I have this minivan that belongs to my wife and the brakes are driving me crazy. The pedal goes all the way to the floor when the van is on but I'm able to pump up the pedal when it is off. I have already done the following list of jobs on the brake system.

-Rebuilt drum rear brakes including cylinders, drums, springs, and pads- and adjusted to point of rubbing when wheel is spun by hand
-new front flex lines
-new master cylinder(twice)(bench bled correctly)
-new front brake pads and hardware
-both calipers rebuilt (not pistons, just seal and dust boot)

I have also done the following tests which are followed by their results.
-Pinch off front flex hose (both pinched off: pedal feels 100% better, right pinched off: pedal is 50% better, left pinched off: pedal is 50% better
-Check system for leaks: no leaks, brake fluid NOT LOW AT ANY TIME
-Place a board in each of the front calipers and press brake pedal with van on: problem still exists
-bleed A GALLON of brake fluid through the system over the last two weeks after each invasive attempt
-check valve to booster: WORKS
-engine vacuum going to booster: YES
-booster retaining vacuum for five minutes: YES, HOLDS VACUUM INDEFINITELY
-pump up and hold brake pedal while starting the vehicle: PEDAL SINKS TO FLOOR WITH NO FEEDBACK
-pump up pedal while vehicle is running: NOT POSSIBLE- PRESSURE EXISTS FOR MILLISECONDS even when pumping repeatedly as fast as possible
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Braking has always been good when the pedal is all the way down at the floor, but the point is you have to push the pedal all the way down there before any braking really starts to happen. I can feel the brakes applying very slightly as soon as my foot begins to push the pedal but it sinks really fast and doesn't slow or stop the vehicle at all until the pedal is basically on the floor.

Please Help!

 

If pinching off the front brake hoses makes the pedal 100% better, the problem is most likely isolated to the front calipers but you don’t want to rule anything out.

Some questions and suggestions (you’ll need a helper for some of these):

1) How have you been bleeding the brakes? (Manually, gravity, vacuum or pressure) Did you make sure to deplete the vacuum in the booster before doing so? If manual bleeding, what process are you using? (I have my helper pump the pedal 5 times and hold, crack the bleeder, then close it after about 1/2 second but there are other ways to do it.)

2) Did you clean the bleeder screws? Sometimes crud can clog them to the point that it restricts the flow and makes proper bleeding more difficult.

3) Remove wheels and watch the caliper pistons while a helper pumps the pedal - they should extend squarely/evenly when the pedal is pressed and retract 1/16” or less when the pedal is released (easiest to see/measure if they’re already pressing against the pads) If they retract more than that, something is causing the pistons not to extend properly - I recommend replacement if this is the case.

4) I didn’t see any mention of new drums on the rear - sometimes drums can be so worn out that even new shoes won’t take up the gap properly and it takes extended travel at the cylinders to get enough pushback from them to make the pedal feel solid.

 

The drums are new along with everything else except starwheel adjusters.

I have tried bleeding with a helper and tried the vacuum tool which was junk and broke after five minutes and then the hose to jar method which works great for me. There are no issues with bleeding.

The caliper pistons do press and retract correctly.

 

Ok - what sequence are you using to bleed them?

Your van uses a diagonally split hydraulic circuit, and Dodge doesn’t recommend using the standard sequence of starting with the longest line first and working toward the MC. Dodge’s sequence is:

LR - RF - RR - LF

I’ll do some more digging for you when I have time.

 

I used the bleeding sequence in the factory service manual which was left rear, front right, right rear, left front as you listed above.

 

I looked for TSB’s for anything regarding the brakes for your van and didn’t find anything related to a low pedal. In terms of mechanical-hydraulic function, there’s only a few things that can cause a soft/spongy pedal or excessive pedal travel:

1) Air in the lines.
2) Drum brakes out of adjustment - you said they’re adjusted out to where they drag, so that’s not it.
3) Caliper pistons getting pushed back by warped rotors - doesn’t sound like you’ve even had it on the road yet.
4) Caliper pistons not extending/retracting properly - we already looked at this.
5) Brake pedal linkage out of adjustment - it would have to have more than a couple inches of free play for this to be the case, so I don’t think that’s likely either.

Believe me when I say that I understand you don’t want to hear it (I’ve had more than my share of frustration bleeding brakes) but I think there’s probably air still trapped in the lines. Here’s some suggestions on getting it out:

1) Bleed using a helper on the pedal. Keep in mind that the rear lines are up to 15 feet long - it may seem as though you’ve gotten all the air out but it could still be trapped a few feet upstream. My own “rule” is to see at least 5 “spurts” of air free fluid before moving on to the next wheel.

2) If using the jar and hose method, put thread tape on the bleeder screws to create as tight a seal as possible. Even if the screw isn’t cracked open very far, air can still get sucked into the system around the threads.

3) Try gravity bleeding. I’ve found that gravity bleeding can actually work quite well if you’re patient. My method is to allow it to bleed for one minute after seeing air. If air purges again within that minute, I reset my “stopwatch” (timer on phone). Once I’ve gotten each wheel done, I pump the pedal to check the feel and if there’s any doubt, I bleed each wheel again following the one minute rule.

4) See if you can borrow/rent a pressure bleeder. Not sure where you’d go for it though - we’ll let our regular customers borrow tools but that’s in large part because we know them well. I’ve also heard of building your own pressure bleeder using a pump bottle but never tried it.

I’m not trying to offend you by asking this, but did you possibly get the calipers switched from side to side after rebuilding them? The bleeder screw should be above the hose, so if that’s not where they’re positioned, the calipers are on the wrong sides.

The only other possibility I can think of is the ABS module needs to be bled which requires a scan tool to do, but generally speaking this doesn’t need to be done unless the module has been replaced. There’s no requirement from Dodge to do it during standard bleeding procedures, but there’s exceptions to everything.

 

The bleeding cannot possibly be the problem here. I have used a full gallon of brake fluid.

Why would the problem go away when I pinch off the front flex hoses? And also how does air in the brake lines explain the fact that when I remove the booster vacuum line off the intake, the pedal no longer sinks to the floor but rather becomes firm at the top of the pedal position?

Also, if there was air in the line, the brakes would gradually activate more and more as the pedal traveled down, and in my case the pedal begins really working all in a very short distance at the bottom of pedal position. I am wondering if there is a problem in the feedback mechanism of the booster because the van brakes extremely well as long as the pedal is all the way down. None of the work I have done on this van has affected the condition in the slightest, which makes me believe it is related to a system I have not yet touched.

I'm pretty sure bleeding a GALLON of brake fluid is proof that I've bled the brakes enough. And I do know what is sounds like when air spurts out of the bleeders. Just to put things in perspective, I had this problem on my Ford 1991 truck and ended up replacing the master cylinder a second time, and the problem promptly went away. However that problem was accompanied by extreme difficulty braking enough to stop. This problem is strictly related to pedal travel with no impact whatsoever on braking performance.

Another forum had a response on an older Buick and that person had this exact symptom and diagnosis with removing the vacuum line. When he replaced his brake booster the problem was gone. However I am tired of spending money on this van and it has proven to be a reliable brake system all along. I am just sensitive to issues like this. Also brake boosters seem pretty expensive.

 

1) Air will always rise to the highest point possible in the system. Any point where a line changes from running horizontally to vertically is a place for air to get trapped. Depending on the vehicle and the method being used to bleed, the amount of fluid being used means very little. I’ve worked on a couple of trucks where I put 2+ gallons of fluid through the lines with a pressure bleeder and it didn’t matter because what it ultimately came down to was that air was trapped in the wheel cylinders because of how they were mounted on the backing plates (these were older trucks with cylinders mounted at an angle/vertically, allowing air to become trapped above the bleeder screws - I know that’s not how they’re mounted on your van but it proves the point that more brake fluid through the lines doesn’t necessarily mean air is getting out).

2) Air can be compressed - brake fluid can’t. Pinching off the lines will either greatly reduce or completely cut off hydraulic flow to the front calipers. If air is trapped in them, the hydraulic force is now focusing on the rear brakes which don’t have air trapped in them and pedal response is normal because the hydraulic system is operating properly. When the front lines aren’t being pinched off, the air trapped in the calipers is now being compressed and it allows the pedal to sink.

3) The vacuum booster is there to provide extra mechanical advantage on the master cylinder - it provides in the neighborhood of an additional 500# of force (depending on the size). The pedal feels solid to you without the booster assist because you can’t come close to putting 500# of force on the pedal. Have you ever used a manual well pump and filled a 5 gallon bucket? It gets tough pretty quickly for most people. Or what about a manual tire pump to fill a bicycle tire? It doesn’t take long to get frustrated because you pump forever and aren’t even close to being at the right pressure - that’s because it takes humans significantly more effort to pump fluids and compress air.

4) The pedal stiffens up and brake operation feels good near the bottom of pedal travel because of how master cylinders are designed. Having air in the system is, in effect, the same as having a leak in that adequate hydraulic force can’t be applied. I’m not gonna explain every little detail, but basically, the MC prevents total brake failure through a mechanical contact between the primary and secondary pistons that allows hydraulic force to be exerted on the functional circuits of the system.

5) If you think the booster is the problem, all you need to do is unbolt the MC from it (you shouldn’t have to disconnect the lines - just make sure to brace/hang it so it can’t tip over) and slowly press the pedal to the floor, then let off. If you feel anything catch or the pedal doesn’t return, there’s a problem with it.

6) Hospital visits and insurance deductibles are more expensive than any booster....

 

There is no air in the system. The fluid level does not rise and fall with pedal application as it would when air is compressed within the system.

I will try checking the booster that way. The booster has already failed one of the vacuum tests. I wish I could just take it apart and inspect it but I have no idea what's in there.

 

Just checking in - Have you figured anything out with this? I’ve been researching/thinking on it but still don’t have any other suggestions for you.