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New rotors?

blkmgkblkmgk Member Posts: 54
if you need new rotors before u go to the repair shop?

Comments

  • bretfrazbretfraz Member Posts: 2,021
    There are ways to determine how out-of-spec your rotors are. One way is to use a micrometer and measure their thickness in several spots. Another way is to use a runout gauge to determine how badly warped the rotors are.

    On most rotors the minimum safe thickness is cast into the rotor itself. Measure the rotor, subtract the amount of material that will be removed by turning them, and you have a number that will tell you whether you should replace them or just have them turned.

    Of course, if the rotor is cracked or shows any kind of damage, they should be replaced. For most cars new rotors are cheap so most folks just replace them and don't worry about it.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    I may be a bit more liberal than you, in that I don't feel the rotor needs to be turned or discarded for "any bit of damage". A few light grooves I don't think appreciably hurts braking performance...but I do mean "light" grooves.
  • namfflownamfflow Member Posts: 202
    Boy Shiftwrong, I'm glad you don't work on my vehicles. Rotors HAVE to be turned to remove the "insignificant" damage or else you are gonna have brakes that chatter all over the place.

    Too bad that most new rotors (OEM) are such junk that they almost always have to be replaced. Either because of warpage or the pads go right through them.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Hasn't been my experience, namfflow. With light scoring, I have inserted new pads and had no problems whatsoever, and I've done this on any number of vehicles. What happens is that the pads bed into the light grooves after a short time....in fact, if you think about it, with grooves you actually get a slight improvement in surface area.

    I think rotor turning is sometimes wasteful for the consumer but a nice little moneymaker for shops.

    Of course, I would not do this with any rotor that is heavily scored or warped. But on a car that has been braking smoothly and only needs new pads, I wouldn't turn light scoring, no.
  • isellhondasisellhondas Issaquah WashingtonMember Posts: 20,350
    If a rotor isn't warped or scored and is within specs, why bother machining it?

    Every time a layer of metal is taken off that rotor or drum can't deal with heat as well.
  • gslevegsleve Member Posts: 183
    I think it might be appropriate to use emery cloth or sand paper to take of the glazing existent on the rotor the effect of glazing on a rotor is similar to a tire that is hydroplaning the pads never really grip the rotor that well there is always a light barrier that could impede breaking efficency
  • zueslewiszueslewis Member Posts: 2,353
    have relaxed on always machining rotors. If there aren't any major grooves, they spec out above the spec and there's no warpage (vibration), just clean them up so they don't scream when the new pads hit them.
  • oldharryoldharry Member Posts: 413
    has been recommended by Ford for several years. They say to replace if sanding doesn't suffice. I like to hit them with fine abrasive on the DA (random orbital) sander. There is a bit of material transfer between the discs and the pads during use, and I don't like old pad material contaminating new pads. I scrub with a scotch-brite (tm) and detergent and water after sanding.

    The cleaner and smoother the surface, the less likely you will have undesirable noise.

    Harry
  • alcanalcan Member Posts: 2,550
    At least one carmaker specifies in their factory manuals NOT to resurface rotors when replacing pads unless there's a pedal pulsation concern or grooving more than .060" deep. The correct non-directional surface finish is critical to brake performance, noise, and pad life.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    There you go, thanks.
  • mrl11777mrl11777 Member Posts: 154
    I have 2 Ford Taurus', and the rotors definitely warp after a while. I would rather replace the rotors with higher quality ones than OEM, but who makes 'em?
  • mastermechanicmastermechanic Member Posts: 31
    image


    "I may be a bit more liberal than you, in that I don't feel the rotor needs to be turned or discarded for "any bit of damage". A few light grooves I don't think appreciably hurts braking performance...but I do mean 'light' grooves. "
    However, the pads will form to the configuration of the rotors. The key thing to look for is straightness of the rotor. A warped rotor will indeed provide premature wear of the pads.


    "Hasn't been my experience, namfflow. With light scoring, I have inserted new pads and had no problems whatsoever, and I've done this on any number of vehicles. {lucky thus far} What happens is that the pads bed into the light grooves after a short time....in fact, if you think about it, with grooves you actually get a slight improvement in surface area.

    I think rotor turning is sometimes wasteful for the consumer but a nice little moneymaker for shops. "

    For five bucks a rotor, it is worth it.


    "I think it might be appropriate to use emery cloth or sand paper to take of the glazing existent on the rotor the effect of glazing on a rotor is similar to a tire that is hydroplaning the pads never really grip the rotor that well there is always a light barrier that could impede breaking efficency "

    Sand the pads to a roughness turn the rotors to a straightness to provide a uniform contact and avoid future problems.

  • kevinc5kevinc5 Member Posts: 204
    I brought my 99 Passat V6 Tip in for 50,000 mile service. Caar has been bulletproof but I suspected I'd need front pads. Was told by the service writer that the rear pads usually wear out before the front pads...and that "customarily..90% of the time..." they need to replace rotors. "They wear with the pads and usually can't be resurfaced.."
    Routinely replacing rotors with pads??? That's a new one on me...am I being scammed??
    Does anyone have the Passat rotor specs??
  • gslevegsleve Member Posts: 183
    I've recently experienced that, because cars are mostly disc brakes all around and the brunt of the braking has always been borne out by the front pads usually.

    However there has no been a paradigm shift, with regards to wear in that the rear brake pads can wear out quicker or just as fast as the front reason being that the rear brake pads material is organic and susceptible to faster wear rates in part due to the softer compound whereas the front brakes are now semi-metallic or ceramic or kevlar or carbon materials, yet in most cases just using sandpaper or emery cloth to take out the glazing is sufficent and not more attention needs to be given barring of course you didn't deeply score them
  • q45manq45man Member Posts: 416
    Most vehicles have a rotor run out spec [0.028" or so] most drivers are so isolated [ill connected] with their car that they don't feel [don't recognize] the vibration when braking as it blends with the out of balance tire vibrations.
    Long before the rotors are worn out they are out of spec [runout] thus the need for periodic refinishing [trueing] of surfaces.
    The major problem occurs when people buy used as they have no new reference.
    Typically the rotor wear spec is 1 mm per side to replacement and the pads have a 3-4 mm to midpoint thickness.
    Most rotors on even very heavy luxury cars should last at least 40,000 miles before replacement some can double this life, not true with SUV.
  • alcanalcan Member Posts: 2,550
    I think you just did the same thing I've done before when mixing metric and Imperial measurements. General specs usually call for .003" runout, .0005" parallelism max. Rotor runout of .028" is a bit excessive. :o)
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Ain't nobody gonna turn a rotor for $5 where I live. First, you have to take it off at $85 an hour shop rates, and then do that four times R&R.

    I can live with a few grooves at those prices.
  • q45manq45man Member Posts: 416
    Misplaced decimal, anyway after you correctly true the rotor on lathe and check at 4 points around circumference, then you have the problem of indexing the rotor on the hub for minimal error.

    This takes 15 minutes per rotor additional.

    We charge $40 per rotor for trueing plus another $25 for this precision alignment on Q45, after much work we can usually get below 0.0028" installed with lugs tightened to torque against rotor.

    Less than 1 in 500 owners are willing to pay for a perfect brake job they perfer to save $80-$150 and put up with the vibrations [and rear rotor skipping] when stopping from 70 mph.

    A perfect spec rotor can be way out when mounted to a dirty warped hub [which must be held to 0.001" or better].

    http://www.brakealign.com/

    For brake runout correction plates

    http://www.hunter.com/pub/product/lathe/3947T/3947t-10.htm
  • jgmilbergjgmilberg Member Posts: 872
    What about those shops that have on car rotor turning. Are they good bad or ugly? Seems to me it would save the time or removal, and a bearing repack. Never had it done that way, I do my brakes myself.
  • silvercoupesilvercoupe Member Posts: 326
    I had to have this done on my 91 Accord to eliminate the pedal pulsation. $75 for 2 wheels at the local Midas shop. $100 at local Honda shop.

    I might add that this was never a problem until a local independent shop turned the rotors off the car and used Bendix pads. I now use OEM pads and don't bother turning the rotors unless the pulsation has returned.
  • mastermechanicmastermechanic Member Posts: 31
    image

    That's odd! I've used ol Bendix on my stroller when I was six months old. I never had any problems with bendix. I use them today.

    I must mention that if you use the same pads, use a piece of sand paper on a wooden block to rough em up a bit and to get them flat. After a rotor turn, you need to (excuse the pun) re-brake em in.
  • q45manq45man Member Posts: 416
    Is used to mistrue rotors to compensate for errors in hub. This will make rotor effectively true to the car as properly done off car turning doesn't compensate for bad bearings or hubs.
    The proper way is to use hub compensation plates [between hubs and rotors] [or replace out of spec hubs] and index rotors to better than factory runout specs.
    Some cars are very sensitive to runout errors some are not. Any [steering wheel] vibration when brakes are applied at 60-70 mph indicates rotor runout problems!
  • oldharryoldharry Member Posts: 413
    Using a cup wire brush on your power drill to clean the hub and both sides of the rotor helps a lot. Be sure to get a brush deep enough to do all around the lug studs. With Aluminum wheels, the back of the wheel should be cleaned too. Corrosion there can interfere with proper tightening of the lugs and cause wheels to loosen as you drive. If you are doing your own brakes, and not turning the rotors, mark the rotor and a lug so that if you had no pulsation before, you can put the rotor back in the same relationship to the hub.

    Harry
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaMember Posts: 64,482
    Master---could you please not place logos in your posts in the future?

    thank you,

    Mr. Shiftright
    Host
  • jvirginiajvirginia Member Posts: 65
    What a major rip-off that is. My local Twin-B auto store charges $5.00 to turn and true rotors or drums. Quite honestly, nobody would pay much more than that considering a new replacement rotor can be purchased from any one of many local auto stores (Advance Auto, AutoZone, Pep-Boys, Car Quest, Twin-B, etc..) for under $20 for most cars these days. And in the spring, many auto stores run specials when the price drops to $14.95 per rotor. With replacement prices so affordable, it won't be much longer before rotor servicing disappears.
  • silvercoupesilvercoupe Member Posts: 326
    Go back and reread my post. That was the cost to turn 2 rotors on the car!!! Not many shops do this. I know what it costs to have rotors turned when carried in to the brake shop and turned on their lathe.

    I also know what new rotors for this car cost. I just have not figured out how to remove the old ones. They are bolted on with 4 bolts and also appear to be pressed on the hub.

    I am open to suggestions for the next brake job.
  • jvirginiajvirginia Member Posts: 65
    I had forgotten that Honda was using those confounded brake designs in the early 90's. Most Honda dealership service centers have on-car lathes just for those rotor types. I'm not aware of any shortcuts but maybe someone else out there is. Sorry about any confusion.
  • q45manq45man Member Posts: 416
    Sure you can by CHEAP rotors and they may be the same overall thickness. Try weighting them vs OEM and measure the metal edge vs vent area thickness. You will be surprised at how much less metal and how much more air you can buy.
    90% of Cheap rotors don't meet OEM specs for runout out of the box, plus what metal there is is usually less dense [poorer quality than OEM].
  • jvirginiajvirginia Member Posts: 65
    I have only ever encountered one isolated problem with replacement rotors, either OEM type or the 'cheap' type as you called them. The occasions when I have found it necessary to address rotor replacement have been linked to either damage (grooves) caused by jammed/stuck caliper slide pins or normal wear below min acceptable thickness well after 100K miles. I did have one occasion where the metal in a replacement rotor was rusting and rotting away on the wear surface area after only 5000 miles. I returned it to the shop where I purchased it and they agreed it was a casting problem and replaced it at no charge. But, maybe I've just been fortunate in avoiding the poorer quality replacements.
This discussion has been closed.