Soft and Spongy Brake pedal

Tiny
VIJAY1974K
  • MEMBER
  • 2006 SKODA OCTAVIA
  • 1.9L
  • 4 CYL
  • TURBO
  • FWD
  • MANUAL
  • 82,000 MILES
Hi there, real wandering problem I have been stuck with for months now.

It all started after a full clutch replacement, vehicle delivered post clutch job, drove for around fifteen miles, no issues. The next day I notice that the brake pedal sinks to the floor. (A clutch bleed was performed during the clutch job) we did a complete brake system bleed, brakes are now back, gone the next day morning. Multiple rounds of bleed were attempted with no success. Took the vehicle to the manufacturer service center to bleed through VCDS activating ABS but of not much help, they advised replacing the master cylinder and brake booster. Yet I was not convinced since this happened just after a clutch job and feel something amiss could have caused this. Took to another Skoda expert where we found that RLHS wheel do not have oil supply (this is a RHD vehicle), we starting taking lines to ABS pump one by one and found one line do not have oil supply at all, ran VCDS again activated ABS pump, they run fine, no error or warning lights on instrument cluster, now this expert states the ABS pump has gone kaput and need replacement. Guess what I am now super confused and have not taken either of the replacements convincing, your expertise may matter, please advise
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Monday, November 28th, 2016 AT 4:00 AM

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Tiny
VIJAY1974K
  • MEMBER
Addition to the note above.

It appears to be the inlet line (one) to ABS has no oil supply (line from the reservoir to unit)pump the brake pedal gets pressure back and is off on next braking. ABS unit works when activated through VCDS. No obvious leak found near booster, wheel cylinders, checked vacuum pipes, no visible leak found on clutch slave cylinder.
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Monday, November 28th, 2016 AT 4:22 AM
Tiny
CARADIODOC
  • EXPERT
I'm not familiar with your brand, but I see you've been waiting a while for a reply. A few of your comments caught my attention. First of all, please do not even refer to brake fluid as "oil" because I don't want to take the slightest chance of causing a misunderstanding. The rubber parts that contact brake fluid are absolutely not compatible with any petroleum products, including engine oil, transmission fluid, power steering fluid, penetrating oil, axle grease, or gear lube. Every year I did a demonstration for my students where I put fresh, clean brake fluid into two beakers with a rubber wheel cylinder lip seal in each one. In one of them I added a single drop of power steering fluid or engine oil, then let both of them sit for a week. One week later the contaminated seal had grown from about an inch in diameter to about 1 1/8", and it was soft and mushy. That is what happens in a car with contaminated fluid. The first hint is usually the lip seals in the master cylinder grow past the fluid return ports and block them. That prevents the fluid from releasing back to the reservoir, so it keeps the brakes applied. As the dragging brakes heat up, the brake fluid does too, and it expands. Since it still can't release, it applies the brakes even harder, often until the car won't move. An additional clue is if you try to push the brake pedal, it will be too high and hard. The next clue, once you start looking further, is the rubber bladder seal under the reservoir's cap will be blown up and mushy, and you won't be able to stuff it back into place.

It is critical you understand that the only acceptable repair for contaminated brake fluid is to remove every single part that contains rubber parts that contact the brake fluid, flush and dry all the steel lines, then install all new parts that have rubber in them. That includes the calipers, wheel cylinders, rubber flex hoses, master cylinder, ABS hydraulic controller for vehicles with ABS, or the combination valve and / or height-sensing proportioning valve. The cost of this repair can easily exceed an older car's value. The contamination soaks into every part in the system. If one part is not replaced, the contamination will leach out of it and recontaminate all the new parts. Experienced brake system specialists even wash their hands with soap and water to prevent contaminating parts with fingerprint grease. I know you didn't say you contaminated the system. I feel compelled to point this out for the benefit of others who might read your reference to "oil" while researching their topic.

The next thing I noticed was your reference to nothing coming out from part of the hydraulic system. That is a very common mystery on GM front-wheel-drive cars. There are always two parts to the hydraulic system. In the past, one part ran the front brakes and one part ran the rear brakes. Since well over 80 percent of stopping is done by the front brakes on front-wheel-drive cars, since they have a much higher percentage of total weight on the front, if the front brakes failed, the rear brakes would lock up the two rear wheels, and you'd skid and skid, and they'd find you in the next county! Instead, all front-wheel-drive cars now use a "split-diagonal" system where one part of the hydraulic system runs the left front and right rear, and the other part of the system runs the other two wheels. With a failure of one part of the system, you'll still have one working front brake. Some of the non-adjustable suspension geometry has been modified to prevent a horrendous brake pull to one side when one font brake isn't working. On Chrysler products, that alignment geometry has been so well perfected, that the only way to know there is a failure in the hydraulic system is the red warning light turns on. On other brands, at most you will see a very tiny wiggle in the steering wheel as you apply the brakes, ... And that red warning light.

GM went a little further with this design. Imagine a teeter totter inside the master cylinder with a valve on each end. As long as both halves of the hydraulic system have no leaks and are working properly, both will have equal fluid pressure when you press the brake pedal. Those two equal pressures keep that teeter totter balanced and it stays in a neutral position. When you have a leak in half of the system, no pressure can build up in it, but it does in the good half. Those unequal pressures cause the teeter totter to move, and one of the valves blocks the port leading to the half of the system with the leak. By far the most common complaint from car owners is the left front brake pads, for example, are worn out and are being replaced for the third time, while the right front pads still look like new. The complaint from mechanics is they can't get any fluid to flow from the right front or left rear bleeder screws. Both problems are caused by the right front brake never applying because no fluid can get out of the master cylinder from that one port.

Besides that valve closing due to a leak, it will also close when anything causes unequal pressures in the two halves of the system. That includes improper bleeding procedures. All master cylinders will build up crud and corrosion in the lower halves of their bores where the pistons don't normally travel. It is critically important that when you feel you must bleed brakes with a helper, he must never push the pedal over half way to the floor. Doing so runs the rubber lip seals over that crud and can rip them. The symptom usually is a slowly sinking pedal, and that often doesn't show up for two or three days. Instead, I have only used "gravity-bleeding for over 30 years. Most of the time I don't even have a helper around. This damage to the master cylinder can occur too when the driver is suddenly surprised by a leak, like a popped rubber flex hose. If you catch yourself fast enough, you can avoid pushing the pedal too far, but most drivers instinctively push it all the way to the floor. For precisely that reason, many mechanics automatically include a rebuilt master cylinder in the repair estimates, rather than waiting for you to come back angry because you still have a problem after the repairs were completed.

When you do bleed with a helper, if you have a master cylinder like that GM style, as soon as you open a bleeder screw, you lose the pressure in that half of the system, and that valve trips. From then on you won't get any more fluid flow to that wheel and the one diagonally-opposite it. Many mechanics think that can be avoided by bleeding the wheels in a specific sequence, but that is not true. Also, some people diagnose the problem as something wrong in the master cylinder, replace it, then pedal-bleed the system and cause the exact same problem. The solution to this, ... And it is the only solution I have ever found that works every time, ... Is to go to one of the bleeder screws that is not flowing any fluid, open it, and give it a very short, quick burst of compressed air. Leave the cap loose on the reservoir. The goal is not to push the fluid all the way back up to he reservoir. All you need to do is give it a tiny shove to unseat that valve, then let the fluid gravity-bleed. Most of the time, if you do this right, you'll have brake fluid running out of the bleeder screw within less than 15 to 20 seconds.

When you bleed one or all wheels by gravity-bleeding, close each bleeder screw, one at a time when fluid shows up. If none of them flow any fluid after a few minutes, "irritate" the brake pedal by hand a little, just enough to convince the fluid to start flowing. Once it starts, it will siphon out on its own. Once all four wheels are bled this way, push the brake pedal down no further than half way just once. That will wash any remaining bubbles into the calipers and wheel cylinders. Open each bleeder screw, one at a time, for a couple of seconds to burp those last bubbles out, and you're done.

If you need to replace the master cylinder, I can share how I do that so bleeding at the wheels is not necessary. I don't even have to remove the wheels.

For my next comment of value, part of what you described is a common symptom of rear drum brakes that are out of adjustment. The difference is though, you described the problem as being different at different times of the day. A seriously-out-of-adjustment problem acts differently. You will have an unusually-low brake pedal because it takes a lot of fluid to run the rear shoes out all the way until they contact the drums. When you release the pedal, it takes some time for the shoes to slowly retract. If you push the pedal a second time right away before the shoes are fully retracted, it will take less fluid to run them out to the drums, so the pedal won't go down so far. Pump the pedal rapidly two or three times, and the pedal will get nice and high and hard, and it will stay that way as long as you hold pressure on it. As soon as you release it for more than four or five seconds, the shoes will fully retract, and the next time you push the pedal it will be real low again.

This adjustment issue usually occurs when the self adjuster cable or some other part of the adjusting system breaks, and sometimes when the drums are machined excessively and the shoes are not manually adjusted when the brakes are reassembled.

As for the mechanic who says you need a new power booster, if that has failed, the brake pedal will be hard to push, that's all. It has nothing to do with how far the pedal moves, just how easily it moves.

Now that I've posted this wondrous reply, your request will go "off the list", and no one else will see it or have the chance to reply. You and I are the only two who will be in this conversation and get automated e-mails directing us back here. For that reason, if you think I can't be of further help because I'm not familiar with your vehicle, you should post a new question. That will give the other experts a chance to reply. Of course, feel free to ask me followup questions. I've never seen your car brand or model, but I am a brake system specialist.
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Monday, November 28th, 2016 AT 9:17 PM
Tiny
VIJAY1974K
  • MEMBER
Hi Caradiodoc, Nicely and detailed explanation, appreciate that, I am happy that I got hold of a real brake specialist to look into the issue

with the way we pumped through the pedal for brake bleed I am sure that we would have damaged the MC. From what you explained I am ruling out the power booster since the pedal travels smoothly

rear brake shoes were looked at and they are in good condition and sits in right angle

other thing I consider is the self adjuster cable, don't think we ever looked at it

Now have couple of question:
you stated - "On other brands, at most you will see a very tiny wiggle in the steering wheel as you apply the brakes, . And that red warning light."

I notice very obvious wiggle in the steering wheel when applying brakes (this is a RHD vehicle) I feel its happening on the front LHS wheel, again as I mentioned above the fluid supply is missing on RLHS wheel, as you said these would be a split diagonal setup, not sure if its applicable to this vehicle, I hope it is since this is a manufacturer under the Volkswagen group and share the same engine specs of Audi, VW etc and they seem to be using modern techniques as we have now. Thoughts what next?

Since this happened after a clutch change, should I still bother about the master and slave clutch setup for leaks or so? Not that we found any during initial checks

another thing to note is, the steering wiggle started occurring after the manufacturer service center brake bleed, had pressure for some days, i.E. Lasted longer unlike previous times and still has some pressure but is only at the end of pedal

another item to indicate is when I do a complete turn towards right as like an L/7 shaped turn I hear a metal object grinding sound from the front LHS wheel, rotors coming in contact? With what?

Two of one inlet line to ABS do not have fluid supply, ABS works when activated through computer, do you see any issues with ABS here?

Can you help with a sequence what should I start with now

Power bleeder?
Adjuster cables?
ABS, brake, wheel sensors, pressure scan?
MC?

Your advise and assistance would really help narrow this down, thanks in advance.
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Tuesday, November 29th, 2016 AT 3:37 AM
Tiny
CARADIODOC
  • EXPERT
I think where I would start is by having a helper to push the brake pedal, ... Go to the master cylinder with the correct-size line wench, (flare-nut wrench), loosen one of the soft metal nuts, then have the helper slowly push the pedal. It should take him about 15 to 20 seconds to push it half way too the floor. Before it gets that far, you should see brake fluid flowing freely from that connection. Tighten the nut, THEN holler to the helper to release the pedal. Do that to the other steel line. If you find one that doesn't flow fluid after multiple attempts, suspect the master cylinder.

GM, and their other products, are the only ones I've ever run into that valve I described that blocks fluid flow, and they don't trip until the pedal is pushed over half way. I've never heard of that on VW products, ... So far.

Let me stop here to inject a wondrous point of interest. If your helper releases the brake pedal before you get the line nut tightened, air will get sucked in. Don't panic over that. Also, when a person isn't paying attention and they let the reservoir run dry during bleeding, air is not going to show up all the way down to the wheels. In your case, if you catch this before air gets into the ABS hydraulic controller, all you have to do is refill the reservoir, then very slowly push the brake pedal half way down. Wait about five seconds, then let the pedal release quickly. Do that multiple times until the normal feel returns to the pedal. Pushing the pedal slowly pushes brake fluid down the lines while allowing any air bubbles to float back up. Releasing the pedal quickly makes the fluid rushing back up wash the air bubbles back into the reservoir. (This is the second half of the trick I eluded to when replacing a master cylinder and not having to bleed at the wheels).

If it appears you need a master cylinder, consider whether the fluid could have been contaminated during the clutch service. I'm not a transmission specialist, but in my limited experience, I have never seen a hydraulically-operated clutch that shares a master cylinder reservoir with the brake system. The clutch systems I'm familiar with do use brake fluid, so the same precautions apply. Where I would be looking first is to see if the mechanic filled the brake system reservoir, thinking he was doing you a favor. Brake fluid should never be topped off during routine services, like oil changes. If brake fluid is low, there is either an external leak that must be repaired, or it's time for a common brake system inspection.

With an external leak, especially one that isn't yet bad enough for the customer to be aware of, the cause must be found and corrected, for obvious reasons, before it results in a crash. When disc brake pads wear, unlike with drum brakes, their self-adjusting feature is the piston gradually works its way out of the caliper housing. Brake fluid fills in behind it, and that's why the level drops in the reservoir, and that's our clue to recommend a brake system inspection. When new pads are installed, the piston has to be manually retracted back into the caliper housing to make room for them, and doing that pushes the brake fluid back up into the reservoir. If someone had refilled the reservoir previously, the fluid will overflow and make a mess. Brake fluid eats paint, so it must be rinsed off right away. Other than that, the mess is the only harm done.

If the previous mechanic filled the brake fluid with a funnel with oil residue, or he poked the rubber bladder seal back into the reservoir's cap when he had grease on his fingertips, the brake fluid would be contaminated. Admittedly, that would take from about three days to perhaps a week to show up, depending on the amount of the contaminant, but it is not something we want to overlook. The easiest clue to spot is the rubber seal under the reservoir cap will be blown up and mushy, and won't stay in the cap.

If you do get a nice solid fluid stream from both lines at the master cylinder, work your way down to the next place, in this case, the ABS controller. Failure of those is not common, and the few failures that do occur almost always affect the operation during ABS activation. I've never heard of one blocking fluid flow during normal braking. One of the valves in it for each wheel does block fluid flow, but it is only pulsed open and closed very rapidly when that wheel needs to have reduced braking power. If the blocking valve where to stick due to corrosion or some mechanical issue, it would stick in the open condition, hence, a failure to reduce skidding in an ABS stop, not a failure to pass fluid during a normal stop. Regardless, there should be three or four steel lines leaving the controller and going to the wheels. Some cars use a single line to control both rear wheels together. Front-wheel-drive, and many other cars, run the two rear brakes separately, so they'll have four lines leaving the controller. Loosen one line at a time, then have the helper push the brake pedal again. If this is the first place you do not get a strong stream of fluid, I would be surprised, but first I'd be bleeding it some more to be sure the fluid isn't filling a chamber that is full of air. On a lot of vehicles that bleeding has to be done with a scanner. It is needed to make the ABS Computer open the valves to some of those chambers so the air can be expelled. A I recall, you're missing fluid to two wheels. If the cause is a valve in the ABS controller, that would be real uncommon, and you can imagine how much more uncommon it would be to have two of them doing that.

If you get good fluid flow from the hydraulic controller, but not at the wheels, there is still excessive air in the lines after the controller or the affected lines are blocked, as in crushed by a pry bar when working on the clutch. The clue is with a crushed or blocked line, the brake pedal will be unusually high and hard. With air in any line, the pedal will be low and soft. If you suspect air, and multiple bleeding attempts haven't solved it, you may need to resort to pressure-bleeding. Every shop used to have a "bleeder ball", but when there began to appear such a wide variety of reservoir cap sizes and shapes, there were way too many adapters a shop had to buy to be practical. That's when we learned that gravity-bleeding was better. You may not find pressure-bleeding equipment at your favorite shop, and anytime I do see one, I get real nervous about what someone might have put in it previously. I saw one used very effectively once to pressurize engine oil to find an internal oil leak when the engine was out of the car. Once verified the leak was fixed, the instructor destroyed that bleeder ball to insure no one would ever accidentally contaminate a brake system with it.

If you find the brake pedal only gets soft and low well after the engine is warmed up, and given the recent service, look for anyplace a steel brake line might have gotten repositioned and is sitting too close to hot exhaust parts. Brake fluid loves to absorb moisture out of the air, and water in the fluid boils at a much lower temperature than does brake fluid, leading to one form of brake fade. Boiling water causes air bubbles to form, and is one reason we can continually find air during repeated bleeding attempts.

If you collect the brake fluid that is bled at a wheel, and you see it's clear, you know the new fluid has traveled from the reservoir and there shouldn't be any air left in that line. Brake fluid gets dark over time from being hot. If you see dark fluid coming out of a bleeder screw, fresh new fluid hasn't made it that far yet, and air in the line is still a real good suspect.
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Wednesday, November 30th, 2016 AT 10:24 PM
Tiny
VIJAY1974K
  • MEMBER
Update: (but unresolved)

since two weeks I started the ordeal to fix the issue, took the vehicle to a renowned euro car specialists, they verified everything we spoke and suspected its the master cylinder, although the fluid supply off from the cylinder which they claimed to be the culprit. Approved to replace the MC, MC was replaced and then we started the bleeding procedure and now this time the fluid supply is very low on the Rear RHS wheel, remember last time we had seen this issue on the Rear LHS wheel. Multiple bleed procedure was done with little to no help. Took the vehicle back to them after a day's local driving, has the same feeling as the pedal is fading slowly.

Round 2 - this time they suspect if its the rear wheel cylinder, vehicle on the ram, checked both the rear wheels, spray cleaner etc etc, adjusted the hand brakes, bled the brakes again, went for a test drive, slightly firm but can make out that the not all the wheels has brakes, as per me its the Front LHS and Rear RHS wheel which seem to be having no brakes or very less

This time we connected the vehicle to the scanner, bled the brakes through the procedure it said, not much to say, no ABS warning lights, ABS works when activated through VCDS, per them looking at the scanner do not suspect any issues on ABS, they continued work on checking the fluid supply and lines to the ABS pump/module, per them most have a good flow except two (again I wasn't around when this was checked but remember a situation where we did the same and all the lines going to the wheels has good fluid supply)

now they state its the ABS module which would have gone bad and needed replacement, what I felt speaking to them is, they would like to try that as next (basically a try for trail and error kind of)

Please advise. What do you feel about the tests, replacement done so far and what is that I should do next
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Wednesday, December 21st, 2016 AT 3:29 AM
Tiny
HMAC300
  • EXPERT
We don't have this car in usa so it sounds like the valves need to be opened on abs unit and bled that way not sure if it was done with the scanner or not. It needs to be a professional scanner not one bought at auto parts. You might try either a power vacuum bleeder or a power bleeder at same time as scanner.
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Wednesday, December 21st, 2016 AT 6:55 AM
Tiny
CARADIODOC
  • EXPERT
Yup. Also, without rereading everything to update my memory, I get the feeling you may have something similar to a problem that can occur on GM front-wheel-drive vehicles. If you have two wheels, one front and the opposite rear one that no fluid flows when bleeding the brakes, give a quick, short burst of compressed air to one of those open bleeder screws, than wait for gravity-bleeding to cause fluid to flow. Do this with the reservoir cap loose so no pressure or vacuum build up there. If that works, only gravity-bleed those two wheels. If you resort to pedal-bleeding, never push the pedal more than half-way to the floor. Sorry if I brought this up previously. GM vehicles have a valve that trips in the master cylinder, and the compressed air will reset that valve and open it to allow fluid to flow to its two wheels.
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Wednesday, December 21st, 2016 AT 11:01 AM

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