Drilled rotor is backwards on one side. Is it an issue?
04-09-2005, 02:54 PM
#1
Nordschleife Master
Thread Starter
Drilled rotor is backwards on one side. Is it an issue?
I just got my car back from the shop, after having the brake rotors and pads and fluid changed, and my LSD tranny installed.
After I brought it home, I noticed that the rotor on the driver's side is the exact same rotor as the passenger side. IE, they are not mirrored. So on passenger side, the vanes spew air out, whereas on the driver's side, they scoop air up.
Now, I'm not a racer, but I am doing a DE tomorrow. Common sense tells me it won't be much of an issue, but I am concerned that one side might not cool properly and I'll get a pull to one side under braking.
What are your thoughts? The shop is closed for the weekend, so I can't really call them till monday to get their thoughts.
After I brought it home, I noticed that the rotor on the driver's side is the exact same rotor as the passenger side. IE, they are not mirrored. So on passenger side, the vanes spew air out, whereas on the driver's side, they scoop air up.
Now, I'm not a racer, but I am doing a DE tomorrow. Common sense tells me it won't be much of an issue, but I am concerned that one side might not cool properly and I'll get a pull to one side under braking.
What are your thoughts? The shop is closed for the weekend, so I can't really call them till monday to get their thoughts.
04-09-2005, 03:13 PM
#2
Rich,
That seriously sux. Given what we all pay for shop time, its reasonable to expect the tech would have enough of a clue to know that rotors are sided.
OK, sounds like to pass side is correct, and the drivers side is wrong. Air flows through the vents from the hub to the outside of the rotor [which is why cooling ducts supply air at the hub].
I can't think of a reason why this would be unsafe, but the drivers side front wheel is certainly the hottest wheel on the car. It takes most of the loads on a clockwise track, and its always the tire that gets hottest on a 944T. If it is possible to find a local source that can lend you a rotor, do it. They are a snap to change out. If not, just go very carefully and watch for uneven braking on the front - it should pull right if the temperature imbalance gets high.
Back to the shop. New rotors means new pads too, right? They should replace the rotor with the right part#, AND repLace the pads with a new set. You do NOT want to hit the new replacement rotor with pads that have had a weekend of hard riding. The shop owes you a new set of pads as well, at least.
So why don't you try to find the shop owner's home number and call him immediately? He should feel bad enough about this screw up to help you out.
Good luck with it, and have a great track weekend.
That seriously sux. Given what we all pay for shop time, its reasonable to expect the tech would have enough of a clue to know that rotors are sided.
OK, sounds like to pass side is correct, and the drivers side is wrong. Air flows through the vents from the hub to the outside of the rotor [which is why cooling ducts supply air at the hub].
I can't think of a reason why this would be unsafe, but the drivers side front wheel is certainly the hottest wheel on the car. It takes most of the loads on a clockwise track, and its always the tire that gets hottest on a 944T. If it is possible to find a local source that can lend you a rotor, do it. They are a snap to change out. If not, just go very carefully and watch for uneven braking on the front - it should pull right if the temperature imbalance gets high.
Back to the shop. New rotors means new pads too, right? They should replace the rotor with the right part#, AND repLace the pads with a new set. You do NOT want to hit the new replacement rotor with pads that have had a weekend of hard riding. The shop owes you a new set of pads as well, at least.
So why don't you try to find the shop owner's home number and call him immediately? He should feel bad enough about this screw up to help you out.
Good luck with it, and have a great track weekend.
04-09-2005, 03:21 PM
#3
Nordschleife Master
Thread Starter
They are OEM 86 951 rotors, but crossdrilled. The thing is, I looked in the PET and it only shows ONE part number for stock undrilled 86 951 rotors. I therefore assume that the STOCK undrilled/unslotted 951 rotors also have the venting vanes backwards on the Driver's side wheel.
Now you would never notice the cooling vanes backwards on an undrilled rotor - but on a drilled one, it just doesn't look right...
I looked at a 996TT, 993TT, boxster and a few other p-cars this morning, and all of them had the cooling vanes mirrored on the other side of the car. (unlike mine.)
I feel a bit let down, but I don't blame the shop..
Now you would never notice the cooling vanes backwards on an undrilled rotor - but on a drilled one, it just doesn't look right...
I looked at a 996TT, 993TT, boxster and a few other p-cars this morning, and all of them had the cooling vanes mirrored on the other side of the car. (unlike mine.)
I feel a bit let down, but I don't blame the shop..
04-09-2005, 05:58 PM
#4
I am unfamiliar w/ 944 rotors but one part # for L or R means that the rotor vanes are straight not curved. 911 is the same way as are many of the more inexpensive aftermarket rotors. There is no directionality to the rotors. Now the drilling operation will certainly impart a directionality to the rotor. Sometimes the sweep is forward sometimes back but generally there will be a L and R so that there is consistancy from side to side.
04-09-2005, 09:26 PM
#5
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Hmmm...
To be honest, I've never really looked to see if the early Turbo rotor was directionally vaned, but my memory tells me NO. Only 1 part number sort of confirms that. The first 944 variants to see left and right rotors were the M758 S cars in 88 that had the 928S4 brakes on the front. The rear were non directional. The 964 Turbo and all 993 rotors are also directional, on both ends.
I would wager that the supplier might do all the non directional ones in the same pattern to save setup time. If this is not the case, then no one at the supplier or shop seemed to have thought to ask.
In any event, I don't see it causing any problems with a non directional rotor, other than perhaps to your esthetic sense... or peace of mind. In the final analysis, drilled rotors are a waste of money for recreational use anyway. Bling aint the thing for track use.
To be honest, I've never really looked to see if the early Turbo rotor was directionally vaned, but my memory tells me NO. Only 1 part number sort of confirms that. The first 944 variants to see left and right rotors were the M758 S cars in 88 that had the 928S4 brakes on the front. The rear were non directional. The 964 Turbo and all 993 rotors are also directional, on both ends.
I would wager that the supplier might do all the non directional ones in the same pattern to save setup time. If this is not the case, then no one at the supplier or shop seemed to have thought to ask.
In any event, I don't see it causing any problems with a non directional rotor, other than perhaps to your esthetic sense... or peace of mind. In the final analysis, drilled rotors are a waste of money for recreational use anyway. Bling aint the thing for track use.
04-09-2005, 09:46 PM
#6
Nordschleife Master
Thread Starter
The thing is, I'm am pretty sure they are directional, but for only for the passenger side. The pattern of the drilled holes in the rotor confirm this, because they are swept/twisted and not radiating out perpendicular to the hub.
What bugs me is that Porsche later on decided to mirror the rotors on the other side. (m758) They obviously saw benefit to this. Yet there is no part number for a driver's side 86 951 rotor.
I only went with drilled rotors because I wanted to see for myself if there is any different between plain ones. They were only a few bucks more, so what the hell. I know they are not cast, but they aren't going to last long anyways, as my goal is to go thru a full set of brakes by the end of October. (aka: do as many track days as possible) After that, I'll be upgrading to radial mount m030 spindles and trying S4's or big reds.
So no harm done, I was just kinda surprised and annoyed by this. Realistically, I don't believe there will be any noticeable negative affect at a DE, but I am a bit parnoid about brakes ever since my pedal went to the floor once. (major pucker factor there man.)
What bugs me is that Porsche later on decided to mirror the rotors on the other side. (m758) They obviously saw benefit to this. Yet there is no part number for a driver's side 86 951 rotor.
I only went with drilled rotors because I wanted to see for myself if there is any different between plain ones. They were only a few bucks more, so what the hell. I know they are not cast, but they aren't going to last long anyways, as my goal is to go thru a full set of brakes by the end of October. (aka: do as many track days as possible) After that, I'll be upgrading to radial mount m030 spindles and trying S4's or big reds.
So no harm done, I was just kinda surprised and annoyed by this. Realistically, I don't believe there will be any noticeable negative affect at a DE, but I am a bit parnoid about brakes ever since my pedal went to the floor once. (major pucker factor there man.)
04-09-2005, 10:44 PM
#7
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"If" your rotors are supposed to be mirrored, you'll never notice a thing IMO. I'm not even sure cooling ducts do much on 944's. Lost one at Road Atlanta last weekend and didn't notice any difference of any kind.
Enjoy your DE!!
Enjoy your DE!!
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04-09-2005, 11:42 PM
#9
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The hose, not the duct....my bad. I just don't think they do anything on our NA cars, I followed suit when building my car, everyone else did it so I did too. Hindsight 20/20...I would spend the $$$ for those high temp hoses somewhere else.
04-10-2005, 10:35 AM
#10
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Hey Rich;
The cooling holes are NOT directional. The holes themselves do not function to "move" air. The vanes inside the rotor ARE directional on the cars I mentioned previously, and are QUITE designed to facilitate the moving of air. The early Turbo are not directional.
Therefore, any pattern to the holes is either to miss the cooling vanes, and/or is strictly ornamental. In the case of the directional rotors, it accomplishes both!
I have wondered for some time what the initial reason for holing the rotors was? This drilling accomplishes two main things. I don't think lighter weight or increased air flow are on the list. (1) Everyone accepts that they are there to give unwanted substances interfering with the pad/rotor interface (water, mud, pad gasses) a place to escape. However (2) I believe they also increase the friction on the pads, which helps spike the brake temps up quickly, and therefore can help to reduce braking distances IN RACING.
If you have even circular rows of holes, such as Big Red rotors, these holes will machine grooves in your pads. These grooves will then wear grooves in your rotors. All the while this is going on, your rotors are cracking as well. They just don't make sense for anything but a full blown race car, where rotors are consdiered a consumable. If you have Big Reds with no grooving or cracking, your car is significantly over-braked, and your wallet needlessly light!
It occurs to me that perhaps clearing the pad/rotor interface was NOT the main reason. If you think about it, the wearing of the grooves proves that the holes are not sweeping the entire pad surface clean, and so would not be terribly effective at cleaning them either.
I can think of one reason that you would want to arrange the holes in a very specific pattern. If you could develope an uneven drilling pattern, this would even out the pad/rotor wear, and leave you with only cracking to contend with. It would also tend to sweep the pad more thoroughly.
Quite waxing theoretical this morning.
I myself prefer slotting.
The cooling holes are NOT directional. The holes themselves do not function to "move" air. The vanes inside the rotor ARE directional on the cars I mentioned previously, and are QUITE designed to facilitate the moving of air. The early Turbo are not directional.
Therefore, any pattern to the holes is either to miss the cooling vanes, and/or is strictly ornamental. In the case of the directional rotors, it accomplishes both!
I have wondered for some time what the initial reason for holing the rotors was? This drilling accomplishes two main things. I don't think lighter weight or increased air flow are on the list. (1) Everyone accepts that they are there to give unwanted substances interfering with the pad/rotor interface (water, mud, pad gasses) a place to escape. However (2) I believe they also increase the friction on the pads, which helps spike the brake temps up quickly, and therefore can help to reduce braking distances IN RACING.
If you have even circular rows of holes, such as Big Red rotors, these holes will machine grooves in your pads. These grooves will then wear grooves in your rotors. All the while this is going on, your rotors are cracking as well. They just don't make sense for anything but a full blown race car, where rotors are consdiered a consumable. If you have Big Reds with no grooving or cracking, your car is significantly over-braked, and your wallet needlessly light!
It occurs to me that perhaps clearing the pad/rotor interface was NOT the main reason. If you think about it, the wearing of the grooves proves that the holes are not sweeping the entire pad surface clean, and so would not be terribly effective at cleaning them either.
I can think of one reason that you would want to arrange the holes in a very specific pattern. If you could develope an uneven drilling pattern, this would even out the pad/rotor wear, and leave you with only cracking to contend with. It would also tend to sweep the pad more thoroughly.
Quite waxing theoretical this morning.
I myself prefer slotting.
04-10-2005, 12:03 PM
#11
Not that Rich or anyne else with after-market drilled rotors wants to hear this, but we have had an epidemic of Zimmerman rotors failing with severe cracks after a few DE events. Solid stock rotors or slotted rotors are a much better investment.
If you have drilled rotors, check them for cracking carefuly and regularly [every day minimum at a DE]. You only have to see the damage an rotor break-up can cause to be motivated.
If you have drilled rotors, check them for cracking carefuly and regularly [every day minimum at a DE]. You only have to see the damage an rotor break-up can cause to be motivated.
04-10-2005, 07:37 PM
#12
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Originally Posted by APKhaos
Not that Rich or anyne else with after-market drilled rotors wants to hear this, but we have had an epidemic of Zimmerman rotors failing with severe cracks after a few DE events. Solid stock rotors or slotted rotors are a much better investment.
If you have drilled rotors, check them for cracking carefuly and regularly [every day minimum at a DE]. You only have to see the damage an rotor break-up can cause to be motivated.
If you have drilled rotors, check them for cracking carefuly and regularly [every day minimum at a DE]. You only have to see the damage an rotor break-up can cause to be motivated.
04-11-2005, 02:34 AM
#14
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....why are drilled rotors the standard on my 996, and why is it that i can't find aftermarket rotors that are slotted only? i've been searching for some time and you'd think they'd have something like this out by now
04-11-2005, 01:55 PM
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Hmmm...
I have always been skeptical of Porsche's reasoning behind making holed rotors an OE item. I really would like to know the reason for it. If it is simply s matter of styling, then I would welcome the opportunity to fully **** in their ear for foisting such folly on its customers. If their are solid engineering reasons for their existence, in comparison with the same product with no holes, then I stand down... sort of.
Generally, I think Porsche is pretty good about not junking up their products. But given these and the carbon brakes, I am struggling a bit to hold onto that position. Until I see the performance merits clearly demonstrated, I will remain a skeptic.
Unfortunately, no OE suppliers have seen fit to deviate from the factory offerings.
I have always been skeptical of Porsche's reasoning behind making holed rotors an OE item. I really would like to know the reason for it. If it is simply s matter of styling, then I would welcome the opportunity to fully **** in their ear for foisting such folly on its customers. If their are solid engineering reasons for their existence, in comparison with the same product with no holes, then I stand down... sort of.
Generally, I think Porsche is pretty good about not junking up their products. But given these and the carbon brakes, I am struggling a bit to hold onto that position. Until I see the performance merits clearly demonstrated, I will remain a skeptic.
Unfortunately, no OE suppliers have seen fit to deviate from the factory offerings.