05 impala break problim

bmans05August 24, 2007

About a month ago i was rotating my tires and i striped a lug nut, found that i had to take the spindle completly off to give me room to remove the old one and instal the new one.Had to wait a week because nobody localy carried a deep 34mm socket, went to pull the new lug through the spindle and it was aparntly was a hair to big and would't seat complety. I know it was a bad dicison to leave it but with no interfearance with the spindle rotation and the wheel being held by 5 lugnuts i lefi it.I had some break chatter before replacing the lug and since i decided to replace the front breaks so i had the rotors turned and replaced the pads (38,000 on car),not much differance,took the rotors back to the garage and had them turned again and was told that were perfictly true,still have break chatter,bought new rotors,still have breake chatter a little bit.What am i missing? The vibration only accurs when breaking. Could it be a torque issue? Would appreciate some feedback. Thanks

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Check the runout of the rotors as mounted. They may be wobbling. Although machined true, if there is a speck of rust/debris under a rotor when it was remounted, it will not run true. You may have to remove the rotors and clean their mounting surfaces. If this is not the case and the rotors are wobbling, look for the cause.

    Bookmark   August 24, 2007 at 4:45PM
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Thanks for that info i'll give that a try. When i took the rotors back for the second time the mechanic ask me if i marked the orentation of the rotors before removing them, I ask if he ment if i marked them left or right, He said no he ment making sure that they went back on the exact way they came off, I said i have been doing my own break work for 20 years and mever herd of that or ever had any problims with that! That tells me that the rotors and spindle are ballanced at the factory, witch tells me that can't be true because what do you do when you have to buy new rotors, you have only a 1 in 5 chance of getting it right. Thanks i'll try the run-out and see if thats the problim.

    Bookmark   August 24, 2007 at 10:56PM
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So you have been doing your own brake work for about 20 years. Guess then you know everything there is to know about brake work and "the mechanic" is wrong???

I don't think so...

Sorry but I just had to jump on that first. Doing your own automotive repair work for any period of time is not enough exposure to gain real experience. The "mechanic" is in fact correct, rotors are indeed oriented to the hub from the factory, in fact the wheels are too. To go one step further the valve stem is actually drilled at the high spot of the rim, and new tires have a match mounting mark that identifies the low spot of the tire, this allows for a "a more true circle" of the wheel/tire assembly.

No matter how precise we attempt to machine parts, there will always be some variance. The wheel hub, that's the hub bearing surface that the wheel studs stick through is not actually totally flat. It will have a slight wobble, and that's not taking into account any surface corrosion, or use damage that occurs with age. Shops today generally have two ways to machine rotors. One is off the car as you have had done, and the other is on the car which allows the machining of the rotor to take into account any wheel hub runout.

Depending on the way the front hub bearing mounts to the knuckle, you may not have any holes in the face of the hub. (The hub has no holes when rearward bolts go through knuckle and thread into the hub) Or you could have three holes in the face for access to the hub bolts, one larger hole, and two smaller ones. (Front side bolts through hub bearing, and thread into knuckle) That latter style rotor/hub is easy to re-align, simply line up the large hole in the hub with the large holes rust shadow on the back side of the rotor. This does allow for re-indexing the rotor exactly as it came from the factory.

When new rotors are installed, a professional technician knows to bolt the rotors to the hub, and then take a runout measurement. If runout is out of spec, the rotor gets marked at the high spot, and then turned two wheel studs, tightened down and marked again. If the runout high spot is in the same place on the rotor, then the rotor has the runout. If the runout remained with the original wheel stud, then the hub has the runout. Either way the fix could be to machine the rotors on the car.

Here in Pa. It's common to have corrosion to the point that sanding alone in inefficient to remove all of the surface corrosion to allow the rotor to sit flush against the hub. This is especially true if the rotor once removed gets it's mounting surface properlly cleaned so that it will sit correctly on the lathe. Some of this rust is much easier to remove if it is chipped off, such as by tapping it with a hammer, and occasionally with a chisel, and then re-sanding.

Now going back to the start of this response. Hardly a week goes by that I don't hear someone claim that some Back Yard Bob has been doing brakes since (insert your cliche') and the "mechanics" don't have any idea what they are doing. A DIY person doing their own brakes for twenty years does not equal even six months time as an apprentice mechanic. The fact that you have never heard of something like this run out problem until now is actually a measure of the inexperience that you have. If you attempted to become a professional mechanic, this would jump up and bite you in your first week! There are about fifty other suprises just lurking that you may, but more likely may not have run into yet, just with brake work. The assertion that pulling the wheels off of a car, pulling the calipers, and slamming a set of pads in is doing front brake work "just like the pro's do" is wrong. There are a lot of steps that a pro takes, that DIY's have no idea about.

I am reminded of a debate I saw online a couple years back. One poster was cutting down mechanics, because some young fellow started to hook the battery cables onto a car backwards. The most common cause of this BTW is trying to use a "one size fits most" style battery, when an original battery is what is known as a Right Hand offset terminal. The posters contention, and that of several other responders was that anyone doing that had to be an idiot, and that they all have never done that. They were proud of their extensive automotive knowledge...

Their voices fell silent when I argued that a limited number of chances to perform this battery service is not proof that they are immune to making this mistake. In fact, I argued given enough chances, each of them WOULD make this exact mistake eventually. Which if you think about it, the more times you install a battery, the more experience you would have so one might think that experience would shield you from this error. In fact, that's not the case. The only thing that shields you is attentiveness on each attempt, and then the one time you allow yourself to be distracted.......

    Bookmark   August 25, 2007 at 2:51PM
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First of all i never said i was a professional mechanic or know as much as the pro that i had turn the rotors. I have heard of run out before, I had never heard of having to orentate the rotors to the exact way they came off!I guess i'm the luckest person this side of the mississippi to never had a problim with match marking before in all those 20 years of unprofessional break work. Thanks for the information.

    Bookmark   August 26, 2007 at 4:45PM
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Probably some minor runout but you may also want to check your caliper and the flexible brake line to the caliper. These flex lines are prone to interior lining seperation which can cause all types of strange braking problems from severe pull to chattering.

    Bookmark   August 26, 2007 at 9:36PM
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Lets be just a little more accurate. It's not that you never had a problem, you simply didn't have any problems big enough to make you aware something was wrong.

dnt1. In a way, that's sound advice to check those components. But exactly how would you explain to someone to check them? Exactly what would they see or not see depending on if there was a problem or not? Lets expand on your response, and take it to a complete thought.

This is where hands on experience trumps almost anything else. It can be years before someone runs into their first brake hose that holds the brakes applied, or causes a slow application. In either of those events, what are the symptoms that the driver actually feels? Smells?

A technician, like myself when driving a car and feeling a brake pulsation can tell if that pulsation is from runout, or if it's from parrallelism right from the front seat. What do you think the difference is in the way the car feels that are the clues? BTW many times the pulsation can be identified to an exact wheel, be it on the left or right, or the front or rear of the car.

    Bookmark   August 27, 2007 at 8:47AM
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