Hey Fellas,

I was hoping you guys can help settle a dispute I recently had with someone concerning proper brake job with disc brakes. Say you have a car that isn't tracked, just street driving...I am from the school of thought that when you replace the pads, you're always supposed to turn the rotors. Especially if you have good ceramic pads that last between 50k and 60k miles. Am in wrong about this? (My feelings won't be hurt if I'm dead wrong here... I value the expert opinions out there!).

Thanks!

 

no, you are not wrong.

side note: nice front bumper

 

I'm sure that turning rotors is the minimum....with the price of rotors so cheap, think about new rotors. That's the way to go.

 

BUT.....consider why rotors are "so cheap" these days. Most of them are from China, and unless you're VERY careful about what you buy, those inexpensive rotors may not be a good deal.

One of the big problems today, is because "garden variety" rotors are indeed cheap, repair shops don't bother to turn rotors, they simply replace them. That means, while many shops still have a brake lathe, few of them don't have someone who still remembers how to use one properly.

After I retired from full time work, I spent 5 years working part-time working for Advance Auto parts. I drove the truck and delivered the parts to the commercial shops. Our brake rotor inventory was HUGE. The bulk of my work was delivering pads and rotors, while the brake lathes collected dust. For a shop, it's quicker to slap on a new rotor, than resurface an existing one.

 

Yep, those skills are gone, it seems.

Some years back, when I was working full time, I used a local repair shop to put new pads on my K1500. They said the rotors needing turning, so I said OK.

Wrong answer. The brakes were still juddery, so I pulled a wheel to take a look. Whoever ran the lathe had left turning marks on the disc you could feel with a finger nail, and interestingly, the disc was thinner at the periphery than in the hub area. That takes planning - or incompetence.

So, I went out and bought new rotors from Advance Auto - not their cheapies - and set to changing them. That's when I found the bolts holding the calipers on could easily be removed by a small "L" shaped Allen wrench (Loctite, Loctite, we don't need no stinkin' Loctite - or torques wrenches apparently....), and the rotors had transferred their "grooves" to the new pads....

Strike that shop off the list.

The traditional advice when putting new pads in always was not to turn the rotors, but to use sandpaper or emory cloth to remove any old pad material from the rotor surfaces, plus rough up the surface a little to help the new pads bed in. We used to do exactly the same thing for drum brakes. All of which of course takes a shop more time than grabbing a new rotor and slapping it on.

 

 

If the rotors are smooth and not grooved, there is no need to turn them. I've put new pads on old rotors dozens of times with excellent results. In fact, I've had many rotors where I've gone through 3 sets of pads and never turned the rotors. They never got grooved, and always worked great and perfectly smooth.

I always give my brakes a good exercise too. If you are never hard on the brakes, then they start to develop high spots and grooving. By being hard on the brakes every now and then you give them a fresh burnishing keeping the braking interface nice and new as it should be.

Although I always use semi-metallic pads which wear the rotors significantly less and more evenly than ceramics. I hate ceramic pads. They suck in almost every way except for creating less dust.

As with new rotors and old pads, I put a piece of sandpaper on the workbench and sand the pads down smooth before they go on the new rotors. a bench style belt sander works great for this if you have one.

 

WOULD not do this on the vette... but, on some of my old work trucks that had pretty grooved rotors I just put on new pads... the grooves just wore into the new pads and worked fine... I was too cheap to buy new rotors or have them turned...lol NOT recommending anyone else do this, it has worked great for me.

 

I do not like to have them turned. I would buy new rotors instead. As stated above, there is not that much difference in price and who knows how competent they are to do them.

That being said, I have used new pads on old rotors too. If the rotor surface is smooth and you don't have any brake pulsing from a warped rotor, then I don't see a problem with just new pads.

I also have had a work truck that the rotors were not very good and just put pads on it anyway. The pads conformed to the grooves and seem to work fine. Although this is not the right way to do it, it can be done. This year I also bought a winter beater car that I just replaced the rotors and pads since they were 165k miles and grooved so bad the outer 3/8" of the swept area was not even contacting. There was a lot of pulsing going on too. The new pads and rotors made a huge change to the way it feels and stops.

 

I've always done the same things on all my cars and trucks for 50 years, always worked fine for me, no problems.

 

There is a kit to rough up the rotor some so the new pads will seat, for instance:
http://www.summitracing.com/parts/oe...FQmnaQodM8sL5Q

 

....or you can buy a couple of sheets of emory cloth. Done that for years on many cars. Works just fine.

 

Yes and no
Back in the 80s I never turn a rotor on all my trans am and other cars I worked on.
Now later years we had an Astro van that I just change the pads on rotors looked okay. Week later pedal vibrates really bad every time I push the brakes. Change rotors all fixed.

Present brake job on rear wifes odyssey could not get the screw out that holds the rotor to axle. Just do pads. No problems. Time to do front take rotors to get turned "oh these are out of spec. you need to buy need" . Hum spec was fine at home. So instead of hunting for a shop to do the work I just buy replacements and be done with it.

At midas we used to use a dill with a 80 grit papper after turning. Some still do this to new rotors also but I have not

 

To the best of my knowledge, the purpose of turning rotors was twofold. First, to remove any trace of warping. Secondly, to provide a clean surface for the new pads to "acclimate", or "bed in" to. This is important, especially if you're changing the material of the pads, like going from ceramic to metallic, etc.


A few years back, I installed a set of Porterfield Racing, street HP pads on my Z/28. The instructions stated that the rotors not only needed to be turned, if being reused, but turned with a tool that gave a non grooved finish.

 

But you also want a non-directional surface, that's what that kit is designed for. The binders that hold the brake pad material together is all over the rotor, getting that off and a fresh non-directional finish on them give you the best bedding for the new pads. If the junk on the rotor make the new pads "grab" in spots on the rotor, you'll feel what seems like warped rotors when it really isn't in most cases.

 

 

Afer a few times that I had rotors turned, and they warped relatively soon afterward, or they were turned looking like a phonograph record, I learned my lesson.

IF the rotors were bad enough, I just purchased good new rotors.

Plasticman

 

Several technical studies report that warped rotors are an old wives tale. They found that the pulsations are due to a variation in surface finish of the rotor's contact area with the pad. By cleaning the surface with fine Emery cloth, they could "straighten" a "warped" rotor to new performance. Obviously, a badly grooved rotor cannot be saved.

 

I don't believe it is a wive's tale. Yes there may be other issues that cause pulsations such as variation in surface finish, but some are warped.

I just did my winter Buick's brakes last week. On mine the run out was so bad that spinning the rotor by hand with new pads I would have a contact mark on one section of the outboard side and on one section of the inboard side. As I spun the rotor I could find "free" spots and "drag" spots around the rotor. The run out was bad. They were warped. I replaced the rotors and had a smooth even contact.

 

Nope, they are very real. A dial indicator will tell the tale. A poorly turned rotor by an inept "machinist" using too fast a speed or too aggresive a feed (or both), or poor initial setup, and you end up with a junked rotor. This puts stress risers into the rotor surface which will warp first time they are used, and if cooled rapidly (like going through a rain puddle), will become even worse. Poorly trained machinist (or just being in a hurry) does not result in an acceptable turned rotor, and that seems to be the norm.

I don't discount that some reported "warped" rotors are really the result of hot rotors and pads glazing off pad material onto the very hot rotor surface when the vehicle is stopped quickly and let sitting. Pad materal will transfer to the rotor surface under those conditions, and will result in a pulsation. But that is a completely different condition and is easily determined and rectified.

Plasticman