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An old thread I know, but while looking for information on the ABD Porsche system I came across this thread. the answer is if your diff has a true LSD both wheels will turn in the same direction. If not, then the opposite will go the other way even if the transmission is engaged. I this this is even true if you have a full locker (opposite direction).
I am looking for comments on Torque Vectoring vs. the stock set up and am finding nothing. The big problem with a clutch pack LSD is the clutches wear out. Most of my knowledge of traction aids comes from off road vehicles, but the theory is the same. Personally I like the ABD as brake pads are cheaper to replace than an LSD is to rebuild.
ABD only works upto 40mph, it's really meant to just get you out of a slippery situation kind of like a traction control. It's not like torque vectoring on the new car 911s. Stock clutches in LSD do wear out quickly and that's why many rebuild them with Guards internals.
On US cars option M220 was a 25/65% lsd and ABD, thru '95 it was a Zf from '96 a GKN, RS used a 40/65 GKN as standard. For these asymmetric lsd's the first # is acceleration the second deceleration
the #s are notional not metrics, the actual breakaway torque is determined byt the actual condition and setup of the lsd.
on acceleration an open diff delivers all of the torque to the wheel w/ least traction, this is why if one wheel is on ice it spins and the other does nothing, there is some friction so eventually the car usually moves unless there is something else preventing motion.
w/ an lsd the torque to the less traction wheel is limited so a % does get to the wheel w/ more friction
on track this is useful because in a corner the inside wheel has less traction than the outside wheel, lsd thuds aids acceleration out of a corner.
On deceleration the lsd couples the drive wheels and stabilizes the rear of the car, under hard deceleration the rear dances around less.
lsd can be dangerous if both wheels have no traction, both will spin generating a chassis rotation torque that cause the rear of the car to go to the right.
abd is couple w/ lsd on 993 it applies the brakes to the rear wheel w/ least traction and only works up to ~40mph, It uses a 4 channel abs where the non abd cars only have a 3 channel abs.
You can tell what the car has by looking at the rear of the abs pump, 4 channel bas w/ abd and lsd has 2 proportioning valves that go to the rear brakes, non has 1
This is a 4 channel ABS the 2 p/v can be seen below the brake lines which go to the bulkhead fitting which has 4 lines
Bill,
Do you know if all the 993 have the 4th brake line behind the bulkhead fitting to the rear?
So when the vehicle is going straight both half shafts coming out of the gearcase are providing equal a Amounts of power to the ground would that be correct? And be turning at the same speed?
So does a car with LSD have more power and be more stable than a non-LSD equipped car?
1) assuming grip for both tyres is the same, yes
2) LSD does not affect engine power. It can only optimize available power delivery.
As an example, if you were used to rolling on, say 30 lb. cast RUF boat anchors, and switched to a set of forged RAYS, you woult think you had more hp, and steering would be crisper, but the hp would remain the same.
.
On US cars option M220 was a 25/65% lsd and ABD, thru '95 it was a Zf from '96 a GKN, RS used a 40/65 GKN as standard. For these asymmetric lsd's the first # is acceleration the second deceleration
the #s are notional not metrics, the actual breakaway torque is determined byt the actual condition and setup of the lsd.
on acceleration an open diff delivers all of the torque to the wheel w/ least traction, this is why if one wheel is on ice it spins and the other does nothing, there is some friction so eventually the car usually moves unless there is something else preventing motion.
w/ an lsd the torque to the less traction wheel is limited so a % does get to the wheel w/ more friction
on track this is useful because in a corner the inside wheel has less traction than the outside wheel, lsd thuds aids acceleration out of a corner.
On deceleration the lsd couples the drive wheels and stabilizes the rear of the car, under hard deceleration the rear dances around less.
lsd can be dangerous if both wheels have no traction, both will spin generating a chassis rotation torque that cause the rear of the car to go to the right.
abd is couple w/ lsd on 993 it applies the brakes to the rear wheel w/ least traction and only works up to ~40mph, It uses a 4 channel abs where the non abd cars only have a 3 channel abs.
You can tell what the car has by looking at the rear of the abs pump, 4 channel bas w/ abd and lsd has 2 proportioning valves that go to the rear brakes, non has 1
This is a 4 channel ABS the 2 p/v can be seen below the brake lines which go to the bulkhead fitting which has 4 lines
Hi,
After fixing my SAI light, I noticed that my ABD lights did not turn on.
Mine is 1997 993 C2 Tip.
Ever since I bought the car about 3+ years, I was preoccupied with SAI(engine) light and don't remember if my green/red ABD lights were ever on when I turn the key to ready position.
My brake line are set up as shown below with 3 lines to the bulkhead.
I ran Durametric and there is nor error code on ABS system.
Do I have an ABD system?
Last edited by 1997hmc993; 07-24-2023 at 11:38 PM.
My understanding in simple terms ABS, Antilock Brake System pulses the braking improving grip, it is most advantageous in rain, snow, or where there is loose pavement.
It renders the earlier driver input of pressing the brake peddle sever times to improve braking unnecessary and can even make it counterproductive.
The system works better than foot pulsing because the pulses are faster and the system does a better job of keeping the car from drifting out of a straight line.
My understanding is that Automatic Brake Differential enhances driver control under braking and acceleration by transferring torque away from an individual wheel that is slipping and also keeps the car from drifting from a straight line during both braking and acceleration.
My understanding is that the non-limited slip differential seems to release torque to an individual drive wheel that has lost grip and so working against stability. Whereas the limited-slip differential limits this behavior.
For a street-driven Carrera ABD is a less primary need because the normally asperated engine simply doesn't generally put enough torque to the ground to initiate wheel spin on dry pavement. Also, rear-wheel drive behaves more predicably when it loses grip.
For the C4 and Turbo where all 4 wheels are drive wheels, ABD manages unpredictable behavior inherent in when a 4-wheel dive vehicle becomes unstable due to loss of grip.
[QUOTE=1997hmc993;18925251]Hi,
After fixing my SAI light, I noticed that my ABD lights did not turn on.
Mine is 1997 993 C2 Tip.
Ever since I bought the car about 3+ years, I was preoccupied with SAI(engine) light and don't remember if my green/red ABD lights were ever on when I turn the key to ready position.
My brake line are set up as shown below with 3 lines to the bulkhead.
I ran Durametric and there is nor error code on ABS system.
Do I have an ABD system?
Hi HMC,
My experience is that the OBD system will not always throw an OBD error when the ABS/ABD is nonfunctional. If you can't get it to go active by purposely forcing it to by aggressive braking on loose pavement
I would first replace the relays in the frunk, they are not expensive.
I would then look into the wheel end sensors. First, clean their connectors and see if it helps. Then consider replacing them in pairs front first then back,
The reason I say in pairs is my thinking is that if two sensors across an axel are not signaling the controller may think the car is simply not in motion, this is just an unsubstantiated theory I have.
Andy
Hi,
After fixing my SAI light, I noticed that my ABD lights did not turn on.
Mine is 1997 993 C2 Tip.
Ever since I bought the car about 3+ years, I was preoccupied with SAI(engine) light and don't remember if my green/red ABD lights were ever on when I turn the key to ready position.
My brake line are set up as shown below with 3 lines to the bulkhead.
I ran Durametric and there is nor error code on ABS system.
Do I have an ABD system?
03-24-2017, 11:29 PM
