turning 930 rotors?

[panzerfaust]

hello guys

anything special procedure or problems turning factory 930 rotors with the holes?

they are still within thickness spec but mine got a mm or two ridges i want to turn down before putting new track pads on.

thanks in advance

pf

[T77911S]

new rotors are not that expensive.

not sure what the min thickness is but I would be very leery of warping after a few hard heat cycles. that's just me.

other thing is, look at the holes in the rotors, they are chamfered. if you cut them that is removed.

on that note and little OT, I just had mine off. I pressure washed the rotors and blew lots of dust out of them. might be good PM to help cooling.

[Iciclehead]

I have had the same question and for me, with the floating rotors, the new ones are not cheap, particularly if you want the Porsche rotors.

From what I read in the factory manuals, they are supposed to be Blanchard ground...technically referred to as Rotary Surface Grinding, quickly removes stock from one side of a part that is typically too large to be Double-Disc Ground. I went to a machine shop and they looked at me like I had three heads when I asked if they did Blanchard grinding.

If I recall, the original finish on my rotors (new) was obviously ground in some way, I also think that the amount removed is very small, just enough to take the lip off and to remove any waves, so I do think that the chamfer on the holes would largely remain.

Most shops with a disc lathe take off way too much, usually they take it down to just over the minimum disk thickness, partly to make sure they get all the grooves out (not necessary) and partly as a way to sell you unneeded services.

There are places on the web that do Blanchard grinding, the Turbo brakes are coming off my car to get it ready to sell, I may well send them out to be ground and will report back on any findings should I do that.

Dennis

[T77911S]

there was a thread on the 911 side about 930 brakes and rotors.
I think they mentioned a good sub for floating rotors.

once again people cant make the effort to put the year of their car in their sig so now any answers have to cover the different years.

[Jeff NJ]

Originally Posted by Iciclehead

I have had the same question and for me, with the floating rotors, the new ones are not cheap, particularly if you want the Porsche rotors.

From what I read in the factory manuals, they are supposed to be Blanchard ground...technically referred to as Rotary Surface Grinding, quickly removes stock from one side of a part that is typically too large to be Double-Disc Ground. I went to a machine shop and they looked at me like I had three heads when I asked if they did Blanchard grinding.

If I recall, the original finish on my rotors (new) was obviously ground in some way, I also think that the amount removed is very small, just enough to take the lip off and to remove any waves, so I do think that the chamfer on the holes would largely remain.

Most shops with a disc lathe take off way too much, usually they take it down to just over the minimum disk thickness, partly to make sure they get all the grooves out (not necessary) and partly as a way to sell you unneeded services.

There are places on the web that do Blanchard grinding, the Turbo brakes are coming off my car to get it ready to sell, I may well send them out to be ground and will report back on any findings should I do that.

Dennis

My clutch flywheel was Blanchard ground by my local pcar indy shop. Maybe a shop that can re-surface a flywheel can do the same for a rotor?

[TurboKraft]

Originally Posted by Jeff NJ

My clutch flywheel was Blanchard ground by my local pcar indy shop. Maybe a shop that can re-surface a flywheel can do the same for a rotor?

Correct, same style machine.

1982-89 rotors are fairly reasonably priced.
For 1978-81, there are aftermarket rotor packages (ex: Rebel Racing) that usually use heavy-duty domestic-made racing rotors.

[1979-930]

I had mine looked at and it's not worth the time and cost to machine IMO. It's better to replace with new while it's apart. Sebro makes the floating rotors and they are cheap. 1979 Porsche 930 Turbo Coupe - Brake Pads & Rotors - Page 3
$160.00 each. The new thicker Sebro will be better than thin Porsche rotors.
And I wouldn't even consider paying $500 for the Porsche part number on the box.

[T77911S]

still don't know what year he has.

zimmermann are 130 for 82+

[panzerfaust]

i have an 84 and prefer the porsche brakes since i intend to track it. no sebro or oem for me as of now. perhaps go with some aftermarket bells and coleman low cost rotors down the road for just rotor replacements.

im not sure what a blanchard cut is? is it same as a fly cut for flywheel or cylinder heads? seem like it would risk run-out if not done properly over a lathe.

thanks for chiming in guys

pf

[Jeff NJ]

Here is a before and after pic of my flywheel showing Blanchard grinding. It's more of a circlular pattern compared to the typical rotor turning.

[full quack]

In my opinion machined rotors are for grocery getters and econo boxes....do it right, do it once, do it complete.....new rotors, new pads and a fresh full brake fluid flush.

Machined rotors only save a little $ at the onset, but the savings are a short lived folly, as they will not last the distance, so you will get the opportunity to do it all again much sooner than you would initially think.

Mark

[panzerfaust]

yes i can easily put new the sebro crap on for the cars and coffee crowd

what distance are you talking about? ive change new brembo rotors on another track car once or twice a year. depending on the aggressiveness of the pad they can chew up rotors pretty fast.

factory 930 casted hole brakes already crack under hard use on new rotors.

[full quack]

The term "will not last the distance" was a figure of speech, meaning something that will not last as long as a new.

Direct meaning, turned/ground rotors will end up obviously thinner than new, thus will wear out of spec faster than new, thinner rotors tend to warp much more easily as well, but I'm not telling you anything you don't already know.

When dealing with track conditions and track rated pads, everything is thrown out the window, for as you stated "depending on the aggressiveness of the pad they can chew up rotors pretty fast". So given the sole use of rotors on the track, I guess you really have nothing to loose, as they are going to die an early death no matter what.

As far as new replacement rotors, I do not know the quality of Sebro, but I would be suspect, simply due to the price point.

Zimmerman are direct O.E.M. rotors. I have bought factory direct Porsche rotors for my 944 turbo that came in Porsche sealed boxes, but inside were rotors with a Zimmerman sticker right on them, as well as a "made in Germany" sticker, so.........

Mark