Rebuilding the LSD
06-08-2011, 12:32 PM
#16
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Reasonable? Yes. I give it a seven out of ten in difficulty. I am no mechanic by anyone's definition but I managed it. I also have a scissor lift in my garage that helps.
Mikymu's DIY is very good. Only subtle differences with our car. The axle flange bolts are hex head rather than torx.
Mikymu's DIY is very good. Only subtle differences with our car. The axle flange bolts are hex head rather than torx.
06-08-2011, 01:32 PM
#18
Nordschleife Master
Actually it's 40/65 on the OEM ramps. Subtly different than our 40/60 ramps. I should have clarified that when we were on the phone. But the bottomline is on a 996, unless it's aggressively raced and requires 50/80 ramps, there's just very little argument to be made in spending the extra money on new ramps.
06-08-2011, 01:57 PM
#20
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Matt, you also mentioned beforethat the 6GT3 diff also come w/ better gears, right? (not casted.. compared to the 7GT3) (other than the ramp differences)
06-08-2011, 02:18 PM
#21
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Actually it's 40/65 on the OEM ramps. Subtly different than our 40/60 ramps. I should have clarified that when we were on the phone. But the bottomline is on a 996, unless it's aggressively raced and requires 50/80 ramps, there's just very little argument to be made in spending the extra money on new ramps.
Oem '04 GT3 is 40/60.
The housing of the limited-slip differential (1) is driven by the crown wheel of the drive assembly.
The pressure pieces (3) and (7) interlock with the housing (1), but can move axially and are shifted to the left and right-hand disc sets by the differential pins (2) when loads are applied. The expansion force generated (Pax) depends on the applied torque, the overrun angles (a) and the pressure pieces (3) and (7).
The higher the expansion forces Pax acting in both directions on the friction discs are, the higher the locking force of the multiple-disc limited-slip differential will be.
The limited-slip differential is preloaded by the diaphragm springs (6) in both disc sets so that it is ready for operation without torque having to be applied. The static friction moment produced by preloading the disc sets is increased considerably under driving conditions by the expansion force which also acts on the disc sets.
In the case of the 911 GT3, the overrun angles in the acceleration phase are such that a locking value of 60% can be achieved (expansion force Pax + preloading by diaphragm springs). The overrun angles in the acceleration phase have been configured such that a locking value of 40% can be achieved.
06-08-2011, 04:22 PM
#23
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BTW, the belleville washers (#6 in John's diagram) supplied apply substantially more preload than OEM. In fact, when you assemble the LSD back together, there is about a 1/4" gap between the top and bottom housing which you have to compress.
The preload is almost high enough to torque the LSD housing bolts, which are 148 lb/ft. The weight alone of a 1/2 drive socket wrench turned my OEM unit.
The preload is almost high enough to torque the LSD housing bolts, which are 148 lb/ft. The weight alone of a 1/2 drive socket wrench turned my OEM unit.
06-08-2011, 06:18 PM
#24
Nordschleife Master
Not according to US PET it isn't:
http://www.porsche.com/all/media/pdf...SA_KATALOG.pdf
Click to page 70 for the differentials.
This isn't the first time your world market information has disagreed with US market specs. For example, most of the G96:90 gearboxes I have seen had brass synchros in 3rd through 6th.
Serge944,
That sounds about right. The initial preload will come down by +/15% in the first 500-1000 miles. After that break-in period you will want to change your gear oil once. There's no special treatment to the LSD during break-in and you can take it to the track during that time. It will exhibit a bit more braking lock up and corner entry push initially, but once it's fully worn in, that will loosen up a bit toward more neutral handling characteristics.
http://www.porsche.com/all/media/pdf...SA_KATALOG.pdf
Click to page 70 for the differentials.
This isn't the first time your world market information has disagreed with US market specs. For example, most of the G96:90 gearboxes I have seen had brass synchros in 3rd through 6th.
Serge944,
That sounds about right. The initial preload will come down by +/15% in the first 500-1000 miles. After that break-in period you will want to change your gear oil once. There's no special treatment to the LSD during break-in and you can take it to the track during that time. It will exhibit a bit more braking lock up and corner entry push initially, but once it's fully worn in, that will loosen up a bit toward more neutral handling characteristics.
06-08-2011, 07:16 PM
#25
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Not according to US PET it isn't:
http://www.porsche.com/all/media/pdf...SA_KATALOG.pdf
Click to page 70 for the differentials.
This isn't the first time your world market information has disagreed with US market specs. For example, most of the G96:90 gearboxes I have seen had brass synchros in 3rd through 6th.
Serge944,
That sounds about right. The initial preload will come down by +/15% in the first 500-1000 miles. After that break-in period you will want to change your gear oil once. There's no special treatment to the LSD during break-in and you can take it to the track during that time. It will exhibit a bit more braking lock up and corner entry push initially, but once it's fully worn in, that will loosen up a bit toward more neutral handling characteristics.
http://www.porsche.com/all/media/pdf...SA_KATALOG.pdf
Click to page 70 for the differentials.
This isn't the first time your world market information has disagreed with US market specs. For example, most of the G96:90 gearboxes I have seen had brass synchros in 3rd through 6th.
Serge944,
That sounds about right. The initial preload will come down by +/15% in the first 500-1000 miles. After that break-in period you will want to change your gear oil once. There's no special treatment to the LSD during break-in and you can take it to the track during that time. It will exhibit a bit more braking lock up and corner entry push initially, but once it's fully worn in, that will loosen up a bit toward more neutral handling characteristics.
According to the official technical information database and the latest update of the PET 268/27.
The 96.90 is not the gearbox of a GT3 '04.
There is no such thing as a US spec GT3 gearbox.
The G96.96 was based on the GT2 G96.88 gearbox and includes :
• Cable-operated gearshift
• Splash-oil lubrication with pressure oil supply
from dedicated pump
• Transmission oil cooling via oil/water heat
exchanger
• Steel baulk rings on gears three to five
The synchronisation mechanism used for gears 3 - 6 and for the R gear is a singlecone synchronisation mechanism.
The synchronising rings for gears 3 - 5 are made of steel. The synchronising rings for the 6th and R gear are made of special bronze. The friction surfaces of all synchronising rings (except the synchronising ring for the R gear) have a molybdenum coating.
• Interchangeable gear ratios
• Shorter ratios on gears five and six (compared with previous mk1 GT3 model).
• Dual-mass flywheel (DMF) and pressure plate
• Cable-operated clutch without assisted clutch
• Limited-slip differential with asymmetrical lockfactor (40% under power, 60% on overrun) same lock percentage as the cup cars of the era. (Cup cars had a basic torque of between 90 Nm and 180 Nm.)
06-08-2011, 07:45 PM
#26
Nordschleife Master
I'm just telling you what I've seen having had a number of these gearboxes and diffs apart. I fully know that the G96.90 is not a 2004 GT3. The steel synchros on that gearbox are something you previously disagreed with me on. I was using it as an additional example to show that what Porsche puts in print isn't always what they do. I will reiterate what I said above, in a significant number of the G96.90 gearboxes I have had apart, they had brass synchros in them. For a period we were the OEM for Mosler and taking G96.90 crate gearboxes that we were getting directly from both Porsche and Freisinger, disassembling them, inverting them for mid-engine application, and changing the gear ratios. These were brand new gearboxes,and we had to install steel synchros into them because they didn't have them from the factory.
Every set of cups aka ramps or pressure rings is hand stamped with a two digit number at the GKN factory. The .9C late 996 and early 997 Cup Cars, which run a 40/60 published locking factor all get cups stamped 55 and 56, respectively. The vast majority of US 996 GT3 LSDs I've had through here have different cups in them. They are stamped 35 and 36, respectively. And when set side by side with the 40/60 Cup ramps one can visually see that they are in fact different. Based on my direct observation of these ramps and their differences, I have always taken it at face value that they are 40/65 as described in PET.
Attached is a picture for you to see with your own eyes. The ramp on the left is the 56 from the .9C Cup LSD. The one on the right is the 36 ramp from a US 2004 GT3 LSD that we're in the process of rebuilding. There's clearly a difference, with the street car ramp being lower angle on the braking side of the cut out.
Every set of cups aka ramps or pressure rings is hand stamped with a two digit number at the GKN factory. The .9C late 996 and early 997 Cup Cars, which run a 40/60 published locking factor all get cups stamped 55 and 56, respectively. The vast majority of US 996 GT3 LSDs I've had through here have different cups in them. They are stamped 35 and 36, respectively. And when set side by side with the 40/60 Cup ramps one can visually see that they are in fact different. Based on my direct observation of these ramps and their differences, I have always taken it at face value that they are 40/65 as described in PET.
Attached is a picture for you to see with your own eyes. The ramp on the left is the 56 from the .9C Cup LSD. The one on the right is the 36 ramp from a US 2004 GT3 LSD that we're in the process of rebuilding. There's clearly a difference, with the street car ramp being lower angle on the braking side of the cut out.
06-08-2011, 08:22 PM
#27
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I'm just telling you what I've seen having had a number of these gearboxes and diffs apart. I fully know that the G96.90 is not a 2004 GT3. The steel synchros on that gearbox are something you previously disagreed with me on. I was using it as an additional example to show that what Porsche puts in print isn't always what they do. I will reiterate what I said above, in a significant number of the G96.90 gearboxes I have had apart, they had brass synchros in them. For a period we were the OEM for Mosler and taking G96.90 crate gearboxes that we were getting directly from both Porsche and Freisinger, disassembling them, inverting them for mid-engine application, and changing the gear ratios. These were brand new gearboxes,and we had to install steel synchros into them because they didn't have them from the factory.
Every set of cups aka ramps or pressure rings is hand stamped with a two digit number at the GKN factory. The .9C late 996 and early 997 Cup Cars, which run a 40/60 published locking factor all get cups stamped 55 and 56, respectively. The vast majority of US 996 GT3 LSDs I've had through here have different cups in them. They are stamped 35 and 36, respectively. And when set side by side with the 40/60 Cup ramps one can visually see that they are in fact different. Based on my direct observation of these ramps and their differences, I have always taken it at face value that they are 40/65 as described in PET.
Attached is a picture for you to see with your own eyes. The ramp on the left is the 56 from the .9C Cup LSD. The one on the right is the 36 ramp from a US 2004 GT3 LSD that we're in the process of rebuilding. There's clearly a difference, with the street car ramp being lower angle on the braking side of the cut out.
Every set of cups aka ramps or pressure rings is hand stamped with a two digit number at the GKN factory. The .9C late 996 and early 997 Cup Cars, which run a 40/60 published locking factor all get cups stamped 55 and 56, respectively. The vast majority of US 996 GT3 LSDs I've had through here have different cups in them. They are stamped 35 and 36, respectively. And when set side by side with the 40/60 Cup ramps one can visually see that they are in fact different. Based on my direct observation of these ramps and their differences, I have always taken it at face value that they are 40/65 as described in PET.
Attached is a picture for you to see with your own eyes. The ramp on the left is the 56 from the .9C Cup LSD. The one on the right is the 36 ramp from a US 2004 GT3 LSD that we're in the process of rebuilding. There's clearly a difference, with the street car ramp being lower angle on the braking side of the cut out.
Last time we disagreed because you posted this:
which was wrong as all 2004 GT3s have steel rings world wide.
About the LSD don't rely on the PET. If that was the reason that you changed your mind about the locking rates..
Given that I have never heard of this problem on a 996 LSD I don't think I'm going to change my recommendation. I think there's a lot to be gained on the 997 by changing the ramps because of the increased locking rate. The 996 is 40/60 already and I haven't seen them chip so I'm not going to just sound the alarm and tell everyone they need new parts.
...
...
I have about a dozen different official documents published in different dates that give 60/40; until Porsche decides to change something, I will keep referring to them.
If you want I can send you some over e-mail.
Besides 60/65 are very close, it's a non issue, even if it is 65.
Best
06-08-2011, 09:43 PM
#29
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I did it on jack stands. It's mostly a matter of pushing stuff out of the way, wiggling things around, holding your tongue just right and the properly applied curse word. I had my son push the hoses up using a long bar while I got it out.
As mentioned, getting it back in is tougher, but all the same principles apply. I did not take out the axle, I moved it around and tied it up with tie wraps. A helper is worth the price of the beer.
And BTW, the first time back on track, you'll feel like you've got a new car. It's well worth it. Kyle
As mentioned, getting it back in is tougher, but all the same principles apply. I did not take out the axle, I moved it around and tied it up with tie wraps. A helper is worth the price of the beer.
And BTW, the first time back on track, you'll feel like you've got a new car. It's well worth it. Kyle
06-14-2011, 11:53 PM
#30
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SHE"S IN!
My LSD from Guard is back in! Thanks Matt - great job and quick turn-around.
Mike! Thank you for the excellent write up! I used jack stands to load the suspension to provide a little more space between the transmission and the half, axles to maneuver the LSD. I also removed the bolt that held the bracket that kept the hoses rigid to the top of the transmission - provided a lot more movement. I loosened one of the diagonal cross braces as well. I had a number different sized wooden blocks to hold everything in different positions while I insert the LSD because the install was a one man show.
Other than that, I followed Mike's DIY to the letter.
Go Bruins.
Mike! Thank you for the excellent write up! I used jack stands to load the suspension to provide a little more space between the transmission and the half, axles to maneuver the LSD. I also removed the bolt that held the bracket that kept the hoses rigid to the top of the transmission - provided a lot more movement. I loosened one of the diagonal cross braces as well. I had a number different sized wooden blocks to hold everything in different positions while I insert the LSD because the install was a one man show.
Other than that, I followed Mike's DIY to the letter.
Go Bruins.
Last edited by Dudley; 06-15-2011 at 03:14 PM.