Bilstein saga continiue
#47
04-18-2011, 10:05 PM
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#49
04-19-2011, 11:24 AM
sometimes we don't have the luxury of conducting proper scientific studies on these tips. There is no reason to think the tip is based on any secondary gain though.
#50
04-19-2011, 02:47 PM
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What do you guys think the max camber the front diff can tolerate ?
I'm thinking less than 2.0
I'm thinking less than 2.0
#51
04-19-2011, 03:41 PM
Join Date: Jan 2007
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When I've had Eibach springs on mine car the front camber was set at 1,6 adjusted from the top mount with stock LKA. I think GT-TT is right on money, if you looking for more camber in front best would be to use top mounted adjustable camber plates and stay away from to many shims at the bottom
#52
04-19-2011, 04:53 PM
Facts? How about getting -2.2 in the front with use of shims and then finding the front diff leaking since 1 of the 2 shafts was out of the housing?
Is that fact enough? Almost had my front differential destroyed..
With the top mount adjustment i am running -2.2 as we speak with no problem for over 18 months.
Is that fact enough? Almost had my front differential destroyed..
With the top mount adjustment i am running -2.2 as we speak with no problem for over 18 months.
#53
04-19-2011, 04:56 PM
Also it is crucial to get corner balancing when you run a setup like this.
#54
04-19-2011, 08:28 PM
There is no scientific study required here. A commonsense explanation will do.
Having first hand experience with the workings and assembly of the front diff on the 997tt on more than one occassion now, i am failing to see the connection between the use of shims on LFCA's and destroying diff seals and diffs. Eclou, i would have thought with your knowledge of these cars you of all people would be able to put something on the table here? I assume you are aware of the the diff flanges that run through the diff seals and how they are assembled into the diff?.....and, how the drive shafts connect, the lateral movement in the drive shafts to accommodate for suspension travel etc? I also assume you are aware of the differences in length between the 996 and 997 gt3 LFCA's....and why tarrats and/or other top strut modifications are sometimes required when using the 996 arms to achieve certain neg camber settings......depending upon how aggressive one wishes to go.
My intention is not to set anyone on fire here...so lets make that clear. What i am pointing out is that there is a lot missing to this "tip" that shimming causes the front diff seals to leak and front diff to fail. There has been nothing supplied to support that theory. I'm happy to learn something new so please....explain how and why.....because it presently makes no logical sense whatsoever to me or anyone else i have since spoken to that has worked on these cars doing these alignment set ups (Porsche included).
For those members that may not be aware, you can get one deg neg from doing nothing other than moving the top of the struts all the way in on the small adjustment on the strut towers. So with a set of say 997 GT3 LFCA's, the small thickness of shim that is required to achieve the last neg and a half is minuscule. How much shims are you guys (GT TT/ Slawek) talking about and how much neg are you trying to apply? Must be one hell of a lot......even then....where is the connection?
Last edited by speed21; 04-19-2011 at 08:32 PM.
#55
04-19-2011, 08:42 PM
GT-TT's finding makes sense. You can either increase negative camber by
1)pushing the tops of the struts closer towards centerline
....../-><-\.....
...../.........\....
.O/........... \O
2)pushing the bottoms further out towards the wheel well
......./...... \.......
...../......... \......
..../........... \......
O/<-------->\O
Since the front driveshafts are of a fixed length, it would make sense that if you try to push the bottoms of the struts too far apart, you could exceed the tolerances of the seals in the differential, effectively pulling them out of place.
Speed21 you have a good point in that many times spurious internet statements become gospel without any supporting photos, diagrams, etc.
Let's try to give each other a bit of credit though. There are many knowledgeable members here who have found through trial and error some of the limitations/quirks of this platform.
1)pushing the tops of the struts closer towards centerline
....../-><-\.....
...../.........\....
.O/........... \O
2)pushing the bottoms further out towards the wheel well
......./...... \.......
...../......... \......
..../........... \......
O/<-------->\O
Since the front driveshafts are of a fixed length, it would make sense that if you try to push the bottoms of the struts too far apart, you could exceed the tolerances of the seals in the differential, effectively pulling them out of place.
Speed21 you have a good point in that many times spurious internet statements become gospel without any supporting photos, diagrams, etc.
Let's try to give each other a bit of credit though. There are many knowledgeable members here who have found through trial and error some of the limitations/quirks of this platform.
Last edited by eclou; 04-19-2011 at 08:48 PM.
#56
04-19-2011, 09:58 PM
GT-TT's finding makes sense. You can either increase negative camber by
1)pushing the tops of the struts closer towards centerline
....../-><-\.....
...../.........\....
.O/........... \O
2)pushing the bottoms further out towards the wheel well
......./...... \.......
...../......... \......
..../........... \......
O/<-------->\O
Since the front driveshafts are of a fixed length, it would make sense that if you try to push the bottoms of the struts too far apart, you could exceed the tolerances of the seals in the differential, effectively pulling them out of place.
Speed21 you have a good point in that many times spurious internet statements become gospel without any supporting photos, diagrams, etc.
Let's try to give each other a bit of credit though. There are many knowledgeable members here who have found through trial and error some of the limitations/quirks of this platform.
1)pushing the tops of the struts closer towards centerline
....../-><-\.....
...../.........\....
.O/........... \O
2)pushing the bottoms further out towards the wheel well
......./...... \.......
...../......... \......
..../........... \......
O/<-------->\O
Since the front driveshafts are of a fixed length, it would make sense that if you try to push the bottoms of the struts too far apart, you could exceed the tolerances of the seals in the differential, effectively pulling them out of place.
Speed21 you have a good point in that many times spurious internet statements become gospel without any supporting photos, diagrams, etc.
Let's try to give each other a bit of credit though. There are many knowledgeable members here who have found through trial and error some of the limitations/quirks of this platform.
Also, I completely understand the concept of how camber is applied.....either at top or bottom or a combination thereof.
Anyway, the driveshafts are not of fixed length though eclou. They have lateral movement to provide for suspension travel. (P also confirms this as well as others in the biz). Are you suggesting that the cv drive shafts have no lateral movement to accommodate for suspension travel?
Additionally, the diff flanges are extremely rigid. They are locked as part of the diff assembly. They spigot through into the carrier race bearings and are circlip locked at the end of the splines that mate with the side gears...inside the diff. So, these have no lateral or vertical movement period. The spigot section of the diff flanges which run through and onto the rubber seals can only move up or down if the carrier race bearings lose correct adjustment. But that is a different scenario from different causes.
So, understanding the diff flanges are locked/rock solid, and rigid to the diff assy, the only way lateral pressure can be applied (to the flanges) externally is if the drive shafts have been pulled beyond their movement range. Now, to do that the there would need to be a heck of a lot of spacers used on the lower control arms to completely exhaust that movement. And, lets say that happened, any negative force/movement would be lateral, not vertical....and not able to cause seal issues anyway....logically speaking. Again, how much neg camber do you think would actually be able to create the scenario of the drive shafts using up all the allowable travel? I'd suggest perhaps race car type settings of say 4 deg or more upward, a lot of shim thickness applied with no consideration given to sharing the camber settings between the upper and lower strut. That may create a lateral tugging action upon the diff flanges at certain suspension movements but even so they are locked by the circlips. So, unless the tugging pulls/breaks the retaining circlips of the end of the splines inside the diff, allowing the diff flanges to then free slide in the carrier race bearings, you still have a fair degree of sealing area on the flanges to work on the oil seals without losing oil etc.
Comments eclou?
Or, better still, how about some detailed info from GT TT and Slawek. I assume they are speaking from first hand experience? So surely it would not be difficult to hear the detail on the hows and whys? After all we all want to learn don't we?
Last edited by speed21; 04-19-2011 at 10:04 PM.
#57
04-19-2011, 10:36 PM
I don't have an exploded diagram of the front axles/diff, but there is going to be some limit as to how far the front track can be widened (not in wheels/offsets) before the axles/flanges are stressed. I would also imagine there is more movement/stress to accommodate on the front axles than on the rear due to the steering changes.
All the GTx variants of the 911's have adjustable strut tops which can be rotated to allow for larger ranges of camber. Without being able to adjust the tops on our cars could mean having to excessively shim the bottom beyond what a GTx car would require in shims. I have no personal experience because I stopped tracking/tweaking the car - too easy to get fast lap times without having to develop better driving skills.
All the GTx variants of the 911's have adjustable strut tops which can be rotated to allow for larger ranges of camber. Without being able to adjust the tops on our cars could mean having to excessively shim the bottom beyond what a GTx car would require in shims. I have no personal experience because I stopped tracking/tweaking the car - too easy to get fast lap times without having to develop better driving skills.
#58
04-19-2011, 11:34 PM
I don't have an exploded diagram of the front axles/diff, but there is going to be some limit as to how far the front track can be widened (not in wheels/offsets) before the axles/flanges are stressed. I would also imagine there is more movement/stress to accommodate on the front axles than on the rear due to the steering changes.
All the GTx variants of the 911's have adjustable strut tops which can be rotated to allow for larger ranges of camber. Without being able to adjust the tops on our cars could mean having to excessively shim the bottom beyond what a GTx car would require in shims. I have no personal experience because I stopped tracking/tweaking the car - too easy to get fast lap times without having to develop better driving skills.
All the GTx variants of the 911's have adjustable strut tops which can be rotated to allow for larger ranges of camber. Without being able to adjust the tops on our cars could mean having to excessively shim the bottom beyond what a GTx car would require in shims. I have no personal experience because I stopped tracking/tweaking the car - too easy to get fast lap times without having to develop better driving skills.
. And, agree there are limits for everything but what we are effectively talking about here is extending the base of the wheel an inordinate distance outward to achieve what would appear on the surface to be a very substantial degree of neg camber. But lets say that was done (for what ever crazy reason) without giving any consideration to the more sensible approach (and options) of balancing the camber extension between the top mount and lower control arm but that still doesn't answer for how that would cause stress to the seals . As i said the diff flanges are locked inside the carrier race bearings and effectively become part of the diff carrier....which is solid as a rock. Once the cv (velocity joint) drive shaft flanges are bolted up to the diff flanges and, on the opposing end to the flanges at the disc wheel bearing carrier end (at wheel), the suspension movement is accommodated for by the lateral movement provided within the parameters of the drive shafts. Lets imagine the lateral movement built in to the drive shafts was somehow totally exhausted by some ignorant wacky application of spacers then what may happen is that at certain angles of suspension travel the shaft, exhausted of lateral movement will tug against the diff carrier flanges and the disc/wheel bearing carrier flanges. A driver in tune with his car would surely feel that restriction (one would think/hope), needless to say if the tugging was so servere the cirlips would become so stressed to the point of breakage and dislodgment off the end of the diff flange end splines.....but then there is the flange at the wheel bearing/disc end....why then does that escape damage? The tugging at the diff flanges may well result in dislodging or breaking the circlips, then becoming munched up in the planetary gears/ CW and P gears etc etc. Then you'd have a big problem worthy of mention. But then why not damage at the wheel bearing end as well?....the stress would be equal at both ends (flanges). But so far as diff seals popping out and leaking etc? The only way these are going to become damaged or pop out of the diff housing is if they are subjected to a reasonable degree of vertical up and down movement by the diff flanges which as we know are effectively part of the main crownwheel/hemishere carrier assy....locked solid by the carrier race bearings to the main diff housing. So unless the carrier race bearings lose adjustment then how are the flanges going to move up and down so to cause the flange spigots to damage the seals? As i said earlier....it doesn't make any logical sense at all!!Then there is the sepatate issue why anyone would space LFCA's out to such an extreme the drive shaft movement is exhausted. It certainly doesn't say much for the guys that did the job......that is if they really did that. And again i ask at how much neg camber did the drive shaft movement become exhausted? Must have been some serious shims and camber used. The whole thing simply doesn't ad up
How about some answers here guys? slawek/GT TT. eclou?
Now re the GT cars; i'm told you can use their top strut mounts on the turbo too as well as modding the turbos existing mounts to get more adjustment at top of strut where needed....in combination with lower control arm adjustment/shimming. Separate issue though. Each in moderation.
Last edited by speed21; 04-19-2011 at 11:40 PM.
#59
04-20-2011, 04:15 AM
Agree, but what is missing here before any credit can be claimed is some quality info to substantiate the "tip". Thats all i'm asking. No flaming intended but agree there is a lot of BS out in cyberspace....and therfore one needs to be wary what they are told and what they believe.
Also, I completely understand the concept of how camber is applied.....either at top or bottom or a combination thereof.
Anyway, the driveshafts are not of fixed length though eclou. They have lateral movement to provide for suspension travel. (P also confirms this as well as others in the biz). Are you suggesting that the cv drive shafts have no lateral movement to accommodate for suspension travel?
Additionally, the diff flanges are extremely rigid. They are locked as part of the diff assembly. They spigot through into the carrier race bearings and are circlip locked at the end of the splines that mate with the side gears...inside the diff. So, these have no lateral or vertical movement period. The spigot section of the diff flanges which run through and onto the rubber seals can only move up or down if the carrier race bearings lose correct adjustment. But that is a different scenario from different causes.
So, understanding the diff flanges are locked/rock solid, and rigid to the diff assy, the only way lateral pressure can be applied (to the flanges) externally is if the drive shafts have been pulled beyond their movement range. Now, to do that the there would need to be a heck of a lot of spacers used on the lower control arms to completely exhaust that movement. And, lets say that happened, any negative force/movement would be lateral, not vertical....and not able to cause seal issues anyway....logically speaking. Again, how much neg camber do you think would actually be able to create the scenario of the drive shafts using up all the allowable travel? I'd suggest perhaps race car type settings of say 4 deg or more upward, a lot of shim thickness applied with no consideration given to sharing the camber settings between the upper and lower strut. That may create a lateral tugging action upon the diff flanges at certain suspension movements but even so they are locked by the circlips. So, unless the tugging pulls/breaks the retaining circlips of the end of the splines inside the diff, allowing the diff flanges to then free slide in the carrier race bearings, you still have a fair degree of sealing area on the flanges to work on the oil seals without losing oil etc.
Comments eclou?
Or, better still, how about some detailed info from GT TT and Slawek. I assume they are speaking from first hand experience? So surely it would not be difficult to hear the detail on the hows and whys? After all we all want to learn don't we?
Also, I completely understand the concept of how camber is applied.....either at top or bottom or a combination thereof.
Anyway, the driveshafts are not of fixed length though eclou. They have lateral movement to provide for suspension travel. (P also confirms this as well as others in the biz). Are you suggesting that the cv drive shafts have no lateral movement to accommodate for suspension travel?
Additionally, the diff flanges are extremely rigid. They are locked as part of the diff assembly. They spigot through into the carrier race bearings and are circlip locked at the end of the splines that mate with the side gears...inside the diff. So, these have no lateral or vertical movement period. The spigot section of the diff flanges which run through and onto the rubber seals can only move up or down if the carrier race bearings lose correct adjustment. But that is a different scenario from different causes.
So, understanding the diff flanges are locked/rock solid, and rigid to the diff assy, the only way lateral pressure can be applied (to the flanges) externally is if the drive shafts have been pulled beyond their movement range. Now, to do that the there would need to be a heck of a lot of spacers used on the lower control arms to completely exhaust that movement. And, lets say that happened, any negative force/movement would be lateral, not vertical....and not able to cause seal issues anyway....logically speaking. Again, how much neg camber do you think would actually be able to create the scenario of the drive shafts using up all the allowable travel? I'd suggest perhaps race car type settings of say 4 deg or more upward, a lot of shim thickness applied with no consideration given to sharing the camber settings between the upper and lower strut. That may create a lateral tugging action upon the diff flanges at certain suspension movements but even so they are locked by the circlips. So, unless the tugging pulls/breaks the retaining circlips of the end of the splines inside the diff, allowing the diff flanges to then free slide in the carrier race bearings, you still have a fair degree of sealing area on the flanges to work on the oil seals without losing oil etc.
Comments eclou?
Or, better still, how about some detailed info from GT TT and Slawek. I assume they are speaking from first hand experience? So surely it would not be difficult to hear the detail on the hows and whys? After all we all want to learn don't we?
Example; gt3 front sway for turbo. Been using it for 2 years, always had clearance problem on sharp turns even using first hole. Literally impossible to use beyond second hole at best. Tried all sort of adjustments using custom adjustable drop links etc. Now it may be possible to solve the diff issue with the shims but I bet it will be a marginal solution.. Why bother then? You don't need more than 2.3 neg on the front on a turbo and you can get that with an adjustment from the top.
Why are we discussing this so much? I just posted my experience learned the hard way. Everyone pls feel free to replicate my experiment by all means!
Could try to call my tuner and find out if they remember what, who, when etc broke but life is too short really.. Shaft came out for one unlucky user and let's keep it at that. Present solution works like a dream. Not too long, not too short, just perfect..
#60
04-20-2011, 05:22 AM
Trying to answer some of the numerous comments above. Wish I had asked mechanic to take pictures but indeed shaft went off (and I assume seals etc consistently destroyed) with I believe 0.5 or 1 cm shims. Car was running 2.2 or 2.4 neg camber at the time.
When you say shaft went off, did you see what exactly went off with your own eyes? Was it the stubby round flange that goes into the side of the diff.... that came out of the diff itself or was it the drive shaft flange that bolts up to that flange that detatched from the diff flange or was it a cv that popped out??? Its very relevant to your claim with the diff...so please lets hear the detail.
Anyway the 2.2 to 2.5 neg on the front is a setting recommended for a track/street compromise over here as well. Many guys run that and the hard core 997tt guys that dont do much street and mainly track run much more than that again....with shimed LFCas and top mounts. The turbo does have more of a tendency to understeer than the 2wd so needs a bit more neg to get the R tires to hook up without wearing out on the outers.
Control arms I have are from it3 cup so designed for 2wd. Not hard to imagine why this happened as its not the only component designed for rwd application by the factory that has clearance limitations on a car with front diff.
Now it may be possible to solve the diff issue with the shims but I bet it will be a marginal solution.. Why bother then?
You don't need more than 2.3 neg on the front on a turbo and you can get that with an adjustment from the top.
On the front neg, more than 2.3 2.5 agree is going to shorten the life of the street tires up a bit but if the car does more track than street then more neg is better and will give better contact patch on the tires in hard corners.....
Why are we discussing this so much?
I just posted my experience learned the hard way. Everyone pls feel free to replicate my experiment by all means!
Could try to call my tuner and find out if they remember what, who, when etc broke but life is too short really.. Shaft came out for one unlucky user and let's keep it at that. Present solution works like a dream. Not too long, not too short, just perfect..
Last edited by speed21; 04-20-2011 at 05:56 AM.