FYI

GNC - Gas nitrocarburization

https://www.sciencedirect.com/topics.../gas-nitriding

 

Well my 12 CTT is at the Porsche garage getting a new TC on my CPO warranty. I wouldn't have known what was going on if it wasn't for all of the knowledge and insight that I have gather from this forum the last few years. Thank you to everybody who has contributed. Such a great resource.

 

You maybe already doing this, but I recommend that you have them confirm for you on the paperwork that they have installed the latest model transfer case (bottom of page 1 of the 2017 Transfer Case...pdf) and that they have installed the updated vent and front seal protection (2016...pdf). These Porsche generated docs may have been presented earlier in this thread so apologies in advance.

 

I picked up a 2012 Cayenne Base with 58K on the odo. With the help of this thread, I noticed the transfer case issue, a lag or stutter between 3rd and 4th and a sort of binding feeling or sharp turns (probably why the previous owner got rid of it) I ordered up some Ravenol, and bolts. Figured I had nothing to lose.

What came out was a mess of black with a slight burn smell, l poured in the new fluid and closed everything up. As others have mentioned, the difference was night and day. A short drive around the block and the "binding feeling" was gone. After 10 miles, it felt like a different car. Before, the trans felt almost like an early CVT transmission is the best way I can describe it. Now power delivery is very very smooth all the way to redline. I know it's too early to tell so I'll keep my fingers crossed.

Does anyone know why the fluid is so dark? I used to change the TC fluid in my jeep between 30-50k and what would come out would look almost like what I put in. I know it's not the same but just curious.

 

Well new transfer case last week did not fix my problem. Sharp corners and even some long sweeping corners there is still a growl coming from the rear end. Sounds almost like a crunching sound. So back to the Porsche dealer on Jan 2, 2020.

 

I believe the theory on this one is that the vent design here allows for contamination (dirt and water) to make it's way in; hence the reason they revised the part.
Interesting though, as my TC fluid on my 2016 at 85k miles was dark and due for a change, but not as bad as yours.

 

Yeah give it about 1000 miles and see if it holds up.

 

Xx

 

What type of slip lock and how much in dif. & TC?

 

Xx

 

Thanks!

 

Let me know if you can tell a difference. I sure could. And mine weren't bad to begin with.

 

I had the transfer case problems (had about 20k miles on a new design replacement TC) and did the fluid change.

Has ran smooth since the change back in April. Probably 7k miles since fluid change.

 

I would caution people to not simply dump slip-lock (aka a friction modifier) into a working transfer case because you read about it on the Internet.

Slip-Lock is a friction modifier - intended for use in limited-slip clutch-type differentials. It makes the plates slip a bit more easily, limiting the amount of friction between the plates. In a differential the sign you need this is a cracking noise on small radius turns (when the inner and outer wheels are turning at considerably different speeds..) The noise is the plates in the clutch binding against each other then suddenly releasing. The friction modifier changes the friction coefficient making the clutch plates/disks slide easier. You lose some of the limited-slip potential, but you have a driveable differential.

So what will this do in an active transfer case..? First consider how the Cayenne transfer case works. In normal straight-ahead travel, on a smooth road, no wheel slip due to ice/snow/oil - the transfer case sends about 20% of the engine power to the front wheels and the remaining 80% to the rear wheels. At steady highway speeds, it is capable of sending 100% of the torque to the rear wheels and none to the fronts. This improves fuel economy. At this point - most of this power distribution is done by the ratio design of the case and very little slippage of the clutch is needed. The transfer case stays cool since the clutch isn't slipping and wear on the clutch is minimal.

When the car determines that more power must be sent to a different end of the vehicle (say front wheels have traction and rear wheels are slipping) - a stepper motor actuates a ramp type device (rolling ball in a track that changes depth) that changes the pressure on the clutch plates, allowing it to direct more power to the front of the vehicle. All of this is figured out based on the designed normal friction characteristics of the clutch. When you change those friction characteristics the clutch adjustment will use a different pressure until it finds one where the clutch is distributing power as the PSM system desires. There is a limit to the range that the adjustment is designed to take place over. Lowering the friction on the clutch may lead to more wear, or more heating of the transfer case.. both of which are not desirable. Having too little friction may mean excessive clutch wear as the system tries to reach the power transfer asked for by the car's stability/traction (PCM) system.

Out of curiosity I tried adding a slug of the Ford friction modifier (available at many car parts stores..) It did make things feel a bit different, but not in a good way. It felt as if there was some slippage that didn't use to be there on shifts. My transfer case is an original - 105k miles on it. After about 2 weeks of the doped up fluid in the case was enough for me. I went back to fresh Pensotin with no friction modifiers - and my transfer case felt fine again.

I would only add a friction modifier if I had symptoms (the stutter/slip 2nd-3rd gear) that new oil didn't clear up. The stutter/slip indicates too much clutch friction - and in this case, if changing the oil didn't help - the friction modifier might be just the right answer. Since this isn't a factory solution - there is no specification on how much to add. I'd start small, and only increase the amount until the symptoms go away. Then stop. It isn't a case where if some is good, more will be better - more will not be better.

 

Doug,

Unless you have limited slip or PTV (Porsche torque vectoring - aka - computer-controlled torque-distribution on the rear diff) I can't begin to fathom why adding a slip-lock additive to a differential would make ANY difference at all.

There is no clutch in an open differential, and that's what the vast majority of Cayennes are equipped with. Porsche decided they could use electronic control of the brake system to provide the same benefits (and more, better) than mechanical limited-slip differentials could and at the same time eliminate the complexity, cost, and weight of limited-slip diffs. The only reason they use a clutch-type differential in the PTV is to computer control distribution of torque on the rear wheels. the computer tells the differential to put more torque on the outside wheel in a turn, effectively pushing the car around the turn. And if you do have PTV - I suspect adding slip to the differential is exactly the wrong thing to do since the car's computer is counting on a certain torque-force pushing the car into a turn, coming from the rear outside wheel. Having less power there would probably result in going wide in a corner unless the computer and differential can compensate for the change in clutch friction.

I use straight 75W-90 GL5 in my differentials, and they've been trouble-free for an awfully long time.