What is brake glazing? How do you prevent it?

In a recent thread, we were discussing brake glazing and I was surprised to see that the term was not widely understood or defined so I looked it up. Here's what I found:

What causes brake pad glazing?
Brake pad glazing is caused when the brake pad friction material is overheated. This results in crystallized friction material on the pad surface and the brake disc. Typical symptoms of glazed brake pads include: Poor stopping performance, vibration or brake judder, and cracks or fissures in the brake pad material. Pad glazing is typically caused by operating the brake pads at a temperature above the specified temperature range of the friction material or not properly following the 'Bedding-in' instructions for the brake pads. Always follow the manufacturers brake pad bedding-in instructions and use a brake pad that has a temperature range that is sufficient for its intended use.

What can happen to my brake pads if not bedded properly?
Proper break-in will assure that small amounts of heat are introduced to the brake pad. Brake pads that are brought up to temperature too fast and not properly allowed to cool down may quickly become glazed and not perform as originally intended. The pad’s rubbing surface reaches extreme heat levels during racing use. The surface needs slow temperature increases to help prepare the pad. Large amounts of heat all at one time can cause the brake pad rubbing surface to become somewhat liquified and coat the pad surface with a glaze. This will dramatically reduce stopping performance as certain ingredients in the friction compound breakdown and cause glazing of the rubbing surface of the brake pad.

First off, does everyone agree with the above text? If so, then what's the best way to prevent glazing while driving a motorhome? For example, would constant use of the Jake brake help the situation? Do we need to bed in our brakes when we get a new MH? Finally, does the rotor / drum glaze differently from the brake pads? Or is it the same thing?

Class A

16 Replies

rgatijnet1
Explorer III
Aug 17, 2015
Polished surfaces are only good for machine surfaces where you do not want friction, like bearings. Textured machined surfaces are needed for friction components like brake rotors/drums, cylinder walls, etc. A properly operating brake system will wear away both the pads/shoes to a greater extent, as well as the rotors/drums to a lessor extent.
Even a rubber belt that becomes glazed/smooth, will slip and not grip the pulley surfaces.
holstein13
Explorer
Aug 17, 2015
DSDP Don wrote:
No I'm not confusing anything. You read a definition of glazing and believe it only applies to high heat situations wear things melt. If you lightly drag two items together, they build heat, but not always to the level of melting things. The light application of brakes causes a slight heating issue and will polish/glaze the brakes. After this occurs, dust gets between them and cause the squeal.

Some day, take a look at a freshly turned brake rotor or drum. They're NOT smooth, because they're cut with a machine. Put ten thousand miles on them and they're as smooth as glass. This is wear and glazing.

You're having a difficult time understanding this because you're laser locked on one definition of glazing.

Here is an example, maybe not a good one, but you might be able to relate to....When you buy a donut, you can get plain or glazed. What does that mean, one is just a rough cake surface and the other has a light glazing of sugar that's not burned on/on.

Many definitions of glazing...here is just one...."to lose abrasive quality through polishing of the surface from wear". This isn't a difficult topic, you're just being too literal!
I don't know what to tell you except that polished brakes are a good thing. Look it up on Google. You can find videos on how to polish your rotors and lots of stores that sell polished rotors. You use the term "polish/glaze" in your post as if it's the same thing and it's simply not. But I may be wrong. I don't fully understand all of this and that's why I've posted the question.

So if you can post some links supporting the idea that lightly using the brakes without building excessive heat causes glazing, I would love to see them and try and understand the principles behind such a thing.

I found an interesting article on Brake Myths.

"There are two types of friction at play here, abrasive friction and adherent fiction. Abrasive friction literally breaks the bonds of the crystalline structure of the pad and even the cast iron of the disc, creating heat. Mohs Law tells us that the harder material (ideally the disc) wears away at the softer material of the pad as the two materials rub together. Picture a sanding pad against a board. Same concept.

Adherent friction is where some of the pad material literally adheres to the opposing surface as they s****e by each other, creating a thin and (ideally) even layer of pad material on the face of the rotor. That material can continually break its bonds and transfer from surface to surface back and forth between the disc and the pad, continually breaking and reforming like they were bouncing across political parties between elections (heyoo!)."

This is what I think a normal, functioning rotor looks like:

http://img.autobytel.com/car-reviews/autobytel/105716-identifying-weird-car-noises/bigstock-Car-wheel-brake-rusty-disc-wit-61080689.jpg

I wouldn't call it polished or glazed. Just looks like every rotor I've ever seen.
Itasca55
Explorer
Aug 17, 2015
holstein13 wrote:
In a recent thread, we were discussing brake glazing and I was surprised to see that the term was not widely understood or defined so I looked it up. Here's what I found:

What causes brake pad glazing?
Brake pad glazing is caused when the brake pad friction material is overheated. This results in crystallized friction material on the pad surface and the brake disc. Typical symptoms of glazed brake pads include: Poor stopping performance, vibration or brake judder, and cracks or fissures in the brake pad material. Pad glazing is typically caused by operating the brake pads at a temperature above the specified temperature range of the friction material or not properly following the 'Bedding-in' instructions for the brake pads. Always follow the manufacturers brake pad bedding-in instructions and use a brake pad that has a temperature range that is sufficient for its intended use.

What can happen to my brake pads if not bedded properly?
Proper break-in will assure that small amounts of heat are introduced to the brake pad. Brake pads that are brought up to temperature too fast and not properly allowed to cool down may quickly become glazed and not perform as originally intended. The pad’s rubbing surface reaches extreme heat levels during racing use. The surface needs slow temperature increases to help prepare the pad. Large amounts of heat all at one time can cause the brake pad rubbing surface to become somewhat liquified and coat the pad surface with a glaze. This will dramatically reduce stopping performance as certain ingredients in the friction compound breakdown and cause glazing of the rubbing surface of the brake pad.

First off, does everyone agree with the above text? If so, then what's the best way to prevent glazing while driving a motorhome? For example, would constant use of the Jake brake help the situation? Do we need to bed in our brakes when we get a new MH? Finally, does the rotor / drum glaze differently from the brake pads? Or is it the same thing?

Here are my findings about brakes. If you put on ceramic brake pads it tares up the rotors more ( good braking ) . meaning if rotors not cracked or colored and not surging . I dont even turn them :)just put pads on . every time I took rotors in to have them turned they always started to surge in under 10,000 miles . did brakes like this on motorhome had 150,000 miles on it . never turned the front rotors ever . and yes it was drove through mountains all over . only once pads got glazed pads that was before I put ceramic ones on . never had any problems after ceramic pads . but a note ceramic ones do heat up faster in extreme conditions . down shifting is keey . This is just my findings on 21 foot van style . But this is how Im doing brakes on my 27ft class a now also no problems yet. theres my 2 cents .
Itasca55
DSDP_Don
Explorer
Aug 17, 2015
No I'm not confusing anything. You read a definition of glazing and believe it only applies to high heat situations wear things melt. If you lightly drag two items together, they build heat, but not always to the level of melting things. The light application of brakes causes a slight heating issue and will polish/glaze the brakes. After this occurs, dust gets between them and cause the squeal.

Some day, take a look at a freshly turned brake rotor or drum. They're NOT smooth, because they're cut with a machine. Put ten thousand miles on them and they're as smooth as glass. This is wear and glazing.

You're having a difficult time understanding this because you're laser locked on one definition of glazing.

Here is an example, maybe not a good one, but you might be able to relate to....When you buy a donut, you can get plain or glazed. What does that mean, one is just a rough cake surface and the other has a light glazing of sugar that's not burned on/on.

Many definitions of glazing...here is just one...."to lose abrasive quality through polishing of the surface from wear". This isn't a difficult topic, you're just being too literal!
holstein13
Explorer
Aug 17, 2015
DSDP Don wrote:
Both hard braking and light braking can cause glazing. Think of it this way. When you drive down a hill to fast and have to use your brakes excessively, you heat them to the point that they glaze from the heat. Typically, to repair this damage you would have to turn the drums/rotors and replace the shoes/pads. Something you want to stay away from doing by using your engine/exhaust brake.

When you use them lightly, you're really polishing the drum/rotors and shoes/pads. Typically, a few hard stops will remove this type of glazing and get rid of the squealing that's usually associated with it.

This is why it's recommended not to use your engine/exhaust brake to extremes. In traffic and around town, exercise the brakes by using them. You're not going to wear them out.

I think you are confusing polished rotors with brake glazing. They are not the same thing. As far as I know, there is nothing wrong with shiny polished rotors. Is there?

Glazing means you melted the resins in the brake pads and they have turned into a glass like substance that doesn't have much friction. Most of that glazing will be on the brake pads, but you are correct that it could end up on the disc / drum as well and might have to be turned to remove the glazing. But glazed brakes look very different than smooth polished rotors or drums. (it looks like shiny spots on the brakes and they could look cracked). Polished = good, glazed = bad.

And if you drive down a hill too fast, yes, you will overheat the brakes whether you do it slowly or quickly, probably doesn't make a difference assuming you are driving too fast to begin with. That's exactly why you should use the engine brake -- to prevent this situation.
DSDP_Don
Explorer
Aug 17, 2015
Both hard braking and light braking can cause glazing. Think of it this way. When you drive down a hill to fast and have to use your brakes excessively, you heat them to the point that they glaze from the heat. Typically, to repair this damage you would have to turn the drums/rotors and replace the shoes/pads. Something you want to stay away from doing by using your engine/exhaust brake.

When you use them lightly, you're really polishing the drum/rotors and shoes/pads. Typically, a few hard stops will remove this type of glazing and get rid of the squealing that's usually associated with it.

This is why it's recommended not to use your engine/exhaust brake to extremes. In traffic and around town, exercise the brakes by using them. You're not going to wear them out.
Golden_HVAC
Explorer
Aug 16, 2015
rgatijnet1 wrote:
When the brake pad material, that has overheated and glazed, gets deposited on the rotor, it makes the rotor look like it is glazed. This can usually be removed from the rotor by turning them.
Pad glazing occurs whenever the pads are overheated. This can be because the wrong pad material was used for the brakes on a certain vehicle. OEM pad material is usually the best choice and will dissipate heat better than some ceramic pads which may transfer more heat to the rotors. Basically all of the same thing apply to shoes and drums. Drum brakes were still used on some vehicles. My Chevy HHR toad has drum brakes on the rear.

The brake glazing shown in this picture is the brake material heated to the temperatures required to melt sand and turn it to glass.

Getting the brakes up to the 1,400F mark will glaze them and cause them to make a lot more noise.

Jake brake, or other engine braking will prevent this to some extent. Sometimes it requires the driver to downshift from 4 to 3 on some roads that have more curves, and might be steeper than average. Monitor your engine RPM as you descend the hills, and you will get an idea of how much RPM you can handle, and how much braking the engine can provide.

When I was leaving Sequoia National Park, I was in 3 and 4 gears, going down the hill, marked as about 45 MPH, with 35 MPH curves every 1/4 mile or so. I think it was a 6% downgrade as well. IN areas where it leveled out for a bit, I would shift to 5th gear, and turn off the engine brake for a bit. Then as I picked up speed, I could shift back to 4, and turn on the engine brake, slowing the RV even further.

If I had just left the transmission in 'drive' it would have been in 6 speed, then shift to 4 when the brake is applied, and as I shut it off, it would go back to 6, giving a slight jerk to the RV, as well as letting it coast up to a higher speed fairly quickly.

Overall, I did not need to use the service brakes very much, until I was going to make a left turn at the bottom of the hill. I think I used the service brakes a bit before each tight curve in the road, but had the engine brake on at the same time, most of the way down that 5-8 mile long 4,000' descent on highway 180.

Of course when you are descending a long hill like this, be aware that you might collect about 10 cars behind you, wanting to drive the speed limit, and pass you. Pull off if there is a turn out.

Good luck,

Fred.
holstein13
Explorer
Aug 16, 2015
et2 wrote:
http://www.rvtechmag.com/docs/burnishing.php

http://www.rvtechmag.com/tech/43_chassissvc.php?pg=all
Great links. Thanks. They support the idea that only overheated brakes will cause glazing. The conclusion I draw is don't overheat the brakes to begin with. Use the Jake Brake and don't ride the brakes.
et2
Explorer
Aug 16, 2015
http://www.rvtechmag.com/docs/burnishing.php

http://www.rvtechmag.com/tech/43_chassissvc.php?pg=all
holstein13
Explorer
Aug 16, 2015
FormerBoater wrote:
My understanding has always been that brake glazing in a Motorhome application is due to being too light on the brakes...too much dependence upon the Pac or Jake brake and very little full engagement of the service brakes.
This appears to be the exact opposite thing to do according to my research and what Busskeeper wrote.

There is a grain of truth to it, however, because too light an application over a prolonged period of time (riding the brakes) will result in brake overheating. Full engagement of the service brakes should only be performed in short bursts to allow the brakes to cool in between.

Light use of the brakes will result in less glazing than full engagement of the brakes. Not using the brakes at all will eliminate the possibility of glazing. That's why we should all use the Jake brake constantly. Besides, it will clean the turbo cooler.