BRM's Flexible Honing, Surface Finishing, and Deburring Blog Blog

BRM's Flexible Honing, Surface Finishing, and Deburring Blog

BRM's Flexible Honing, Surface Finishing, and Deburring Blog is the place for conversation and discussion about how to solve difficult finishing problems. For over 50 years, Brush Research Manufacturing (BRM) has helped customers use brushing technology to clean, rebuild, and resurface components ranging from engine cylinders to brake rotors to flywheels to firearms. BRM's Blog on CR4 provides real-world examples of how flex hones and wire brushes work. It also evaluates related technologies and invites questions from the community.

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DIY Disc Brake Rotor Resurfacing

Posted July 14, 2014 1:05 PM by Brush Research

Do your disc brakes squeak or squeal? As DSPORT magazine explains in a new article, and as Brush Research Manufacturing (BRM) shows in a new YouTube video, you may want to look at your brake rotors. Brake pad glaze and surface corrosion are common causes of noisy disc brakes. Fortunately, there's a surface finishing solution that's as easy-to-use as a power drill. Trusted by professional and DIY brake mechanics alike, the Flex-Hone for Rotors is ideal for new and turned rotors.

Rotor Refurbishment

In Glaze is for Donuts: Do-It-Yourself Disc Brake Resurfacing, Jun Chen of DSPORT magazine explains why BRM's Flex-Hone for Rotors is the right tool for rotor refurbishment. For years, Flex-Hone users such as machine shops, manufacturers, and engine builders have been using flexible hones to improve the surface finish of cylinder walls. The Flex-Hone for Rotors is designed for flat surfaces instead, but uses BRM's Flex-Hone technology to impart a superior, non-directional surface finish.

As the "Quick Tech" article in DSPORT's August edition explains, some motorists blame vibrations while braking on warped rotors. Most modern rotors are made of iron, however, and are unlikely to warp because of this metal's hardness and stability. Typically then, brake vibration is caused an uneven layer of material that's transferred from the brake pad to the brake rotor. Improper pad bedding isn't the only cause of brake problems, however, as surface corrosion and improper machining may be to blame.

Brush Tool Selection and Use

Suitable for use with a handheld electric drill, the Flex-Hone for Rotors comes in coarse, medium, and fine grits. Coarse-grit brush tools remove heavy buildup and corrosion. They also remove sharp edges on rotor slots and cross-drilled holes that can contribute to rotor cracking. Medium-grit Flex-Hone for Rotors tools also remove layers of pad material, but impart a smoother surface. Fine-grit flexible rotor hones impart the finest finish of all, and may be used after coarse-grit and then medium-grit tools.

To test the Flex-Hone for Rotors under real-world conditions, DSPORT magazine acquired four brake rotors from a race car with some time at the track. Equipped with cordless drill and a coarse-grit brush tool, the crew removed the transfer layer from each rotor's face. The DIY mechanics then switched to a medium-grit tool, and finally to a fine-grit tool. Because the Flex-Hone for Rotors is self-leveling and applies uniform pressure, keeping the brush tool square and flat was an easy task.

Best Practices for Resurfacing Brake Rotors

"Be sure to have at least a 50-percent overlap between passes to ensure that no rough our untouched edges remain," author Jun Chen advised DSPORT readers. As BRM explains in its Flex-Hone for Rotors brochure, users should work in towards the center and then out to the edge, applying light pressure to the rotor's face. Rotate the tool between 300 and 600 RPM, and remember that dwell time - not excessive pressure - produces the desired finish.

BRM also advises Flex-Hone for Rotors users to hold the rotor in a brake lathe, and to spin the rotor between 125 and 210 RPM during honing. DSPORT magazine recognized that some DIY brake mechanics don't have a lathe, however, so its crew placed the brake rotors on a workbench. "This process will leave a finish very similar to a new rotor", the author explained before concluding that "the Flex-Hone for Rotors can help you save a few bucks and get rid of that annoying brake judder for good.

Flex-Hone for Rotors users to hold the rotor in a brake lathe, and to spin the rotor between 125 and 210 RPM during honing. DSPORT magazine recognized that some DIY brake mechanics don't have a lathe, however, so its crew placed the brake rotors on a workbench. "This process will leave a finish very similar to a new rotor", the author explained before concluding that "the Flex-Hone for Rotors can help you save a few bucks and get rid of that annoying brake judder for good.

Author's Note: This CR4 blog entry originally appeared in BRM's Flex-Hone Blog.

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#1

Re: DIY Disc Brake Rotor Resurfacing

07/14/2014 1:44 PM

The issue with resurfacing rotors is that it removes material.

Rotors are designed to act as heat sinks as part of the process of converting kinetic energy to heat, which is exactly what brakes do.

As rotors wear the ability to absorb the heat goes down. This degrades brake performance and transfers more heat through the pads and into the calipers. Hot calipers increase the temperature of the brake fluid, which reduces performance further.

Demanding braking situations can also cause thinned out rotors to anneal and cause uneven wearing of the rotor, which further exasperates the problem.

While the point of the article is more about honing, the practice cited is not really a good one from a brake performance standpoint. The best course of action is to simply replaced worn or "warped" rotors with new.

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#8
In reply to #1

Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 1:35 AM

You said, "While the point of the article is more about honing".

I say the point of the article is more about selling hones.

Honing removes very little material from the rotor, but does nothing to correct warping, if the rotor is warped.

Machining the rotor, on a lathe, will remove much more material, but correct warping, if present.

Personally, I have never machined a rotor on any vehicle I have owned. If I had a problem, normally I'd just put a new rotor on and drive away.

Shops will turn a new rotor, and most old rotors whenever they install new pads, whether it needs it or not. I think a properly manufactured rotor is absolutely OK to install out of the box and have always done so.

Too thin rotors should definitely be replaced.

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#9
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Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 2:43 AM

Planing rotors while mounted on the car at first seems a good idea, but it is mostly useless and benefits only the wallet of the company doing it. I was not impressed.

Its far better to remove them (if that is the way you want to go) and get them professionally done on a lathe.

Though I am personally very happy with the "braking" method of cleaning the glaze off, but when that is not enough and before I invest one cent in fixing the old ones, I simply buy new rotors nowadays......aftermarket quality disks are easy to find at a cost of about 1.5 hours of mechanic's work!

Thankfully, mine are easy to replace with minimum tools too....as I believe most are nowadays....80's Nissans/Datsuns were a pain......bearings must also be replaced!!!

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#10
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Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 8:27 AM

The problem with turning rotors is two-fold.

The first is as I originally mentioned, that it removes material that is used to sink heat. When we stop we are converting kinetic energy into heat. That heat needs to go somewhere.

If there is insufficient material to sink the heat, rotors will warp and braking will quickly fade. The latter is a more serious concern.

The second issue is with warped rotors. I bought a car that braked fine during the test drive, but the owner must have taken one last spirited drive after that test drive and when the car was delivered I noticed the typical wobbling vibration of bad rotors.

I had them turned and they lasted few days before they began shuddering again.

The reason they did that was that the rotor metal was no longer homogenous in its hardness and the heat caused soft spots that wore unevenly. That is why you should simply replace them when they warp or have excessive grooving. Turning them is most likely to be a false economy.

I guess that many shops turn rotors simply because they have the machine and they need to feel like they are paying it off and it gives the customer a feeling like they are saving money.

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#11
In reply to #10

Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 10:23 AM

I actually seriously believe that almost, maybe every time I had disks replaced (only planed disks once in my life and the effects were minimal, mostly rubbish....), up until the last 3 years of so, were probably ALL due to glazing....

Obviously I cannot prove it either way now, except for my present car!!! But the symptoms were always the same........I am a seldom and light braker, which basically causes the problem....I had an ABS fitted car in the 90's and never ever felt the ABS pumping in almost 2 years of driving. So I thought it might be defective.....

I eventually asked a colleague and he said that I needed to brake firmly on a wet day. I did and that was the first time I had ever felt it....which demonstrates lust how light I am on brakes.....

All I will do from now on is to measure them, file off the rusty edge if needed and clean them by braking.....once they are approximately of minimum thickness, I will replace them myself in about 1.5 hours or so......

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#13
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Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 11:27 AM

Oh, I wear mine down inside of two years or 24K miles. My pads are very aggressive as is the dust.

That's the fronts, the rears are coming up for their first replacement at over 90K miles.

It's good to explore the limits of your car (in a safe and controlled environment). I am convinced a number of accidents happen just because people have no clue of their car's limits (and their own) and what they can do about it.

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#14
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Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 11:36 AM

Totally agree with you last statement. Even with ABS brakes, stablility and traction control, these dip-itshays around here in Martyland still manage to put their SUV's into the ditch after two snowflakes fall on the road.

I think every drivers license road test needs to start on an autocross track and end on the skid pad.

These turds have no idea of what causes vehicles to go into a spin, how to prevent it from happening, or when it does, how the hell to drive out of it. (And it ain't your brakes).

(But man, you are TOUGH on your brakes. Nice car by the way. )

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#15
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Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 1:04 PM

Due to the lack of snow in Florida those same drivers you see in the ditches do that every time it rains here. That's four seasons here.

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#2

Re: DIY Disc Brake Rotor Resurfacing

07/15/2014 6:48 AM

It depends upon the usage that causes the glazing I suspect, my cars for example (different models) have all suffered over the years with glazing when the rotors were not measurably worn....or still well within tolerance....

I paid out or replaced them myself several times over many, many years, till an older experienced mechanic friend told me what the problems were that I, and my wife, are "far too good" as drivers, we both anticipate early, take our right foot off the accelerator pedal (save fuel and tyres too) and basically only need a short braking to stop the car - sometimes, no need to brake at all!!

It seems that older cars rarely had the problem, probably due to the asbestos in the pads.

THIS STYLE OF DRIVING IS TERRIBLE FOR MODERN BRAKE DISKS WITH ASBESTOS FREE BRAKE PADS!!!!

This basically only polishes the surface and makes smooth braking next to impossible.

The brakes will still work as normal in an emergency I find though.

He told me that when I notice it happening again, I should find an empty road and do a couple of emergency stops to remove the glazing. I have tried it out and his advice works beautifully.

No need to be completely brutal, the ABS should not kick in when doing this for example!!! Just a few harder stops will usually do it....

This then gives me 3-6 months of no glazing, but it does come back.

People who "ride" the brakes will probably rarely have such problems....

The Flex-Hone advertized here will simply do the same job at a higher cost in money and time......

I kick myself for not understanding the problem better much earlier. I thought that the rotors were either unbalanced or even slightly bent.....TOTALLY WRONG!

The effects are that when braking lightly, you get light vibration. As though the driver was going on and off the pedal rapidly....Sometimes there and sometimes not, due I now believe to whether the glazing is on one or both discs, and how the glazed points "sync" or not together....but not proved.

I have wasted some good money over the years on this (easy to fix yourself) problem..... DUUUHHHHHH!!!

Even if this does not fix YOUR problems, it is easy and cheap to try out once you have checked that the rotors/pads are not worn out....

Best of luck to all concerned.

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#3
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Re: DIY Disc Brake Rotor Resurfacing

07/15/2014 7:52 AM

Very good point on bedding the brakes!

While we are on that subject, you should have your brake fluid flushed and replaced every two or so years, particularly if the climate is humid or vacillates between warm and cold.

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#4
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Re: DIY Disc Brake Rotor Resurfacing

07/15/2014 11:09 AM

I have had brake rotors that exhibited the slight 'judder' as they say under light braking conditions. I tried a series of 70 mph to zero hard stops but the pulsating feeling still existed. I tried this brake hone and it did the trick. Kinda pricey at about US $36 but a few minutes with a pistol drill dressed the rotors nicely. Pulsating feeling went away for a couple of years. I don't normally brake very hard, so I'm sure I'm "too nice" to my brakes as well. The hones do not remove very much material unlike a brake lathe. The hone also helps with the 'rust band' that sometimes tends to develop on the rotor.

Cheers !

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#5
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Re: DIY Disc Brake Rotor Resurfacing

07/15/2014 12:46 PM

I ha a similar experience, I simply had to keep repeating the braking, with time for cooling in between and eventually the glaze was gone.....since then, I have never ever let it get so bad.....as soon as I notice it, a few sharp brakings and it is fixed...

It would appear that if not corrected, it simply gets worse (thicker???) and worse and more difficult to clear up.....

With the rusty edge on some models, I get someone to drive slowly in first gear, car on a jack, wheel off and file it off.....takes seconds. But DO use a file with a proper handle, just in case!!! You do know why I suspect!!!

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#6
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Re: DIY Disc Brake Rotor Resurfacing

07/15/2014 11:11 PM

Done that too. Found I had to leave the other wheel on the ground to get enough torque to actually machine off the crud. (Don't try this at home kids without asking your Mom or Dad) Spins the spider gearsin the diff pretty good but I figure the load is real low compared to actually driving so I didn't sweat it.

I always make sure my appendages are always in position away from pinch or shear zones so the worst I do is bugger up a tool or rotor or caliper. Just a few stitches at the emergency room makes a whole pile of new parts look pretty damn cheap.

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#7
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Re: DIY Disc Brake Rotor Resurfacing

07/16/2014 5:25 AM

Well put!

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#12

Re: DIY Disc Brake Rotor Resurfacing

07/17/2014 11:08 AM

I'm due for brakes, front and rear. I'll put new rotors on since I'm at 180k miles.

I say "I", I'm actually going to have our 15 year old do the work and just supervise.

He'll be driving in a few months and he might as well know about mechanical things.

Fortunately, he's interested enough in cars trucks to want to do it.

I heartily agree with everything put forth here.

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#16

Re: DIY Disc Brake Rotor Resurfacing

07/18/2014 10:47 AM

I am in agreement with AH that hones for the removal of "glaze" are a sales gimmick. taking a very fine grit electric sander very lightly and evenly to the rotors is really all that is needed unless the rotors have warped. That said, I rarely even do that because after the first couple stops, any roughening or surface hardness changes are moot. in years gone by, rotors were cast in once piece, but for the last 15 years or so, more and more rotors are weldments made from a cast wear ring welded to a drawn mild steel hub, these types do not lend themselves to being remachined, if they start vibrating it is time for a new rotor.

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#17
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Re: DIY Disc Brake Rotor Resurfacing

07/18/2014 11:22 AM

Basically agree, but if its only glazing, then a few hard stops removes that problem completely I find on my present car and basically costs nothing!!!

Or should say, costs nothing to try first!!!

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