How bad does this rotor look?

wastintime · 08-18-2005, 12:22 PM

Hey everyone,
I'm leaving for a DE tomorrow and I hadn't realized that one of my rotors is looking a little tired. I thought I'd post a pic and see if anyone thought it would be too dangerous to run on them just for the weekend and replace them as soon as I get back. I've always heard that you're going to get little cracks in drilled rotors as they wear, it's only if you notice two cracks from different holes touching that you need to really worry and replace them. None of the cracks are touching, it's just that it looks worse than the opposite side, and it's probably time to replace them... I think they've got almost 2000 racetrack laps on them, plus street driving. BTW, if it matters they are '94 965 Turbo rotors.

Thanks

}{arlequin · }{arlequin's Garage

i'm no expert but they look pretty bad to me. While you're right about cracks not connecting the holes, I'd at least keep a real close eye on them between every session.

If you can, I'd source a pair and swap them in. Compared to the car, rotors are cheap. Who knows what will happen when it fails on you on the track.

Bill Verburg · Bill Verburg's Garage

Spec on the cracks is ok<7mm, but the disc is heavily grooved. I would replace it now.

JeremyD · JeremyD's Garage

Wow - I wouldn't run that at a DE

David · David's Garage

That looks close to the limit. I was surprised to see similar cracks on the front rotors of a new RUF RGT when I was in Dallas a few months ago. It had obviously seen a couple of track days.

wastintime · 08-18-2005, 01:57 PM

If I had the option of replacing them now I would... the soonest I can get new ones is Tuesday... If 7mm is in spec I think I am ok on cracks... most are about 3mm and the two longest ones were 5mm

I think I'm going to run them, and maybe take it a little easy, just keep an eye on them, and if I get any weird vibrations or anything, stop for the weekend.

NoLift911 · 02:26 PM

Quote:

Originally posted by wastintime
If I had the option of replacing them now I would... the soonest I can get new ones is Tuesday... If 7mm is in spec I think I am ok on cracks... most are about 3mm and the two longest ones were 5mm

I think I'm going to run them, and maybe take it a little easy, just keep an eye on them, and if I get any weird vibrations or anything, stop for the weekend.

Uhhh...take it easy at a DE? Isn't the point of a DE not to take it easy?

Ever see a rotor explode at speed?

It's kinda cool - first you get a black puff from the fender well, you lose all braking, pedal goes to the floor, and the car takes a hard right or left and you crash into the first imovable object, then huge chunks of glowing rotor follow you wherever you land...

Then there is the stuff that gets broken when the rotor shatters at speed...caliper gets ripped off the strut housing, strut is usually destroyed, fender damage etc.

Just saw one at Watkins Glen this past weekend...pretty damned cool.

And of course there are your fellow DE buddies on the track that probably did a thorough inspection and tech on their cars so if you wipe one of them out with you...you may owe them some parts too and a couple beers if you/they survive...

2000 race track laps eh? You weren't the guy in school that was never prepared and the dog always ate his homework were you?

Lotsa drama for no reason...

-Jeff

masraum · 08-18-2005, 02:26 PM

Quote:

Originally posted by nolift911

Just saw one at Watkins Glen this past weekend...pretty damned cool.

-Jeff

as long as it's not your car, no one gets hurt, and the owner has a relatively unlimited supply of money...

JonT · 08-18-2005, 02:27 PM

What causes the rotor to groove like that? Wouldnt changing the pads frequently tend to smooth them over time?

NoLift911 · 08-18-2005, 02:30 PM

Quote:

Originally posted by masraum
as long as it's not your car, no one gets hurt, and the owner has a relatively unlimited supply of money...

I thought I laid the sarcasm on pretty thick...

Note to self - DO NOT ATTEND A DE WITH WASTINTIME...

-Jeff

Jack Olsen · 08-18-2005, 02:43 PM

To my eyes, those cracks look fine. The grooves are more of a concern.

Bill Verburg · Bill Verburg's Garage

Quote:

What causes the rotor to groove like that? Wouldnt changing the pads frequently tend to smooth them over time?

It's a normal wear pattern

Changing pads will only wear ot the pad quicker

wastintime · 08-18-2005, 02:51 PM

I haven't really had to change the pads frequently... I'm still on the second set of pads. Since installing the brakes. 1 set of Hawk Blues and 1 set of Pagid Oranges...

Lol, yes I have seen a rotor explode at speed, and yeah it is actually pretty cool to see, but as was said only if no one gets hurt. Actually I was the guy sleeping in the back of class that never did homework, who taught the next class as a favor for the professor, got a 1600 on the SATs and started doing high energy astrophysics research at 17, but close enough. As far as being able to do that many laps on them... they're frozen rotors... I've seen some guys with non drilled frozen rotors get almost double that kind of durability. What can I say, that's how long they lasted. Just because the brakes were inspected last doesn't mean a thorough inspection of the car wasn't done. A non-thorough inspection would have missed this... but it was found and now the issue is how to deal with it, hence the inspection worked... any more questions class? and yeah I got the sarcasm did you catch mine?

all kidding aside though, I don't know... I honestly don't think they look that bad, yes there is grooving, and yes there are cracks, but such is the nature of a cross drilled rotor. I've seen way worse on some cars. I don't think one weekend which is what like... 90 laps at a course as gentle on brakes as Roebling Road is, is really going to cause a sudden massive failure, especially when really everything about the rotors is in spec, they're just tired... I'm going with Jack on this one it's the grooves that bother me more than the cracks

efhughes3 · efhughes3's Garage

Not to be a jerk here, but how does something like (the whole question whether the rotor is safe) this come up the day before you leave for a track event? Am I the only one who crawls around their car the weekend before going to the track or two weekends before if my schedule is busy to look for this kind of stuff? Especially brake components?

There are people above here on this post that know a whole lot more about brakes than I do, but I'd think twice: heat does a number on metal parts, and yours doesn't look too good to begin with.

wastintime · 08-18-2005, 05:08 PM

Ed, you don't sound like a jerk, that's a perfectly reasonable question to ask... I only got a little pissed at no lift for obvious reasons.

I've been going crazy for the past week getting the car ready. It basically needed a major service, the valve adjust was the big part, and it needed a tensioner replaced... these took precedence. Then we ended up redoing the alignment, figuring the track tech on the car was going to be simple... well I simply hadn't looked at the brakes until today because that was kind of moot in comparison to the engine running.

Unfortunately this happens a lot with me, I've been working in a Porsche shop for about 3 years and usually customer cars take precedence and mine doesn't. What can I say I'm human, sometimes it happens you figure you have the recources to tackle things at the last minute, before my last event I ended up replacing a CV boot the night before I left. PIA, but no biggie. This just happens to be a crappy instance where I don't have new rotors on hand. Before I even posted I'd shown them to my ex boss, who was only a 962 crew chief, spoken Dave at SSF, Frozen Rotors, and Smart Racing about it. Everyone had told me to go ahead and drive the weekend, they'd be fine if I replaced them as soon as I got back.

It's a little hard to be dispassionate when it's your own car so I posted some pics on here just to get some opinions, because yes, there are some incredibly knowledgeable guys on here. Like Bill and Jack who replied... we don't always agree, but I value their opinions anyway. How this makes me an unsafe DE goer I'm not sure.

ecm911 · 08-18-2005, 05:24 PM

I use the same rotors ( 965 ) on RSA - they will crack the first DE event. Everytime. I have run with rotors cracked - you have too. I am not alone. I do keep track of them - if the do touch - esp at the outside of the rotor is when I replace them. I know many DE/Club racers that run wiyh cracked rotors. Like I said they will crack after the first hot run.

In fact becasue the rotors are very expensive and crack so d#$# easy, I switched to solid rotors. I think I have 2 sets of cracked rotors ( not worned) in my garage - I replace every year.

Anyway look into 928 S4(?) rotors same size, but solid.
I was concerned about heat, but has not been an issue yet. And I have done about 5-6 events on them .

mattduncan · 08-18-2005, 05:37 PM

my dad's TT had rotors that looked like that minus the grooves. The "cracks" looked like a consern of mine, but the car stopped very well at PIR w/o overheating or fade. The grooves is what I would be concerned with only because it would imply uneven breaking. My dad did eventualy replace the rotors (only because he has the money to dump WAY to much money in the car...) and it doesn't perform any different.

ecm911 · 08-18-2005, 05:39 PM

Originally posted by nolift911

Just saw one at Watkins Glen this past weekend...pretty damned cool.

-Jeff

NASCAR?

JeremyD · JeremyD's Garage

Me - I don't take chances at DE's I replace my tires before I need it, My brake components before they are due and yes, just like Ed I start crawling around my car two weeks before a DE checking all the components.

On the street I rarely get over 100 mph - On the track I always go over 125-130. I know that the only person responsible for my safety and those of my DE partners is me.

Of course I am to damn handsome to waste all these good looks by stuffing my car in the wall (and have two small kids that wouldn't appreciate their dad taking a chance).

Bad things happen on the street - bad things happen 3x as fast on the track. You will probably be fine - but is it worth the risk, especially with Brakes?

911 heathen · 08-18-2005, 06:17 PM

When you do swap them (like, right now), change for slotted not drilled....

Drilled rotors will give you the grooved wear pattern as the pad dust accumulates in the holes...

Also slotted rotors don't tend to crack like the drilled items.