These are difficult complaints. If the tech cannot confirm the complaint, then he/she really does not know if anything they try to do is going to have a result. Plus, there are other details that like it or not have forced shops into a defensive position. 1. If the shop replaces the master cylinder, there is no gurantee they will be paid. There is also no guarantee that the car will be fixed either! The problem could be in the ABS system, and one or more of the "vent valves" in it could be seeping. It's also quite possible a tiny piece of some type of debris is moving in the fluid right near the compensating port inside the master cylinder, and causing the bypass valve to not seal after a pedal release. The bypass valve in the master cylinder is designed to prevent the system from going into a vacuum as the pedal is released. 2. If the shop replaces the master cylinder, and the car is not fixed the finger pointing really starts. Many techs feel that with a random pedal fades complaint, that cannot be confirmed the way to approach it is the customer must OK the replacement of the master cylinder, and acknowledge in writing that this service is by choice, and not a guarantee of any repair. In the past, techs would do the master cylinder and since there really was almost no chance that it could be anything else get away with it. But today, there is a significant chance that the failure could be in the ABS, or elswhere in the system. So the customer must agree in advance that if the problem persists, the continued repair is NOT FREE. Keep in mind that refers to non warrantied vehicles in for direct customer pay services. Being under warranty it creates an entirely different senario. But the O.E. has the same interests as the average consumer, they don't want to pay for things needlessly any more than anyone reading this does. All that aside, sometimes you have to do something, even if it's wrong! 3. You say they bled the system, and they said it had an air bubble? So basically, the car went into the dealer with a very low pedal, they bled the brakes and now it has a good pedal. That is a plausible senario, and your claim of it being BS, without testing just might be totally unfair. Air bubbles can occur for a couple of reasons. The air could have been trapped in the ABS system, and released to the brake system. The fluid could have gotten very hot under heavy brake useage, and boiled water vapor, and other gasses out of solution creating a bubble that may have been unable to be reabsorbed by the brake fluid. So lacking any proof otherwise, the tech and the shop have to go with what they can confirm. If you were not there, and did not bleed the brakes yourself then you really don't know if they did bleed air out of the system. Once again, you might not be fair here with your claims. In some ways Lexus has two problems, a car they cannot confirm that is broken, and an owner that dosen't trust them or the car. Granted, I would be very concerned with the car under the circumstances you outlined. Given my own resources if I was in your place, I would replace the master cylinder myself out of pocket just for my own piece of mind. If I get reimbursed, great, if not I have the peace of mind knowing I have eliminated a very likely source of the trouble. One other thing to think about. Your master cylinder controls the LF and RR wheels together off of one piston, and the RF and LR wheels off of the second piston. They do this to try and ensure that no matter what, you at least have 50% of the cars total braking capacity. Sure if one of them bypass fluid the pedal drops, but the opposite pair is being applied ever fuller when that happens. Thats part of how as I tech I figure out exactly what is happening when I have a car with the symptom you have described. You have my sympathy with this situation, and the dealer does too. Once again, for your own peace of mind, and trying to ensure that there isn't a hidden problem I would recommend pay them to replace the master cylinder, and do a brake fluid flush. Then take it up with your selling dealer and see if they can help you out in this circumstance. Remember, without getting to confirm the actual cause, even with replacng the master cylinder, and doing a brake fluid flush you could still have a problem lurking. The only thing I can tell you is you will be the first to know....... :(

I have encountered this problem on many vehicles in the shop i work at and it might be normal for a brake pedal to travel quite a bit when your are at idle in park. However, you would never press the pedal that hard or as far down when driving. You would end up through the windshield for sure. In my experience your particular vehicle has this weird feeling pedal travel when you are idling in park but the brakes perform as they should when driving. Air in the hydraulic system would cause a spongy feeling not a fading pedal, so bleeding is not likely to fix the problem. if there is in fact a failure in the system I would be checking to see if the ABS module is bypassing fluid pressure by blocking off the master cyl. if the pedal is high and firm( no travel) I would then block off the flex hoses and check for pedal height and drop. if this is ok un-block one flex hose at a time and see how much drop if there is a substantial drop at a certain wheel I would verify the hydraulic circuit to that wheel. first by bleeding to see if there is any air. Then I would put my attention to the hydraulic unit. Though I am confident that this is how these vehicles are and you don't have anything to be concerned about. Hope it works out

First, a brake caliper is a device that squeezes the pads from the sides against the rotor. If you think of a "vernier caliper" where you are measuring the thickness of an object from the sides, you get the picture of a motion that the brake caliper reproduces, hydraulicly. Second, brake calipers do seize and often times parts are available to rebuild them, as well as there are replacement calipers, both new and remanufactured. It comes down to considerations of cost, availability, and a fair profit for the shop doing the work, while limiting potential warranty exposure. As some others have mentioned the parking brake is often part of the rear brake calipers on many cars, and without seeing one, I would expect this is the case on the Mazda. IMO the rear calipers that incorporate the parking brake have been a weak link, and very troublesome poprtion of the brake system on four wheel disc. The movement to systems that use small brake shoes that fit inside the rotors in the rear have been a major improvement, except for the fact that we are seeing these rear shoes delaminate in high road salt areas, but thats a different story. The addition of the parking brake to the rear caliper makes it more difficult to repair in the feild. Plus no regular shop is going to have an acid bath that will allow them to completely remove all of the rust and scale that builds up in the caliper slides. So a tech has to improvise the routine and tools that he/she will use to service that portion of the caliper. Trust me, it's not easy in many circumstances and can take a considerable amount of time and not always produce a satisfactory, if not durable result. So given that single point, a shop/tech has to ask why even bother spending the time attempting a difficult task, where the outcome is not assured? Plus we have not even disscussed the actual servicing of the piston and the e-brake components in the caliper! Combine that with the fact that the "cheaper, faster, etc. attitude also applies to how many shops try to hire techs and you will see this becomes even more complicated. "It takes less talent, and less time to replace a component than it does to remove a component, rebuild it, and reinstall it" Think about that, less time means of course more time to do more work, as in other cars. Less talent means a less expensive work force. That actually means an over all a cheaper cost of doing business, and to a degree a cheaper form of auto service to the consumer. But this comes at a trade-off to some other consumers who might be better served on an individual basis. Jason, in your position, where you think having the tech repair the caliper would be cheaper for your MIL you are partially correct. But, for a shop to routinely do that level of a repair, they would have to hire a more expensive tech, who quite often would be doing more difficult work, which means he/she would turn fewer labor hours a week. The shop would in fact have to use a much higher labor rate and the net result ultimately would be you would get the caliper rebuilt onsite, but the end cost to your MIL, might be the same, if not higher than the bill as it's presently being quoted! By repairing the caliper, the shop wont be making as large of a profit on the parts either, yet the profit margin per hour that the shop needs must be met or the shop will fail as a business. If this all seems like doubletalk, I'm not suprised. But the bottom line is, the shop is making the correct call by replacing the calipers instead of repairing them. There are techs out there that can and do rebuild calipers on a fairly regular basis. (Me) It's actually expensive to do it that way in most cases, so it's done more out of necessity. Frankly having looked at this many times and quoting replacing calipers VS repairing them, I can actually make more money repairing them dollar wise for a single job. But since we can normally replace them in a fraction of the time for slightly less gross profit, and have all that extra time to do a different car. It becomes a wise choice that ends up costing my customers less in the long run to routinely replace instead of repair calipers.

Brake pulls can be caused by pad or rotor contamination. They can be caused by a brake hose failure which I will describe. The traditional brake hose failure is the result of the inner lining of the brake hose splitting, and then acting a bit like a check valve. It could slow a brake on apply, which would make the vehicle pull towards the side that operates normally, it could hold a brake applied which of course results in overheating, and then the pull can be consistent to one side, or even change sides at different times. Then we have the one that confuses a lot of people. Look at your brake hoses on the truck, you will see a bracket that supports the hose. This bracket wraps around the hose making a firm grip. Should this bracket rust on the inside against the hose, the rust causes the bracket to squeeze the hose ever harder, until it restricts fluid flow through the hose, in both directions. You end up with a pull that goes one way when you first hit the pedal, and then the other way when you release the pedal. You will also notice, the pull goes away after a second or two because while the fluid is restricted and slowed down, it does eventually reach the same pressure as the other side. While the hose still needs replaced, simply relieving the brackets grip on the hose will allow it to work better, and that pull will be changed right away. If pad contamination is the cause of the pull, swapping the pads AND the rotors side to side will make the pull go to the other side. Pad contamination can occur if someone greases the tie rods or ball joints, and uses too much grease, or if the joint seals are bad. The "evidence" of this kind of contamination disappears very quickly, but the brakes can simply pull until they are replaced. This could be what has happened, and they didn't see anything that would tip them off to the cause. There are more possible reasons for brake pulls, front suspension issues can easily come into play. It takes real detective work by a good technician to sort through problems like this. Just remember, "anyone can do brakes" at least that's what people always want to tell me.