Replaced rear rotors and pads, front pads (rotors were fine).

Bled from back right to back left, front right, then front left. All new fluid out of each, no air.

Brake pedal still squishy and goes to floor.

Need to get another bottle of fluid (ran two small and one large of prestone high temp dot 3 already) to double check each brake, make sure I didn't miss any air. But could I have missed something else? Is there a nonstandard way to bleed these brakes?

Thanks,
Matt

 

Did you happen to run the master cyl dry?
I did just the rears two weeks ago and went thru about a quarter or less of the big bottle so you should have been good by now.

 

I guess it's possible but not intentionally. Some bled out as I swapped to new hoses and calipers in the rear, so depending on how much leaked out then maybe? Must hold alot. I'll keep bleeding and report back.

 

Get yourself some Russell speed bleeders, they are the money ticket for bleeding your brakes. Sounds like you have air in the system. Nothing special to bleeding the brakes on these trucks.

 

Good to know thanks, I was just going to comment if this was a set up that needed a special way to bleed the ABS.........dealt with a few of those that needed to be commanded through the ABS module to get them bled right.

 

Perfect thanks. Will just start from top again and do all four. Just wanted to make sure I wasn't spinning my wheels missing a special valve or something.

 

Get a clear hose from the local hardware store and run it from the bleeder to the master cylinder reservoir. This should bleed the master cylinder while on the truck and remove air from the lines.

 

You're bleeding but you don't see air bubbles anymore, and the pedal drifts or drops to what you perceive as the floor.

The are a couple of issues that could be happening. If you had replaced the calipers there is the possibility of some air lodged between the pistons and caliper bore. Due to the surface tension that can happen with dry calipers. Lightly tapping on the caliper during bleeding would take care of this.

If during a caliper change the fluid bled all the way out of the reservoir then air could be trapped in the ABS controller. In time with the initial engine on ABS controllers self test this air can get moved into the tubing so it can be bled, or the best thing is to use a scanner that can run the ABS bleeding routine. A number of stops on a loose surface can also facilitate the movement, but you'll spend a half day and a lot of fluid doing that.

Both of those is not what you said happened. So in all likelyhood you damaged one or both of the master cylinder seal cups while bleeding. If the truck has had brake fluid with moisture in it for a number of years and not flushed, there will be oxidation in the back areas of the bore where the cups rarely go. So when a person bleeds the brakes and moves the pedal long the cups ride over the oxidation and nip the edges. Now brake fluid bypasses the cups and you can't build volume, and pressure. Aka long pedal or to floor. Sometimes you can diagnose this as a light to moderate pedal application will allow the fluid to bypass, but a rapid hard application gets the cups expanded to the point of sealing. Not a foolproof tell as it depends on how badly the cups are damaged.

Consumer vehicles can end up with this within 100k miles. We had test vehicle that made it well over this mileage without any issues, but they had the brake fluid changed every week or two. Not that I'm proposing that, but brake fluid should be flushed every two or three years. And from a safety perspective a vehicle should have a master cylinder changed every 150k or 12 years just as a precaution, but that can change depending on how many applications per year and how often the fluid was flushed.

I also recomend staying with a high quality replacement, Motorcraft is my choice.

 

Would one not notice leaking between the booster and master at this point Jack?
Seem like a lot of fluid for the OP to not notice that area would at least be damp by now....just thinking out loud here. I'm not sure how tight a seal these trucks have between the booster and the master.

 

Common thought Mike, but no. The bypass of the cup stays internal. There is a rear seal that is not pressurized, and while that is another fault a Powerstroke owner may see, it manifests itself as oxidation between the hydrobooster and master cylinder cavity. The rust builds up and gets between the pushrod and master cylinder piston, taking up all the slack and eventually keeps all four brakes on since the cups never return all the way to open the chambers to the reservoir. This doesn't haven with a vacuum boosted system as the leaking brake fluid is sucked up by the vacuum, into the booster and into the vacuum source, engine or pump.

Best illustration I've seen. Where the springs are is what gets pressurized. Every where else is at atmospheric.

 

Appreciate the info....so this is related to the well known issue of brakes sticking on these trucks? I realize the caliper pins are a major sticking point but am guessing this will only magnify early wear.

 

It's multiple. If all four brakes are staying on then the first place I look is at the m/c connection, removing the two retaining nuts and moving the m/c forward to see if there is rust dropping out. You can have the extreme situation where all of the individual wheel brakes at the same time, but then it's time to get a lottery ticket.

If the master is an aftermarket item, all bets are off. Some companies manufacturing tolerance is not that good, so you can have a situation where a new master is installed and all four wheels are dragging. That's because the depth of the bore in the master cylinder piston is not deep enough and the correction is there adjustment of the pushrod out of the booster. I've all seen inconsistencies between this contact point and where the primary or secondary cup in machined on the piston, so you can have a new master install and one hydraulic circuits brakes staying on. The location depends if the vehicle layout splits the brakes by axle or diagonally. And if the locating during manufacture was off, such that the rear circuit has less clearance to the compensating port, as the rust builds up you can have only one axle's brakes stick. Aftermarket parts make it more complicated.

Most of the locking brake problems I've dealt with come from either rusting pins, rusted pads in the bracket, frozen caliper pistons, or damaged brake hoses. The pins are easy to check with every oil change without much effort while your waiting. But I keep wrenches in the truck so if I ever have one dragging brake I can open the bleed screw for that caliper and see if there is pressurized fluid. If it's pressurized then I know it's a brake hose issue for that one caliper. If not I'll back off the slide pin bolts and see hoe easily they move. If they are free I know I'll be pulling the brake to see what is going on.

Yesterday I replaced the brake pads (pads only) on my wife's MDX. All but one pads wore evenly, but the left rear inner pad was trapped by rust on one tab causing tapered wear. So even though she drives the vehicle 7 days a week, rust can form in those locations. All caliper pistons and slides were free.

 

Not saying I have done this or anything but... one simple thing to check if you installed new calipers on the rear is the location of the bleed valve (the only difference between the left and right) it should be on the top... if they are swapped (on the bottom) you won't be able to bled out the air.

 

Way off the OP's dilemma, here are the left rear pads. You can see the taper of the inner pad, and the tab on the right is where it was rusted and kept the pad against the rotor. The outer pad developed a slight taper too, but this was due to the slight twisting of the caliper due to the inner pad issue.

 

If you have a lot of miles on your truck and have never changed the fluid this is normally what happens. You install all of the new stuff and then bleed the brakes. You have someone press the pedal all the way to the floor. This is not normal and over the years a rust ring builds up just after the normal travel of the master cylinder plunger seals. The master cylinder internal seals are not that robust. So when you now exceed the normal pedal travel and engage the rust ring, as the pedal goes to the floor, the seals are possibly damaged and they leak. Result, no pedal. Depending on the brake reservoir design, you may be able to see the bypassed fluid returning to the reservoir. that is not good. Just ask me how I know. When ever I bleed brakes on any older vehicle, I find the normal pedal travel and do not exceed that.


Worst case, you may be looking at a new master cylinder.


Ed