Coolant leak behind front wheel (drivers side)
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From: santa barbara
See if you can get a picture of the old rack. I'm still a little skeptical of their diagnosis really would like to see the leak. I could be wrong, probably am. i always try to learn.. carl
Intermediate
Joined: Dec 2015
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From: Bay Area CA
neanicu and 4carl where did you get the pictures of the steering rack? Sorry if this is common knowledge around here.
So it appears that the steering rack is still hydraulic, but instead of being assisted by a pump driven by the motor, it is assisted by an electric motor driven by the battery. I would like to know why Porsche decided to go this way. I would assume that it was to save space (electric motor is smaller than a mechanical pump). Saves on a extra serpentine belt (or shortens one). Less drag on the engine?
Also wondering why the electric drive system offers less feed back than 100% hydraulic? Perhaps that is not actually the case as the system is still hydraulic.
I am a little concerned with the belt drive on the motor. I wonder what the recommended replacement schedule is on that? Wonder why they chose that over direct drive. IMHO direct drive would last much longer.
Dave
So it appears that the steering rack is still hydraulic, but instead of being assisted by a pump driven by the motor, it is assisted by an electric motor driven by the battery. I would like to know why Porsche decided to go this way. I would assume that it was to save space (electric motor is smaller than a mechanical pump). Saves on a extra serpentine belt (or shortens one). Less drag on the engine?
Also wondering why the electric drive system offers less feed back than 100% hydraulic? Perhaps that is not actually the case as the system is still hydraulic.
I am a little concerned with the belt drive on the motor. I wonder what the recommended replacement schedule is on that? Wonder why they chose that over direct drive. IMHO direct drive would last much longer.
Dave
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From: Ny
neanicu and 4carl where did you get the pictures of the steering rack? Sorry if this is common knowledge around here. So it appears that the steering rack is still hydraulic, but instead of being assisted by a pump driven by the motor, it is assisted by an electric motor driven by the battery. I would like to know why Porsche decided to go this way. I would assume that it was to save space (electric motor is smaller than a mechanical pump). Saves on a extra serpentine belt (or shortens one). Less drag on the engine? Also wondering why the electric drive system offers less feed back than 100% hydraulic? Perhaps that is not actually the case as the system is still hydraulic. I am a little concerned with the belt drive on the motor. I wonder what the recommended replacement schedule is on that? Wonder why they chose that over direct drive. IMHO direct drive would last much longer. Dave
What you can't see in the pic is the inside of the rack,where there are still gears driven by fluid pressure,in the case of the hydraulic system and by the electric motor in the case of the electric steering rack. Those gears are precision cut but they still make metal to metal contact. They would get destroyed very quickly without lubrication. There has to be fluid inside the housing of the rack where the gears live,even in the case of the electric steering rack.
Car manufacturers in general have gone down the electric steering route because of ever needed improvement in fuel consumption. Since the rack is driven by the electric motor,there is no drag on the engine,thus improved power and most importantly better fuel consumption.
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IMO...
WHY did they do it (move to EPAS)?
1) No parasitic losses from running a hydraulic pump, which increases fuel economy by something like up to 5% (don't quote me on it) - this is by far the main reason everyone is switching to EPAS (electric power assisted steering)
2) Packaging - much nicer than running hydraulic lines from rear engine to front, though older CUP cars had an electric pump up front.
3) Fewer problems theoretically.
Why is feedback an issue?
1) The transmission of most systems is a ball screw setup or similar, and it is difficult to push forces the reverse direction through the system, because of the leverage/gear ratio back into the electric motor. Look at the picture.
2) The polar moment of inertia of the electric motor that needs to move in order for the steering rack to move, and combined with 1), any small movement coming into the rack, or acceleration of the rack will require a massive movement or acceleration of the electric motor, which results in a huge dampening effect/resistance to movement to forces coming back through the system.
Which is better?
I think hydraulic was better because there was way less mass to accelerate. My experience with both systems in GT3s has been that the older hydraulic system can transmit the texture of the road surface, and detailed context of the grip of the front tires. EPAS can't do it, but still does a good job of weighting the steering based on the grip of the tires. So you get feedback, just not the fine grained texture.
EPAS has the benefit of being able to hide all the distracting forces from you, from say bumps, so it feels more accurate and stable. I'm sure EPAS will get better as they lower the mass of the motor or reduce the gear ratio.
WHY did they do it (move to EPAS)?
1) No parasitic losses from running a hydraulic pump, which increases fuel economy by something like up to 5% (don't quote me on it) - this is by far the main reason everyone is switching to EPAS (electric power assisted steering)
2) Packaging - much nicer than running hydraulic lines from rear engine to front, though older CUP cars had an electric pump up front.
3) Fewer problems theoretically.
Why is feedback an issue?
1) The transmission of most systems is a ball screw setup or similar, and it is difficult to push forces the reverse direction through the system, because of the leverage/gear ratio back into the electric motor. Look at the picture.
2) The polar moment of inertia of the electric motor that needs to move in order for the steering rack to move, and combined with 1), any small movement coming into the rack, or acceleration of the rack will require a massive movement or acceleration of the electric motor, which results in a huge dampening effect/resistance to movement to forces coming back through the system.
Which is better?
I think hydraulic was better because there was way less mass to accelerate. My experience with both systems in GT3s has been that the older hydraulic system can transmit the texture of the road surface, and detailed context of the grip of the front tires. EPAS can't do it, but still does a good job of weighting the steering based on the grip of the tires. So you get feedback, just not the fine grained texture.
EPAS has the benefit of being able to hide all the distracting forces from you, from say bumps, so it feels more accurate and stable. I'm sure EPAS will get better as they lower the mass of the motor or reduce the gear ratio.
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From: santa barbara
If you look at the picture of the GT4 rack you will see there are no hydraulic lines. The rack is driven directly by the motor. I don't believe there is any real hydraulic pressure in the rack . That's why I'm skeptical of a hydraulic fluid leak?carl
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From: Ny
I'm not referring to " hydraulic pressure ",but splashed lubrication...oil to keep assemblies lubricated,not actual pressure created by oil being pushed around...
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From: santa barbara
I don't disagree and I don't want to be argumentative. The problem I have is usually in a oil bath gearbox there is a plug to fill it. It doesn't look like there's one where the motor drive connects to the rack? Carl
Race Director
Joined: Apr 2010
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From: Ny
One thing I can 100% confirm is that these electric racks are deemed " unserviceable " and they can only be replaced.
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Joined: Dec 2015
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From: Bay Area CA
Sorry for the redundancy, but where can I go to download pictures of the GT4 components?
I am definitely curious to find out if the system is a hybrid or the leaking fluid is for lubrication only. If lube only, maybe it is intend to be a "lifetime" seal and that is why the shop must replace the full unit.
So I would guess that the motor is a servo motor and that the computer sets the torque applied by the motor. The less torque supplied by the motor, the more steering feel and more forces on the steering wheel. Also, I would imagine that the motor can be turned by the drivers action on the steering wheel, when the computer senses no electric assist is needed. Also, I bet the computer knows the position of the wheels based upon the feedback from the servo motor.
I would love to know what feedback the computer is getting and from where (how many sensors and type) and what the algorithm is for setting the power (torque) on the motor.
Agreed on the efficiency… cruising on the freeway … motor is likely essentially off.
I am definitely curious to find out if the system is a hybrid or the leaking fluid is for lubrication only. If lube only, maybe it is intend to be a "lifetime" seal and that is why the shop must replace the full unit.
So I would guess that the motor is a servo motor and that the computer sets the torque applied by the motor. The less torque supplied by the motor, the more steering feel and more forces on the steering wheel. Also, I would imagine that the motor can be turned by the drivers action on the steering wheel, when the computer senses no electric assist is needed. Also, I bet the computer knows the position of the wheels based upon the feedback from the servo motor.
I would love to know what feedback the computer is getting and from where (how many sensors and type) and what the algorithm is for setting the power (torque) on the motor.
Agreed on the efficiency… cruising on the freeway … motor is likely essentially off.
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Joined: Mar 2009
Posts: 5,682
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Sorry for the redundancy, but where can I go to download pictures of the GT4 components?
I am definitely curious to find out if the system is a hybrid or the leaking fluid is for lubrication only. If lube only, maybe it is intend to be a "lifetime" seal and that is why the shop must replace the full unit.
So I would guess that the motor is a servo motor and that the computer sets the torque applied by the motor. The less torque supplied by the motor, the more steering feel and more forces on the steering wheel. Also, I would imagine that the motor can be turned by the drivers action on the steering wheel, when the computer senses no electric assist is needed. Also, I bet the computer knows the position of the wheels based upon the feedback from the servo motor.
I would love to know what feedback the computer is getting and from where (how many sensors and type) and what the algorithm is for setting the power (torque) on the motor.
Agreed on the efficiency… cruising on the freeway … motor is likely essentially off.
I am definitely curious to find out if the system is a hybrid or the leaking fluid is for lubrication only. If lube only, maybe it is intend to be a "lifetime" seal and that is why the shop must replace the full unit.
So I would guess that the motor is a servo motor and that the computer sets the torque applied by the motor. The less torque supplied by the motor, the more steering feel and more forces on the steering wheel. Also, I would imagine that the motor can be turned by the drivers action on the steering wheel, when the computer senses no electric assist is needed. Also, I bet the computer knows the position of the wheels based upon the feedback from the servo motor.
I would love to know what feedback the computer is getting and from where (how many sensors and type) and what the algorithm is for setting the power (torque) on the motor.
Agreed on the efficiency… cruising on the freeway … motor is likely essentially off.
Hold a balloon up to a speaker playing loud music......now hold a bowling ball up to and tell me which lets you feel the sound.
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From: USA PNW + AZ
Not a discount to negotiate the price down, but an all out deal pass.
Put yourself in the buyer's mindset, you are about to drop six figures on a car and the CarFax show blemishes while the competition shows clean. Which car do you buy?
The CarFax reporting today is really detailed, almost scary to potential buyers. I just bought a GT3 and the Carfax had amazingly picky stuff like wiper blades on it
Put yourself in the buyer's mindset, you are about to drop six figures on a car and the CarFax show blemishes while the competition shows clean. Which car do you buy?
The CarFax reporting today is really detailed, almost scary to potential buyers. I just bought a GT3 and the Carfax had amazingly picky stuff like wiper blades on it
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From: USA PNW + AZ
Does that leave the end seals at the inner tie rod ends for the only exit point?
Thread Starter
Instructor
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Update from this morning. Replacement steering rack assembly arrived overnight via FedEx from Germany. Replacement floor pan also arrived from their PA parts warehouse. Car should be ready and aligned by tmw afternoon or Sat pickup. Fingers crossed car is immaculate the way i dropped it off.. What am I entitled to ask for from the dealer or Porsche? Salesman assured me that only "exterior trim replaced" may show up on carfax... ;-P
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From: santa barbara
Update from this morning. Replacement steering rack assembly arrived overnight via FedEx from Germany. Replacement floor pan also arrived from their PA parts warehouse. Car should be ready and aligned by tmw afternoon or Sat pickup. Fingers crossed car is immaculate the way i dropped it off.. What am I entitled to ask for from the dealer or Porsche? Salesman assured me that only "exterior trim replaced" may show up on carfax... ;-P
Thread Starter
Instructor
Joined: Oct 2015
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Ok will do...I will ask to see the old one and see what the defect/damage is. Assuming the dealer will likely send the unit back to headquarters for examination and having it dissect it to find out the cause....