Edge codes were a practice established by manufactures. In general they don't seem to be government mandated, but something the industry found helpful for themselves and maybe because the OEMs wanted it. However, since I last looked at this two states have mandated a phased reduction of certain lining materials and a revised edge code is being used to show the compliance level of the material.

The marking standard is SAE J866
The first letters represent the manufacturer.
(web search for a AMECA list of edge codes for abreviations)
The next segment is the material.
This is followed by a two letter Friction Code.
The Friction code is based on the SAE J661.

The new marking standard adds onto that as shown.

[img]https://www.toyota-4runner.org/atta...um-brake-shoe-replacement-leaf_codes-jpg[/img]

Not all manufacturer's complied with marking the old friction code when selling aftermarket pads and shoes. But most did.

The J661 specifies a pretty basic test to come up with a coefficient of friction in two temperature ranges:
First letter represents the "Normal" test coefficient of friction (some interpret as 0-250 degrees F)
Second letter represents "Hot" coefficient of friction from (some say representative of 200-600 degrees F)

D Over 0.15 up to 0.25
E Over 0.25 up to 0.35
F Over 0.35 up tp 0.45
G Over 0.45 up to 0.55
H Over 0.55

So for example a shoe marked ED would suggest it looses friction once over 200 or 250 F. On drum brake, especially in the front, that could mean a notible loss in braking when hot and increasing force needed on the pedal just to get maintain the stopping power. Maybe on the rear effect would not as bad and even reduce possibility of lock up.

Keep in mind these ratings only are a rough indication. For example they don't show the trends from 200 to 600 F, and the range of friction coeficient within each letter designation is really wide. They also don't reflect other real application characteristics, just friction of a sample against a turning wheel.

As far as the temperatures go, an article in SHO Times gives some idea of how hot an undersized OEM brake can get. These are heavy cars and the front disks were pretty small.

"...measured 385 F on my front rotors in rush hour traffic on a 45 mph street because of several sequential stoplights. (I have an 89 SHO with 10.1 in. rotors.)
...four back to back 60 mph stops generated 550 F."

Here's an example that's actually stamped in the edge. With some pads the code is inked on the backing plates.

This is a genuine Mopar replacement pad for the 4 piston Kelsey Hayes brakes. Friction rating is FF. If nothing else, this lets you and your mechanic know that anything less, such as EF or EE is probably not going to stop as well as original.

(PS I did not love these pads in case anyone thinks I'm promoting NOS pads as the hot ticket to braking bliss)

A bit more on expected temperatures:
The SHO Times author used Fred Puhn's calculations and graphed the expected temperatures for factory rotors making one stop. The smallest Ford SHO rotor was from 1989.

Stock 1989 Ford SHO
From 60 mph the front rotors would experience about 220 F degree rise in temperature.
(That matches surprisingly well with his real life test of four 60 mph stops cited in the first post.)

From 120 mph, the 10.1" rotors calculate to increase around 750 F degrees.

Using the same method with a
3400 lb A-body with factory 4 piston calipers and 10x1.75 rear drums:
60 mph stop calculates to 107 F degrees
and even if the rear drums did nothing, the disks would only increase 147 F degrees.

From 120 mph the temperature rise will be 430 F degrees
and if the drums did nothing it still only calculates to 590 degrees.

I thought this comparison would be helpful in clarifying what temperature ranges our brakes will see typical street driving, as well as a single high speed stop.

The reason for calculating both with and without rear brake contribution is because its not known which way the SHO calculations were done. The SHO is a front engined, front wheel drive car so the rear brakes remove less energy than our better balanced RWD cars.

Very nice. Thank you.
This should go right to archives after it gets discussed.

Thanks. I've modified the original post after looking at my notes and some more internet searching to settle some conflicting info.

Best I can tell right now, since I apparently never got a copy of the J866 or J661, is that the temperatures I first posted with the Friction codes are a simplified interpretation. The 0-200/200-600 F can be found in articles from Motor Magazine and Hot Rod. The 0-250 F came from SHO Times and maybe other places.

But when you look at J661 test reports, its clear that not how the test is done. There are tests at increasing temperatures, then recovery after heating. The J866 codes use the results of the J661 to come up with the first letter which is 'Normal' and the second letter which represents 'Hot'.

As the Chase machine this testing has been done on is a drum, many argue it is not a particulalry good test for actual brakes. There have been ongoing attempts to come up with a more representative more repeatible US standard, but so far no dice. So it continues to be one of the few available means to compare lining materials.

were these tests done with new, properly bedded in linings, or just whatever factory lining was on the particular car being tested ?

Neither.
The procedure is a series of tests of the friction lining material; not the pads or shoes. A sample of a given size, I think its 1" x 1", is tested on a Chase Machine which has a drum that can be brought to different temperatures by the operator.

Therefore friction rating can only be used to compare identical shoes or pads.

AFAIK bedding is/was not really an issue with factory or factory replacement brakes. Brake service needs to put them on, adjust the shoes, check the parking brake, road check (maybe) and done. That said, its certainly possible that an aftermarket manufacturer could run the test so that the material is bedded into the drum. Would need to actually know much more about the J661 procedure and testing requirements. An OEM supplier would most certainly be expected to share something like that, if done, with the car's engineers for several reasons. One is that it might fail in independent testing verification during design or production validation. Second, the bed-in procedure has to be so consistant that the resulting performance meets spec every time. Car systems are designed for at least 6 sigma statistical performance..maybe higher, its been a while. Safety systems are often higher anyway. It comes down like this, even 1 failure to be in spec for every 100,000 cars is too high a percentage to be acceptable by any manufacturer.

Car systems are designed for at least 6 sigma statistical performance"

OK you lost me, care to explain?

Sigma is shorthand for Standard Deviation. In brief, standard deviation is how far off from the normal most items will be.

Automotive manufacturers implemented statistical quality assurance programs that built into both the design and manufacturing a whole range of practices to insure the final assembly of the subsystem would always be in specification.

In brief.
If a part is being made there is going to be variation. There will be an average (mean), a maximum and a minumum. If the item is measured and plotted and there are enough samples most of the measurements should fall in the middle. Here's an example I found on-line showing Tire Pressures for a motorcyle.


With enough samples, the histogram ends up being shaped like a bell, hence bell curve. Most of the results will be within one standard deviation of the average (mean).

Going out plus minus three standard deviations (ie 6 sigma) covers most of the results.


So six sigma helps insure minumum defects


But if we are making 100,000 parts or filling 500,000 tires we need to know whether its likely that every one will fall within the acceptable plus/minus limits of our product.
If we're planning on making a million cars, then statistically 12 sigma as shown below could still potentially have out of spec items. This is why I mentioned that 6 sigma is not enough on safety systems. So in addition to going beyond 6 sigma for safety systems, engineers have always added factors of safety to the design limits.

the ultimate goal is 100% defect free, but that is usually unobtainable. what is obtainable, however, [if monitored correctly] is the end consumer gets 100% reliability because no defective product is released for consumption. but we all know that goal is VERY hard to accomplish as well. the company i worked for as a machinist/shift supervisor [before my retirement] practiced 6 Sigma. the objective goal was no defective parts reached the customer. as such, there were many inspections during machining that caught defects before the parts machined went to final assembly. when defects were caught in subsequent steps that were caused in the previous operations of the part in question, i was called upon the carpet even if my crew had nothing to do with the defect. unqualified parts were then sent back for rework [if possible, and i came up with some truly unique ways of repairing things that worked better than the original design called for], or scrapped. and when the company hired unqualified workers, it got bit hard every time.

Found a summary of the J661 friction test procedure. The description seems to be in line with the test results that can be found on the web (with some effort).
This summary comes from an orphaned webpage which in turn appears to reference http://ducatigarage.netfirms.com/brakepads.html which is a defunct website.

The Chase Test
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The Chase Test is used to assign a two character code (e.g. EE, FF, GG, HH, etc) to a specific friction formulation. These characters represent the coefficient of friction when a 1" square piece of friction material is subjected to varying conditions of load, temperature, pressure and rubbing speed on a test apparatus known as the Chase machine.

The first letter of the code represents the normal friction coefficient. This is defined as the the average of four test data points measured at 200, 250, 300 and 400 degrees Farenheit.

The second letter of the code represents the hot friction coefficient based on a fade and recovery test. We all should know what brake fade is. If you've ever had to use the front brake extensively and found that its effectiveness quickly diminished, that's fade. Recovery is basically the period where the brakes are gradually cooling off.

The hot friction coefficient is defined as the average of 10 data points located at
400 and 300F. on the first recovery cycle of the pad;
450, 500, 550, 600 and 650F. on the second fade cycle;
and 500, 400, and 300F on the second recovery cycle.
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