How to bed a beautiful woman...........OR, brakes

Sorry for the cheesy title.

Ok, so I read an article last night about the “myths” of warped brake discs and other brake system myths, and now I’m confused…about several things, but focusing on “bedding brakes” here.

I’ve always understood that rotors warp when overheated, etc., causing a vibration when braking…this article, written by someone who seems to know what he’s talking about (or should, anyway), states that so-called warped discs are actually caused by friction pad material transferred unevenly to the surface of the disc.

What do the experts here have to say about this? Here’s the article:


In the above article, the author states that the proper bedding-in technique involves a series of ten increasingly hard stops from 60mph to 5 mph with normal acceleration in between, to burn off bonding resins on the pads/rotors.

And here’s a Cartalk discussion which basically states the opposite for bedding brakes (see our good friend Karl Sieger’s post where he quotes an automotive textbook):


And I know one of our resident experts, ok4450, posted pics of warped rotors looong ago…so any clarification on this subject of warping and bedding-in would be appreciated.

Thanks guys (and girls). Sorry there wasn’t anything in here about beautiful women.

Oh come on, is the title really that bad that no one is reading this?

Jad, I think part of the reason there’s confusion on this issue is that the actual ingedients- the composition of the friction material on any given set of pads is a trade secret. I have read that it’s true what you say about the lining material being unevenly distributed on the rotor and causing variations in thickness from spot to spot. But I’m sure that overheating the brakes during panic stops and the like will cause

warpage, too. I’ve seen too many rotors with hard spots that produced severe brake pedal pusation. The spots are blue. Have you ever heated a ferric type metal with a torch? It will leave the metal blue. Same with pistons and rings that have overheated from lack of lubrication. Anyway, if you try to machine the hard-spotted rotor the bit won’t cut away the hard spots as much as the rest of the metal causing bigtime

rotor unevenness which will cause caliper piston knockback and pulsation. I guess this may not actually be warpage but it would seem to be effectively the same thing. Also I’ve heard that if you overheat rotors severely, if the part that got overheated soon gets splahed by a puddle, that part will now have a different expansion rate than the rest of the rotor, but I have no proof of this. Jad, nice post, buddy.

Maybe a beautiful female automotive brake engineer can straighten this one out.

Since there was no absolutely disgusting pics I hit the back button… :slight_smile:

I’ve seen that article long ago and don’t think any better of it now. Wonder why the logic is that every type of metal in the world can warp or distort except for brake rotors?
An engine block out a of Kenworth conventional will deform, when new/before machining and after use, so I fail to understand why a thin brake rotor is assumed to always maintain its shape.

It would take a real sensitive guy (REAL sensitive) to notice a 0.0004 variation. Not.

Here’s some interesting reading on the subject.


Personally I use ceramic pads, because they don’t require bedding, last a along time, and I have yet to encounter brake pulsing with them.

Thanks for that post, Tester, it was a balanced article. Makes sense and kinda goes along with what Karl said.

Haha sorry OK, I’ll put some in my next post, wasn’t sure if the moderators would frown on that…(are there any moderators? Doesn’t seem like it)

Yeah I don’t buy the “I’ve never seen a warped rotor in 40 years of racing” bit either…metal’s metal. But maybe the rotors/pads used in racing are a much higher quality than “street” brakes, and thus warp less often?

But I guess that different pads/rotors have different bedding in procedures depending on the make…no one-size-fits-all unfortunately.

Karl, you make a very good point…that explains a lot, along with Tester’s article below.

And I agree about the female brake engineer…

I have car problems and cant find anyone to help fix it!

On a related topic, on a 4 disc brake setup, when there is vibration during braking, is there a way to tell if the vibration is coming from the front brakes and not the rear brakes (or vice versa…or front and rear), without taking the rotors all off and checking them the proper tools?

One thing I never see mentioned (even on the other websites) is that brake rotors, either new or freshly machined ones, should always be thoroughly cleaned with brake or carb cleaner and wiped down afterwards. Wonder why that is?
No one ever considers that the new rotors may have an anti-corrosion film on them?

All I’ve ever done is the repeated hard brake apply from 40+ mph on new pads. I worry more about the tire shop torquing the wheel nuts too tight or unevenly and have had warped rotors shortly after tire service more than after pads are installed.

I think you’re in the right church, wrong pew, LuLane. Go to the top of this page, right hand corner and click on “Submit a car question”. Give the make, model, and year; engine size if you know it, and a good as you can description of the symptoms your car is exibiting; just like you tell a doctor what’s ailing you.

Yes. Try applying the parking brake while driving. If the vibration is there then it’s coming from the rear brakes.

It can be a bit tricky to apply the parking brake on some vehicles. On vehicles where there is a parking brake handle to pull it is easy but on vehicles with a pedal it is harder. You have to apply the pedal and hold the release lever at the same time.

Now there are some vehicles that don’t use the rear brake pads for a parking brake, they use a separate brake drum inside of the rotor. There are a set of brake shoes that are used for the parking brake so applying the parking brake won’t work in this case.

I’m a firm believer that over torquing of the lug nuts is the cause of rotor warping. Mechanics/tire changers do this as standard procedure. They’re so concerned about a wheel falling off that they overtorque the lug nuts. They don’t care that this will warp the rotors.

Whenever I have to turn my cars over to a mechanic for work I always put my torque wrench in the trunk. Before I leave the garage, I always check wheel nut torque by backing off the torque, then torquing to the proper value. Wheel nut torque on my cars (92 & 98 Honda Accords) is to be 80 ft lbs. I usually find it at 120 ft lbs after someone else has tightened the lug nuts.

My '98 Accord (bought new) has 190,000 miles. Original rotors have never been turned. Have put 3 or 4 sets of pads on it. No vibrations.

My '92 Accord (bought new) has 233,000 miles. At 19,000 miles the rotors were replaced under warranty; vibrated but the runout was minimal, evidently a problem with the metallurgy.
At 105k miles the rotors were turned to eliminate vibrations. The rotors now have 214k miles on them and there are no vibrations. Have put 3 or 4 sets of pads on it.

Living in a town famous for machine tools I have learned this. Cast iron should be aged before it is machined. They used to let the cast bed of a machine age outside for three yars before the surface would be machined. That was done if you wanted high precision. Casting metal as fast as you can is just going to cause some to warp with heat. I don’t think material transfer has much to do with it. Glazing would be pretty even process till it flaked off.

I have wondered why my brake rotors on my car warp while the brake disks on motorcycles don’t. Could it be because motorcycle brake disks are slotted and drilled for better cooling? What about brake upgrades? J.C. Whitney has slotted and drilled brake rotors for my car and I have wondered if upgrading will prevent future warping. I might experiment with them the next time I need to replace the rotors.

A friend of mine (semi-retired) has close to 50 years in as a machinist and gunsmith. This guy is as good as it gets and has machined industrial engine blocks and built 10k dollar shotguns with equal dexterity.
While not degreed in the field, he is about as good a metallurgist as can be found and knows everything about metals, their charateristics, the effects of machining, welding, and heat on them, etc.

He told me one time that when machining engine blocks (which were cast in their own foundry on site) every single block was tossed out into the field and allowed to ripen like a tomato for at least 2 years. At the end of 2 years none of those blocks were the exact same shape they were when removed from the molds.

A thousand pound block of cast iron will tweak so why not a thin brake rotor. (When, and if, the sunshine appears here and temps rocket into the 50s I’m thinking of a little brake rotor experiment with a micrometer, dial indicator, etc. Will see what happens and post the results on this forum. Just something that hit me and aroused my curiosity.)