Brake shudder

Perkuleez

Ok first of all, sorry for posting on this again I know its been discussed many times on this forum however I'm getting conflicting information.

So basically the issue is at freeway speeds 60-80mph and doing moderate braking, there seems to be a shudder. This is noticeable just about everytime I exit the freeway. I also notice this when doing spirited driving around the mountains. During this spirited mountain driving I notice the problem becomes progressively worse. ((again I'm doing what I would still consider moderate braking (no brake fade, when I get out I don't smell brakes)

So on to the question as I'm not sure exactly what the issue is. I've read everything from it being a warped rotor, deposites on the rotor from the pad, air bubbles in the brake fluid, abs malfunctioning, (the list goes on). So is there a definitive logical way we can go about figuring out which of those if any is the issue? Some light on this would be greatly appreciated.

Read T

Welcome first time poster!

When was the last time you changed your brake fluid? sound more like a deposit problem but it might be beneficial to swap out the fluid.

In general most modern brakes won't warp, however they can build up pad deposits on them which most mechanics will (incorrectly) refer to as "warped rotors", and either way a run on the lathe will fix it. You could try re-bedding your pads and this may help get rid of deposits. Shops around here charge about $25 a side to turn rotors. I'm not sure there is a specific list to run down to figure out which it is. I wouldn't guess it's the ABS unless a light is flashing or you're really beating on the car but I'm not a mechanic.

You could try turning the front wheels by hand and see if you can feel any binding, might work?

If it was air in the lines normally the brakes would fade some like you noted (again, another reason to change the fluid, even if it isn't causing the shudder), in my experience the air prevents the brake fluid from biasing side-to side evenly so instead of shuddering the car pulls to one side under heavy braking. Pad condition/rotor condition and tires also could effect this though.

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SouthArk370Z

I'd first try a few 60-5 mph hard braking sessions to see if it will burn off any deposits on the rotor (Read T's re-bedding). If that doesn't work, try having the rotors turned.

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victorofhavoc

you might also check to see how much of your pad you have left. it might be that they're very near done. do you hear any squealing when you step on them lightly or when in reverse?

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SouthArk370Z

I just assumed that had been done. If OP hasn't checked, doing so moves to the top of the list.

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Zauskycop

75% of the time a rotor with deposits on it is misdiagnosed as a warped rotor. When you do your hard stops to rebed brakes...go from 70 down to 20 then start going again...never ever come to a complete stop! If that doesn't stop it, then probably a warped rotor

Tracy Ramsey

victorofhavoc

Sorry to just butcher it entirely, but that was all too confident of an answer when you've never seen the car and the person doesn't have more clear symptoms

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dP3NGU1N

Just FYI. There is supposed to be a certain layer of pad material already on the surface of the rotors. This is called a transfer layer. An uneven transfer layer, as many have mentioned, can very likely be the cause of your issue since it fits most/all the symptoms.

This transfer layer is important for your brakes to function properly. Before you re-bed your brakes, a lot of track people (particularly people like myself who reuse rotors with different pads for the track) would recommend scuffing the rotors with some medium grit sand paper, if possible. I understand not everyone has the tools required to take rims on and off at a whim but it would help with your re-bedding process to make sure most of the original transfer layer is gone. Mind you, you are mostly just scuffing the surface of the rotor to give the pad a cleaner surface to transfer to. You are NOT trying to reshape your bloody rotor yourself (good luck trying to anyway with sandpaper but I just thought I'd mention it).

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sprocket2

I just picked up my 2013 Z with sport package. Love almost everything but I'm seeing the SAME THING- break shudder that is not constant, and is really bad at 80. The crazy part is the car has 5500 miles on it. My first thought was warped rotors but it seems to come and go. I read the other comments on warped rotors, rotor deposits, re-seating the pads, etc. but don't see why any of those would come and go. Anyone with good ideas on this?

SouthArk370Z

My guess is that it's because of temperature, humidity, &c.

Warped rotors will usually cause almost constant vibration at speeds much above a crawl, getting worse as speed increases. Deposits will come and go and usually cause vibration only when braking or at high speeds.

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BGTV8

Ford Australia had a problem with BA and BF model Falcon's in that when the braking system was assembled, the brake pedal has a rod into the vacuum booster that was adjusted "too long" which meant the that there was always some residual brake pressure holding the pads against the brake rotor, and this was felt by the driver as a slight "pulsing" in the steering. It also meant a very slight pulsing with light pedal pressures on the brake pedal (felt thru the pedal) which disappeared with firm or heavy brake-pedal pressure.

Ford also determined that left-foot brakers who habitually held their left foot "over" the brake pedal sometimes rested their foot on the pedal which resulted in a similar situation.

The only reason I make these observations is the the OP drives a 7AT and I am wondering whether (s)he is a left-foot braker and may be experiencing something like the above circumstances.

The cure for the former was to remove the booster unit and adjust the rod from the brake pedal to shorten it by a couple of mm. I took a peek and my car at lunchtime (mine is a 6MT but arguably should be similar to 7AT) and I do not think this is likely to be a problem, so I wonder, "if" the OP is a left-foot braker, whether making sure that the left foot is always clear of the pedal will make a difference.

This may be a complete WOFTAM and absolute mis-direction, but one never knows .....

RB

GSS138

Warped rotors, just replace them. It's not that expensive. Warped rotors are caused by a few things-bad manufacturing, getting rotors hot then driving through puddles of water, getting them really hot then parking with parking brake on.

Warped rotors progressively get worse, and they will start to give you "push back" when you apply brake pedal. Only answer is to replace them. If they are new rotors, they might be able to be turned. But honestly, don't pay someone 100 bucks to turn your f-ed up rotors just go get a decent replacement and enjoy driving the car again.

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Perkuleez

Sorry for taking a few days to get back with you guys..

I'll try to answer all questions/ideas I can here..

I bought the car as a certified pre-owned car with about 30Kish miles on it.. put about 10K miles on it since I got it..

I'm not sure if the brake fluid has ever been changed. I'm in the works of doing that soon. Gonna get some high quality stuff for it.

I went out and tried a few 60-5 mph hard braking sessions. A few of them may have been from around 75ish to 5ish. I didn't ever fully stop.. I noticed the problem appearing as it did before. I did 10 sessions, let the brakes cool for a while and then checked.. problem still persisted.. did another 15 or so, let them cool.. same thing.. so I gave up on that..

As far as checking how much pad is left I will have to put that on the list as well when I'm changing the brake fluid. Last time they were checked is when they did the oil change at the dealership when I bought the car. I have since done all the oil changes because I'm not paying them do to it lol .. just an fyi I change the oil per owners manual every 3750 miles, I use mobile 1 full synthetic oil.

I haven't ever tried the sand paper idea yet however if that is something that will assist the issue its better than paying for new rotors..

I do drive the 7AT, mainly because a decent bit of my driving is stop and go traffic and I wasn't about to deal with a manual again as the last car I had was one and that is a pain. Not to mention the 7AT in this car shifts pretty fast at least from what I can tell.. I do not left foot brake ever.

To my understanding the parking brake is a drum brake, non related to the actual disc itself thus putting it on would have no effect on warped brakes. Correct me if I'm wrong. However the point is mute as I park the car on a level surface and have no use for the parking brake, thus its never on.

I appreciate all the replys, honestly I didn't expect to get as many as I did.

PS. If I am going to go out and buy new rotors and pads, I plan to just upgrade the brakes and get a big brake kit from Brembo or some other reputable brand as I would like the track the car at some point. However a big brake kit isn't the cheapest of things and I would like to hold off on that for now.

AdamRacer

I have a similar issue when braking feeling the vibration in the steering wheel. I looked at my rotors and noticed what looks like a burnt impression of the brake pad on my front rotors. Is this the deposit you guys are talking about? Does that cause a vibration when braking? Can I burn off the deposit like mentioned?

Zauskycop

Thank you for fixing my statement but I stand by what I said. Note, my post was not necessarily telling the OP what was wrong, but giving a "general" statement about "warped" rotors and how to fix them. And my statement of 70-20 stands as going from 20 to 5 only increases your chance of stopping on them and adding more deposits. You need RPM on the wheels to clean them...and a good brake foot.

MOST original diagnosis of "warped rotor" is actually residue, or deposits, on the brake rotor. This is not according to ME, but to some guy known as Carrol Smith. It comes from coming to a stop with a hot rotor, and just letting the brake sit on the rotor under pressure unless they are REALLY hot, then pressure doesn't really matter much.

If you come to a stop with a HARD brake, try to not sit with your foot on the brake pedal, or minimize pressure on it as much as possible. This creates a "transfer" in the shape of your brake pad and leaves a deposit.

"Rebedding" **can** clean that deposit, but sometimes if it is way bad, a new rotor, or turning the rotor, is in order.

I think that the material used in stock Z brakes lends itself to leaving a lot of material behind, as I have also experienced this shudder under hard braking (autocross or occasional "lap" at a track when I haven't changed pads). It always cleans up though.

Tracy Ramsey