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06-29-2010, 09:41 PM
| | Porsche Chatter | | Join Date: May 2007
Posts: 37
Country:  | | | 996TT rear brake ducts
I have been having bad problems this year with overheating my rear brakes at tight tracks like Gingerman and Autobahn. After about 25 minutes of driving, (with PSM off) I would get a completely squishy brake pedal, requiring pumping to get any braking done.
Strangely enough, the problem seemed to be with the back brakes. The calipers have turned a dark brown/purple color, much more so than the fronts. I was having to bleed the brakes at the beginning of each day, and the back calipers always seemed to have the air bubbles in them.
What could be causing this? I think it most likely was the "Active Brake Differential" feature, which apparently is on even when PSM is off. So, I recently went "mod crazy" and had the Guard 50/80 LSD installed, along with the Softronic ECU flash and Agency Power exhaust. I also found these brake ducts, which are Porsche OEM parts, from Vivid Racing: Porsche OEM 996 C2/C4/TT Rear Brake Ducts 99-05 Image2
The Porsche PNs are 996-331-127-90 and 996-331-128-90, for the left and right duct respectively.
We had to trim the ends off a bit to get the ducts to fit around the cross braces, but they did attach to the control arms quite snugly:  
The shields behind the rotors were also removed.
I tried all this stuff out at Gingerman this last weekend, and my brake pedal was solid the whole time. I attribute this mostly to the LSD, as the "brake diff" feature was no longer necessary. I tried running one session with PSM on with dry pavement, and it really cut in much less than usual. Turns 2 and 3 at this track usually cause a lot of "chatter" from PSM, but with this new LSD it apparently didnt have to intervene.
I cant really quantify how much these brake ducts helped my problem, but I figure its never a bad thing to get more air channeled towards your brake rotors.  |  |  |  | | PSM - Porsche Stability Management |  | While it can’t overcome the laws of physics, the revolutionary Porsche Stability Management (PSM) system does lend an added degree of balance and control to the Cayman’s mid-engine driving dynamics, inspiring surefooted confidence in corners and extreme situations.
A standard feature on the Cayman and Cayman S, PSM continuously monitors steering input, road speed, yaw velocity and lateral acceleration to calculate the actual direction of travel. If the car begins to steer off line, PSM instantly intervenes with precision brake inputs on individual wheels to help bring the car back onto the driver’s intended path.
If braking alone isn’t enough to correct the vehicle’s cornering line, PSM then calls on the Cayman’s engine management system, adjusting engine output as needed to help stabilize handling. PSM can also compensate in an instant for mid-corner changes in load resulting from deceleration or braking. When Sport mode is selected with the optional Sport Chrono Package, PSM’s threshold for intervention is raised, allowing for greater driver involvement. If you prefer driving without automatic PSM assistance, the system can be set to standby at any time. In this case, it will only intervene under heavy braking, where both front wheels exceed the ABS threshold.
For all of its technical ability, PSM goes virtually unnoticed in everyday driving situations, preserving the Cayman’s natural agility. | |  |  |  |  | | | | | | LSD - Limited Slip Differential |  | A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely– the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels. To see the installation of a LSD style unit Click Here | | | | | | |
06-29-2010, 11:03 PM
|  | Porsche Purist 1,000 post club | | Join Date: May 2009 Location: Ohio
Posts: 1,189
Country: | | | Re: 996TT rear brake ducts
I wore out a set of rears on my 09 CS As well. Thanks for the information.
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Alan C.
Cincinnati
2011 Carrera GTS Basalt Black/Black - PDK, LSD, Sharkwerks Center Muffler Delete, Forgeline GA3 Center Locks, MPSS |
06-30-2010, 06:26 AM
|  | Super Moderator | | Join Date: Aug 2007 Location: DFW TX
Posts: 3,851
Country: | | | Re: 996TT rear brake ducts
Originally Posted by astoddard  I have been having bad problems this year with overheating my rear brakes at tight tracks like Gingerman and Autobahn. . . | What kind of pads do you run on the track? With Pagid yellows front and rear, my brakes seem to be pretty much front biased.
Thanks for posting up the novel cooling solution. |
06-30-2010, 07:55 AM
| | Porsche Chatter | | Join Date: May 2007
Posts: 37
Country: | | | Re: 996TT rear brake ducts
Pagid yellow or black. I was running black for a while then started having this problem. I experimented with a set of orange in the back on the theory that the black created too much friction, therefore too much heat. I dont think it helped much. The car really needs an LSD to stop the electronic wizard from applying the back brakes to counter the wheelspin from the open diff. | | | | | LSD - Limited Slip Differential | | A limited slip differential (LSD) is a modified or derived type of differential gear arrangement that allows for some difference in rotational velocity of the output shafts, but does not allow the difference in speed to increase beyond a preset amount. In an automobile, such limited slip differentials are sometimes used in place of a standard differential, where they convey certain dynamic advantages, at the expense of greater complexity.
The main advantage of a limited slip differential is found by considering the case of a standard (or "open") differential where one wheel has no contact with the ground at all. In such a case, the contacting wheel will remain stationary, and the non-contacting wheel will rotate freely– the torque transmitted will be equal at both wheels, but will not exceed the threshold of torque needed to move the vehicle, thus the vehicle will remain stationary. In everyday use on typical roads, such a situation is very unlikely, and so a normal differential suffices. For more demanding use however, such as driving off-road, or for high performance vehicles, such a state of affairs is undesirable, and the LSD can be employed to deal with it. By limiting the velocity difference between a pair of driven wheels, useful torque can be transmitted as long as there is some friction available on at least one of the wheels. To see the installation of a LSD style unit Click Here | | | | | | |
02-23-2011, 05:08 AM
| | Cayman The Destroyer!  1,000 post club | | Join Date: Mar 2008 Location: NV
Posts: 1,895
Country: | | | Re: 996TT rear brake ducts
This looked like such an elegant solution I decided to add it to my car. With the turbo I want to keep the rear brakes & hubs as cool as possible. I added a little improvement by bending the plastic to close off the cut end of the duct.
Here are some shots of the cutting & shaping process. The plastic material cuts nicely with snips. It will hold a new shape if you bend it carefully. Don't bend it more than once though or it will crack. The pic with the through hole for the bolt is in the wrong place. It should be equidistant from where it is now and the big existing hole. I used a 3" 10/32 screw & stop nut to mount as the supplied clips will interfere with my TPC roll bar links. There is a conveniently supplied hole it the control arm it jut the right spot! With stock links the clips will work fine.
I'm sure some of you eagle eyes viewers noticed that this is the second ducting I have on the rear brakes. The deflectors shown in the wider wheel well shot where installed by TPC. They came from their junk pile of old race car parts.
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02-25-2011, 01:07 PM
| | Bronze Sponsor  1,000 post club | | Join Date: Jun 2007 Location: Kirkland, WA
Posts: 1,772
| | | Re: 996TT rear brake ducts
GREAT advice here! Smart modification, the rears are often overlooked...you ought to see what happens with a *997 GT3 with PSM left on* ...OMG the rears wear TWICE AS FAST AS THE FRONTS* | | | | | PSM - Porsche Stability Management | | While it can’t overcome the laws of physics, the revolutionary Porsche Stability Management (PSM) system does lend an added degree of balance and control to the Cayman’s mid-engine driving dynamics, inspiring surefooted confidence in corners and extreme situations.
A standard feature on the Cayman and Cayman S, PSM continuously monitors steering input, road speed, yaw velocity and lateral acceleration to calculate the actual direction of travel. If the car begins to steer off line, PSM instantly intervenes with precision brake inputs on individual wheels to help bring the car back onto the driver’s intended path.
If braking alone isn’t enough to correct the vehicle’s cornering line, PSM then calls on the Cayman’s engine management system, adjusting engine output as needed to help stabilize handling. PSM can also compensate in an instant for mid-corner changes in load resulting from deceleration or braking. When Sport mode is selected with the optional Sport Chrono Package, PSM’s threshold for intervention is raised, allowing for greater driver involvement. If you prefer driving without automatic PSM assistance, the system can be set to standby at any time. In this case, it will only intervene under heavy braking, where both front wheels exceed the ABS threshold.
For all of its technical ability, PSM goes virtually unnoticed in everyday driving situations, preserving the Cayman’s natural agility. | | | | | |
__________________ Craig  425-765-1090, www.Rennstore.com --assistance & discussion for your pad selection welcomed  PAGID brake pads - Daytona 24 hr winners in every podium position  GiroDisc brake systems and pad spreaders NOW AVAILABLE - SPECIAL PRICING! E-mail for any questions: Rennstore@Comcast.net |
02-25-2011, 02:43 PM
|  | Porsche Enthusiast | | Join Date: Nov 2005 Location: RI
Posts: 247
Country: | | | Re: 996TT rear brake ducts
Nicely done! Mind if I copy your homework? I've had a set of the rear Turbo ducts sitting in the basement since November, just waiting for some better weather here in the Northeast...
BTW the GT2 front ducts are going back on. While the GT2 fronts are easily torn off on the street, the GT3 front ducts just dont get the job done on my NA CS. |
02-25-2011, 06:58 PM
| | Cayman The Destroyer! 1,000 post club | | Join Date: Mar 2008 Location: NV
Posts: 1,895
Country: | | | Re: 996TT rear brake ducts
Mark, glad I can help you out for a change. You do know it was you that started my down the slipery slope of mods? 
I think GT2 ducts will be my last mod this season. Any mods necessary to add them to a CS?
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Daily Driven CS Supercar "Leaps GT3's In A Single Bound" |
02-26-2011, 08:17 AM
| | Porsche Enthusiast | | Join Date: Nov 2005 Location: RI
Posts: 247
Country: | |  Re: 996TT rear brake ducts
Hey Bruce! The Gt2 fronts are easy installs, just some small snips in the pan to open a slot to fit the longer leading edge of the scoop... Alternately you could remove material from the scoop itself but that's going backwards! |
04-17-2012, 07:54 PM
| | Site Donor | | Join Date: Apr 2009 Location: Sunnyvale CA, Fort Collins CO
Posts: 495
Country: | | | Re: 996TT rear brake ducts
Just updating this thread a bit, had a set of 996 TT rear brake ducts that I had purchased from Suncoast sitting in the garage and decided to install them on the car.
As per diverdog's modification, ended up sealing the end of the duct closer to the diagonal brace/skid pate and added a bit of a lip on the exit of the duct to help direct the air upwards towards the rotor.
Used alternating layers of duct tape along with aluminum HVAC tape to form the various shapes as well as reusing bits of plastic to form the lip at the exit of the duct.
Also had to do a bit more trimming at the end to clear the longer bolt used to attach the RSS Tarmac LCA to the rear upright.
Still using the stock swaybar with some aftermarket droplinks so was able to use the stock 996 bracket along with some zipties to hold the duct in place.
Wasn't too happy with the performance of the hacked 996TT ducts so ended up ordering a set of 997 GT3 rear brake ducts from Suncoast along with the RSS LCA specific brackets from RSS to see if they could be modified to work on the 987 platform.
Sadly after receiving the GT3 rear ducts and doing a quick check it became obvious that they would not work. The duct won't clear the diagonal brace of the skid plate nor will it clear the ends of the rear sway bar, given it's shape it won't work on a 987 at all.
Currently pursuing a lead on a custom rear brake duct solution, hoping that it will pan out. |
04-17-2012, 08:34 PM
| | Cayman The Destroyer! 1,000 post club | | Join Date: Mar 2008 Location: NV
Posts: 1,895
Country: | | | Re: 996TT rear brake ducts
I like the NACA ducts the Interseries cars use.
You can see that the bigger Girodisks I have on my rears get a more direct hit from the ducts
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Daily Driven CS Supercar "Leaps GT3's In A Single Bound" |
04-18-2012, 05:49 AM
|  | Site Donor  3,000 post club | | Join Date: Sep 2007 Location: IL
Posts: 3,314
Country: | | | Re: 996TT rear brake ducts
Originally Posted by 2slow2speed Just updating this thread a bit, had a set of 996 TT rear brake ducts that I had purchased from Suncoast sitting in the garage and decided to install them on the car.
As per diverdog's modification, ended up sealing the end of the duct closer to the diagonal brace/skid pate and added a bit of a lip on the exit of the duct to help direct the air upwards towards the rotor.
Used alternating layers of duct tape along with aluminum HVAC tape to form the various shapes as well as reusing bits of plastic to form the lip at the exit of the duct.
Also had to do a bit more trimming at the end to clear the longer bolt used to attach the RSS Tarmac LCA to the rear upright.
Still using the stock swaybar with some aftermarket droplinks so was able to use the stock 996 bracket along with some zipties to hold the duct in place. Wasn't too happy with the performance of the hacked 996TT ducts so ended up ordering a set of 997 GT3 rear brake ducts from Suncoast along with the RSS LCA specific brackets from RSS to see if they could be modified to work on the 987 platform.
Sadly after receiving the GT3 rear ducts and doing a quick check it became obvious that they would not work. The duct won't clear the diagonal brace of the skid plate nor will it clear the ends of the rear sway bar, given it's shape it won't work on a 987 at all.
Currently pursuing a lead on a custom rear brake duct solution, hoping that it will pan out. | I had looked into the GT3 ducts myself but had read that they're a no go for the 987 before pulling the trigger.
I do have the 996TT ducts awaiting 987 fitment surgery though. What didn't you like about their performance? Did you take temp measurements? Also, did you trim the rotor backing plate? |
04-18-2012, 11:10 AM
| | Site Donor | | Join Date: Apr 2009 Location: Sunnyvale CA, Fort Collins CO
Posts: 495
Country: | | | Re: 996TT rear brake ducts
Originally Posted by rubber_ducky I had looked into the GT3 ducts myself but had read that they're a no go for the 987 before pulling the trigger.
I do have the 996TT ducts awaiting 987 fitment surgery though. What didn't you like about their performance? Did you take temp measurements? Also, did you trim the rotor backing plate? | The only post that I could find about the GT3 rear ducts was from Krokodril over at rennlist without any definitive conclusions so I just gave it a quick try. The folks over at Suncoast and RSS were very accommodating with the test fitting experiment.
As far as the modified Turbo ducts, temps on the rear rotors only went down about 50-70 degrees F vs running without having the ducts. Ended up removing the entire heat shield (rotor backing plate) since there are no rubber bushings in that area of my modified R's suspension.
The rear rotor still runs about 200 degrees hotter than the fronts at Laguna Seca so trying to get a better handle on temps to make it easier with pad selection as well as pad/rotor longevity.
Diverdog's post pretty much reflects the direction that I am pursuing with a couple of shops, trying to source the correct parts from the shops as a kit instead of having to order multiple sets of NACA ducts and hoses to see what will work. |
07-04-2012, 05:31 PM
| | Site Donor | | Join Date: Apr 2009 Location: Sunnyvale CA, Fort Collins CO
Posts: 495
Country: | | | Re: 996TT rear brake ducts
So dropped by the local Porsche dealer again this afternoon, while looking a bit more on the 981 a friend pointed out that the rear wheel well area of the car seems to be a bit more open to allow for more engine/tranny cooling on the 981.
I happened to notice that there is now a rear brake duct on the 981, makes sense considering that PTV uses the rear brakes to help rotate the car.
Maybe Suncoast can check and see if the part will be plug and play compatible with the 987's rear suspension bits. From what I could tell the 981 rear suspension did not seem to be that much different from the 981's, but then again that was with only a cursory examination of the car on the showroom floor and not on a lift. | | | | | PTV - Porsche Torque Vectoring |  | (FAQ in progress)
Available for the 911 Turbo for the first time is the optional Porsche Torque Vectoring with variable torque distribution to the rear wheels and a mechanical limited-slip rear differential.
PTV is a system that actively enhances vehicle dynamics and stability. As a function of steering angle and steering speed, accelerator pedal position, yaw rate and vehicle speed, PTV is able to improve steering response and steering precision significantly by specific braking of the right or left rear wheel.
In simple terms, this means that when the car is driven assertively into a corner, moderate brake pressure is applied to the inside rear wheel. At the same time, different amounts of drive torque are distributed to each rear wheel via the rear axle differential. Consequently, there is more drive force at the outside wheel and a rotational pulse (yaw movement) is generated around the vehicle’s vertical axis. This assists the steering input and results in a more assured steering manoeuvre.
At low and medium vehicle speeds, the system significantly increases agility and steering precision, whilst at high speeds, and in combination with the mechanical limited-slip differential, it additionally ensures greater driving stability.
The system, combined with Porsche Traction Management (PTM) and Porsche Stability Management (PSM), also puts its stabilising effect to good use on road surfaces with varying levels of grip and on snow and ice.
As PTV increases the car’s dynamic performance, the system remains active when driving on the racetrack, even if PSM has been deactivated.
Where efficiency is concerned, this enhanced performance and stability are achieved without the need for any additional components, apart from the mechanical limited-slip rear differential. In other words, a more enjoyable drive with no additional weight. | | | | | | |
11-27-2012, 09:19 PM
|  | PCA Member 1,000 post club | | Join Date: Sep 2011 Location: PA
Posts: 1,237
Country: | | | Re: 996TT rear brake ducts
Originally Posted by 2slow2speed So dropped by the local Porsche dealer again this afternoon, while looking a bit more on the 981 a friend pointed out that the rear wheel well area of the car seems to be a bit more open to allow for more engine/tranny cooling on the 981.
I happened to notice that there is now a rear brake duct on the 981, makes sense considering that PTV uses the rear brakes to help rotate the car.
Maybe Suncoast can check and see if the part will be plug and play compatible with the 987's rear suspension bits. From what I could tell the 981 rear suspension did not seem to be that much different from the 981's, but then again that was with only a cursory examination of the car on the showroom floor and not on a lift. | Any update on the 981 solution? | | | | | PTV - Porsche Torque Vectoring | | (FAQ in progress)
Available for the 911 Turbo for the first time is the optional Porsche Torque Vectoring with variable torque distribution to the rear wheels and a mechanical limited-slip rear differential.
PTV is a system that actively enhances vehicle dynamics and stability. As a function of steering angle and steering speed, accelerator pedal position, yaw rate and vehicle speed, PTV is able to improve steering response and steering precision significantly by specific braking of the right or left rear wheel.
In simple terms, this means that when the car is driven assertively into a corner, moderate brake pressure is applied to the inside rear wheel. At the same time, different amounts of drive torque are distributed to each rear wheel via the rear axle differential. Consequently, there is more drive force at the outside wheel and a rotational pulse (yaw movement) is generated around the vehicle’s vertical axis. This assists the steering input and results in a more assured steering manoeuvre.
At low and medium vehicle speeds, the system significantly increases agility and steering precision, whilst at high speeds, and in combination with the mechanical limited-slip differential, it additionally ensures greater driving stability.
The system, combined with Porsche Traction Management (PTM) and Porsche Stability Management (PSM), also puts its stabilising effect to good use on road surfaces with varying levels of grip and on snow and ice.
As PTV increases the car’s dynamic performance, the system remains active when driving on the racetrack, even if PSM has been deactivated.
Where efficiency is concerned, this enhanced performance and stability are achieved without the need for any additional components, apart from the mechanical limited-slip rear differential. In other words, a more enjoyable drive with no additional weight. | | | | | |
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02-18-2013, 08:15 PM
|  | PCA Member | | Join Date: Jun 2012 Location: NE
Posts: 207
Country: | | | Re: 996TT rear brake ducts
please, update on the 981 solution, I'm interested as well.
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04-12-2013, 05:50 PM
|  | Porsche Activist | | Join Date: Jan 2012 Location: Chicago Burbs
Posts: 411
Country: | | | Re: 996TT rear brake ducts
Originally Posted by sho-one please, update on the 981 solution, I'm interested as well. |
I'm interested as well.
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04-13-2013, 10:55 AM
|  | Porsche Enthusiast | | Join Date: Mar 2009 Location: Florida
Posts: 115
Country: | | | Re: 996TT rear brake ducts
Couldn't get the 981 part number from Porsche yet, so I just did the 996tt ducts-small easy fab work to get them on. Took 45 minutes to complete. Only had to cut 2.5 inches off the engine end of the duct and Viola it was like it was made for the Cayman, all the holes lined up perfectly. I spent more time with the wheels and jack than the ducts.
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2007 Cayman/S, Meteor Gray, Black & Wood int, 19" Sports, GT3 front brake ducts, 996TT rear brake ducts, Clear Side Markers, Porsche SSK, GT3 TB, Rear Window Sun Shade, Agency Exhaust & Tips, Dream 1, K&N air filter, Pagid sport pads, IPD Pleumn, Sprint Booster, Das Schild.
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04-15-2013, 04:43 AM
| | Porsche Enthusiast | | Join Date: Mar 2009 Location: Florida
Posts: 115
Country: | | | Re: 996TT rear brake ducts
I saw the 2014 Cayman/S Brake Duct yesterday at the St Pete Autocross event. The rear ducts were clearly visible, but IMO I don't think the would be as effective at cooling than the 966TT mod-awesome looking car tho 
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2007 Cayman/S, Meteor Gray, Black & Wood int, 19" Sports, GT3 front brake ducts, 996TT rear brake ducts, Clear Side Markers, Porsche SSK, GT3 TB, Rear Window Sun Shade, Agency Exhaust & Tips, Dream 1, K&N air filter, Pagid sport pads, IPD Pleumn, Sprint Booster, Das Schild.
2011 Infiniti G37 Dark Gray Pearle Convertible | |
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