Turning Discs

Hugh R · 11-28-2003, 09:18 AM

I'll be putting in new brake pads front and rear this afternoon, which I bought from Pelican. Wayne's 101 book states how to do it, and I've done brakes before, but the book doesn't mention turning the discs. They look good, no scoring and they're not warpped. Should I turn them?

Superman · 11-28-2003, 09:23 AM

There is a lip at the outer edge. The depth of that lip will give you some indication of how worn they are. If you take them in to get them turned, they will measure them and tell you if there is still enough meat left on them. The full job would involve taking the hubs off and the bearings out. You'd need a new inner grease seal upon reinstallation. Also a good time to change bearings.

The cheap guy's method (yes, I'm pretty cheap) would be to score the rotors with scotchbrite. Rough stuff. I have a fixture that goes on my drill that makes this easier. They are hard and you really have to get aggressive with them. Your goal is to at least break the shiny glaze.

Formerly Steve Wilkinson · 11-28-2003, 09:27 AM

Turning the rotors really isn't done much anymore. It just makes them all that much more susceptible to warping, particularly on a performance car. If your rotors "need" turning, you're better off buying new ones.

Stephan

makaio · 11-28-2003, 09:52 AM

I have always just installed new pads. I have been told what Stephan said by the pro's, if they need turning, just replace them.

Hugh R · 11-28-2003, 10:10 AM

Thanks for the good advise.

Formerly Steve Wilkinson · 11-28-2003, 10:13 AM

Hugh, what's your DB4's s/n? Years ago, I owned 161, engine #163.

Stephan

84toy · 11-28-2003, 10:25 AM

Well, I guess I don't agree. Being a machinist and having a lathe at home spoils me. I think rotors are like engine blocks. The racers like used blocks because they have been "seasoned" meaning many hot cold cycles which will eventually allow the block to settle to whatever warpage it 's inner stresses want to go. Then you machine it straight and you have a block that won't warp so easy. Others may disagree but I think rotors are similar. They get very hot and very cold and warp as well as wear. In addition, I would never bolt on a set of new rotors on the front hubs and "run them" without checking with a dial indicator. Many times they will have runout because someone did not get the races in properly or there is a hammer mark on the face etc, etc. Anyway, whatever route you choose, check the rotor runout when everything is bolted together. Most any car should be less than .002" and I like mine at .001 or less if you want great feeling brakes

Bill Verburg · Bill Verburg's Garage

The problem w/ turning rotors is that they are marginal to begin w/, being thinner doesn't help. Often a resurfacing which doesn't take off much material is the way to refresh them.

Same w/ pads for track use, replace them before they are 50% used up.

Hugh R · 11-28-2003, 10:32 AM

Steve:

438L Engine No. 484

Red, owned it about 32 years (first car I ever bought)

Formerly Steve Wilkinson · 11-28-2003, 11:23 AM

Can't find my old AMOC guides, but wouldn't that number make it a '61?

Stephan

911pcars · 11-28-2003, 11:37 AM

Some will say grinding is a preferred method to remove metal from a heat-checked surface like a brake rotor or flywheel. If there are any hardened spots caused by localized heating, the lathe tool will merely skip over it.

JMO,
Sherwood
http://members.rennlist.org/911pcars

Bill Verburg · Bill Verburg's Garage

Quote:

Some will say grinding is a preferred method to remove metal from a heat-checked surface like a brake rotor or flywheel. If there are any hardened spots caused by localized heating, the lathe tool will merely skip over it

I agree 100% w/ Sherwood here but need to add that it's not if, there will definitely be localized hard spots and the cutters will lift.

In addition w/ surface grinding only a tiny amount of material is removed, as little as .0001"

I only have mine ground when necessary(a rare event)

Hugh R · 11-29-2003, 01:27 PM

Steve:

You're right, however, it was registered as a 1960 when I shipped it into the country and I had enough problems getting it here, I never bother to change the registration.

masraum · 11-29-2003, 01:45 PM

My main aversion to turning rotors is that you never know who or what is turning your rotors. If you get it done don't take it to your local autoparts store. Often the people who work there may or may not really know/understand what they are doing, and the equipment could be in horrible shape.

I'm sure they can be turned and that it is an effective treatment, but without knowing if it is going to be done right they could end up worse than when you started.

84toy · 11-29-2003, 02:05 PM

Steve, you are absolutely correct. Being honest, I machine them myself and I don't know if I would let a shop do them unless I knew them. In fact, when I turn them, I take a skim cut on the face where it bolts to the hub and then I know they will run perfecly true. One time I had my wife's rotors turned and they had a whopping .018'" run out when the shop finished. Most people don't have a dial indicater and can't check them so they are stuck with whatever workmanship or lousy equipment does the work. As I previously stated, always check the run out whether new or machined.