Auto-techs... when to replace front rotors?

[Cobra4B]

I've serviced disk brake systems about 1000x on my Corvettes, but I've never had to replace a rotor due to wear. With track use they always crack long before wearing out.

My truck is just over 76,000 miles now and the pads are getting close to needing replacement. I rotate the tires every 10k and check. At 70k they were still ok, but the truck is starting to require more pedal effort to stop the truck which leads me to believe the pads are getting near the backing plates.

What do I look for to determine if it needs rotors too? I'd rather not replace the rotors if not needed because it requires me to remove the spindle, then seperate the hub to get them off. (On the Corvette you just remove the caliper/caliper bracket) and just pull them off.

Thanks for any advice

 

[moserjj]

Any brake shop or most auto parts stores should be able to measure them for you to see if they can be turned. If they are too thin, they'll need to be placed. For the cost of new rotors these days, I generally don't bother with turning them and usually just replace them. If you have a micrometer, you can measure them yourself and ask the parts store if they are within spec.

If the pedal "moves" more than you expect, it's probably because the rear brakes need adjustment. Worn down front pads won't have any effect on pedal travel.

 

[moserjj]

Also, is it for the Canyon you are referring to? If so, is that 2wd or 4wd? You shouldn't have to remove any spindles, bearings maybe but then you should disassemble and repack those (with new seals) at every brake service anyway.

 

[APEowner]

On most of today's cars I change rotors when I change the pads. On trucks my official recommendation is that you turn them when you replace the pads and replace them when they won't be in spec after they're turned. Unofficially, on my own trucks I've been known to just stick fresh pads on against unturned rotors if they look good.

I've never seen anything in writing to say that this is always the case but every rotor I've ever seen has a bevel on the edge that tapers to the minimum thickness. If the bevel is gone then the rotor is worn/turned to it's limit.

 

[ishiboo]

My truck, purchased new, has 82,000 miles and both the rotors and pads have lots of life left. Plus I haul *** and tow big trailers with it

Guess it depends a lot on the application.

 

[FLACOMAN]

Most rotors have a minimum thickness number in the casting somewhere, a micrometer is your friend

 

[dankicksass]

If you're thinking about rotors, it's time for rotors. That's my policy. Check them for thickness and runout/warpage if you have the tools, but if you don't it's probably best to go on the safe side and replace them. GM's stock rotors are junk anyway. Code P20 will get you 20% off online at Advanceautoparts.com if you shop there.

 

[scott37300]

I usually just replace them, they are so cheap now a days. It costs me 15-20 bucks a peice to have them turned and 25-40 bucks new for most vehicles. Usually it's only a savings of 20 bucks for the pair which isn't really worth it to me to tear everything apart and then run around town to drop them off and then come back later to pick them up.

Most of the rotors I have seen have the minimum thickness ingraved in the outer edge. If you want to get them turned instead of replace then you can measure and see if there is enough material left to turn them.

I also picked up one of these, http://www.tooltopia.com/central-tools-central-lighting-6450.aspx on ebay. I wasn't looking for one but ran across one that was like new and sold for dirt cheap so I bought it. It's pretty nice to see if the rotors are warped.

 

[sberry]

I routinely toss pads on about as long as I can, even change them out one at a time in some cases. I live in a dirt hole, brake service and inspection is as routine as oil change and usually goes right along with it, never look at the odometer for that, only at the brakes themselves and my usual concern is with stuck calipers and leaking wheel cyl seals or drum brakes that come out of adjustment.

 

[rwhite692]

I usually just replace them, they are so cheap now a days. It costs me 15-20 bucks a peice to have them turned and 25-40 bucks new for most vehicles. Usually it's only a savings of 20 bucks for the pair which isn't really worth it to me to tear everything apart and then run around town to drop them off and then come back later to pick them up.

Same here.

I also order everything I need for my brake jobs and other car maintenance projects during the week from rockauto.com, and then when Saturday AM comes around I can tear right into it, as opposed to having to spend the bulk of a Saturday morning driving around trying to get what I need locally (which are almost never on the shelf).

 

[Cobra4B]

The point isn't saving money... the point is that swapping pads is much less involved than taking the front suspension apart to change the rotor on this truck. It's a 2WD and the spindle has to come off to get the hub off to get the rotor off.

It's my DD and in my experience anything that has never been apart before won't come apart easily and it'll probably take the weekend to find/fish some broken part.

AFAIK the wheel hub/bearing assembly is similar to my Corvette in that it's not a servicable item... when it goes bad you have to replace, it's a sealed unit.

The rotors are in find condition..... there is no pad shudder, it's simply taking more force to stop the truck than normal. My old Toyota beater truck did the same thing as the pads got worn out.

 

[Jack Olsen]

How many track days do you get out of front rotors on the Corvette?

 

[Busted_Knuckles]

I put rotors on my 05 Yukon XL (suburban) yesterday, with 73k on the clock. The rust had totally screwed them up, and the pad tips where "rusted" to the caliper bracket (not wanting to move or slide), and one side of the pad was gone in the metal, but the wear indicator was still untouched.

As a side note I bought Bendix ceramic oe replacement pads, Ive only driven on them for a day, they are not broke in, but I really like the way its stops, much better than the Centric pads I used on my last brake job, which where also ceramic.

 

[JamieK]

Wow, I just looked up the procedure to replace rotors and it is a bit inolved. But it probably just looks worse than it is. (Unless you have a rusty truck)Nothing but turning some bolts. And no bearing adjustments!

http://www.355nation.net/forum/how-...-how-front-hub-wheel-bearing-replacement.html

 

[Cobra4B]

How many track days do you get out of front rotors on the Corvette?

It depends on pads and car weight. In my old Z06 which was full weight (about 3350 with me in it) using Wilwood H pads (very hard on rotors) I'd crack a front rotor every weekend. Good thing is that they're $25-$35 each at NAPA so you just carry spares.

On my latest car it's only 3130 with me in it (3118 min comp weight for NASA TTA in a C5 Z06) and I'm running DBA 2-piece front rotors with Carbotech XP12s up front and XP10s out back. I've run 2 weekends with that stetup. First weekend was just a normal HPDE format to shakedown the car so 4 20-25 min sessions a day. Last time out was with NASA @ VIR so I did testing on Friday (4 30-35 min sessions) then Timetrials (4 15 min sessions per day) Saturday/Sunday. My rotors are pretty heat checked but no cracks... they look fine. I did replace the front brake pads after the Friday testing last time out (so I got 3 trackdays out of them). I'm still running on the same set of rears and the fronts looked fine when I nut/bolted the car last week.

Next track event will be the first weekend in December @ Road Atlanta.

Wow, I just looked up the procedure to replace rotors and it is a bit inolved. But it probably just looks worse than it is. (Unless you have a rusty truck)Nothing but turning some bolts. And no bearing adjustments!

http://www.355nation.net/forum/how-...-how-front-hub-wheel-bearing-replacement.html

Yeah I was wrong you don't have to pull the spindle/knuckle but you have to get the hub assembly out to get the rotor off and there seems to be a high instance of damaging the ABS sensor or sensor wire.

I'm going to pull a wheel this weekend and see if I can find a minimum rotor thickness marking and re-check the pads.

EDIT - That link is WAY better than what's on coloradofans.com. That is really no harder than changing hubs on a Corvette.... not sure why those guys were making it out to be so hard. Just beat it with a rubber mallet and use a gear puller in the right spots to get old fused hubs off. I'm going to check min rotor thickness this weekend and see if I need to tackle the rotors.

 

[Falcon67]

Having worked in the parts business at one time, I would say the general public's idea of when to replace front rotors is well after the squealing stops, sometime after front pad friction material is gone and shortly after the cooling slots in the rotors become visible from the side.


I used to beat the **** out of my old T/A. It never cracked a rotor, but they sure got warped. I would just cut them flat until they turned below spec, then replaced the rotor. The thickness spec leaves a good margin for safety from what I've seen.

 

[Busted_Knuckles]

Having worked in the parts business at one time, I would say the general public's idea of when to replace front rotors is well after the squealing stops, sometime after front pad friction material is gone and shortly after the cooling slots in the rotors become visible from the side.


I used to beat the **** out of my old T/A. It never cracked a rotor, but they sure got warped. I would just cut them flat until they turned below spec, then replaced the rotor. The thickness spec leaves a good margin for safety from what I've seen.

I was at a tire company sale this summer, I brought home a Ammco brake lathe, because I got tired of my Napa telling me my rotors where under spec and I needed new... Im thinking NOT (like rotors coming off cars and trucks that are well under 100k miles). Funny thing, the guy who owns the Napa store was the guy I had to bid against to get the lathe. When the bidding was done, I asked him, "did yours take a dump ?", hes says "no, Ive got three, thought Id buy it just to have !" Im thinking, WTF !!!???

 

[e-tek]

On most of today's cars I change rotors when I change the pads. On trucks my official recommendation is that you turn them when you replace the pads and replace them when they won't be in spec after they're turned. Unofficially, on my own trucks I've been known to just stick fresh pads on against unturned rotors if they look good.

I've never seen anything in writing to say that this is always the case but every rotor I've ever seen has a bevel on the edge that tapers to the minimum thickness. If the bevel is gone then the rotor is worn/turned to it's limit.

Pads are cheap and easy to replace - why would you change rotors out with them? If they're warped I'll have them turned, but otherwise rarely. Even if they are scored, I'd sooner change pads twice to even them out.

Having worked in the parts business at one time, I would say the general public's idea of when to replace front rotors is well after the squealing stops, sometime after front pad friction material is gone and shortly after the cooling slots in the rotors become visible from the side.

I must be "the general public" - but it works!!

I used to beat the **** out of my old T/A. It never cracked a rotor, but they sure got warped. I would just cut them flat until they turned below spec, then replaced the rotor. The thickness spec leaves a good margin for safety from what I've seen.

EXACTLY. You just gave reasoning for being in the "general public" camp!

 

[6768rogues]

I usually put on good pads and lower cost rotors on my daily drivers. Then the pads and rotors are both shot at the same time.

 

[oldgoat]

In the past several year it seems like there is no material for turning a rotor so you either put new pads on and go or replace them. Part of the reason I don't like RWD vehicles when replacing fron rotors. Don't understand why they can't make them a separate part like the do on FWD vehicles.

 

[dougmac]

I generally don't replace the rotors provided .... they are not grooved, I do not have pulsation when braking and I have measured them to confirm that they are not worn beyond the minimum thickness.

Also ... the minimum specification printed on the rotor is often the minimum allowed in service. The "turn to" and "reuse" guidelines are usually found in the service manual. Along with runout and thickness variation specifications.

Doug

 

[PAToyota]

When they look like this...

Always thought that those pictures were fake. That they turned down a rotor on a lathe as a joke to show people. Then I actually saw it on a neighbor's car. She did say that the car had been making "funny noises for a few months" when I questioned her about it...

 

[Busted_Knuckles]

When they look like this...

Always thought that those pictures were fake. That they turned down a rotor on a lathe as a joke to show people. Then I actually saw it on a neighbor's car. She did say that the car had been making "funny noises for a few months" when I questioned her about it...

I bought a Cj5, that had a stuck caliper, and one rotor was a little more farther gone than your pic. What was interesting, other than the noise, it stopped straight !

 

[sberry]

Most of the time they finally get those looked at when it doesn't wanna stop cause it blew the piston out of the caliper. Seems everyone that buys a used car figures its new??? They drive it for year before looking at it.
I had someone a while back tell me,, I got a new car, you did? I look out there and its a 10 yr old Lumina, ha Another, bud was telling me about the loss of his Jimmy, its a 35K truck,, I said, no, its 1 yrs old, worth about 4 or 5 max considering the condition and if thats all it cost to get rid of her he should feel lucky.

 

[IDASHO]

My 3/4 ton Ford diesel has more than 250k on the factory installed rotors.

My SHO Taurus, slightly different story. It eats front rotors for breakfast, lunch, and dinner.

 

[haggis]

Brake discs are made of cast iron, they do not warp. The pulsation you feel when braking is the effect of uneven pad deposits on the surface of the disc.

Whenever I have gotten a brake pulsation I have installed some Hawk Blue race pads (very aggressive) and driven around the block a few times to scrub off the deposits.

If your discs have heavy scoring and you can feel a significant lip on the edge of the disc, they should be replaced.

 

[Cobra4B]

In the past several year it seems like there is no material for turning a rotor so you either put new pads on and go or replace them. Part of the reason I don't like RWD vehicles when replacing fron rotors. Don't understand why they can't make them a separate part like the do on FWD vehicles.

Huh? My Corvette's rotors just pull off.... they're held in place by the caliper and the wheel.

 

[jeffk14]

Cobra: if the rotors look good and you've got no pedal pulse, why mess with the rotors? If it were my truck, and that was the case, I'd just hit the rotors with a scotchbrite pad on a die grinder to break the glaze and replace the pads.

 

[Cobra4B]

Cobra: if the rotors look good and you've got no pedal pulse, why mess with the rotors? If it were my truck, and that was the case, I'd just hit the rotors with a scotchbrite pad on a die grinder to break the glaze and replace the pads.

I don't intend to mess with them if I don't have to, just trying to determine what to look for. I guess I need to figure out what min thickness is. They do have a slight lip at the ege, but other than that no issues. If it's above min thickness I plan on just putting fresh pads on.

 

[Falcon67]

Quote:
<table border="0" cellpadding="6" cellspacing="0" width="100%"> <tbody><tr> <td class="alt2" style="border: 1px inset;"> I used to beat the **** out of my old T/A. It never cracked a rotor, but they sure got warped. I would just cut them flat until they turned below spec, then replaced the rotor. The thickness spec leaves a good margin for safety from what I've seen. </td> </tr> </tbody></table>
EXACTLY. You just gave reasoning for being in the "general public" camp!

These were pre-Chinese rotors, back in 1979. I had access to plenty of good USA made rotors back then and they were plenty thick even when cut to the min spec. Now - I'd toss if the rotors got tweaked. I replaced a set of rotors on the Mustang drag car last year - sad stuff.

OR - go up to something like Wildwood and get away from anything OEM.

 

[Lugnut64052]

Older car rotors (say, from the 70's and 80's) were thicker than newer cars, so they had plenty of rotor meat which you could machine. You could cut them undersize and they were still beefy enough not to cause any problems, hence the testimonials about abusing Trans Am rotors with no ill effects.

By design and on purpose, newer vehicle rotors are lighter (which has been done to reduce weight and up gas mileage, for one reason). There are specifications for minimum rotor thickness, and the spec is sometimes cast into the edge of the disk. You can also have the parts guy look up the spec, or maybe find it on-line. Nowadays you may get one cut before you hit the minimum, or if they're really worn, you may get no cuts. Rotors are light enough these days I wouldn't cut one much below minimums.

.....getting back to the original question.....the amount of pad wear should not effect braking effort. You shouldn't need any more pedal pressure to stop with 1/16" of pad as with a new, fat lining. If you do, something else is up, like the rotor is highly polished and the pad is glazed, or you have drum brakes on the back which are out of adjustment. You might have to do some investigation to figure out why you have increased pedal effort.

Chinese made replacement rotors are pretty cheap and they work fine. I'm not making any suggestions or judgments about Chinese stuff but it's been my experience that using Chinese rotors and a high-quality American pad works great, and I've done lots and lots of brake jobs. And you can always get good American rotors too. The parts stores will carry both.

If you're having pedal pulsation, you may as well chuck the rotors and install new ones. As a previous poster pointed out, rotors are cast iron and do not warp. They will, however, get hard spot occlusions if overheated. Then, the hard spot wears less than the rest of the rotor, causing the pulse you feel through the pedal. You can machine them off flat, but the hard spot remains and the pulsation will come right back as soon as the rotor begins to wear again.

 

[BillK]

Brian,
I am going to differ with the other guys somewhat. If the pads have not worn to the metal backing, and there is no pulsation when you hit the brakes, replace the pads and keep on driving. I think you will find that this is actually GM's recommendation also. Of course if the rotors are badly worn and cannot be machined, then obviously you need to replace them.

We were having a discussiona bout this the other day at the shop. I have been driving since 1967 and have NEVER had to either machine or replace a drum or rotor on any vehicle I have owned. My 99 Tahoe has 120k and I just heard the wear indicators squeeking a bit the other day. This will be the second set of pads for it. My WIfe's 84 Riviera is close to 180K and is on its second set of brakes, rotors or drums have never been touched, my S-10 shop truck just turned 270K and I honestly cannot remember putting brakes on it since I bought it and it had about 170k on it then.

Now I will tell you that both of us are pretty easy on brakes. No tailgating, coast to lights whenever possible, etc. Also, and I think this has a lot to do with it .... I will only use GM OEM (not the Goodwrench) brake pads and shoes. I think they last a lot longer and are a lot easier on the rotors. I also hear a lot of horror stories from my repair shop customers about the "cheap" rotors. Most of them need to be machined to make them true before you even install them. If I needed rotors or drums, they would come from the dealer.

Some people are just plain rough on brakes and they always get them hot etc ... those are the ones that are always needing rotors etc. It doesn't sound like you are one of those.

Also, if you are requiring more pressure, make sure that the back brakes are adjusted properly if they are drums. The ones on my Tahoe get adjusted every time I change the oil (about every 7k) and it makes a BIG difference in how the truck stops and probably in the life of the front discs.

Just my opinion,

 

[Cobra4B]

Thanks for the input.... I've never adjusted the drums. I've only pulled the drum off to inspect the shoes. I'll have to look up how to adjust the rear drums.

 

[Lugnut64052]

I like to adjust my drums tight enough so they drag just a *tiny* bit. After you've test driven and tromped on the brakes good and hard a time or two they usually are not touching at all any more. You'd be amazed how much higher and firmer the pedal feels if you've been driving around with loose shoes on the back.

I'll agree with BillK-- you can just replace the pads if you have no other problems. I used to work on and manage medium duty truck fleets--school buses-- and we seldom to never replaced a rotor. They were all driven in urban settings with numerous, repeated stops, and we never had any problems just pad slapping them. In my experience cars and pickup trucks have seemed to be more sensitive with pulsations, etc, telegraphing up through the pedal, so I always either cut the rotors or replaced them when doing brake jobs. As with everything, your mileage may vary.

 

[DCarr]

The point isn't saving money... the point is that swapping pads is much less involved than taking the front suspension apart to change the rotor on this truck. It's a 2WD and the spindle has to come off to get the hub off to get the rotor off.

.

Sounds like a Colorodo or Canyon ... thing to do is to take it to a shop that can turn the rotors while they are on the vehicles .... What was GM thinking with that idea ????

I always turn my rotors every time the pads are changed. Just a skim cut to get rid of the glazing.