Suddenly lost the brake pedal

When there is no loss of brake fluid, the master cylinder has to be leaking internally. Here's a link to an article about how to replace it: I would suspect there is air in the lines. Here are the master cylinder installation instruction you have requested. Here is a guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://youtu.be/WDxvEQrMkBg

and

https://youtu.be/w7gUsj2us0U

and

https://www.2carpros.com/articles/how-to-replace-a-brake-master-cylinder

Check out the diagrams (Below). Please let us know if you need anything else to get the problem fixed.

I use a trick that avoids having to bleed at the wheels. If your van has anti-lock brakes, doing so will push air into the hydraulic controller where it will become trapped. You will need a scanner to command the computer to open two valves to bleed that air out, then you have to push that air all the way to the wheels.

Instead, when you replace the master cylinder with two steel lines, loosen the line nuts a little, remove the mounting nuts to the power booster, pull the master cylinder forward, then use it as a handle to bend the steel lines up a little. That will keep the fluid from running out of the lines.

Remove the two lines all the way, then remove the master cylinder. Brake fluid eats paint, so be careful to not allow any to drip onto the car.

Screw the two lines into the new master cylinder that has been bench-bled, then use it to bend those lines back down to their normal shape. Bolt it to the booster, then snug one of the line nuts. Have a helper slowly push the brake pedal half way to the floor. It should take about 15 seconds to do that. You'll see bubbles coming out by that nut. Snug the nut, then holler to the helper to quickly release the pedal.

Do that a second time, and perhaps a third time, until you see only clear fluid with no bubbles coming out, then do that for the other line. By pushing slowly, fluid will get pushed down the lines, and air will float back up. By releasing the pedal quickly, the fluid rushing back will wash the air back up into the reservoir with it. This can even work when working on the car by yourself, just keep the line nuts tight.

This wondrous trick might not work on Fords that have four lines at the master cylinder.

It's good practice to never push the pedal over half way to the floor, although it won't matter with a rebuilt master cylinder. Once they get to be about a year old, crud and corrosion build up in the lower halves of the bores where the pistons don't normally travel. Pushing the pedal to the floor, like most do-it-yourselfers do, runs the rubber lips seals over that crud and can rip them. That results in a slowly-sinking brake pedal, and that often doesn't show up until two or three days later.

https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor

Did you bleed at the wheels? Do you have anti-lock brakes?

There is going to be air in the hydraulic controller. Removing that requires a scanner. The typical procedure only takes a few seconds. It will usually have you press the brake pedal once and hold it after a helper opens a right bleeder screw, front or rear, then again while the other right bleeder screw is opened.

The hydraulic controller has between six and nine valves that control the flow of brake fluid to the wheels. For one wheel there is a "block" valve that stops fluid flow to that wheel when you're on the brakes and the computer sees that wheel slowing down faster than the others. If blocking additional fluid flow doesn't get that wheel back up to speed, a different "bleed" valve opens to allow some of that fluid to return from the wheel. Once the fluid pressure is reduced enough that the wheel is back up to the same speed as the others, a third "apply" valve opens to let more brake fluid flow back to the wheel. That "block, bleed, apply" sequence can be done up to 30 times per second, but more commonly it's designed to do that 15 times per second. That's the buzzing you hear and feel in the pedal when the system activates.

Some ABS systems use a very high-pressure pump to build up and store brake fluid under high pressure for this purpose. That's where the "apply" pressurized fluid comes from. Other systems, including all rear-wheel-abs, (RWAL) systems found on older pick-up trucks, use brake fluid from the master cylinder for the "apply" function. That means that for each "block, bleed, apply" cycle, the brake pedal will drop a little. That is considered normal operation, and it is expected the vehicle will be fully stopped long before the brake pedal runs out of travel. With those RWAL systems, no special bleeding procedures are needed. Even if the entire system were to be disabled, it would leave you with the standard brake system, and you would treat it as such.

It's when you have the more-effective four-channel system that you have the more-complicated hydraulic controller. That's the big metal box with the two steel lines from the master cylinder running to it. Four separate steel lines will leave that box, one for each wheel. GM likes to put the two rear brakes together on one channel, so they reduce braking power to both rear wheels when just one of them starts to lock up. Chrysler operates all four wheels independent of each other, so every one is always at its maximum stopping power.

Under normal braking, the brake fluid just flows through the channels in the hydraulic controller, and all the solenoids are turned off, so the valves are at rest. When a valve does activate to bleed off brake fluid pressure, there needs to be a place for that fluid to return to, because it can't get back to the reservoir, and when the "apply" valve opens, there needs to be a place for that brake fluid to come from. That fluid is not coming from the reservoir. Those are the chambers where air can get in and be trapped. Once air is in a chamber, it can be compressed, making the system unable to build pressure in that channel during an ABS-activated stop, and that air is what causes the mushy brake pedal during a normal stop.

A valve needs to be opened to let the air out where it can travel down to the wheel and be bled out. The only way you can get that valve to open is to drive the vehicle, then force an ABS-activated stop. The problem is while the valves are being pulsed open, the bleeder screws had better be closed, so there's no movement of the brake fluid, and no movement of the air. Nothing is going to flow until the bleeder screws are opened, and that can only occur when the vehicle is standing still and you're standing next to it. You can't have an open bleeder screw and an activated ABS valve at the same time, except by commanding the ABS Computer to do that when the vehicle is on the hoist. The scanner is what gives you the ability to do that.

First you select "Brakes" from a drop-down menu, then you might have to know the type of ABS system you have if you're using an aftermarket scanner. I have a Chrysler DRB3 for all of my vehicles. That one selects the right system automatically, then, under another drop-down menu, you select "Bleed Brakes". From there the scanner tells you which bleeder screw to open and when to press the brake pedal. It pumps the brake fluid to that wheel very quickly, along with the air. It's done in two or three seconds, then it tells you to repeat that for the second wheel. Typically it uses the right front wheel, then the right rear wheel.

The DRB3 scanner became obsolete between 2004 and 208 on different models, so you're going to need an aftermarket scanner that can access your ABS Computer. I have a Snapon Solus Edge for my 2014 truck. I used it for bleeding a 2012 Grand Caravan a few years ago, and this one also took just a few seconds. It was already programmed for the right brake system for the model selected.

If you want to see what these scanners look like, you'll find both of them on eBay. The Snapon gets you with the very high cost of annual updates, and if you want it to work on the latest models, you can't skip any years. That means if you have one that is updated through 2014, you would have to buy the 2015 update, for $995.00, before you can buy the 2016 update, then the 2017 update, and 2018 update, all for $995.00 each, then you can buy the 2019 update. It would be less-expensive to just buy a brand new scanner for $3895.00 with the latest updates already in it. For that reason, when these get to be three or four years out-of-date, they lose their value for repair shops, and for that reason, you can find these on eBay for as little as $500.00. All you need is one updated through 2011 to be sure it has the software for your 2010 model.

Once you have "pumped up" the brake pedal does it stay firm? I have seen a bad bearing hub cause this problem, bad brake flex line. Can you please shoot a quick video with your phone so we can see what's going on, that would be great. You can upload it here with your response.

Nice work, we are here to help, please use 2CarPros anytime.