Transfer case
12-18-2018, 07:59 PM
#541
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I've read only perhaps a quarter of the comments on this huge thread, so please excuse me if I'm repeating a question here. But I'm very curious as to why the transfer-case fluid gets so dark so quickly and why the transfer cases fail at such high rates (or at least degrade so rapidly). Faulty engineering, for sure -- but where is it faulty? It seems reasonable to assume that the wheels/tires are causing this problem in Porsche AWD vehicles. Is it that the staggering of the wheel sizes (front-to-back) has not been properly allowed for in the engineering? Is it that improper air pressure (whether what's recommended by Porsche or what's neglected by the owner) is a big part of the blame? Is part of the problem that tires are being changed on individual wheels/axles so that there's uneven tread? Is it that wheels aren't aligned properly/often enough? It just seems mind-boggling that Porsche can't get a handle on this, from the huge number of cases reported here.
If you'd read the entire thread, perhaps the issue of water in the transfer case might have explained what Porsche thinks the problem was/is. New transfer cases from Porsche come with a kit designed to divert water from being tossed up on top of the case - where the vent for the case is. On the original design, the vent was protected by one of the stupid rubber birds-mouth type vents (very similar to the cowl drains.) Then to compound this - Porsche added an air scoop under the transfer case designed to blow air up at the case. Thing is - that scoop is even more effective in channeling water up to the spinning forward driveshaft, that then throws it right on top of the vent. The result is - if you drive through deep puddles you're going to end up with water in the transfer case oil. The Porsche fix was to add a higher vent kit to the case (that vents it up into the engine compartment) and add a water deflector for the CV joint on the output for the front driveshaft.
A few people have documented rebuilding their own cases. In every case I've seen photos of the mutliplate clutches had rust on them. The rust will cause the clutch to stick. Sticking causes the issues with judder on acceleration. There have been very few repeat failures when the new kit was installed with a new transfer case. It might have been interesting (but complex) to add to the survey where the vehicle is primarily driven - I imagine places like Phoenix AZ experience less failures than somewhere in Washington state..
That's my failure theory. Changing the oil means the water in the oil goes out with the old oil. If the clutches aren't badly rusted they'll probably free up with some use. And the use of a friction modifier allows the clutches to slip a bit more when engaging which probably helps wear the rusted bits back to a useful state.
Adding the vent kit is only doable (as best I can find) by removing/dropping the transfer case - there isn't clearance above it to do it otherwise.
12-18-2018, 08:28 PM
#542
RL Community Team
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Some thoughts on the matter: the 958 transfer case got rid of the internal oil pump that was present in the 955/957 Cayennes. So in a 958, oil lubricates the clutch pack only when the front driveshaft/wheels are turning which moves the chain to deliver oil to the clutch pack (does this equal insufficient oil flow?). Since the 958 is an active transfer case that fluctuates from 0-100% engagement during driving versus the 955/957 which has a built in mechanical torque split starting at 38% which is then increased to 100% if needed due to slippage, there is more work going on in a 958 clutch pack (more work should require greater lubrication, right?) which varies the engagement amount constantly changes to alter the driving dynamics (not necessarily with slippage occurring): so if you do a lot of start/stop city driving with frequent accelerations, your clutch pack is varying its torque setting significantly. Also, originally the 958 had a ratio difference between the chain sprockets of 1.12 (input/rear axle and the front axle drive) which the clutch pack will be accounting for the difference when wheel speeds are equal.
Possible formula:
Possible formula:
constantly varied clutch engagements + low oil flow to the clutch pack + long oil change interval = transfer case issues
958 Cayennes that see mostly freeway miles may have a transfer case last 100K miles since when cruising on the freeway, the clutch is open to increase system efficiency. City start/stop driven 958s would likely get far less life out of their transfer case clutches due to the above formula.
12-18-2018, 10:12 PM
#543
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Some thoughts on the matter: the 958 transfer case got rid of the internal oil pump that was present in the 955/957 Cayennes. So in a 958, oil lubricates the clutch pack only when the front driveshaft/wheels are turning which moves the chain to deliver oil to the clutch pack (does this equal insufficient oil flow?).
Since the 958 is an active transfer case that fluctuates from 0-100% engagement during driving versus the 955/957 which has a built in mechanical torque split starting at 38% which is then increased to 100% if needed due to slippage, there is more work going on in a 958 clutch pack (more work should require greater lubrication, right?) which varies the engagement amount constantly changes to alter the driving dynamics (not necessarily with slippage occurring): so if you do a lot of start/stop city driving with frequent accelerations, your clutch pack is varying its torque setting significantly. Also, originally the 958 had a ratio difference between the chain sprockets of 1.12 (input/rear axle and the front axle drive) which the clutch pack will be accounting for the difference when wheel speeds are equal.
Possible formula:
958 Cayennes that see mostly freeway miles may have a transfer case last 100K miles since when cruising on the freeway, the clutch is open to increase system efficiency. City start/stop driven 958s would likely get far less life out of their transfer case clutches due to the above formula.
constantly varied clutch engagements + low oil flow to the clutch pack + long oil change interval = transfer case issues
958 Cayennes that see mostly freeway miles may have a transfer case last 100K miles since when cruising on the freeway, the clutch is open to increase system efficiency. City start/stop driven 958s would likely get far less life out of their transfer case clutches due to the above formula.
I'm confused..
12-18-2018, 10:21 PM
#544
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I didn't mean to confuse... just provoke some thought on the possibilities for 958 transfer case shortcomings.
The chain, being the only means of delivery of oil, does not seem adequate at low speeds vs. the older box which has a pump dedicated to move the oil.
The front and rear differentials have the same ratios.
There is no drive force sent to the front axle when cruising - clutch is not engaged at all. With zero engagement, there is no wear, which is why I hypothesized that freeway drive Cayennes will have longer transfer case lifespans.
The chain, being the only means of delivery of oil, does not seem adequate at low speeds vs. the older box which has a pump dedicated to move the oil.
The front and rear differentials have the same ratios.
There is no drive force sent to the front axle when cruising - clutch is not engaged at all. With zero engagement, there is no wear, which is why I hypothesized that freeway drive Cayennes will have longer transfer case lifespans.
12-18-2018, 10:36 PM
#545
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Just went to the Service Technology introduction, and looks like you're absolutely correct:
It may be a combination of what you've proposed and water problems. It's apparent that Porsche thinks water is at least part of the problem since they came up with the revised vent kit and water deflector... and they do have enough broken ones to examine for clues...
BTW - they were quite proud of the lack of an oil pump:
The distribution of the drive torque across the front and rear axles depends on a number of factors such as speed, acceleration, the selection of Normal or Sport as well as the selected PSM mode, etc. In order to achieve good traction when driving off or accelerating, the front axle torques tend to be higher in these situations than when the vehicle travels constantly in a straight line. The vehicle reacts to a consistent driving style by reducing the drive torque on the front axis to minimize friction losses, for example.
BTW - they were quite proud of the lack of an oil pump:
Even though the PTM can generate extremely powerful forces and temperatures and some components require good lubrication and efficient cooling, the PTM can operate without requiring an additional pump. The drive chain (6) turns when the front wheels turn. At the same time, oil is drawn from the sump and supplied to the chain enclosure (arrow). Oil guide devices integrated in the chain enclosure channel the oil into the multiple-disc clutch and create a flow of oil from the inside outwards.
Lubrication of the clutch without an additional oil pump helps minimize losses in efficiency and reduce fuel consumption.
Lubrication of the clutch without an additional oil pump helps minimize losses in efficiency and reduce fuel consumption.
12-22-2018, 08:54 PM
#547
Drifting
Hahaha, well if you recall in the early promotion material Porsche released for the 958s they were also quite proud of this too...
“As you’d expect, the Turbo’s rigorous diet entailed painstaking reengineering of various components—a new aluminum valve-timing adjuster, for example, is 3.8 pounds lighter than the previous piece—“
And we know how that played out!
“As you’d expect, the Turbo’s rigorous diet entailed painstaking reengineering of various components—a new aluminum valve-timing adjuster, for example, is 3.8 pounds lighter than the previous piece—“
And we know how that played out!
12-28-2018, 11:40 AM
#548
Instructor
I just changed my transfer case oil in my 13 CD at 50k miles, and it looked pretty good. I just bought it this year off lease CPO, so I assume it's never been changed. Not completely black and no smell of burn oil or clutch packs.
The oil doesn't have the same strong sulfur smell as standard gear oil, so it should be pretty easy to smell if it degrades.
I replaced it with the Ravenol fluid recommended and purchased on Amazon for $35/L. It comes with a fantastic pour spout, so I didn't even need to use a fluid pump to fill the TC. I reused the plugs and just wire brushed them to clean the threads off before using Permatex thread sealant. The recommended 15 ft-lbs seemed pretty high for a pipe thread, so I progressively increased torque until satisfied, which happened to be 12 ft-lbs. For reference, the recommended torque for a 1/8" NPT fitting is 12 ft-lbs or 1.5 to 3 TFFT (turns from finger tight).
I was investigating the transfer case vent, which has numerous revisions, but it looks near impossible access the top of the TC in the vehicle. The parts are about $70 for the relocated vent line and all the random doodads.
Total time to change the engine oil, TC, and both diffs is about 2 hours. Pretty darn easy job too.
The oil doesn't have the same strong sulfur smell as standard gear oil, so it should be pretty easy to smell if it degrades.
I replaced it with the Ravenol fluid recommended and purchased on Amazon for $35/L. It comes with a fantastic pour spout, so I didn't even need to use a fluid pump to fill the TC. I reused the plugs and just wire brushed them to clean the threads off before using Permatex thread sealant. The recommended 15 ft-lbs seemed pretty high for a pipe thread, so I progressively increased torque until satisfied, which happened to be 12 ft-lbs. For reference, the recommended torque for a 1/8" NPT fitting is 12 ft-lbs or 1.5 to 3 TFFT (turns from finger tight).
I was investigating the transfer case vent, which has numerous revisions, but it looks near impossible access the top of the TC in the vehicle. The parts are about $70 for the relocated vent line and all the random doodads.
Total time to change the engine oil, TC, and both diffs is about 2 hours. Pretty darn easy job too.
01-02-2019, 01:12 PM
#549
Rennlist Member
I didn't mean to confuse... just provoke some thought on the possibilities for 958 transfer case shortcomings.
The chain, being the only means of delivery of oil, does not seem adequate at low speeds vs. the older box which has a pump dedicated to move the oil.
The front and rear differentials have the same ratios.
There is no drive force sent to the front axle when cruising - clutch is not engaged at all. With zero engagement, there is no wear, which is why I hypothesized that freeway drive Cayennes will have longer transfer case lifespans.
The chain, being the only means of delivery of oil, does not seem adequate at low speeds vs. the older box which has a pump dedicated to move the oil.
The front and rear differentials have the same ratios.
There is no drive force sent to the front axle when cruising - clutch is not engaged at all. With zero engagement, there is no wear, which is why I hypothesized that freeway drive Cayennes will have longer transfer case lifespans.
01-02-2019, 04:39 PM
#550
Burning Brakes
Garretts theory on highway miles holds true for me also at 174k, a few minor issues solved with the couple fluid changes.(turning shudder and thumping under acceleration.)
01-22-2019, 03:01 PM
#551
Burning Brakes
2014 Cayenne S. First x-case failure in May 2017 at about 30K miles. Replaced under warranty. Now x-case is doing same thing. Sounds/feels like same exact failure at 48K miles. I am dropping it off soon for what will likely be x-case replacement #2. I cannot possible imagine owning this beyond CPO expiration. This must be very expensive if you are paying out of pocket.
01-22-2019, 03:04 PM
#552
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2014 Cayenne S. First x-case failure in May 2017 at about 30K miles. Replaced under warranty. Now x-case is doing same thing. Sounds/feels like same exact failure at 48K miles. I am dropping it off soon for what will likely be x-case replacement #2. I cannot possible imagine owning this beyond CPO expiration. This must be very expensive if you are paying out of pocket.
01-22-2019, 03:38 PM
#553
Burning Brakes
2014 Cayenne S. First x-case failure in May 2017 at about 30K miles. Replaced under warranty. Now x-case is doing same thing. Sounds/feels like same exact failure at 48K miles. I am dropping it off soon for what will likely be x-case replacement #2. I cannot possible imagine owning this beyond CPO expiration. This must be very expensive if you are paying out of pocket.
What kind of driving are you doing is it mixed city/highway? any towing?
01-23-2019, 12:34 AM
#554
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2014 Cayenne S. First x-case failure in May 2017 at about 30K miles. Replaced under warranty. Now x-case is doing same thing. Sounds/feels like same exact failure at 48K miles. I am dropping it off soon for what will likely be x-case replacement #2. I cannot possible imagine owning this beyond CPO expiration. This must be very expensive if you are paying out of pocket.
01-23-2019, 12:41 PM
#555
Burning Brakes