Hi folks - working on a 2002 Hyundai Elantra GT. 4 disc, no ABS. Problem is the brake pedal goes to the floor without much force. I bled all 4 lines, but no improvement. Rigid lines from the brake master cylinder to the rear wheels were very corroded, so I ran new lines. The old ones pretty much fell apart when I took them off the car. I also replaced the brake master cylinder. I tried to bleed the brakes again, but couldn’t get much (if any) fluid pressure at any of the wheels. Yes, I found a couple leaks at the junction points for the rigid lines, but I re-flanged those connections and got rid of all the leaks. Still no real pressure when trying to bleed.
So, I tried a second, then a third master cylinder with a new attached resevoir. No improvement. I bench bled the snot out of this third master cylinder because the symptoms clearly suggest air was likely trapped somewhere in the system. I used a wood dowel to fully actuate the cylinder many times after all the air had been released while I had short clear hoses running from the master cylinder outlets into a little plastic cup filled with clean brake fluid. I wanted to make sure there was no way air could be in the MC, and no air drawn back in when I released the wood dowel.
Next, I quickly capped off the MC outlets and connected a hose to each brake line individually where they normally screw into the MC. I then let clear fluid drain through each line until it was spilling out clear of each caliper bleeder with no air bubbles. So, no lines are kinked, clogged, or contain air.
I took every precaution to keep air out of the system, yet when I push the brake pedal, there is still virtually no real pressure generated by the MC. The power booster rod is shoving the master cylinder in as it should. I don’t think there’s any problem with the power booster.
I’ve used gravity bleeding, manual “push & hold the brake pedal” bleeding, vacuum bleeding, and I’m certain there is no air in the lines or calipers. Still no significant pressure coming from the MC when I push & hold the brake pedal to the floor. It takes maybe 20-25 pounds of foot pressure, but always goes completely to the floor with all the bleeders closed. If the pedal is held to the floor, fluid slowly seeps from the bleeders. I’m used to it spraying when doing this on a healthy brake system. This is beyond maddening. Any suggestions other than torching this car would be most welcome.
I would have guessed this is an ABS problem, but you got no ABS … hmmm … well, air is trapped somewhere. Did you bleed each brake line separately, one at a time, in the correct order, longest to shortest, or however the FSM says is the correct order?
Is there some kind of extra gadget in the brake system, like an accumulator or pressure proportioner? Maybe that has to be bled separately.
When you bleed, do you push on the brake pedal? You might have to resort to a pressure bleeding technique. If you do the push-pedal technique, try it this way: Open one line (all others closed), push on the pedal with your hand, not with your foot, and only 3/4 of the way down, not all the way. Then close the bleeder, up on the pedal, and repeat. Sometimes pressing too hard on the pedal or pressing all the way to the floor causes this.
Edit: I think you are already aware, but if there’s anything weird going on with the caliper pistons, like some extra space between the piston and what it is supposed to contact with has materialized when you re-did the lines for some reason, that could cause this too. A bad flexible brake line is another possibility. You didn’t remove or replace any calipers, right?
Maybe a booster problem? A failed booster would allow the pedal loads of travel with little resistance and force the pedal effort to be very high to stop the car, especially with 4 wheel disks.
IF you replaced the Brake Master cylinder…I have to ask… Did you BENCH BLEED the Master? If not… That is your problem. No if’s ands or Butts about it. So…did you Bench Bleed it? From your original post and the reported issue after you replaced the Master…it sounds to me like you skipped an Extremely important and Un skippable part of Master Cyl replacement. I HOPE you didnt because that will be your problem resolution.
Thanks for the feedback. 4 disc (no drums). I mainly did pressure bleeding (correct order - farthest caliper to the closest), but will try the 3/4 pedal travel ideal. No recent caliper replacements.
I bench bled each one of the master cylinders - I even did one while it was submerged in a clean container with clean brake fluid.
The pedal is always very soft. Never too firm. The kicker is none of the calipers are getting much fluid pressure. All 4 lines and calipers have been bled till clear fluid drains out, and no air bubbles. I’ll take the MC back off and bench bleed it one more time, then see what happens.
That sounds like a good plan. Besides the good ideas posted above, one other thing to consider is the new brake lines. Those have to be a suspect b/c you didn’t have this problem (presumably) before you installed, among other things, new brake lines.
It’s possible that one or more of the new connections is bad, and allowing air to enter the system. It seems like if that were the case they’d leak fluid too, but it’s possible for a one-way valve situation to happen at a malfunctioning connection, where it will suck air in as the pedal is released, but seal tight as a drum when the pedal is pressed. Like a bicycle pump.
Ok, here’s one more idea, if you simply get so frustrated you have to try something new. I’ve never tried this myself, but what if you somehow – not sure how to do it, but it must be possible --blocked off half the lines, or even all the lines but one? Then you move the blocking around, until you get a soft pedal one way, and a firm pedal all the other ways. That way you could isolate where in the brake system the problem was occurring, so at least you’d know where to focus your att’n, which caliper to remove and disassemble, lines to replace, etc.
You mentioned that you replaced brake lines… these are steel lines… Sometimes you need to watch how you route and or bend those lines… Sometimes you can have a steel line in the shape that will Harbor Air and not let it easily escape.
You could try pressure bleeding…or Gravity Bleeding. Ive become an expert in this procedure as Ive encountered vehicles that were EXTREMELY difficult to bleed properly.
Sometimes you need an assistant to work the pedal for you… Other times a pressure bleed works in seconds. Look for steel line in funky shapes that might harbor air…and correct them.
Of late Ive been letting the brakes bleed themselves. Attach a 6 inch piece of hose to the bleeder screw and have the hose rise vertically from the bleeder until it bends over to drain. Crack the bleeder screw…not too far open…and allow the fluid to fill the drain hose… Allow it to leak for about 15 min… Move to the next wheel. Using a metal hammer or other device…Knock on the calipers and lines to knock loose air bubbles. Ive seen many an air bubble after tapping on a few calipers that would not have appeared if I didnt tap on them
Reverse bleeding works wonders too. Sometimes better than pressure bleeding from the master reservoir itself… I have all methods at my disposal. Some work better on different vehicles than others…
Great tips. I think imperfect line connections and air trapped in one or more lines/calipers are surely the problem. I bench bled the MC again and gravity bled all 4 lines. Will reinstall the MC today and use various bleeding techniques including pressure bleeding and the vertical length of hose off the bleeder screws. Really appreciate you all monitoring these posts!
OK is correcto…Out of adjustment Rear Drums SURE WILL Mimic a failed master…It will fool most people… But if you pay attn you wont be fooled. There is a difference between an air pocket and simple pedal travel for the sake of shoring up those out of adjusted shoes… Ha…I just fixed that problem last week actually… I thought it could be the master…but it didnt feel like air…just pedal travel.
I dont expect many people to be able to tell the diff…but there are diffs…
Just because you can’t see it right now, doesn’t mean everything is fine
Put the car on jack stands
Remove all of the calipers from the bracket and closely examine all of the pistons. Perhaps one of the boots is buggered up, letting air in, or brake fluid out. Remove the brake pads, but don’t take off the hose. Hook the caliper to the coil spring, so that it doesn’t hang by the hose
As @GeorgeSanJose suggested, perhaps one of the copper sealing washers . . . that seal the brake hose to the caliper . . . is leaking. That would allow brake fluid to seep past, creating a sinking brake pedal
Here’s an idea . . . while you have that car on jack stands, put a stick on the brake pedal. Now look at every single hose, line, connection, piston, etc. for a brake fluid leak. I used that method a few days ago to locate an elusive leak
You want to have the brake calipers securely attached to their bracket, when you do this. Otherwise, you might push one of the pistons out of its bore
Have you tried pumping the brake pedal hard and fast several (a dozen or so) times to see if the pressure returns?
If pumping it fast and hard brings the pedal back, you have a lot of air in the lines. Try this first, hard and fast until you get pressure, hold the pressure and have your assistant open the bleed valve till the pedal drops, then close and release pedal. Repeat until pedal start getting hard on the first pump and little air comes out the caliper under test, then move to the next wheel.