I think where I would start is by having a helper to push the brake pedal, ... Go to the master cylinder with the correct-size line wench, (flare-nut wrench), loosen one of the soft metal nuts, then have the helper slowly push the pedal. It should take him about 15 to 20 seconds to push it half way too the floor. Before it gets that far, you should see brake fluid flowing freely from that connection. Tighten the nut, THEN holler to the helper to release the pedal. Do that to the other steel line. If you find one that doesn't flow fluid after multiple attempts, suspect the master cylinder.
GM, and their other products, are the only ones I've ever run into that valve I described that blocks fluid flow, and they don't trip until the pedal is pushed over half way. I've never heard of that on VW products, ... So far.
Let me stop here to inject a wondrous point of interest. If your helper releases the brake pedal before you get the line nut tightened, air will get sucked in. Don't panic over that. Also, when a person isn't paying attention and they let the reservoir run dry during bleeding, air is not going to show up all the way down to the wheels. In your case, if you catch this before air gets into the ABS hydraulic controller, all you have to do is refill the reservoir, then very slowly push the brake pedal half way down. Wait about five seconds, then let the pedal release quickly. Do that multiple times until the normal feel returns to the pedal. Pushing the pedal slowly pushes brake fluid down the lines while allowing any air bubbles to float back up. Releasing the pedal quickly makes the fluid rushing back up wash the air bubbles back into the reservoir. (This is the second half of the trick I eluded to when replacing a master cylinder and not having to bleed at the wheels).
If it appears you need a master cylinder, consider whether the fluid could have been contaminated during the clutch service. I'm not a transmission specialist, but in my limited experience, I have never seen a hydraulically-operated clutch that shares a master cylinder reservoir with the brake system. The clutch systems I'm familiar with do use brake fluid, so the same precautions apply. Where I would be looking first is to see if the mechanic filled the brake system reservoir, thinking he was doing you a favor. Brake fluid should never be topped off during routine services, like oil changes. If brake fluid is low, there is either an external leak that must be repaired, or it's time for a common brake system inspection.
With an external leak, especially one that isn't yet bad enough for the customer to be aware of, the cause must be found and corrected, for obvious reasons, before it results in a crash. When disc brake pads wear, unlike with drum brakes, their self-adjusting feature is the piston gradually works its way out of the caliper housing. Brake fluid fills in behind it, and that's why the level drops in the reservoir, and that's our clue to recommend a brake system inspection. When new pads are installed, the piston has to be manually retracted back into the caliper housing to make room for them, and doing that pushes the brake fluid back up into the reservoir. If someone had refilled the reservoir previously, the fluid will overflow and make a mess. Brake fluid eats paint, so it must be rinsed off right away. Other than that, the mess is the only harm done.
If the previous mechanic filled the brake fluid with a funnel with oil residue, or he poked the rubber bladder seal back into the reservoir's cap when he had grease on his fingertips, the brake fluid would be contaminated. Admittedly, that would take from about three days to perhaps a week to show up, depending on the amount of the contaminant, but it is not something we want to overlook. The easiest clue to spot is the rubber seal under the reservoir cap will be blown up and mushy, and won't stay in the cap.
If you do get a nice solid fluid stream from both lines at the master cylinder, work your way down to the next place, in this case, the ABS controller. Failure of those is not common, and the few failures that do occur almost always affect the operation during ABS activation. I've never heard of one blocking fluid flow during normal braking. One of the valves in it for each wheel does block fluid flow, but it is only pulsed open and closed very rapidly when that wheel needs to have reduced braking power. If the blocking valve where to stick due to corrosion or some mechanical issue, it would stick in the open condition, hence, a failure to reduce skidding in an ABS stop, not a failure to pass fluid during a normal stop. Regardless, there should be three or four steel lines leaving the controller and going to the wheels. Some cars use a single line to control both rear wheels together. Front-wheel-drive, and many other cars, run the two rear brakes separately, so they'll have four lines leaving the controller. Loosen one line at a time, then have the helper push the brake pedal again. If this is the first place you do not get a strong stream of fluid, I would be surprised, but first I'd be bleeding it some more to be sure the fluid isn't filling a chamber that is full of air. On a lot of vehicles that bleeding has to be done with a scanner. It is needed to make the ABS Computer open the valves to some of those chambers so the air can be expelled. A I recall, you're missing fluid to two wheels. If the cause is a valve in the ABS controller, that would be real uncommon, and you can imagine how much more uncommon it would be to have two of them doing that.
If you get good fluid flow from the hydraulic controller, but not at the wheels, there is still excessive air in the lines after the controller or the affected lines are blocked, as in crushed by a pry bar when working on the clutch. The clue is with a crushed or blocked line, the brake pedal will be unusually high and hard. With air in any line, the pedal will be low and soft. If you suspect air, and multiple bleeding attempts haven't solved it, you may need to resort to pressure-bleeding. Every shop used to have a "bleeder ball", but when there began to appear such a wide variety of reservoir cap sizes and shapes, there were way too many adapters a shop had to buy to be practical. That's when we learned that gravity-bleeding was better. You may not find pressure-bleeding equipment at your favorite shop, and anytime I do see one, I get real nervous about what someone might have put in it previously. I saw one used very effectively once to pressurize engine oil to find an internal oil leak when the engine was out of the car. Once verified the leak was fixed, the instructor destroyed that bleeder ball to insure no one would ever accidentally contaminate a brake system with it.
If you find the brake pedal only gets soft and low well after the engine is warmed up, and given the recent service, look for anyplace a steel brake line might have gotten repositioned and is sitting too close to hot exhaust parts. Brake fluid loves to absorb moisture out of the air, and water in the fluid boils at a much lower temperature than does brake fluid, leading to one form of brake fade. Boiling water causes air bubbles to form, and is one reason we can continually find air during repeated bleeding attempts.
If you collect the brake fluid that is bled at a wheel, and you see it's clear, you know the new fluid has traveled from the reservoir and there shouldn't be any air left in that line. Brake fluid gets dark over time from being hot. If you see dark fluid coming out of a bleeder screw, fresh new fluid hasn't made it that far yet, and air in the line is still a real good suspect.
Wednesday, November 30th, 2016 AT 10:24 PM