheels first without cross bleeding.
2. Bleeding the front wheels first (to get any air that might be trapped in the system out the shortest route) and then moving to the back wheels. I've also started with the front wheels first both with and without cross bleeding.
3. Reverse bleeding with a handheld vacuum pump. This was useless and simply introduced more air into the system due to an improper seal.
4. Standard bleeding (rears first, then front in cross bleed pattern) with a Motiv pump affixed to the brake fluid reservoir. This also had a less than optimal seal and did nothing but add some amount of air to the system.

With all this in mind...here's the current situation:
1. As of this morning, I've attempted to bleed all the wheels by starting with the fronts, then rears without a cross bleed pattern. For consistency's sake, each pedal has been pumped 75 times to make absolutely sure there is no air in the system. Because I've bled the brakes so many times, I know the fluid is clean and clear, so it's just being fed back into the reservoir from each wheel via a long rubber tube fitted over the bleeder nipples.
2. Both front wheels and the passenger's rear wheel bleed perfectly; fluid flows healthily through the lines during pedal pumping, pedal feel is good, and the pedal itself depresses while under constant pressure the moment I crack open the bleeder valve.
3. The driver's rear wheel still refuses to let anything through...no fluid, no air, nothing. The pedal feel remains hard (as there is no air being introduced into the system, or trapped in the system itself).
4. Pedal feel is hard as long as the car is off or the key is switched on to battery power with all systems ready.
5. The moment I start the car, the pedal immediately sinks to the floor with very little foot-induced pressure and I can hear an extremely audible "squishy" sound as if there were air in the system.
6. Turning the car off, I can build pressure again as the booster is functional. It is able to maintain this pressure indefinitely.
7. After building pressure again, cracking open the bleeder screws on all wheels show there is still no air in the system, and the pedal feel remains good. Fluid continues to flow under pumping from all three wheels, and the driver's rear wheel continues to do nothing.

So I'm at a loss of what to do here...the car is pretty much undriveable in this condition as there is no brake feel whatsoever.

Is this a proportioning valve issue? ABS unit failure? Vacuum line issue?

I'd love to hear some feedback before I try taking apart the master cylinder and brake booster to see just what the hell is going on.

 

[arathol]

Did you try replacing the bleeder valve? It might just be stuck...

 

[AgnosticRaptor]

Did you try replacing the bleeder valve? It might just be stuck...

Yea the valve has been replaced as well.

 

[arathol]

If the other 3 brake calipers work fine, chances are the problem has something to do with the one that isn't working.........
Sounds like there is a blockage somewhere. Have you actually disconnected the line from the caliper to see if there is pressure at that end, or disconnected the line from the master cylinder to see if the port is blocked?
Do you have any way to flush the line out? That is, disconnect it at both ends and blow it out?
Its possible that there is something blocked inside the caliper also. Did you try pumping the brakes with the valve removed to clear it? You might need to pull the caliper apart if there is no fluid passing through it.

 

[AgnosticRaptor]

If the other 3 brake calipers work fine, chances are the problem has something to do with the one that isn't working.........
Sounds like there is a blockage somewhere. Have you actually disconnected the line from the caliper to see if there is pressure at that end, or disconnected the line from the master cylinder to see if the port is blocked?
Do you have any way to flush the line out? That is, disconnect it at both ends and blow it out?
Its possible that there is something blocked inside the caliper also. Did you try pumping the brakes with the valve removed to clear it? You might need to pull the caliper apart if there is no fluid passing through it.

A week ago fluid was pumping through this wheel's line just fine during the bleeding process. Seeing as that the caliper/bleed valve/flex hose is brand new, and fluid has been shown to flow from it, I'm more inclined to think that there isn't a blockage within the line at any point.

I guess disconnecting the line just to make sure is next on the agenda though.

 

[arathol]

The only way you are going to find out is by pulling the bleed valve to see if the caliper will flush out, then work back to see where the pressure is stopping.
Any new part is suspect, check the flex hose and connections too....

 

[AgnosticRaptor]

The only way you are going to find out is by pulling the bleed valve to see if the caliper will flush out, then work back to see where the pressure is stopping.
Any new part is suspect, check the flex hose and connections too....

I understand this train of thought, but considering that this same problem manifested itself prior to swapping out the hose/caliper/valve, I'm not really sure if this will accomplish anything. Connections are secure, there is no leakage whatsoever.

I'm suspecting that it might have to do with something electronic related...perhaps the ABS unit. I decided to pull the fuses while the car's on jackstands and will test tomorrow to see if this allows the valve preventing flow to the driver's rear wheel to open up.

 

[Cdn17Sport6MT]

Bingo. Exactly what I was thinking. Others chime in here - but I think you need to be able to command clear passage out the L R brake... operating the abs pump to flow the fluid. ????

 

[arathol]

I understand this train of thought, but considering that this same problem manifested itself prior to swapping out the hose/caliper/valve, I'm not really sure if this will accomplish anything. Connections are secure, there is no leakage whatsoever.

This will tell you where the problem is. Its not about tight connections or leakages, its about finding where the system is blocked.
Remove the bleeder valve from the caliper and pump the pedal....does fluid come out? If yes, the bleeder is bad, if no, replace the bleeder valve and remove the flex line from the caliper. Pump the pedal, does fluid come out? If yes, the caliper is plugged up, if no reattach the flex line to the caliper and disconnect it from the hard line. Follow the brake line until you figure out which part isn't allowing pressure to pass through and go from there.
One other thing - did you properly bleed the ABS system by activating it through the OBD system? You need a scan tool with the correct ABS software to do this.

 

[Cdn17Sport6MT]

I think he said he changed caliper and hose. Could be dud caliper... not properly drilled-out bleed port? Not likely though. I suspect an abs capable obd-II unit is required.

 

[arathol]

I think he said he changed caliper and hose. Could be dud caliper... not properly drilled-out bleed port? Not likely though. I suspect an abs capable obd-II unit is required.

Yes, parts were replaced, but why? It worked a few days before.....and apparently wasn't working before the parts were replaced.
In order to fix the problem, you need to find the problem. Guessing and throwing parts at the car isn't the answer......

 

[AgnosticRaptor]

Yes, parts were replaced, but why? It worked a few days before.....and apparently wasn't working before the parts were replaced.
In order to fix the problem, you need to find the problem. Guessing and throwing parts at the car isn't the answer......

Parts were replaced because the flex hoses were inflated and awfully rusty. I can upload pictures tomorrow, but they were in extremely poor shape. Likewise the caliper was replaced due to its age and wear.

I didn't replace these parts to solve this issue, they were just components that needed replacing based on visual inspection once I was checking the lines, etc.

 

[arathol]

I didn't replace these parts to solve this issue, they were just components that needed replacing based on visual inspection once I was checking the lines, etc.

However.....
In the first post you said

What I've tried and done so far: In attempting to fix this problem, I've replaced the rear flex hoses and rear calipers

Soooo....when did the brake actually stop working, before or after the parts replacement?
If after, all the more reason to check the new parts for functionality.

 

[AgnosticRaptor]

Update:

After removing all 3 ABS fuses from the fuse box (the 10A, 20A, & 30A) last night and reconnecting the battery, I decided to turn the ignition to "on" under battery power (without cranking the engine). Cracking open the bleeder valve for the troublesome wheel (driver's side rear) and trying to pump still produced no fluid through the line...so I closed the valve and pumped the brake pedal about 20 times total with swift, forceful pumps. I then removed the keys from the ignition, cracked open the bleeder valve again, and tried pumping. This produced some fluid through the line, but not as much as with other wheels that are functional. I decided to turn the ignition to "on" under battery power again, pumped the pedal with the same cadence and pressure as before, and then switched it to off.

This seem to have fixed the issue with fluid flow from the driver's rear wheel.

Cracking open the bleeder valve and pumping now saw fluid flow normally through the line. I must note however that there wasn't much air in the system at all. The pedal still felt firm while pumping. Just to verify that any possible air didn't travel to any other wheels upstream (if it was caught somewhere in the ABS module), I went ahead and bled the other wheels. Same thing, no air, perfect fluid flow, great pedal feel.

However, a new problem seems to have come up...

In the cross circuit wheel from the driver's rear - that is, the passenger front wheel - even though fluid flows normally through the line during pumping, there is a noticeable hissing/squelching sound that seems to come from somewhere near the brake booster/master cylinder/ABS module area. The pedal doesn't feel as tight as the other circuit's wheels (driver's front and passenger rear), and it doesn't feel as tight as the once-troublesome driver's rear wheel. I've pumped the passenger front wheel about 30-40 times in the same method as the others, and can confirm that there aren't any air bubbles passing out through the system.

Here's a video of what it sounds like: PassengerFrontWheel_BrakeBleed_AirSound - Streamable

Important to note is that there is no visible fluid leak anywhere near the calipers/brake lines/master cylinder/brake booster/ABS module etc. Probably something internal then. There is also no noticeable drop in brake fluid level at the reservoir.

Sounds like it might be a master cylinder issue? The brake booster itself is able to build pressure nicely when I pump the pedal, and can hold it indefinitely (several weeks+). Could a broken master cylinder seal allow a very small amount of fluid to leak into the booster?

 

[Gary_L]

The flexible brake hose has most likely swelled shut on the caliper that won't bleed. Could also be clogged with debris.

 

[AgnosticRaptor]

The flexible brake hose has most likely swelled shut on the caliper that won't bleed. Could also be clogged with debris.

In my OP I state that I've replaced the flex hoses with brand new, functional ones (I've verified this prior to installation as well).

In my update, I state that the wheel that didn't bleed is now able to bleed fine. I also mention that I've encountered a new problem when bleeding the passenger front wheel: PassengerFrontWheel_BrakeBleed_AirSound - Streamable

I think it's a MC/booster/ABS modulator issue.

 

[Wolfe]

Update:

After removing all 3 ABS fuses from the fuse box (the 10A, 20A, & 30A) last night and reconnecting the battery, I decided to turn the ignition to "on" under battery power (without cranking the engine). Cracking open the bleeder valve for the troublesome wheel (driver's side rear) and trying to pump still produced no fluid through the line...so I closed the valve and pumped the brake pedal about 20 times total with swift, forceful pumps. I then removed the keys from the ignition, cracked open the bleeder valve again, and tried pumping. This produced some fluid through the line, but not as much as with other wheels that are functional. I decided to turn the ignition to "on" under battery power again, pumped the pedal with the same cadence and pressure as before, and then switched it to off.

This seem to have fixed the issue with fluid flow from the driver's rear wheel.

Cracking open the bleeder valve and pumping now saw fluid flow normally through the line. I must note however that there wasn't much air in the system at all. The pedal still felt firm while pumping. Just to verify that any possible air didn't travel to any other wheels upstream (if it was caught somewhere in the ABS module), I went ahead and bled the other wheels. Same thing, no air, perfect fluid flow, great pedal feel.

However, a new problem seems to have come up...

In the cross circuit wheel from the driver's rear - that is, the passenger front wheel - even though fluid flows normally through the line during pumping, there is a noticeable hissing/squelching sound that seems to come from somewhere near the brake booster/master cylinder/ABS module area. The pedal doesn't feel as tight as the other circuit's wheels (driver's front and passenger rear), and it doesn't feel as tight as the once-troublesome driver's rear wheel. I've pumped the passenger front wheel about 30-40 times in the same method as the others, and can confirm that there aren't any air bubbles passing out through the system.

Here's a video of what it sounds like: PassengerFrontWheel_BrakeBleed_AirSound - Streamable

Important to note is that there is no visible fluid leak anywhere near the calipers/brake lines/master cylinder/brake booster/ABS module etc. Probably something internal then. There is also no noticeable drop in brake fluid level at the reservoir.

Sounds like it might be a master cylinder issue? The brake booster itself is able to build pressure nicely when I pump the pedal, and can hold it indefinitely (several weeks+). Could a broken master cylinder seal allow a very small amount of fluid to leak into the booster?

Yes, and then gets sucked through the engine (on many cars) (M3 ?).

 

[AgnosticRaptor]

Yes, and then gets sucked through the engine (on many cars) (M3 ?).

I'm not sure I understand what you're asking/suggesting here.

 

[Gary_L]

In my OP I state that I've replaced the flex hoses with brand new, functional ones (I've verified this prior to installation as well).

In my update, I state that the wheel that didn't bleed is now able to bleed fine. I also mention that I've encountered a new problem when bleeding the passenger front wheel: PassengerFrontWheel_BrakeBleed_AirSound - Streamable

I think it's a MC/booster/ABS modulator issue.

Sorry I missed that part. I skimmed your post and that caught my eye straight away. When is that last time the brake system of your vehicle was thoroughly flushed? People are surprised when I explain that should be done every two to three years. The telling sign is the fluid is no longer translucent. I'm betting your work disturbed debris in the system which has resulted in a blockage.

What you're enduring appear maddening.

 

[AgnosticRaptor]

Sorry I missed that part. I skimmed your post and that caught my eye straight away. When is that last time the brake system of your vehicle was thoroughly flushed? People are surprised when I explain that should be done every two to three years. The telling sign is the fluid is no longer translucent. I'm betting your work disturbed debris in the system which has resulted in a blockage.

What you're enduring appear maddening.

The fluid's been regularly flushed for the past month (and even did it a year ago). Prior to that, no idea, as I bought the vehicle used.

I don't think there's a blockage anywhere because fluid can flow out from all 4 wheels now. I just have to track down what's causing the mushy pedal on startup, and see if it's related to the sound that the passenger front wheel causes when bleeding.