2004 w/35K mi. Started mildly pulling to driver's side when braking.
Decided would be a good time to replace brake (and others) fluid, then see if that changed anything and go from there.
Pump and bleed method on drivers side went as expected. Passenger bleeder port had NO fluid coming out even after removing fitting.
Pedal never lost resistance, stayed pumped up even with bleeder removed.

Anyone know what would cause this ?
.

 

One possibility, the brake hose.

Sometimes when hose ages, a piece breaks of internally, creating a blockage. Fluid doesn't want to flow either direction.

So piston can't easily return, brake drags. Then also trying to bleed, things are blocked.

If hoses are original, might be worth replacing them anyway.

 

Yep, a bad brake hose is a really good guess and a good place to start your diagnosis.

Sometimes, rust will swell the metal brackets that hold those lines to the point where they choke off the fluid.

Or sometimes, something goes wrong with a brake hose itself.

 

This is what happened to my rear drivers side caliper on my E36 M3. Put new lines on and had issues bleeding that side. There was a blockage in the actually caliper from the old line.

 

Remove flexible line from caliper, see if fluid comes out of line. If so, may have a blockage where the fluid enters the caliper, replace caliper. If nothing comes out of flexible line, disconnect it from the hard line at the body, see if fluid comes out there, if so replace flexible line. You can work your way back from there.

The master cylinder is 2 channels, front and rear, so its not that or both fronts would have this issue.

It could be an issue at the ABS module but you will find that if you work your way back to it by checking the lines first.

 

Bit of new information. There is no fluid coming out when hardline to flex connection loosened.
Also noticed evidence of some leakage on back of passenger side, none on drivers side (no significant rust either).
See attached images.
Not getting an ABS or fault light. Wonder if the wheel sensor is indicating passenger front is in a skid. Didn't notice any modulation when braking, but didn't try to skid.


Passenger

Driver

 

If the sensor were indicating the wheel was locked all the time I would expect you to notice either an ABS light (aka abs code present) or the abs trying to engage constantly when braking.

Curious if you disconect that hard line from the ABS module, if you see any fluid coming out when pressing the pedal. Do this with the engine/ignition off so ABS module should basically be allowing fluid to pass through it. Be careful as brake fluid eats paint like crazy, so you will really want to have a way to catch it and not make a huge mess.

You could use a brake master cylinder bleed kit which are cheap. You could remove the hard line, and add one of the adaptors and run a hose into a bottle so you dont spray fluid everywhere when testing it.

https://www.oreillyauto.com/detail/c...der/mtm0/14151

Put some fluid in the bottle/jar and submerge the test hose in it too, so if the ABS module is not the issue you at least are not sucking even more air into it testing and making way more bleeding work for yourself later.

 

No fluid out of the ABS unit when FR line loosened,
Confirmed again (beside previous drivers side bleed) fluid is still being pushed to ABS module.

 

Yep if either front brake is receiving fluid then I would think the MC to ABS path is fine, since the MC just has a front and rear channel. This leads me to believe there is a faulty or blocked ABS module. And when you test it, you still get a firm pedal with the passenger side line removed from the ABS module? It does not go to the floor? If the answer is still a firm pedal that does further make me think the ABS module is bad/blocked internally.

Bad news, ABS module is around $1500

Better news, they do not fail often and A Solutions Auto parts is your friend. My ABS module failed on mine, I got a used one from them for <$100.

There could be air trapped in the module, but that should be expelled when you tested it with the line removed, result in a soft pedal, etc. So that is why I am thinking internal blockage in the module or failed module.

 

Seems like a blockage.
Fluid and soft pedal if ABS input loosened, no fluid nor soft pedal if ABS output loosened.
Might have F'd it when I started flushing out the remaining old brake fluid. Which was the original task.

Have an 05 coming from feebay for $25 + shipping. Would not have guessed they are that cheap.

Thank you for your help, I'll continue looking into this until it gets here and eventually post the resolution.


P.S. Dear S2KI, stop doing this it's a PIA.
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