Rotor thickness variation is a condition that can be imagined as the two sides of the rotor not being parrallel to each other. This can be caused by a "crushing" of the rotor by the brakes. It can be caused by uneven wear. Or it simply could have developed over time from a combination of forces. This problem is normally felt in the brake pedal by it pushing back at you with a rythm consistent with the current wheel speed. Rotor run-out is often caused by debris (rust) being caught between the new rotor and the old wheel hub, or by improperlly torquing the wheels, which can bend the hub, rotor and wheel. There is always a chance that excessive heat build up from heavy braking without sufficient time for the system components to cool is playing a role as well. This by the way is the most common cause for the report that we often see where a new car keeps having to get the rotors machined. It's not the cars fault, it is how the driver is using the brakes in heavy traffic! We also have rotor delamination, or rusting if you will. This causes a combination of runout and thickness variation issues. Typically rotor thickness variation of .002" is plenty to feel when driving. Otherwise you would have to use a dial indicator, and mark the high and low points on both sides of the rotor to see it. Rotor runout's of .005 or less will normally give no real signs they are present as the calipers of today have sufficient movement built into the system to "follow" the rotor. Between .005, and about .009 you will often feel the pulsation, but quite often you will hear the brake pads "saw" on the caliper supports as they get pushed back and forth. This "saw" is the grunting sound you get on a light brake pedal application as the car moves slowly such as 15mph or less. As I alluded to in the beginning of this response, a good technician does not even need to put a dial indicator on a car where the problem is rotor thickness variation. He/she will feel that right from the drivers seat. However, the technician DOES need to use a dial indicator, and measure wheel runout, then remove the wheel and (for most cars) put the lugnuts back on and measure rotor runout, then measure the front hub runout so that this problem is repaired the first time. Sadly this is one of the times where the good technician that does the job correctly needs to be paid to do so, yet the allure of the "free" brake inspection often prevents them from getting good at it because many are rewarded for being fast and getting the work in and out and as "cheap as possible" which in some occasions turns around and bites them for the effort. For the record, don't do "free" brake inspections, but I fix them.

I read this thread when it first appeared here on 9-22-05 and didn't respond because of all the flak that my response would probably garner BUT!!! I'm gonna dood it if I dit a whippin anyway. As far as I'm concerned disc brakes are something that should never have been made. If kohokoho had had the old drum type brakes this would never have happened but if it had happened the drums could have been turned (ground down) with no adverse effects. Resurfacing the rotors is a waste of time and money because it simply won't last. The rotors get hot quicker because they are now thinner and warp all over again. I'm aware that disc brakes are supposed to stop the vehicle faster than drum brakes but I've driven many mile with drum brakes and never once had to drag my feet on the road in order to slow down. And then there's the calipers. Has anyone ever had the caliper piston get stuck in the caliper because of rust? Sometimes I've had to force the pistons out with lots of air pressure. Not a safe thing to do but it works and it beats selling someone with little money a new caliper. This didn't happen with the old type wheel cylinder. Most everything in life comes down to money so I suppose the disc set up is cheaper to manufacture than the old drum type. That is to say cheaper to manufacture but more expensive to repair. The manufacturers did the same thing when they switched to front wheel drive, cheaper to make more expensive to repair. You don't really think they did it for the consumers benefit do you. My personal vehicle is a '99 S-10 and right now my brakes are doing the same thing which means I'll replace the rotors instead of resurfacing them. I have never ever had to replace a drum on the older vehicles which is what I mean about being more expensive to maintain. Now people, it's your turn to tear this response apart but you know opinions are like a--ah--well faces most everybody has one and this one is mine. Later Skag

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.

Our Steelers didn't look too good in the second half of sunday's game. Hopefully they have brought back a few lessons that will be very necessary if they get to meet the Pats again this year in the playoffs. The Pat's look almost unbeatable. Now brakes. There are so many things that need to be examined here. Driving habits are important to the diagnosis. Heavy intown use, lot's of stop and go with little time for the brakes to cool off can lead to boiling of the fluid. This happens easier as the brake fluid absorbs water right out of the air overtime. Being a 2006 that would not be something I would expect to see, but that could be part of the puzzle. Question. When the problem happens, is one brake rotoir hotter than the other in the front? Are the front brakes both significantly hotter than the rear? I would use an infrared thermometer and actually measure brake temperatures during both a normal use situation, and then compare them to what is happening during a failure event. Could the pads show signs of whats happening? Not really. No more than what your description of the failure does. We need to seperate whether there is some type of hydraulic problem allowing air into the system, (very rare BTW without a visible leak) or if the brakes are dragging because of a mechanical problem on the car, or if they are dragging because of operator habits. Just like any other "investigator" all of these are possible until they are confidently ruled out. What other details can you tell us about the failure? This will be practice to assist the dealership in their re-creating the failure for testing. If you drove a certain distance today, how far would you have to go in order for the failure to most likely present itself? Does where you drive the car seem to have anything to do with the problem? In town, local highway, interstate? In driving in one of the previous situations, is the failure "Unlikely" to occur? (This is critical for the technician to get to experience the failure for diagnostics) Most of all DONT GUESS, whats wrong such as the way your post title starts, "brake calipers". If you go in telling them the calipers are bad, and they find a problem with them, they would replace them. But that could easily have nothing at all to do with the brake pedal problem! Stick to the symptom, what it feels like, when it occurs, and if there is something that you can think of that is likely to either get the symptom to show up, or not show up at all.