Mechanics

BRAKE PEDAL TRAVELS ALMOST TO FLOOR B

1995 Plymouth Voyager

Brakes problem
1995 Plymouth Voyager 6 cyl Two Wheel Drive Automatic 140000 miles

I have brakes but the pedal goes to the floor & it takes a long time to stop. I noticed it coming on slowly over a few weeks until my brake lights eventually stayed on. Initially I could pump the brakes back up until they had pressure & light went off, but the next time I braked the pressure was gone & to the floor again. MasterCylinder fluid level is good & never been too low.

no visible leaks detected so I took it to BRAKE CHECK. They said NO wheel cylinder/caliper leaks & they tested the MCylinder by putting clamps on the hoses & claiming it was good. They determined it was power booster, but did NO vacuum test. They tried to sell me a loaded booster (w/ MC) for $275 until I called them on it.

bought power booster myself ($55). Removed MC & NO active leak behind or into booster altho there is some rust pattern that looks like something may have leaked at one time.

I am not convinced this is what it is. Almost everything I read indicates bad fluid or bad internal MC -which is my hunch. W/ engine off I can pump up pressure to a hard pedal. When started, pedal drops to floor. Vacuum seems good & don't hear any leaks, but when I push on pedal there is is a hissing & sounds like air leaking inside the booster. I'm quite confused at this point.

also when the weather is COLD, I seem to get more pressure/brake back. Anybody help w/ this? Is this a booster or a MC/fluid issue?
Avatar
Bahop
January 23, 2010.



A defective booster will make it hard to push the brake pedal; it won't affect how far it moves.

Based on your comment about being able to pump it up, start by checking the adjustment of the rear shoes. Failure to automatically adjust will lead to a low brake pedal. Every time you pump the pedal, the shoes will move out a little, but they will retract relatively slowly even though the pedal comes back quickly. A second or third stroke on the pedal grabs a little more fluid. Each stroke causes the pedal to get higher and more solid.

A severely worn front wheel bearing will allow the brake rotor to wobble which will push the piston into the caliper when you bounce over bumpy roads or even just turn corners. The clue is the pedal will stay solid when the van is not moving. This isn't common because the bearings will be very noisy and get replaced long before they get that sloppy.

Be aware too that regadless of the cause of the low pedal, the master cylinder could be damaged. Crud and corrosion build up in the bottom halves of the two bores where the lip seals don't normally run. When the pedal goes down more than half way, the seals can be torn on that crap. That will result in the pedal slowly sinking to the floor at first. Later, you will always have a low pedal and the pressure warning light will be on. I always warned my students to never push the pedal more than half way down when pedal-bleeding the brakes.

The clues come from pumping up the pedal like you mentioned. A leaking wheel cylinder or steel line will cause the pedal to sink slowly to the floor when you hold steady pressure on it. If the pedal can be pumped up, and then it holds pressure, try varying the foot pressure without completely removing it. If the pedal suddenly starts sinking, the lip seals are leaking in the master cylinder. This problem will become permanent very soon as the seals continue to lose their sealing ability.

Caradiodoc

Caradiodoc
Jan 25, 2010.
Hey caradiodoc -thanx for the response.

The rear brake adjustments could be something to check into. In the early stages of this problem, I could get some brake pedal back by stopping/ starting in reverse a few times to adjust rear brakes until my brake light would go off.

Wheel bearing is out -I don't have pedal when stopped & running either. Leaky wheel cylinder/steel line is out -as fluid level doesn't drop.

Some new data- however. When engine OFF I can pump brakes up, but the pedal does fade & drop quite a bit- about half way - if I leave my foot on it. Initially I thot they were solid? But it now seems to me they are softer/spongy & as soon as I start engine ON - they drop all the way.

I'm starting to wonder if it's both the MC & booster? When I removed MC, there was the tiniest bit of wet behind the seal where the booster pushrod enters. I attributed it to lube for that contact to the MC rod. Also- a dried rusty mark on booster from MC down - as if something had leaked in the past? But really not much currently wet, just a miniscule amount of wet that seemed to dry up as I touched it.

Thanx again. I'm trying to save a few $$$ here so correct diagnosis is the 1st step.

Bahop

Tiny
Bahop
Jan 25, 2010.
My vote is for a new master cylinder. There is a simple trick to eliminate the need to bleed at the wheels. Loosen the two line nuts just a little, (less than 1/8 turn), unbolt the master cylinder from the booster and pull it away, then use it as a lever to bend the two steel lines upward a little. Now you can finish unbolting the steel lines without the fluid running out of them.

Be sure to bench-bleed the new unit, connect the two lines, then bend them back down with the master cylinder, and bolt it back on. Have a helper push the brake pedal down very slowly so it takes about 20 seconds to get half way down. At the same time, loosen one of the line nuts 1/4 turn. You will see air bubbles come out, then a nice stream of clear fluid. Tighten the nut, then holler to your helper to let up on the pedal very quickly. He must not let up when the line nut is loose or air will be drawn back in. By pushing the pedal down slowly, fluid will go down the line and any air bubbles will float up. When the helper lets off the pedal quickly, fluid will come rushing back into the reservoir briging any air bubbles with it. Do the same thing with the second line.

Even if you don't have a helper, slowly pushing and quickly releasing the pedal yourself a few times will do the same thing.

Caradiodoc

Caradiodoc
Jan 26, 2010.
Thanx again caradiodoc.

My only question in that is - will the brake lite still come on from just an internal leak in the MC?

I know it will if the fluid level gets low, but that hasn't happened.

Also wondering if it's worth trying to bleed the lines first to see if that makes a diff? From what I've read online that hasn't helped most folks w/ older vehics & can even make it worse (if it can get any worse)

and what about ABS? Could it be involved? As I'm seeing in some posts (w/ different vehicles).

Am picking up a rebuilt MC today. Let me know if you still think that's a go -I won't tear into this for another day or so.

Thanx again

AFTER NOTE; MY MANUAL SAYS THAT MY ABS EQUIPPED VEHICLE REQUIRES AN ELECTRONIC
DRB-II SCAN TOOL TO BLEED THE MODULATOR & THEREFORE ANY REPAIRS OR BLEEDING OF THE SYSTEM SHOULD BE LEFT TO AN AUTHORIZED DEALER.

Are they for real? I can't even bleed my own friggin' brakes? Or is there a work around?

Bahop

Tiny
Bahop
Jan 26, 2010.
Yup, there are three things that will turn on the red warning light. The parking brake pedal, the low fluid switch, (not on all vehicles), and the pressure differential switch. Lower hydraulic pressure in one circuit than the other trips a switch. It's a valve with each circuit's pressure on one end of it. GM and Chrysler switches have always been spring-loaded but they can get stuck in some corrosion. A good quick jab on the pedal usually pops it free once the problem is fixed.

Yes, it's true you will need a scanner if you want to bleed the entire system. I have a '95 Grand Caravan, and had to use the scanner because my student allowed the master cylinder to run empty while replacing a rusted steel line. If you follow the steps I listed earlier, no air will get into the ABS assembly so you won't need a scanner. Also, when replacing a caliper, wheel cylinder, line, or hose, fluid will dribble down through the ABS hydraulic controller. As long as the reservoir doesn't run dry, just refill it and bleed the new parts like normal. If it's going to take a while, rather than constantly running back to keep refilling it, just put a bar from the seat to the brake pedal to hold the pedal down a couple of inches. The seals will move past the ports in the master cylinder, and gravity won't be nearly strong enough to pull fluid past the lip seals.

The scanner allows you to open various valves in the hydraulic control unit to let fluid flow where air would otherwise be trapped. I have the DRB3 and a DRB2. The DRB2 cartridge only goes up to 1994 models, but I found it does work on my '95. Since my DRB3 is a newer model, it only goes back to '98 model cars unless I plug in a card, then it goes back to '83 models. I sold three DRB3s on eBay a couple of years ago. I wasn't in any big hurry to sell the fourth one, but I've only used it on a half dozen cars so it doesn't make much sense to hang onto it. I will never own anything newer than a '95, and I'll be selling that one this spring.

Caradiodoc

Caradiodoc
Jan 26, 2010.
Thanx again.

Just when I'm feeling confident about it being the MC, I get some new behavior/data & makes me wonder if it has as much to do w/ rear brakes self adjusters; so on my way to piock up the MC (of course) I stop/start in reverse a bunch of times to see if they adjust or not & the brake light turns OFF & actually stays OFF as I drive & brake (which it hasn't done for a week or so). Pedal still feels soft tho, but not as bad? &Amp; the light does come back ON & pedal travel goes to floor when I brake hard, but if I pump the pedal light will now go OFF immediately.

So WTF? I say. Do you still think its MC & it's just junk moving around in the piston or should I check rear adjusters before installing 1st?

Any info on this helps so thanx

bahop

Tiny
Bahop
Jan 27, 2010.
Set the parking brake to hold the shoes out against the drums. Then, if the service brake pedal is always high and solid, check the shoe adjustment.

Caradiodoc

Caradiodoc
Jan 27, 2010.
OK. I assume this is when running?

W/ parking brake on-- pedal is normal position, but drops easily to floor w/ foot pressure.

When not running, pedal is normal position but pumps up high & solid when vacuum is released.

So this should indicate rear adjusters are working OK & the focus is back on the MC- yeah?

Thanx for your help -I need to eliminate as many potentials as possible before I start spending money. Times are tough & I'm gonna be doing this meself as a result. But it's been a good learning experience re; brakes: )

bahop

Tiny
Bahop
Jan 27, 2010.
Caradiodoc, fyi- just an update to this situation.

I have NOT been able to work on this master cylinder due to the cold weather & NO indoor space available,

BUT

they have been working as NORMAL for the past several weeks. NO brake lite on & definite firm pedal function restored to before all this began.

I'm not in mind to think it has miraculously cured itself- but I am COMPLETELY at a loss to describe why these brakes failed for over a month & now appear to work fine as if nothing were wrong.

Any ideas anyone? Could it have to do w/ the effect of the cold on brake fluid- maybe making it thicker & less likely to move past a seal? Or could it be crud & corrosion that is now moved on past seals & (currently) not affecting them?

I need some perspective for my sanity -please: )

Tiny
Bahop
Feb 12, 2010.
Hoping never pans out for me, but you might hope there was air that worked its way out. I'm not sure what the ramifications are related to having the ABS hydraulic controller in the circuit, but I can share my experience with my '72 Challenger. Every spring when I dug it out, the master cylinder was empty. There was no sign where the fluid went over the winter although I never pulled the master cylinder lose to look in the booster. This happened every spring for at least five years.

By now I knew to just refill the reservoir and drive it. By the time I got out of my driveway and onto the highway I had a low pedal but at least a hint of brakes. By the time I made the five-mile drive to town and stroked the pedal a few times along the way, I had enough brake power to lock up the wheels. By the time I got home, the pedal was high and solid and stayed that way for the rest of the driving season. As I was sitting at stop lights with the brakes applied lightly, air bubbles vibrated their way back up the steel lines. They flowed into the reservoir when I released the pedal.

After running the pedal down too far for all those years, the seals in the master cylinder finally ripped. First I lost one circuit, ... So of course I kept driving! A week later the second one ripped. Luckily I was going home after midnight and there wasn't much traffic. Car was headed to a restoration shop so I wasn't interested in buying a new master cylinder. I good used one from my rusted out '78 LeBaron wagon worked perfectly.

In your case, I could see air in the system yet. It would contract in the cold weather and have reduced effect. You might try bleeding the two rear wheel cylinders. If a little spurt of air comes out as soon as you open the bleeder screw, the air might have come in past the lip seals. There's an expander spring in there to prevent that and to prevent the seals from falling over. There has always been a residual check valve in the drum port of the master cylinder. It's purpose was to maintain about 10 psi on the fluid to prevent air from entering past the wheel cylinder lip seals when barometric pressure goes up, but it just occurred to me that they can't put that valve in a master cylinder for a split-diagonal hydraulic system because you must not hold any pressure on a disc brake caliper. I don't know what or if they still incorporate a residual check valve.

If you repeatedly get air out of a wheel cylinder, I would replace that one. The clue would be that the air is there as soon as you open the bleeder screw. Air that sneaks in past the lip seal will collect at the top of the cylinder and won't go into the steel line, so it will be the first thing to come out when you bleed it. If you get a lot of bubble-free fluid long before any air comes out, the air got in somewhere else.

It wouldn't hurt to double-check the rear shoe adjustment. Don't try to separate the drums from the hubs. Pull the wheel bearing out to pop the drums off. They make gauges, but I have better luck pulling the drum off about an inch, then moving it left and right, (as you're facing the spindle), to see how much play there is. I adjust the shoes manually until there is no sideways movement but the drum will still slide on and turn freely. Also, shove the shoes up and down and sideways to be sure they're centered in the drum.

If adjusting them helps, look for the obvious broken adjuster cable and stuck star wheel adjuster, but also check the teeth of the star wheel to see if any are worn off. An often overlooked cause of failure to adjust is the adjuster lever is hanging down too low. That is caused by the cable's guide shoe not fully seated on the brake shoe. The only way to seat it properly is to remove the shoe return spring, then check that the lip under the hole of the guide drops all the way into the hole in the shoe. You gotta hold the guide in place until the return spring is installed. I don't want to belabor the obvious, but the return spring must be hooked properly for it to hold the cable guide in place. Some people just try to hang it in the hole by the hook, but that hook must be wound into the hole so it catches on the back of the shoe. That's what keeps the cable guide from popping out.

While you're in there, there are two important observations to make. Before you disturb anything, look at the large anchor pin on top. Both shoes must be resting against it. If one is not, either the return springs are weak or the parking brake is sticking. The second, related observation has to do with the parking brake strut rod right over the spindle, between the two shoes. Use your thumb to push it toward the front of the van, against the anti-rattle spring. There must be some free play. If it doesn't move at least 1/16", flex the two parking brake cables to see if one is sticking. The parking brake lever behind the rear shoe should not move forward when flexing the cable. If it does, a cable is sticking or the main cable is over-adjusted. If the parking brake lever moves backwards when flexing the cable, and the strut rod develops free play, that cable is sticking. In severe cases, you might have to use a pry bar to force the parking brake lever back to its normal resting position. Once the lever is fully released, the only thing that would prevent there being any free play in the strut rod is if the star wheel adjuster isn't extended to its proper adjustment.

Under normal operation, the front brake shoe does very little stopping. Its job is to grab the drum and try to rotate with it. As it does, it pushes on the lower link, (the star wheel adjuster), and pushes the bottom of the rear shoe into the drum. The wedging action gives the rear shoe the greatest braking power, that's why it has a longer lining. It does most of the work so it has the most wear.

When you back up, the roles are reversed. The rear shoe moves out, catches the drum, and helps apply the front shoe. When the rear shoe moves away from the anchor, it moves the cable guide shoe which tugs on the cable and adjuster lever. If anything holds pressure on the parking brake strut rod, it is already holding the shoes away from the anchor pin so the rear shoe can't move far enough to tug on the adjuster cable. That's how a sticking parking brake cable will prevent the shoes from adjusting automatically. A clue would be one of your original symptoms where the brake pedal got higher and harder when you pumped it a few times.

Caradiodoc

Caradiodoc
Feb 12, 2010.