993 C4: is the rear diff an LSD too?
10-05-2005, 07:49 PM
#16
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"Percentage output from a VC device is generally heat controlled. More heat equals more VC output. "
Get your tire sizes wrong and the VC melts !!
Geoff
Get your tire sizes wrong and the VC melts !!
Geoff
10-05-2005, 10:39 PM
#17
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Which takes us back to my original question about the rating of the stock VC.
For example: the VC center diff found in hundreds of thousands of boring US market Subarus is 4kgf-m/100rpm. That's very loose. Takes a little while to heat up and provide any slip limiting. Fine for grandpa and grandma and the golden retriever in the snow, but no fun when you're sliding sideways at 80mph. You could probably run tires differing in size by several % and not burn it out.
The older WRX STI RA (motorsports model--like the RS is to 911) had a VC rated at 20kgf-m/100rpm. Near instant response for when you have all four wheels spinning most of the time. But on dry tarmac, you'd better have the same diameter tires or it'll overheat in a hurry.
For example: the VC center diff found in hundreds of thousands of boring US market Subarus is 4kgf-m/100rpm. That's very loose. Takes a little while to heat up and provide any slip limiting. Fine for grandpa and grandma and the golden retriever in the snow, but no fun when you're sliding sideways at 80mph. You could probably run tires differing in size by several % and not burn it out.
The older WRX STI RA (motorsports model--like the RS is to 911) had a VC rated at 20kgf-m/100rpm. Near instant response for when you have all four wheels spinning most of the time. But on dry tarmac, you'd better have the same diameter tires or it'll overheat in a hurry.
10-07-2005, 04:43 AM
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RallyJon: Does it help you that there should be a tractive force of approx. 800 N (+-350 N), if the front wheels are put onto a brake dynometer with transmission in neutral/parking brake engaged and driven at 5 kph? Maybe you can guess your requested info with this number.
What does the unit "kgf-m" mean?
The ABD does not have the dynamic impact suggested earlier. It is merely a traction support for launching under bad conditions and shuts off at 70 kph.
To get this straight: there is no center differential at all! The front axle is driven like if you took a spoon and whirled in a honey pot, causing the pot itself to rotate. Similar to a torque converter.
Felix
What does the unit "kgf-m" mean?
The ABD does not have the dynamic impact suggested earlier. It is merely a traction support for launching under bad conditions and shuts off at 70 kph.
To get this straight: there is no center differential at all! The front axle is driven like if you took a spoon and whirled in a honey pot, causing the pot itself to rotate. Similar to a torque converter.
Felix
Last edited by Feehliks; 10-09-2005 at 05:24 AM.
10-07-2005, 09:10 AM
#20
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Dear Mr. Felix,
How do you know the contents of my 993 book, for you to say in public what I said about ABD is wrong?
I do not recall sharing its contents with anyone yet except the publisher
Ciao,
Adrian.
How do you know the contents of my 993 book, for you to say in public what I said about ABD is wrong?
I do not recall sharing its contents with anyone yet except the publisher
Ciao,
Adrian.
10-07-2005, 04:38 PM
#21
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Originally Posted by Red rooster
"Percentage output from a VC device is generally heat controlled. More heat equals more VC output. "
Get your tire sizes wrong and the VC melts !!
Geoff
Get your tire sizes wrong and the VC melts !!
Geoff
10-08-2005, 07:05 AM
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Originally Posted by Adrian
Dear Mr. Felix,
How do you know the contents of my 993 book, for you to say in public what I said about ABD is wrong?
I do not recall sharing its contents with anyone yet except the publisher
Ciao,
Adrian.
How do you know the contents of my 993 book, for you to say in public what I said about ABD is wrong?
I do not recall sharing its contents with anyone yet except the publisher
Ciao,
Adrian.
Another quote: "the link between gearbox and front wheels was revised with drive now carried by a viscous coupling. For it to carry any drive to the front wheels though, meant they had to rotate slower than the rears, meaning they required a slightly larger rolling radius. The net result of all this was between five and 15 per cent of drive passing through the front wheels under normal circumstances, but that figure could climb to nearly 100 per cent if the rear wheels were experiencing no grip at all. That seemed an unlikely eventuality when you consider the amount of attention rear-end traction was given. Not only did the 993 have a 25/40 differential (under load/overrun), it was also equipped with Automatically Braked Differential (ABD). The latter’s inclusion meant that should the diff not be able to cope with the amount of slippage, it would step in and, via the ABS system, apply the relevant brake to improve grip. It also helped to control lift-off oversteer into the bargain."
This does not change the content of what I wrote.
Felix
10-08-2005, 11:26 AM
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Dear Felix,
The content of your post is not my concern, but I would appreciate it if you would edit your post to remove my name from association from the quote.
Ciao,
Adrian.
The content of your post is not my concern, but I would appreciate it if you would edit your post to remove my name from association from the quote.
Ciao,
Adrian.
10-09-2005, 05:32 AM
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Originally Posted by RallyJon
Notwithstanding the atribution, is there anything in that paragraph that is incorrect? Thanks! -Jon
The 993 was never prone to lift-off oversteer due to its multilink-suspension.
Felix
10-09-2005, 05:37 AM
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hallo
The LSD on the C4 has a 22/40 ratio , the one from the C4 and Turbos have 25/65 Ratio , the early
94/95 MY ) G50/21 is made by ZF, the later G50/20 and all G 64 Models are made by GKN .
If you have LSD in your Car , you should never change only 1 Tire as this can engage the LSD always and burn it up within a few hundred miles . That is the same effect as if you put higher Tires in the back , you can destroy the Viscous coupling and the Front diff , these Parts are not meant to run always under Load .
Harald
The LSD on the C4 has a 22/40 ratio , the one from the C4 and Turbos have 25/65 Ratio , the early
94/95 MY ) G50/21 is made by ZF, the later G50/20 and all G 64 Models are made by GKN .
If you have LSD in your Car , you should never change only 1 Tire as this can engage the LSD always and burn it up within a few hundred miles . That is the same effect as if you put higher Tires in the back , you can destroy the Viscous coupling and the Front diff , these Parts are not meant to run always under Load .
Harald
10-09-2005, 06:21 AM
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Originally Posted by speedster 94
hallo
The LSD on the C4 has a 22/40 ratio , the one from the C4 and Turbos have 25/65 Ratio , the early
94/95 MY ) G50/21 is made by ZF, the later G50/20 and all G 64 Models are made by GKN .
If you have LSD in your Car , you should never change only 1 Tire as this can engage the LSD always and burn it up within a few hundred miles . That is the same effect as if you put higher Tires in the back , you can destroy the Viscous coupling and the Front diff , these Parts are not meant to run always under Load .
Harald
The LSD on the C4 has a 22/40 ratio , the one from the C4 and Turbos have 25/65 Ratio , the early
94/95 MY ) G50/21 is made by ZF, the later G50/20 and all G 64 Models are made by GKN .
If you have LSD in your Car , you should never change only 1 Tire as this can engage the LSD always and burn it up within a few hundred miles . That is the same effect as if you put higher Tires in the back , you can destroy the Viscous coupling and the Front diff , these Parts are not meant to run always under Load .
Harald
Actually not so important, as there is a wide array available to meet anyone's own preferrences.
About your service-directions: well, yes, if front and rear turn at a substantial difference, the VC builts up too much heat and would eventually get damaged.
Felix
10-09-2005, 09:24 AM
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felix
95033205305 25/65 % G50 20/21 -95 ZF
95033208302 25/65 % G50 20/21 96- GKN
95033208303 22/40 % G 64/20/21/51 GKN
95033208338 40/65 % G50/31/32/33 GKN
Loök it up in the servicemanual or in PET , if you dont believe .
harald
95033205305 25/65 % G50 20/21 -95 ZF
95033208302 25/65 % G50 20/21 96- GKN
95033208303 22/40 % G 64/20/21/51 GKN
95033208338 40/65 % G50/31/32/33 GKN
Loök it up in the servicemanual or in PET , if you dont believe .
harald
