auggie_ss_phx

a co-worker has a 06 2.4 ss and just had his front rotors and pads done. he says they resurface rotors too.now when he is going around 40+mph and starts to apply the brakes the steering wheel shakes. what could it be?
thanks for the help

outtamymind

did he torque the wheel lug nuts properly. and is he sure they resurfaced the rotors.

BlackARCA06

iTrader: (5)

Mine does the same thing! I have the 2.2 though if it makes a difference. But when I apply brakes it shakes then Ill let off and apply again and it won't do it!

auggie_ss_phx

the rotors look like they were resurfaced,and yea they are torque down

SSfamilywagon

iTrader: (2)

Rotors are still warped. Cutting doesn't get rid of warping, only masks it. His prob have to much run out. It'll always come back. Only way to get rid of it is replace them.

auggie_ss_phx

thanks yea he got some new ones and its fine now

tru2nrtt777

iTrader: (1)

Also if the cutting speed was too fast when they were turned they could have cut grooves in his rotors too.

Maven

iTrader: (1)

Um, what?

outtamymind

maven would you care to correct that or shall i

tru2nrtt777

iTrader: (1)

Just ignore it like I did.

outtamymind

its too funny to ignore though

tru2nrtt777

iTrader: (1)

I perfer the term sad. Either he made it up because it makes sence in his mind or he heard it from someone.

outtamymind

well i will give him the benefit of the doubt and assume he heard it from someone that didn't really know what they were doing or had the wrong info to begin with. but still i will correct him and you and maven chime in if i miss anything.

cutting/turning rotors resurfaces the rotor to a flat even surface through the entire rotor, from the inner most point to the outter most point.

tru2nrtt777

iTrader: (1)

You are generally correct but technically he is slightly correct too. When you turn a rotor or drum you are flattening the clamping surfaces but even within spec the rotor itself is still warped but the clamping surface is not. I am not sure of an easy way of explaining it. Think of the space between the clamping disks where the blades/webbing are, that part will still be warped but the outsides where the pads touch the rotor will be correct...

It may be easier to explain using a drum brake assembly since you only have one clamping surface, when it warps the drum gets a slight egg shape. When you turn it, the inside part of the drum is rounding out but the outside is still that egg shape...

The only real part that is truely wrong is that he is using people's perception of warped brakes being fixed to denounce the effects turning would actually have on a warped brake rotor/drum. Turned rotors are not unsafe nor are they more prone to warping again than a new rotor.

outtamymind

thanks for the added info there. also when you turn your rotors you should do a brake service as deglazing your pads and lubricating your slider pins as well.

SSfamilywagon

iTrader: (2)

I was prob just being to vague in my post. I know exactly what cutting rotors does. It's not that I am miss informed in my statement, just giving knowledge from personal experiance with working along side lots of master techs.

I my experiance from servicing cars, we saw alot of come backs from turned/machined rotors for rewarping very fast again. Within a couple thousand miles actually. Mostley due to large runout.

I'm never said they were unsafe, just more prone to warping faster cause obviouslly they are thinner now from being cut

Maven

iTrader: (1)

If you see lots of comebacks on brake jobs I would question whether or not the guys you work along side are truly master techs or if they just have a piece of paper that says they are........

Here is the issue. Brake pulsation is caused by thickness variation. Sounds self explanatory but to be sure thickness variation is a difference in how thick a rotor is in one spot compared to another, if your rotor 26mm thick at the 12oclock position but is 26.045mm thick at the 3 oclock positionm and 26mm at 6oclock and 26.045mm at 9 oclock then it has excessive thickness variation. A quick measurement, even in two spots wouldnt have found it either(and its pretty bad at almost double the max allowable).....you need to measure at least FOUR spots to determine whether or not a rotor is withing thickness spec

SO since you measured in two spots and found TV to be okay(its not) you decide its time to check LRO to determine if car is okay to give to customer as done 100%

You also cant just measure for LRO (lateral runout, or the side to side movement of rotor as viewed from end of vehicle) and decide if the rotor is ok. Lets use the same rotor from above and take an LRO measurement(which we wouldnt even do since its already out of spec on TV) but here we go. You center your measuring equiptment at 12oclock and start to spin, its fine but goes out to +.022mm at 3, back to perfect at 6 and back to +.022mm at 9 oclock, so its got a total of .022mm lateral runout(side to side wobb,e) Okay, so its got some LRO, but its far from excessive at .022, specification is .060, so youre good to go.

(this example shows how excessive thickness variation can be overlooked, even when measuring for it, but it should also show why so many people think the pulsation is caused by lateral runout.....and that is TV looks like LRO if you dont do all the measurements)

You bolt everything back on and within 10k miles this vehicle will be back in your bay with a brake pulsation, and you and your master techs will check your history, see all your documentation, and determine the rotor warped because there is no other possible cause.

Happens all the time(the warping diagnosis, not the actul work I mentioned, because even though the work done in my example was less than what was needed and completely missed the diagnosis of the problem its actually more than you will find gets done on a vast majority of brake services.

SO lets go back to square one.

Thickness variation causes pulsation, in all but the very tiniest percentage of cases you will NEVER find a warped rotor causing a pulsation, and thats assumng you actually find a rotor that is truly just warped. Uneven buildup of road debris, corrosion, uneven brake pad transfer due to excessive heat and other factors, improper maching, these things cause thickness variation.

Excessive lateral runout is caused by poor machining, dirty assembly, corrosion, worn wheel bearings,improper assembly, etc, will eventually lead to a pulsation because the uneven heating of the wobbly rotor will get us our uneven buildup of material on the rotor.

So weve seen how excessive TV is the culprit, weve seen how LRO causes TV, weve seen how TV can be misdiagnosed as LRO and weve seen why some people think LRO keeps coming back if you cut rotors.

How do you avoid this?

If you do youre own work:,ask whomever cut your rotors to measure the thickness in several locations for you, if you use new rotors make sure they are properly cleaned and dont have any burrs or nicks in the braking surface, make sure all the mounting surfaces and all fasteners are cleaned and properly torqued to spec. remvoe all rust, dirt, etc, make sure the hub and rotor are shiny metal or as close as possible,(Remember those $150 service manuals and $30 torque wrench you thought were expensive and didnt buy them when i suggested?????......how much is another set of front rotors?) VERY LIGHTLY coat the mounting part of the rotor and the hub face(but not the lug studs) with a coating of very high quality brake lube(Ceramlub or Permatex Ceramic purple brake lube.....you should have this already anyway, Permatex stuff is available pretty much everywhere) or better yet once of those teflon lube sprays that dries to a film, these things wont fling off and they will keep corrosion from forming under the rotor(the spray is better as youre less likely to use too much.)

If you get it done for you: well......just ask if they can provide you with thickness variation and lateral runout numbers from before and after the service. Their willingness to do this is going to be an excellent indication of the caliber of the shop/tech working on your car. If they wont/cant/give you weird looks when you ask then maybe try somewhere else. There is a Catch22 with this though......you cant expect to be able to get this info on the $59 brake specials, use some sense here, while you are truly asking them to just do their job, you do need to be willing to pay for the service you desire, wuth that said a "full price/full service" brake job shouldnt cost anymore than about $125 in labor in most areas.



Sorry that was so long, but hope it clears things up for people as to what is actually happening, let me know if anything is unclear.

SSfamilywagon

iTrader: (2)

Your explanation is very clear and easy to understand. You are correct in your explanation. I totally understand TV and LRO for sure. Alot of it is too that techs don't clean things properly because they're always in a rush just trying to make more hours. Basically all I was trying to say was that if measurments are out to far, usually cutting won't help and replacment is needed.

I'm not doubting their knowledge of cars as being techs, but who's to say if they were to lazy to do all those measurements themselves. Sadly there were guys there that knew alot but just didn't have the drive anymore for it. Alot of those guys are just there to make money and don't care about alot of things as well.

When I was working as a tech, I personally would always just replace rotors under warrenty to keep the customer happy and not comeback. Saved more time in the end.