LSD buster
#17
11-12-2009, 08:24 PM
Registered User
Join Date: Dec 2005
Location: Gualala, Ca.
Age: 77
Posts: 752
Rep Power: 94 
#18
11-12-2009, 08:47 PM
I'm confused on whether this is a design problem or manufacturing problem. It seems the preload is too low on the factory LSD. Shouldn't Porsche be fixing this?
#19
11-12-2009, 10:44 PM
Matt,
Thank you very much for your great explanation on LSD's. I am also a customer of GUARD LSD's but from the previous owner and I am very glad you kept the tradition of excellent education and customer service!
Mike used the Mobil Delvac but the previous GUARD owner recommended: Lubrication Engineering. What is your opinion on this? After having installed my GUARD with 40/60 ramps, I have driven the car for about 2000 miles with Mobil Delvac (no track miles other than hard street miles), should I change the oil soon and again use Mobil Delvac or use "Lubrication Engineering"?
Feedback will be greatly appreciated.
Thank you very much for your great explanation on LSD's. I am also a customer of GUARD LSD's but from the previous owner and I am very glad you kept the tradition of excellent education and customer service!
Mike used the Mobil Delvac but the previous GUARD owner recommended: Lubrication Engineering. What is your opinion on this? After having installed my GUARD with 40/60 ramps, I have driven the car for about 2000 miles with Mobil Delvac (no track miles other than hard street miles), should I change the oil soon and again use Mobil Delvac or use "Lubrication Engineering"?
Feedback will be greatly appreciated.
#20
11-12-2009, 11:15 PM
Join Date: Apr 2008
Location: Rocklin, California
Posts: 1,120
Rep Power: 131 Hello,
Michael, thank you very much for the kind words. It's customers like you who make it worthwhile to get up in the morning and start answering the phones. Not everyone in this business shows the sort of gratitude you express here. Research says that customers are 10 times more like to talk about a bad customer experience than a good one, so when we see something like this write we really appreciate it.
Just a couple of technical comments to add to Mike's very thorough write up above. If people want to rebuild their factory LSD's installing new ramps in not a requirement. It was something Mike decided to do because he wanted something with more aggressive locking than what was offered from the factory. If your car sees less track time than Mike's, or if you just don't want to spend the extra money ($700 of that $1600 number) the factory ramps still are a good option.
And while I am on the subject I want to clarify and correct something I have been seeing on a couple of other boards. When we talk about the ramps, we are talking about locking percentages. We are not talking about ramp angles. In fact, if you look at the picture of our ramps, you will see that the locking percentage is inversely related to the ramp angles. The 80% ramp is a lower angle because it's designed to be more aggressive and activate more quickly. The way a ZF style LSD works is when there is wheel slip the center spider gears spin the crossshaft that they sit on up the side of the ramp and press the ramps apart, locking the plates and discs together and stopping the wheel spin, while simultaneously transfering the power to the other wheel.
Just to clarify further, when it says 80% locking that means it allows no more than a 20% differential in wheel speeds from side to side. Again, it's an inverse relationship. And once the LSD locks, it's locked. That seems to be another misconception I see floating around. An LSD at rest functions like an open differential. It doesn't matter if it's got zero pre-load on it or 50ft/lb or 80ft/lb. The preload on our differential is actually pressing the ramps together and holding them there while the differential functions like any other open differential. It's only when there's enough wheel slip to accelerate those crossshaft spiders up to the point that they push the ramps apart that the LSD locks and does it's job.
I think that's a very important point because the other thing I have been seeing recently said about how our LSD's (and Porsche's) work are that the preload in them causes the car to push and makes it hard to turn. This is one of the most ridiculous things I have ever heard. As Mike has indicated (as well as I have seen on other threads around here) when the factory POS LSD wears out the car gets super loose and wags it's tail all over the place. Being tail happy and oversteering has always been the achilles heel of the 911 and even though they've made great strides in recent years with respect to suspension and moving the heavy stuff more towards the center, with an open differential a 911 is still a car that has a tendency towards snap oversteer.
Saying that the differential's involvement in giving the car more push is a bad thing is like saying putting wider rubber on the car will reduce performance because it makes it harder to turn. It's a nessecary correlary to the addition of the performance part. And to suggest that the 50ft/lbs or even more like we use on the race LSD's is enough to make the car refuse to turn is really the most fantastic idea of them all. We're talking about cars making 400ft/lb of torque here. Even at 2000rpm just off of idle they're puting down enough power to overcome 50 or 80ft/lb of preload. And no doubt the kind of forces going through the rear end under heavy braking is far more than that. Furthermore, it's under braking that the LSD most aggressively locks and gives the rear end stability and the only pushing it causes is when you trail brake deep into the corner, which is unavoidable with an LSD but is just part of how it does what it does. In fact, in the transition when you quickly lift off the brake and move over to the throttle the LSD returns to it's open state and doesn't lock again until you've buried the throttle so deep that there's a 50% speed differential between the two wheels.This is where the majority of the turning occurs. Mike's experience after this rebuild corroborates that because as he said above it doesn't fight him at all on low speed corners. If that doesn't make sense, say something and I'll explain it in more detail.
Lastly, I want answer a question above about why not get the billet housing of the GT LSD at the same time. Beyond Mike's desire not to have to reset his ring and pinion and do this thing on his own, there's another practical reason. The reason is that it's not required. Sure, you read here and there about cracked LSD bellhousing on the stock cast LSD's. It does happen. But it doesn't happen as often as you might think. And 9 times out of 10 it happens on a dedicated track car that is driven at the limit for extended periods of time (like 4 or 6 or 12 hour races) and is subjected to stresses that most of us will never put our cars through. I tell you this because the way I do business is I am never going to sell you something you don't need. I will give you a benefits and liabilities analysis of why you may or may not want to consider a part, but I'm not going to push you into something unless I am 100% confident you are going to need it. Based on what Mike told me about himself and his car I didn't consider it a risk he really needed to worry about. For most of you, you really don't have to have that pretty billet differential bellhousing unless you really want it. If next year Mike decides he wants to go run the 25 hours of Thunderhill in his car, then maybe he'll want to seriously consider our GT2 Chromoly Billet housing, but for now he should be just fine. So, it's just something to consider for any of you who have factory LSD's in the car. Instead of spending all the money on a new LSD and throwing away a part that does have some merits, you might consider a rebuild. It will cost you less than the cheapest option in the aftermarket and I assure you it will perform better as well. Or as I offered to Mike, if you want one of our complete units, we are always open to a core exchange on a rebuildable factory LSD to help defray the cost of getting you into one of our motorsports units.
Kind Regards,
Matt
Michael, thank you very much for the kind words. It's customers like you who make it worthwhile to get up in the morning and start answering the phones. Not everyone in this business shows the sort of gratitude you express here. Research says that customers are 10 times more like to talk about a bad customer experience than a good one, so when we see something like this write we really appreciate it.
Just a couple of technical comments to add to Mike's very thorough write up above. If people want to rebuild their factory LSD's installing new ramps in not a requirement. It was something Mike decided to do because he wanted something with more aggressive locking than what was offered from the factory. If your car sees less track time than Mike's, or if you just don't want to spend the extra money ($700 of that $1600 number) the factory ramps still are a good option.
And while I am on the subject I want to clarify and correct something I have been seeing on a couple of other boards. When we talk about the ramps, we are talking about locking percentages. We are not talking about ramp angles. In fact, if you look at the picture of our ramps, you will see that the locking percentage is inversely related to the ramp angles. The 80% ramp is a lower angle because it's designed to be more aggressive and activate more quickly. The way a ZF style LSD works is when there is wheel slip the center spider gears spin the crossshaft that they sit on up the side of the ramp and press the ramps apart, locking the plates and discs together and stopping the wheel spin, while simultaneously transfering the power to the other wheel.
Just to clarify further, when it says 80% locking that means it allows no more than a 20% differential in wheel speeds from side to side. Again, it's an inverse relationship. And once the LSD locks, it's locked. That seems to be another misconception I see floating around. An LSD at rest functions like an open differential. It doesn't matter if it's got zero pre-load on it or 50ft/lb or 80ft/lb. The preload on our differential is actually pressing the ramps together and holding them there while the differential functions like any other open differential. It's only when there's enough wheel slip to accelerate those crossshaft spiders up to the point that they push the ramps apart that the LSD locks and does it's job.
I think that's a very important point because the other thing I have been seeing recently said about how our LSD's (and Porsche's) work are that the preload in them causes the car to push and makes it hard to turn. This is one of the most ridiculous things I have ever heard. As Mike has indicated (as well as I have seen on other threads around here) when the factory POS LSD wears out the car gets super loose and wags it's tail all over the place. Being tail happy and oversteering has always been the achilles heel of the 911 and even though they've made great strides in recent years with respect to suspension and moving the heavy stuff more towards the center, with an open differential a 911 is still a car that has a tendency towards snap oversteer.
Saying that the differential's involvement in giving the car more push is a bad thing is like saying putting wider rubber on the car will reduce performance because it makes it harder to turn. It's a nessecary correlary to the addition of the performance part. And to suggest that the 50ft/lbs or even more like we use on the race LSD's is enough to make the car refuse to turn is really the most fantastic idea of them all. We're talking about cars making 400ft/lb of torque here. Even at 2000rpm just off of idle they're puting down enough power to overcome 50 or 80ft/lb of preload. And no doubt the kind of forces going through the rear end under heavy braking is far more than that. Furthermore, it's under braking that the LSD most aggressively locks and gives the rear end stability and the only pushing it causes is when you trail brake deep into the corner, which is unavoidable with an LSD but is just part of how it does what it does. In fact, in the transition when you quickly lift off the brake and move over to the throttle the LSD returns to it's open state and doesn't lock again until you've buried the throttle so deep that there's a 50% speed differential between the two wheels.This is where the majority of the turning occurs. Mike's experience after this rebuild corroborates that because as he said above it doesn't fight him at all on low speed corners. If that doesn't make sense, say something and I'll explain it in more detail.
Lastly, I want answer a question above about why not get the billet housing of the GT LSD at the same time. Beyond Mike's desire not to have to reset his ring and pinion and do this thing on his own, there's another practical reason. The reason is that it's not required. Sure, you read here and there about cracked LSD bellhousing on the stock cast LSD's. It does happen. But it doesn't happen as often as you might think. And 9 times out of 10 it happens on a dedicated track car that is driven at the limit for extended periods of time (like 4 or 6 or 12 hour races) and is subjected to stresses that most of us will never put our cars through. I tell you this because the way I do business is I am never going to sell you something you don't need. I will give you a benefits and liabilities analysis of why you may or may not want to consider a part, but I'm not going to push you into something unless I am 100% confident you are going to need it. Based on what Mike told me about himself and his car I didn't consider it a risk he really needed to worry about. For most of you, you really don't have to have that pretty billet differential bellhousing unless you really want it. If next year Mike decides he wants to go run the 25 hours of Thunderhill in his car, then maybe he'll want to seriously consider our GT2 Chromoly Billet housing, but for now he should be just fine. So, it's just something to consider for any of you who have factory LSD's in the car. Instead of spending all the money on a new LSD and throwing away a part that does have some merits, you might consider a rebuild. It will cost you less than the cheapest option in the aftermarket and I assure you it will perform better as well. Or as I offered to Mike, if you want one of our complete units, we are always open to a core exchange on a rebuildable factory LSD to help defray the cost of getting you into one of our motorsports units.
Kind Regards,
Matt
You are too kind. I am just trying to state the obvious that you provide excellent customer support back by great product. I always try to be as honest as I can on my feedback either good or bad. I agree that too many people like to dwell on the negative when vendors provide nothing but excellent products/support 99.9% of the time. I used to spend a-lot of time at M3forum but it is litter with many negative none sense pointless attack on various vendor/sponsors ... and often times on each other. We all know negative news sell paper but I hope we can avoid these types of childish stuff on this forum
Back to your comments. Boy, am I glad you are the expert and not I. most of the stuff you mentioned just went over my head. I will need some time to absorb it all. Like you have said, aggressive LSD may feel different as I accelerate hard in a turn that is why I went super easy on the first couple sessions. I found out the rebuild LSD really plant the rear in such a way I can push so much harder in a turn and throttle steer to make a smooth turn. If there is any "push" I have not experience it. For example, turn 14 and 15 before the straight at Thunderhill may require you to make two smaller turns which can slow you down. Now I can just throttle steer and make one nice arc and rocket out of the turn down the straight. Once I get my brakes fix I think I will be able to extract 4-5 seconds easy. learning when to downshift and when not to will get me another 3-4 seconds. I try not to go over my pay grade when I track and take small steps on the go fast part
I am glad you can custom build my LSD to my spec and lol on the future 25 hours of Thunderhill. I will most likely sit on the side line eating my popcorn and watch real race car drivers duke it out on the track
#21
11-12-2009, 11:19 PM
Join Date: Apr 2008
Location: Rocklin, California
Posts: 1,120
Rep Power: 131
Hope you find it useful
I am addict to these types of challenge. I don't know what to do with myself if I don't have my car to work on. Maybe performing magic tricks at a nursing home lol
Defiantly a design flaw IMHO. Low preload from the factory and inferior friction disc are the culprits. I am sure Matt can expound on this matter
I am addict to these types of challenge. I don't know what to do with myself if I don't have my car to work on. Maybe performing magic tricks at a nursing home lol
Defiantly a design flaw IMHO. Low preload from the factory and inferior friction disc are the culprits. I am sure Matt can expound on this matter
#22
11-14-2009, 02:34 PM
Mike,
Amazing job, great video information for the plenty of uneducated GT3/GT2/GT3 RS owners with worn out LSD ignoring the fact that a proper LSD improves track times, and makes the car easier to drive at the limits.
Thanks a lot.
Amazing job, great video information for the plenty of uneducated GT3/GT2/GT3 RS owners with worn out LSD ignoring the fact that a proper LSD improves track times, and makes the car easier to drive at the limits.
Thanks a lot.
#23
11-14-2009, 04:10 PM
Excellent post - thanks for taking the time to do the write up, very helpful (though I am afraid to test my LSD for fear that I may need to deliver the 30 lb beast...)
Great video too - it looks like the "wart" was just along for the ride - does anyone actually use it?
Great video too - it looks like the "wart" was just along for the ride - does anyone actually use it?
#24
11-14-2009, 07:12 PM
Join Date: Apr 2008
Location: Rocklin, California
Posts: 1,120
Rep Power: 131 "wart" in the video ???
Matt and Guard Transmission are THE BEST IN THE BUSINESS. Like I've always said.
And for the record, if cost is no object, I say WHY NOT go with the chromoly billet housing??? It is a work of art, and will give you great piece of mind as you putt around the track. Good thing GT offers something for everyone. I recommend all GT2 and 3 owners to at least rebuild their diffs with Guard as the stock stuff is pretty brittle.
And for the record, if cost is no object, I say WHY NOT go with the chromoly billet housing??? It is a work of art, and will give you great piece of mind as you putt around the track. Good thing GT offers something for everyone. I recommend all GT2 and 3 owners to at least rebuild their diffs with Guard as the stock stuff is pretty brittle.
#27
11-15-2009, 03:55 PM
An LSD at rest functions like an open differential. It doesn't matter if it's got zero pre-load on it or 50ft/lb or 80ft/lb. The preload on our differential is actually pressing the ramps together and holding them there while the differential functions like any other open differential. It's only when there's enough wheel slip to accelerate those crossshaft spiders up to the point that they push the ramps apart that the LSD locks and does it's job.
I heard about this simple LSD test but afraid to do it knowing that I will need to take action if it's bad ... and it was. I was told factory LSD is pretty much dead on arrival and can be render useless after even one track session. We tested two other GT3/RS last weekend at Thunderhill and the 996 GT3's LSD was dead as a door nail and the other 997 GT3 RS' LSD was just like mine - maybe 1-2 ft/lb of torque left.
If at rest the diff functions like any other open diff.
How valid is the wheel off the ground test??
If it is the wheel slip to accelerate those crossshaft spiders up to the point that they push the ramps apart that the LSD locks and does it's job.
Just confused
#29
11-15-2009, 08:02 PM
Now I'm really confused
If at rest the diff functions like any other open diff.
How valid is the wheel off the ground test??
If it is the wheel slip to accelerate those crossshaft spiders up to the point that they push the ramps apart that the LSD locks and does it's job.
Just confused
If at rest the diff functions like any other open diff.
How valid is the wheel off the ground test??
If it is the wheel slip to accelerate those crossshaft spiders up to the point that they push the ramps apart that the LSD locks and does it's job.
Just confused
#30
11-15-2009, 08:46 PM
LOL I was wondering when someone is going to get my hot-wheels joke
Hey I see you are local and a doctor too? I am at Rocklin so we might meet at some of the local tracks. My next event will likely be at Infinion on 11/21 with trackmaster
I was pretty timid when I first got the RS - will not even change the windshield wiper. I got over that quickly once I start tracking the car - that's what it's mad for right?
Hey I see you are local and a doctor too? I am at Rocklin so we might meet at some of the local tracks. My next event will likely be at Infinion on 11/21 with trackmaster
I was pretty timid when I first got the RS - will not even change the windshield wiper. I got over that quickly once I start tracking the car - that's what it's mad for right?
