Turning Front Brake Disks

I just changed the pads on my front brakes because they were at that point but also because they would squeal loudly when I used them. The new pads are quiet when I use then, but they are a little squeaky when I don't. The disks have the typical cuts in them from normal use, but nothing to horrible. I was wondering if turning the disks was possible and if it would quiet things up a bit.

 

In my opinion, if the rotor is so gouged or worn that it needs to be turned then it should be replaced. Best thing to do is gently sand the surfaces (with fine grit paper) to dress it up and help the new pads break in. sort of like honing a cylinder. You don't want to remove much metal just break the surface glaze.

Its hard to do this with the rotor on the bike so you have to remove it. Be careful about too much torque on the bolts when you re-install it.

 

They aren't really damaged, just normal wear. You can run your fingernail across and feel grooves, but no deep cuts. I've seen brake rotors that have been subjected to metal-on-metal wear and that's not what I have.

I'm just curious if the rotors can be turned or if it's a real no-no. New rotors aren't cheap.

 

From the reading I have done, the prefered method of repair is replacement, period. True, one could resurface the rotor but the ability to do so and still have a salvageable rotor when all is said and done is pretty slim. If you can't get a good surface out of running a 100 grit wheel around the rotor (both sides folks), start saving your pennies.
That said, I've never replaced any of my rotors to date, even with slight grooving such as what you describe IllMax. Have you tried to slightly chamfer the leading edge of the pads to reduce the chattering?

 

The rotors CAN be turned, but not by the usual suspects. The brake rotors on many of these XJ-era bikes are made from some type of tempered (?) steel, and regular rotor-cutting tools just can't handle it.....the cutting blade "chatters" across the surface, destroying both the rotor surface and the cutting blade.......

I've had very good results in cutting old rotors on a flywheel surfacing machine, like is used in automotive machine shops to "surface" flywheels and clutch pressure plates. Just make sure that they cut the minimum amount needed to both remove any surface imperfections and to make sure the rotor is truly flat and both sides are parallel to each other.

Always a good idea to check the minimum thickness allowed for your rotors (in a factory service manual) and make sure both before and after surfacing that those mins aren't violated. And also check the lateral run-out after surfacing is done. Some old rotors can't be salvaged. Once they are past min. thickness, they're junk, don't use them. Also check for hairline cracks eminating from the mounting holes or at the outer edges of the rotor. Once they're there, the rotors are junk.

And always replace the mounting bolts and lock-washers whenever removing and replacing a rotor. Cheap insurance!

The older I get, the more important big brakes become to me (as well as big motors!).

 

Well said Chacal, I'm not a machinist but the education helps understand why most folks don't bother with turning rotors. I just hit the Haynes, 6.5 mm min on Maxim rotors and 4.5 mm min on the Secas! Couldn't agree more about chucking them when they hit minimums or crack.

 

Yep, I feel that keeping the brakes in top shape is one of the most important items. (However, there are hundreds of posts on tuning the carbs and diddly on brakes!)

The brakes really don't chatter (but I do like the idea on chamfering the front edge), but it's just an annoying squeak... probably from a bit of metal in the metalic pads riding on a bit of a ridge on the rotor.

I'll try 400 - 1000 grit wet/dry paper on a block to see if I can't knock off the high points (or learn to just live with the squeak... my wife does that when there is something wrong with her car; she just turns up the radio).

 

...oh yea, and I'll mic the rotors to check thickness.

 

Mkae sure you mic them in more than one place on each rotor, basically do it at 4 places on each rotor, Noon, 3-oclock, 6-oclock, and 9-oclock, this way you'll also get an idea as to whether the runout is a possible concern........

 

All you really need to do is "Chamfer" the new pads all around.

The hard right-angle has to make some noise. Eliminate the right angle by rounding-off the edged on the pads and NO turning of the Disc will be necessary.

Another point on Front Brake squeal.
It might indicate you are due for some Front Brake maintenance. The channels that the seals are mounted into will have their Inside Diameters reduced by "Brake Cake". A combination of Brake Dust, Brake Fluid and moisture.

If you get enough Brake Cake happening in those grooves; the Caliper Piston won't retract the small distance it needs to ... to release the Rotor and the subsequent Hot Brakes squeal resulting, will remain, despite Chamfering the Pads or adding Disc Brake Quiet adhesive to the back side of the pad where it's pushed by the Piston.