6.7L Cummins Forum

Since we had a member with brake issues I thought I'd go drag this over from another site I have.

I don't know about anyone else but I have always bedded my brakes in on new vehicles and on my last truck (Nissan Titan) I figure that's one of the reasons I never did have the brake problems that most owners suffered from.


Brake Bedding

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.

And this is bedding in :
For optimal use of any given brake system, the pads and rotor have to be compatible with each other. The bed-in procedure establishes that compatibility between the pad and rotor. This is achieved by a combination of rubbing speed, temperature, line pressure, and Inertia. Bed-in is also influenced by pad and rotor material chemistries. It is always recommended that only compatible pads and rotors be used in any given application.

Bedding in advantages:
1. Gradually heat treats the rotor and eliminates any thermal shock in the rotor.
2. Burn off volatiles and moisture from the resin that is near pad surface.
This will eliminate ?green fade.?
3. Establish a layer of transfer film about a few microns thick on the rotor surface. Shearing of the film during friction is an effective source of friction force. Otherwise, when using a freshly ground rotor without the transfer film, the main friction force would come from cutting, plowing, or scoring the asperities on the rotor surface. This leads to inconsistent braking effectiveness.
4. Mate the two surfaces to a near perfect geometrical match, so that the contact area is high, and therefore the friction force is increased.
5. The performance of a fresh rotor/fresh pad system would be inconsistent. This is due to ever-changing structures and properties of the two mating materials. Bed-in of pads and rotor will form a stable transfer film.
6. If bedding in procedure is not applied, a stable transfer film may not be established for a long time. In other words, the rotor surface would have to be constantly regenerating a film that is not quite stable for a long time. This effect would reduce the performance and increase the wear.

I always perform this procedure on all my new vehicles (even motorcycles) and whenever I do a brake job.

Bed In Procedure:

From a speed of about 60mph, gently apply the brakes to slow the car down to about 45mph, then accelerate back up to 60mph and repeat. Do this about four or five times to bring the brakes up to operating temperature. This prevents you from thermally shocking the rotors and pads in the next steps.
Make a series of eight near-stops from 60 to about 10 mph. Do it HARD by pressing on the brakes firmly, just shy of locking the wheels or engaging ABS. At the end of each slowdown, immediately accelerate back to 60mph. DO NOT COME TO A COMPLETE STOP! (Note: With less aggressive street pads and/or stock brake calipers, you may need to do this fewer times. If your pedal gets soft or you feel the brakes going away, then you've done enough. Proceed to the next step.)

During this process, you must not come to a complete stop because you will transfer (imprint) pad material onto the hot rotors, which can lead to vibration, uneven braking, and could even ruin the rotors.

Depending on the pads you are using, the brakes may begin to fade slightly after the 7th or 8th near-stop. This fade will stabilize, but not completely go away until the brakes have fully cooled. A bad smell from the brakes, and even some smoke, is normal.
After the 8th near-stop, accelerate back up to speed and drive around for as long as possible without using the brakes. The brakes will need at least 10 minutes to cool down. Obviously, it's OK to use the brakes to avoid an accident, but try to minimize their use until they have cooled.
After the break-in cycle, there should be a blue tint and a light gray film on the rotor face. The blue tint tells you the rotor has reached break-in temperature and the gray film is pad material starting to transfer onto the rotor face. This is what you are looking for. The best braking occurs when there is an even layer of of pad material deposited across the face of the rotors. This minimizes squealing, increases braking torque, and maximizes pad and rotor life.

After the first break in cycle shown above, the brakes may still not be fully broken in.
A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well. If you've just installed a big brake kit, the pedal travel may not feel as firm as you expected. After the second cycle, the pedal will become noticeably firmer.

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2007.5 Dodge Ram 3500 HD,QC, 6.7L Cummins, 6speed Auto, 4X4, Bighorn Edition.
Click for installs: Carr Steps PML Diff Cover Edge Juice with Attitude Volant Intake Hankook ATM RF10

I must admit, I've never done this but it does make sense on a system that is designed to be compatible...Like materials don't work well against each other, so the "system" is designed to do just that, work well with each other. Just make sure that what you have purchased has indeed been designed as a system and this procedure should work great. Break-in on any system is advisable and I have never seen this before but it makes a hell of a lot of sense...Thanks Squid.

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7.5 3500QC 6.7CTD 68RFE Build date June 2007
Superchips tuner 3808, Boost/EGT Laser Gauge, Airaid cold intake

In racing vehicles, we do this all the time. It is tempering the brakes like you temper metals .... Very noticeable effect

Great instructions, thanks for posting them !

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Guys...

The following is off the cuff so to speak and is general in scope but I do have the SAE journals in my office to give you the facts if necessary... and please remember these are my thoughts at this moment...

Part of what is said in the text above is pure hype and sales stuff.. we're in the brake reline business and brake bonding business and have been in the same location for 35 years.. doing mostly HD truck and Industrial applications... brakes for ski lifts, cranes, elevators, electric motor brakes, 1000's of truck brake shoes monthly... etc...

Just a couple of thoughts on the science....

excessive heat will cause the resins in the friction to burn out, this destroys the surface and will glaze the surface, you either have to get below this surface once the resins have been cooked our or throw away the friction.. in most cases its better and less costly to throw away the friction...

Most pad style friction is bonded to the backing plate.. at the time the bonding takes place, under pressure, usually many thousands of pounds and heat, controlled ramp up, hold the temp and ramp down the bond chemically impregnates the porosity's in the friction and the steel.. at this time any left of chemicals from the manufacturing process of the friction will gas off and do what is called the final cure on the friction..

600-700 *F at the surface of the pad is not uncommon but if you exceed 800* F at the bond it will fail.. any temperature above 800-1000*F at the surface will cause some or all of the resins to cook out thus leaving the friction useless.. again this is a time/temperature chart for failure... hotter, longer, quicker... less expensive friction and the temperatures for failure are much lower... Kevlar in the mix as an example increases life, and resistance to heat..

The metals used in modern rotors and drums and the machining process currently used puts a more select finish on the product before delivery to the end user... its now suggested that this high quality finish not be tampered with by installers and truing of the surface is NOT suggested as most turning equipment in the field will not leave the correct finish for modern friction... the exception is still class 8 truck drums, and I don't now why, other than the manufacturer is in too much of a hurry.. (cheep)

Also, most shops don't clean the finished surface on either the pads or rotors before installation... its suggested that MEK, Alcohol or other suitable chemical be used to remove GREASE, and METAL FILING'S from the machining process... even some grease spots from fingers will give the surface a problem...

One thing I do see that's important is that the owner understand is that all the surfaces are not 100% parallel in the first few hundred miles... but I'm guessing that these surfaces are not off by more than 1-2% on a modern vehicle.. the manufacturing tolerance on a set of pads is now down to a +- .001 or so where 10 years ago +-.005 would have been fine for the pads, the rotors are now down to +-.0005 in most cases from +-.001 or so 10 years ago..

The machining process off shore is every bit as good as ours and soon the metallurgy will catch us as they learn to cast higher grade alloys....

The keys to us..... quality friction from know suppliers who have been in the business and known dyno testing by independent labs, quality bonding adhesive... ours costs close to $500 for a 5 gal pail that has to be kept in a refrigerator to maintain the chemicals from evaporation once the container is opened... and cleaning all surfaces (metal & friction) before assembly to remove any dirt or grime that will effect the quality....

One last thought while I'm on the soap box... we get a lot of calls offering us friction from off shore.... we ask for SAE standard test results from an American testing laboratory, these tests are called "J" tests for short but there's really 10-12 tests that are performed... by doing nothing but reading and understanding these test results you can predict within a 5% margin of what the friction will do in real life.. the key is most of the friction people (manufactures) don't want to really share this... as their printed information often is not in line with the "J" test results...

I promise not to be this long winded all the time..