Front Brake Pad Replacement - Rotors too?

[luke-44]

At the risk of asking a dumb question, do I really need to replace the rotors when doing brake pads? The rotor thickness is showing a nominal 13.0 mm thickness and at a glance look to be OK so I would ideally like to do just pads making it a much smaller job. But I recall reading this may set up the possibility of "chatter" upon braking. My driving habits are occasional use only (<1000 miles/yr) and not what I would call real spirited driving.

Second question - I assume I want pads for a steel "M" caliper - p/n 911.351.938.00?

Thanks in advance, Bruce

[classic]

As long as they are showing even ware, and are in speck pads only will be fine.

If you are concerned at all get them dressed, but make sure they have the specks.

[rockandrollrods]

Any machine show that turns rotors will tell you if they are in spec or not. It's not a bad idea to turn them. Makes the break-in that much easier.

[davep]

If the rotors are in good shape with no deep grooves, then you may be able to find a shop that can grind them. Many years ago a fellow invented a grinder to resurface rotors on the car, and sold the rights to Bear; I think he has repurchased the rights, but most Bear Alignment shops should have the equipment. The finish is ideal for bedding in new pads. The process removes the minimum amount of material needed to provide a like-new surface.

[Flieger]

First, the machining operation would be facing, not turning. Secondly, if you notice there are spots of pad material (not uniform) you want to grind them, not face them.

[rockandrollrods]

It's a regional thing I guess. The common terminology in my area used to describe the process of machining the surface of the rotors is "turning" or "machining". At least around here anyways.

[davep]

"turning" or "machining" is a lathe operation with a bit that makes a spiral cut to remove surface material. The bit needs to remove a minimum amount of metal to make a proper cut.
The grinding operation I spoke of uses two abrasive disks to "sand" the surface; but it really is a surface grinding operation. The depth of "cut" is much less than a machining operation. About 30 years ago I worked in a joint VW & Honda shop. New Honda rotors had to be ground flat and true on the car after installation according to the factory.

The patent I know of for grinding: http://www.freepatentsonline.com/4361988.html
Made the inventor a millionaire.

[luke-44]

Thanks for the input, I guess my question would be viability to replace the pads only and not take off the rotors at all - either to replace them or to "turn/machine" them. If that is mandatory then at that point I would just spring for new rotors as the cost around here is close enough to just buying new.

I was wondering how close the 13.0 mm is in comparison to new ones - that would give me an idea as to how much wear I'm looking at...I guess I should just bite the bullet and install new rotors...

[Flieger]

That sounds pretty low. I think they start at 19mm but I don't know the wear limit. I would do the same as you say- buy new rotors rather than grind.

Turning = feeding the cutter parallel to the lathe axis, makes a part a certain diameter.
Facing = feeding the cutter perpendicular to the lathe axis (radially), makes a flat face on the end of a part.

If you try to turn a flat face you will either end up with a very bad surface finish (lots of deep grooves) or your cutter will grab and bad things will happen to the cutter and workpiece.

[Richardnew]

Actually the real problem is that the different pad materials may not be compatible. You need to remove all the old pad material from the rotor. I usually sand it off. Here's an article I wrote a few years back about all of this.

Now if you're using the exact same pads as you're removing you won't need to do this.

Richard Newton