resurface rotors, absolutely needed or not?

[cudamark]

Seeing as how my old cars don't have ABS, I can lock up the brakes regardless of which quality pads I use. You're just substituting pad wear from rotor wear when using the softer material. Brake fade can be affected a bit between pad material, but, the stopping distance shouldn't change if you can lock all 4 wheels with any of them. If you're an aggressive driver and constantly brake at the last second, yeah, get the high dollar pads. I'm real easy on brakes and clutch, mainly because I'd have to be the one to replace them! My last '78 Dodge 1/2 ton pickup had almost 300k on it with the original clutch and only the 2nd set of front pads. Rear shoes were original, but, getting a bit thin toward the end.

 

[Kern Dog]

Good grief.

Turning the rotor trues the rotor (if necessary) AND provides the proper surface to bed in the new pads. It is how you get the best performance out of your brakes over the life of the pads.

If the rotor isn't warped or gouged and you just put in new pads, the pads will eventually wear to the rotors and create the surface they want and the braking will be fine. But in the time it takes to get to that point the brakes will not be as effective and that process will wear the pads faster. Not the end of the world but definitely not best practice or best for performance.

If you're not measuring the rotor thickness before you change the pads and run them, you're an idiot. Even reproduction rotors for these cars usually won't be in spec for a 2nd pad change. Not with any performance brake pads anyway.

Most shops just buy new rotors now because most new rotors are not thick enough to turn and run again. The rotors don't come with a ton of extra material on them, so if you've gone through a set of pads you've also worn down the rotor, and not a lot of them would remain in spec after you turned them if something is visibly wrong with the rotors. So they get replaced instead of turned.

If you know how to turn a rotor, you know you don't need to take much off. If the rotors are true and smooth you're not losing much thickness, just providing the proper surface. Using a sander on them reduces the thickness too, and won't necessarily provide a flat surface. If you're gonna blast them with a sander, roloc, etc you should just have them turned, you're not saving metal, just introducing the possibility of a non-flat surface.

If a set of rotors won't survive being turned and remain in spec, they're not true or flat anyway. If a rotor has visibly "deep" gouges or is warped enough to cause a vibration, it likely won't true up without going out of spec anymore.

Yes, I've absolutely changed my own brake pads without turning or replacing my rotors. No, I didn't die. No, it's not best practice. And yes, after that 2nd set of pads wore out the rotors were out of spec, so they didn't last any longer than if I'd turned them at the previous change.



If a rotor is visibly scored, grooved, went metal on metal or has a vibration they're most likely junk, and need replaced instead of turned anyway. Most modern rotors aren't thick enough anymore to clean up with obvious damage like that. Maybe 50 years ago, not anymore.

Any rotor within spec should work just fine. That's why there's a spec, some poor bastard actually had to test that. Nowadays if you're able to turn a set of rotors once you're doing good, they wear down with use so it's not like they last forever if you don't turn them. Realistically if you've changed the pads once the rotor will be out of spec when the next set of pads needs to go on regardless of them being turned or not.

Ehrenberg is also a cheap purist. He doesn't advise turning rotors because he doesn't want to buy a new set and when he wrote that article the rotors/drums he was using probably weren't widely reproduced. It's the same argument from people that use less aggressive brake pads. That's fine if you care more about not buying a new set of rotors than how well your car stops. People that actually drive their cars should care more about how well they stop than about saving their rotors.

I'd rather chew up a set of rotors with aggressive pads and stop better than make my rotors last forever. Rotors are wearing parts, stopping is more important than rotor longevity. A set of rotors is a lot cheaper than new bodywork.


Anyone that puts science in quotes is just demonstrating they don't know enough science to have an informed opinion on the topic.

Guys, we found another mask wearing supporter!
When I have a choice between Ehrenberg and you, I’ll take him. You are like a seagull that flies in to crap on opinions then disappears for days.
No thanks.

 

[fishmens67]

let me know how your brakes are after being pushed down a 7 mile 10% grade by a 5000# boat. lol
You might find out how warped the rotors really were, I won't get into the effect of a grooved rotor.

 

[Johnny Dart]

I believe that what both you and Rick say on this "matter" is good advice. It sounds like it is based in "science" to me.

Sounds like cheap skates to me.
Nothing like a nicely turned rotor, and new pads.

 

[Icetech]

If i have no pulsing in the brakes and no scoring on the rotors, i just do pads.... i did pads on the back of my grand cherokee last weekend actually... If the rotors have any issues i replace them (no one here cuts anymore and new are cheap)

 

[harrisonm]

I agree with what a lot of people have said on both sides. However, I look at it like this. Brakes are pretty important. Any time I do a brake job, I do new pads and new rotors. I don't care how good the rotors look. If I do drum brakes, I get a new kit with all the springs, etc. I will have a drum turned if I can't find a new one.

 

[nutz]

really depends on the brake pad
not one euro car i work on you could just replace or resurface the rotor
the pad ware-out the rotor ,and wouldn't last two sets of pads
not uncommon to have rotor cost $400 to $500 each and pads to be $200+
put they last 50/70k and can stop a 4000lb and 130mph with fade
up in the northeast they rust so very uncommon to not need replacement
now 70s/80s cars pads would wareout in 15k to 20k rotor would last 2/3 brake jobs

 

[RustyRatRod]

Well, there are cases where I will not turn the rotors UNLESS I feel that they are warped. Case and point. My 1975 Ford F250. New rotors are available NOWHERE. There are listings for them, but they are all WRONG. That's because this truck is an HD-F250. "You'd figure" that means they'd be the same as an F350, but guess what? They're not. I've had this truck since about 2013 and I've been looking ever since. They are just slap not out there. So far, luckily for me, they have not warped, and they are still well within spec.

 

[nutz]

Well, there are cases where I will not turn the rotors UNLESS I feel that they are warped. Case and point. My 1975 Ford F250. New rotors are available NOWHERE. There are listings for them, but they are all WRONG. That's because this truck is an HD-F250. "You'd figure" that means they'd be the same as an F350, but guess what? They're not. I've had this truck since about 2013 and I've been looking ever since. They are just slap not out there. So far, luckily for me, they have not warped, and they are still well within spec.

lucky for you no salt....
well i guess if you had salt you wouldn't have a 75 ford ....
old dodge power wagons with pressed in hub bearings ....let them vib

 

[mopowers]

I only turn them if they have excess runout, nicks, grooves or other imperfections, aren't flat or parallel. Otherwise, hit them with some emery cloth and reinstall. That's pretty much what the FSM says.

 

[RustyRatRod]

lucky for you no salt....
well i guess if you had salt you wouldn't have a 75 ford ....
old dodge power wagons with pressed in hub bearings ....let them vib

Yeah, somtimes there's no choice.

 

[RustyRatRod]

I only turn them if they have excess runout, nicks, grooves or other imperfections, aren't flat or parallel. Otherwise, hit them with some emery cloth and reinstall. That's pretty much what the FSM says.

I think that's pretty much what all the FSMs say across the board.

 

[rmchrgr]

Good grief.

I mean seriously... are we trying to debunk 120 years of automotive service procedures here? I'm not sure I get the debate on this - there is none. Yes, sometimes circumstances make it impossible to turn rotors when replacing pads but if you have the ability or choice, do it.

Rotors have a minimum thickness spec. Why? To guard against making them too thin. The minimum spec. means they will still perform adequately even though the part may no longer be the OEM thickness. Anything under that though, you're on your own.

Regardless, you don't take a 1/4" of material off them, just enough to clean them up, maybe a few thousandths. On the lathe, you do a first cut and then a finish cut then hit them with sandpaper for a few seconds to give them a crosshatch like new rotors.

Obviously if rotors are too worn or damaged to cut you replace them. If there are grooves and they wind up being deeper than the minimum spec, they're junk. But, if there's just normal wear and/or no pulsing, turn them to true them up and provide a fresh surface for the pads. That's how brakes come when they're new, right? If things have worn evenly and the minimum spec allows it, there is no good reason not to turn rotors when replacing pads. You should only need replace the rotors on the third brake job.

Just a side note about bedding new pads - At Chrysler dealer tech school we were taught a basic though specific procedure to bed pads in after a brake job. On the road test, get to an area where you can accelerate the vehicle and bring it to a stop from three varying speeds - 15 mph, 30 mph and 45. No hard stops, apply the brakes firmly and evenly. Do that and they are good to go. That's for everything from Mini vans to Chargers to trucks.

I get it though - no one does it anymore because rotors are so cheap but why spend the money if you don't have to? Parts store rotors can be a crap shoot. (see * below) If I was still doing my own brake jobs I'd cut 'em. Don't forget, we used to turn drums as well. I only did like 1-2 pairs when I was a tech but it's the same idea. I actually still have an old drum mic. and belts.

Grooves in the rotors actually INCREASES the surface area.....

How do you figure? Both the brake pad faces and rotor faces are solid and flat. As long as both surfaces are flat when they meet, there is no space between them. If there are grooves (voids/air aka spaces) in the rotor face, (however deep) the pad can only make contact with the high points of the grooves. That is the definition of reduced surface area on a flat plane. Warped rotors are the same basic idea but the voids are on a radial axis causing alternating contact between the friction surfaces.

Either way, less surface area = less friction being generated. Less friction means your bakes no worky so much. Period.

*I had a local service station do a brake job on my truck sometime last year. They replaced the OE rotors because they "don't cut rotors anymore". I begrudgingly agreed. The replacements pulsed basically from day one. I was too lazy to go back and fight with them about it. As, you'd expect they have gotten progressively worse to being a hazard, like I now have to replace them ASAP. There's still almost half the pads left. I guarantee that if they cut the OE rotors and bedded the pads in properly they would still be OK. It's getting OE rotors and pads this time and I'll do it myself.

Do what you want, I'm out.

 

[nutz]

yea we always cut rotors if you could ...not on euros ..hard pads ware the rotors out

 

[gdrill]

There are a lot of people who know everything. I think these engineers have a better handle than I do.

You can also read instruction on how to change just pads. That generally implies not turning.
These are from 1986. Pretty sure Chrysler is good with it.

Quote: “Rotors do not have to be refaced every time a disc brake is relined. If the rotor surface is deeply scored or warped or there is a complaint of brake roughness the rotor should be refaced.”

Yes, I have other manuals. Drums are a whole nother story but the same principal.

 

[Kern Dog]

Dudes that wallow in their perceived superiority by stating that all brake jobs need either resurfacing or replacement of rotors while criticizing those that don't...need a swift kick in the rump.
If the FSM, what is thought of by those same people as the bible of knowledge in regards to every service procedure our cars are subject to, states that rotor replacement isn't necessary, why would anyone give respect to the stick-in-the-mud guys that demand you MUST do it?
Oh yeah...in regards to "science" the smarter ones here know what I mean....There are people that think they are smarter than everyone around them and their arrogance is ripe for correction when their "science" is easily disproven/debunked and smashed. It absolutely WAS in regards to the biggest scam of this century.
If YOU want to spend the money to resurface or replace rotors on every brake pad replacement, go ahead but it is not necessary.
Some people get a front end alignment every time they buy new front tires.
I don't. It isn't a matter of money either, it is a matter of not wasting money or parts that are still good.

 

[Icetech]

There are a lot of people who know everything. I think these engineers have a better handle than I do.

You can also read instruction on how to change just pads. That generally implies not turning.
These are from 1986. Pretty sure Chrysler is good with it.

Quote: “Rotors do not have to be refaced every time a disc brake is relined. If the rotor surface is deeply scored or warped or there is a complaint of brake roughness the rotor should be refaced.”

Yes, I have other manuals. Drums are a whole nother story but the same principal.

View attachment 1716389376

View attachment 1716389379

View attachment 1716389380

what's so great about that is guys that scream READ THE FSM! will be arguing against it

 

[DumpsterFire]

Pad slaps make perfect sense when your rotors aren't glazed or warped and you do your own brakes

 

[cudamark]

I mean seriously... are we trying to debunk 120 years of automotive service procedures here? I'm not sure I get the debate on this - there is none. Yes, sometimes circumstances make it impossible to turn rotors when replacing pads but if you have the ability or choice, do it.

Rotors have a minimum thickness spec. Why? To guard against making them too thin. The minimum spec. means they will still perform adequately even though the part may no longer be the OEM thickness. Anything under that though, you're on your own.

Regardless, you don't take a 1/4" of material off them, just enough to clean them up, maybe a few thousandths. On the lathe, you do a first cut and then a finish cut then hit them with sandpaper for a few seconds to give them a crosshatch like new rotors.

Obviously if rotors are too worn or damaged to cut you replace them. If there are grooves and they wind up being deeper than the minimum spec, they're junk. But, if there's just normal wear and/or no pulsing, turn them to true them up and provide a fresh surface for the pads. That's how brakes come when they're new, right? If things have worn evenly and the minimum spec allows it, there is no good reason not to turn rotors when replacing pads. You should only need replace the rotors on the third brake job.

Just a side note about bedding new pads - At Chrysler dealer tech school we were taught a basic though specific procedure to bed pads in after a brake job. On the road test, get to an area where you can accelerate the vehicle and bring it to a stop from three varying speeds - 15 mph, 30 mph and 45. No hard stops, apply the brakes firmly and evenly. Do that and they are good to go. That's for everything from Mini vans to Chargers to trucks.

I get it though - no one does it anymore because rotors are so cheap but why spend the money if you don't have to? Parts store rotors can be a crap shoot. (see * below) If I was still doing my own brake jobs I'd cut 'em. Don't forget, we used to turn drums as well. I only did like 1-2 pairs when I was a tech but it's the same idea. I actually still have an old drum mic. and belts.


How do you figure? Both the brake pad faces and rotor faces are solid and flat. As long as both surfaces are flat when they meet, there is no space between them. If there are grooves (voids/air aka spaces) in the rotor face, (however deep) the pad can only make contact with the high points of the grooves. That is the definition of reduced surface area on a flat plane. Warped rotors are the same basic idea but the voids are on a radial axis causing alternating contact between the friction surfaces.

Either way, less surface area = less friction being generated. Less friction means your bakes no worky so much. Period.

*I had a local service station do a brake job on my truck sometime last year. They replaced the OE rotors because they "don't cut rotors anymore". I begrudgingly agreed. The replacements pulsed basically from day one. I was too lazy to go back and fight with them about it. As, you'd expect they have gotten progressively worse to being a hazard, like I now have to replace them ASAP. There's still almost half the pads left. I guarantee that if they cut the OE rotors and bedded the pads in properly they would still be OK. It's getting OE rotors and pads this time and I'll do it myself.

Do what you want, I'm out.

Not once the pads are seated into those grooves. Picture the edge of a saw blade vs a knife blade. Much more surface area of the saw blade.

 

[Jim Lusk]

I have been known to bead blast rotors to knock the glaze down. Of course, if the rotor and hub are one piece it must be clean of all grease and replace the bearings when done. If you look in the FSM, there is no minimum listed for the Kelsey-Hayes rotors. That tells me they come at minimum.

 

[RLF Cuda]

My '68 FS FB 340 had K-H factory disk brakes with 4 piston calipers. The only problem I had with these brakes was the pistons corroding and seizing in the bore. I rebuilt the calipers 5-6 times over 200,000 miles but never had to machine the rotors. They were true and ungroved for their entire life. But I replace them with the 11.75" brakes which are much better overall but heavier and wider than stock. But still worth it.

 

[cosgig]

On newer vehicles I just swap em out with new ones. On our older vehicles, I have my buddy turn them for me, because no auto parts stores do it anymore, and they wouldn’t do the early stuff anyway. The only time I scuff them up by hand is on my plow truck, it never gets driven over 35mph, and I’m usually always out there by myself with no cars on the road. And I also have the emergency “drop the plow” brake in case of trouble.

 

[Swinger 340]

no not a scam. In fact, now a days hardly anyone turns them anymore. Most just slap on new ones. To me it depends on the particular vehicle in front of you.
One thing, is that to cut, them they get thinner. The less thickness the more likely they are to warp. Back when most had inner + outer bearings and races they were heavier and acted as a better "heat sink" not to mention more leeway between new spec and "machine to/ "discard" (they weren't the same) than current rotors, the formulation of pads back then was easier on rotors than it is now, (or "in between" when everything was semi metallic pads; the ceramics are better than semi's but not quite as easy on rotor wear as old organics were)
the metallurgy back then was better, but todays pads last longer in most cases than old school ones, so rotors are subject to more hot/cold/hot again heat cycles before todays pads are "shot"/
Back in the 70s I remember most GMs had a scratch/ groove in the center of the wear surface that was actually put there as a built in "wear gauge"... you can still see it and have no pulsation, keep using em....
What I do is if theyre not grinding, not pulsating and not rotted away to $#it on the wear surface I'll still "pad slap em.... alot of times the inner 1/3 and the outer 1/3 are bands of rust and the wear surface has actually "chipped away" and just left a "middle band" left for the brake pads to really work; those get **** canned.
When I had access to a brake lathe, rotors like you describe would go on the lathe and see if they could "mostly" be cleaned up and still measure out good.... if there were a few scratches left in them they'd go 'til next brake job. but if while turning them what was left looked like a swirl and not consistent, Id cut them again and see if theyd clean up at thicker than "machine to". if not they'd be trash as well.
Yours being a 1 ton van that's alot of weight to stop, even if not loaded down or towing..... I cant say I have never pad slapped a vehicle that went metal to metal.... but Ive never liked it....

I believe the rotors back in the 70's were harden all the way through, not like today, only the surface. I think the van mentioned here is a 3/4 ton, not 1 ton. Some were 5 lug (standard) and some were 8 lug (HD). My 72' B300 (1 ton) had 8 lug and I never had to replace the rotors in its 38 year life time. The good American stuff.