Decoding GT3 Cup sequential
05-02-2013, 05:05 AM
#1
Addict
Rennlist Member
Rennlist Member
Thread Starter
Decoding GT3 Cup sequential
I like to share this post with you guys on the 997 GT2/GT3 forum since some of you are considering a Cup car in the future ...
When I decided to get a GT3 Cup car the biggest mystery to me was the sequential gearbox. What do I know about it? Almost nothing. I know motorcycle and race car use them and that's about it. I also know GT3 Cup need gearbox rebuild more often than engine for some reason. I was happy to learn my gearbox was "rebuild" with zero hour when I bought it. That's all I know. Well, after driving for two years and 40-50 hours my sequential gave up it's ghost. Granted I was not kind to the tranny when I first learn how to drive a Cup it lasted for a good while. The cost of this repair was very expensive and I like to share my experience for those of you that may entertained a Cup car in the future or currently owns one so you may know what to look out for.
First, a basic sequential transmission 101 from Wikipedia:
A sequential manual transmission (or sequential manual gearbox) is a type of manual transmission used on motorcycles and high-performance cars for auto racing, where gears are selected in order, and direct access to specific gears is not possible.
With traditional manual transmissions, the driver can move from gear to gear, by moving the shifter to the appropriate position. This type of transmission is often referred to as a H-pattern because of the path that the shift lever takes as it selects the various gears. A clutch must be disengaged before the new gear is selected, to disengage the running engine from the transmission, thus stopping all torque transfer. In auto racing, this process is slow and prone to human error; hence the development of the sequential transmission. A true sequential transmission will very often use dog clutch engagement rather than the more usual synchromesh as fitted to a normal H-pattern road car gearbox. Engagement using dogs only requires a very brief interruption of engine torque to complete a shift into any adjacent gear. This allows shifting between gears without the use of the clutch. The clutch would normally be used only for standing starts.
That's the basic about sequential transmission and why it's used in road racing cars to help extract every last horsepower from the drivetrain. So now you got your eyes on a nice 997 Cup and the seller tell you the gearbox has just been refreshed vs rebuild vs rebuild and sealed vs lightly used vs "I only race it couple times". What does all that mean and is there a way to measure the health of a sequential gearbox? Let's take a look at my sequential gearbox repair and it will help shed light on the matter.
The problem I encounter recently was that my sequential did not engage gear from 4th to 3rd and rattle around like crazy. Loud rattle become prominent when clutch was released as shown by video below.
Similar issue happened once before going from 5th to 4th but no loud noise after gears re-engaged. I felt pretty confident about the gearbox thinking it must be robust since it's been rebuild by the race shop and continue to use it for another 20 hours. I drain tranny oil both times and no large mental fragments.
So now the gearbox has to be serviced. After much research I decided to have it repair by Bill Rader motorsports. I chose Bill because he is a Porsche gearbox specialist with years of experience servicing GT3 Cup sequential for various race teams. He was upfront on the phone with repair process and cost and provide detail photo journal to document diagnostic and repair process so customer like myself know exactly what's going on. After diagnosing the problem I was presented with a list of repair options taken into consideration of cost and race purpose. Another good thing is that Bill can arrange expedited freight shipping and deal with my shop directly for FedEx pick up and drop off . It took Bill 2 days to rebuild the gearbox, dyno and ship back to my shop - that is really fast!
Here is what Bill found when he open the gearbox illustrated with photo journal:
I felt sick to learn that majority of the damage was done by two $18 nut that was not replaced and properly secured when it was "rebuild" two years ago. This goes to show the importance of using an experienced gearbox expert to have it done right the first time. The report also pointed out that the only thing that was updated in this gearbox was the 3rd/4th shift fork and the rest of the components are old and dated. It is amazing that the gearbox has lasted this long . It helps that I only DE and club race which kept the damage to a minimum - it will never survive endurance race condition. Now when you look at a shiny GT3 Cup and the seller tells you the gearbox has been rebuild or refreshed you need to ask to see the repair parts list and speak with the repair shop directly and ask to see pictures if available. Without detail documentation like what Bill Rader offer you can not determine the true health and durability of a sequential gearbox.
So, what's my repair options? I want to fix the clunky noise but how about the rest such as cracked first gear dog teeth and the claw collar? I could just replaced the damaged first gear set and be done with only spending $3000 ... but that's not addressing all other issues and the gearbox will not last and the next repair will be even more expensive. Here is what Bill proposed:
I decided to go with option 2 and use Guard gears and components which are stronger than OEM Porsche parts and proven in 24 hours endurance race condition. Guard gears are not as wide as the 2012 super wide OEM Porsche gears shown above but it has the "middle of the road" 2011 wider width which help reduce friction. Guard use stronger manufacture metallurgy which means it does not need the extra width for strength. All this means more power is transfer to the rear wheels with stronger gear set and internals. The other obvious benefit of Guard gears sets is that they are about $1000 less per gear set compare with OEM Porsche parts. Stronger, more mechanical efficiency and price conscious wins every time.
Now let's take a look at the repair process
Here is a video of the sequential gearbox dyno run after repair and assembly
https://www.facebook.com/photo.php?v...type=2&theater
I also took the opportunity when my gearbox are out to replace both rear drive axle and also central bolts on each wheels. Shad at driving ambition did a great job in getting everything done in a timely manner and woke everyone up when he test drove my Cup near his shop
Wheel central bolt for the center lock
996 TT rear axles
Engine view with tranny removed
Bad boy is home after a wild ride at Vegas and ready to go back to work!
So what's the cost of repair? I called PMNA to find out how much a brand new 2012 sequential gearbox cost and they can have it ship directly from Germany for $40K. Wow ... not cheap. A new Quaife QBE85G 997 sequential cost about 1/2 as much at $21K but I decided to use original gearbox and strengthen the internal and make it stronger and more efficient that should last another 40-50 hours before next refresh. Total parts cost for this repair is about the price of a new Honda civic. 1 day expedited freight shipping of gearbox from Northern California to Las Vagas cost $150 each way. Total labor cost both shops combine are about $2500. It was a hard lesson learned and I wish I could have known better ... but how could I if I have not experienced it first hand.
I was eager to try out the new gearbox to feel the difference. Now I know 3rd and 4th gears are the weakest link because most high speed compression gear change on track involves 3rd and 4th gears and that's where all my miss shifts happens. When I fly down a fast straight to a high compression braking zone I have to brake hard - but not hard enough to lock up the brakes which means my right hand also react like my right foot with a slight hesitancy when I push the lever forward to down shift. This lead to not getting gears in from 5th to 4th or 4th to 3rd and I hate that grinding sound.
One thing I immediately noticed when I start up the car with refreshed gearbox is that the engine does not die easily like before when cold and I don't have to crazy rev to engine to 4K RPM to get her going from first gear or reverse. I also notice the engine spool up super fast on the track - so fast I kept on hitting redline before I react to upshift. My ears and reactions times are train to the old gearbox and now the new gearbox is super fast and I had to retrain my muscle memory. Gone are the clunky gear change and now replace with smooth shift which minimize excessive drivetrain movement. All this translate to faster lap time, so fast that I beat my previous best time by 3 seconds under the same track condition - and this was done in traffic with older scrub slicks! 3 seconds is huge for a 2.86 mile track. This is equivalent to more than 50 horsepower gain.
This has been a very trying experience but with a satisfying result. I hope by sharing my experience can help you avoid some of the pitfall when it comes to purchsing a Cup car and servicing sequential gearbox
When I decided to get a GT3 Cup car the biggest mystery to me was the sequential gearbox. What do I know about it? Almost nothing. I know motorcycle and race car use them and that's about it. I also know GT3 Cup need gearbox rebuild more often than engine for some reason. I was happy to learn my gearbox was "rebuild" with zero hour when I bought it. That's all I know. Well, after driving for two years and 40-50 hours my sequential gave up it's ghost. Granted I was not kind to the tranny when I first learn how to drive a Cup it lasted for a good while. The cost of this repair was very expensive and I like to share my experience for those of you that may entertained a Cup car in the future or currently owns one so you may know what to look out for.
First, a basic sequential transmission 101 from Wikipedia:
A sequential manual transmission (or sequential manual gearbox) is a type of manual transmission used on motorcycles and high-performance cars for auto racing, where gears are selected in order, and direct access to specific gears is not possible.
With traditional manual transmissions, the driver can move from gear to gear, by moving the shifter to the appropriate position. This type of transmission is often referred to as a H-pattern because of the path that the shift lever takes as it selects the various gears. A clutch must be disengaged before the new gear is selected, to disengage the running engine from the transmission, thus stopping all torque transfer. In auto racing, this process is slow and prone to human error; hence the development of the sequential transmission. A true sequential transmission will very often use dog clutch engagement rather than the more usual synchromesh as fitted to a normal H-pattern road car gearbox. Engagement using dogs only requires a very brief interruption of engine torque to complete a shift into any adjacent gear. This allows shifting between gears without the use of the clutch. The clutch would normally be used only for standing starts.
That's the basic about sequential transmission and why it's used in road racing cars to help extract every last horsepower from the drivetrain. So now you got your eyes on a nice 997 Cup and the seller tell you the gearbox has just been refreshed vs rebuild vs rebuild and sealed vs lightly used vs "I only race it couple times". What does all that mean and is there a way to measure the health of a sequential gearbox? Let's take a look at my sequential gearbox repair and it will help shed light on the matter.
The problem I encounter recently was that my sequential did not engage gear from 4th to 3rd and rattle around like crazy. Loud rattle become prominent when clutch was released as shown by video below.
Similar issue happened once before going from 5th to 4th but no loud noise after gears re-engaged. I felt pretty confident about the gearbox thinking it must be robust since it's been rebuild by the race shop and continue to use it for another 20 hours. I drain tranny oil both times and no large mental fragments.
So now the gearbox has to be serviced. After much research I decided to have it repair by Bill Rader motorsports. I chose Bill because he is a Porsche gearbox specialist with years of experience servicing GT3 Cup sequential for various race teams. He was upfront on the phone with repair process and cost and provide detail photo journal to document diagnostic and repair process so customer like myself know exactly what's going on. After diagnosing the problem I was presented with a list of repair options taken into consideration of cost and race purpose. Another good thing is that Bill can arrange expedited freight shipping and deal with my shop directly for FedEx pick up and drop off . It took Bill 2 days to rebuild the gearbox, dyno and ship back to my shop - that is really fast!
Here is what Bill found when he open the gearbox illustrated with photo journal:
I felt sick to learn that majority of the damage was done by two $18 nut that was not replaced and properly secured when it was "rebuild" two years ago. This goes to show the importance of using an experienced gearbox expert to have it done right the first time. The report also pointed out that the only thing that was updated in this gearbox was the 3rd/4th shift fork and the rest of the components are old and dated. It is amazing that the gearbox has lasted this long . It helps that I only DE and club race which kept the damage to a minimum - it will never survive endurance race condition. Now when you look at a shiny GT3 Cup and the seller tells you the gearbox has been rebuild or refreshed you need to ask to see the repair parts list and speak with the repair shop directly and ask to see pictures if available. Without detail documentation like what Bill Rader offer you can not determine the true health and durability of a sequential gearbox.
So, what's my repair options? I want to fix the clunky noise but how about the rest such as cracked first gear dog teeth and the claw collar? I could just replaced the damaged first gear set and be done with only spending $3000 ... but that's not addressing all other issues and the gearbox will not last and the next repair will be even more expensive. Here is what Bill proposed:
- This one is the bare minimum I would recommend doing to it to make it a good reliable box, this one will use Guard gears, and I have put in an option by using a perfectly good RSR style main shaft and a Guard slide on 1st gear set. With this one I would clean up the dogs on 2nd gear and we would reuse the old original 5th and 6th.
- This one is the best option and will make it a great reliable box that will be fully updated to 2011 specs with Guard gears
- This one is the same as #1 except will use Factory 2012 super wide 3rd and 4th gears. To do that conversion it would also need to use a standard style 1st gear set so there is a different price for that in the quote.
- This one is to fully update everything in the box to 2012 specs
I decided to go with option 2 and use Guard gears and components which are stronger than OEM Porsche parts and proven in 24 hours endurance race condition. Guard gears are not as wide as the 2012 super wide OEM Porsche gears shown above but it has the "middle of the road" 2011 wider width which help reduce friction. Guard use stronger manufacture metallurgy which means it does not need the extra width for strength. All this means more power is transfer to the rear wheels with stronger gear set and internals. The other obvious benefit of Guard gears sets is that they are about $1000 less per gear set compare with OEM Porsche parts. Stronger, more mechanical efficiency and price conscious wins every time.
Now let's take a look at the repair process
Here is a video of the sequential gearbox dyno run after repair and assembly
https://www.facebook.com/photo.php?v...type=2&theater
I also took the opportunity when my gearbox are out to replace both rear drive axle and also central bolts on each wheels. Shad at driving ambition did a great job in getting everything done in a timely manner and woke everyone up when he test drove my Cup near his shop
Wheel central bolt for the center lock
996 TT rear axles
Engine view with tranny removed
Bad boy is home after a wild ride at Vegas and ready to go back to work!
So what's the cost of repair? I called PMNA to find out how much a brand new 2012 sequential gearbox cost and they can have it ship directly from Germany for $40K. Wow ... not cheap. A new Quaife QBE85G 997 sequential cost about 1/2 as much at $21K but I decided to use original gearbox and strengthen the internal and make it stronger and more efficient that should last another 40-50 hours before next refresh. Total parts cost for this repair is about the price of a new Honda civic. 1 day expedited freight shipping of gearbox from Northern California to Las Vagas cost $150 each way. Total labor cost both shops combine are about $2500. It was a hard lesson learned and I wish I could have known better ... but how could I if I have not experienced it first hand.
I was eager to try out the new gearbox to feel the difference. Now I know 3rd and 4th gears are the weakest link because most high speed compression gear change on track involves 3rd and 4th gears and that's where all my miss shifts happens. When I fly down a fast straight to a high compression braking zone I have to brake hard - but not hard enough to lock up the brakes which means my right hand also react like my right foot with a slight hesitancy when I push the lever forward to down shift. This lead to not getting gears in from 5th to 4th or 4th to 3rd and I hate that grinding sound.
One thing I immediately noticed when I start up the car with refreshed gearbox is that the engine does not die easily like before when cold and I don't have to crazy rev to engine to 4K RPM to get her going from first gear or reverse. I also notice the engine spool up super fast on the track - so fast I kept on hitting redline before I react to upshift. My ears and reactions times are train to the old gearbox and now the new gearbox is super fast and I had to retrain my muscle memory. Gone are the clunky gear change and now replace with smooth shift which minimize excessive drivetrain movement. All this translate to faster lap time, so fast that I beat my previous best time by 3 seconds under the same track condition - and this was done in traffic with older scrub slicks! 3 seconds is huge for a 2.86 mile track. This is equivalent to more than 50 horsepower gain.
This has been a very trying experience but with a satisfying result. I hope by sharing my experience can help you avoid some of the pitfall when it comes to purchsing a Cup car and servicing sequential gearbox
Last edited by mikymu; 05-04-2013 at 05:14 AM.
05-02-2013, 05:20 AM
#3
Addict
Rennlist Member
Rennlist Member
Thread Starter
05-02-2013, 06:30 AM
#4
Wow! Don't see a Cup car in my future but thanks for taking the time to detail the workings and innards of a sequential transmission, and the cost. Great post!
05-02-2013, 07:10 AM
#5
Rennlist Member
Mikymu for president! You just answered one of the biggest questions in the minds of us prospective owners...
Trending Topics
05-02-2013, 09:27 AM
#11
Rennlist Member
Good write up! IMO your early "abuse" of the tranny played an important role in all this, and is common. These sequentials really reward a much more precice timing of clutch & throttle blips than we need to do with most manual transmissions. When we get it right, they last a LONG time. When we don't, they don't.
05-02-2013, 09:46 AM
#13
Nordschleife Master
Join Date: Feb 2011
Location: Deep Downtown Carrier, OK
Posts: 5,297
Likes: 0
Received 6 Likes
on
6 Posts
In addition to the driver' learning curve, my take here is the fact that the original "refresh" was done poorly. These trannys suffer no fools, like most Porsche internals.
05-02-2013, 10:06 AM
#15
Nordschleife Master
Join Date: Feb 2011
Location: Deep Downtown Carrier, OK
Posts: 5,297
Likes: 0
Received 6 Likes
on
6 Posts
In discussion for the next widebody, slide valve, 400hp phase of the build.
I've thought long and hard about a dogbox, but the wonderful thing about a simple analog car is simplicity.
Merely have to drive harder to beat the waterboilers. It's very easy to spend money to go faster, but I find the true challenge lies within. NONE of us are at the level where a quick tranny will make the last 0.50 seconds possible.
Wonderful post by the OP!!!
I've thought long and hard about a dogbox, but the wonderful thing about a simple analog car is simplicity.
Merely have to drive harder to beat the waterboilers. It's very easy to spend money to go faster, but I find the true challenge lies within. NONE of us are at the level where a quick tranny will make the last 0.50 seconds possible.
Wonderful post by the OP!!!