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958 Cayenne DIY: Transfer Case Fluid Change

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Old 08-18-2017, 02:37 AM
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projekt-h
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Default 958 Cayenne DIY: Transfer Case Fluid Change

This topic is all-to-common in the 958 talk, and there's some instruction in the stickied Transfer Case thread, but no actual DIY write-up. Figured I might as well write something up since I already have the pictures, with an additional "What to definitely never ever ever ever do" insight.

"How To" Change Your 958 Transfer Case Fluid
This is a notorious topic for the 958, and from my understanding affects ALL except the diesel models.

What You Will Need
- A 958 Porsche Cayenne (For your sake hopefully one lacking the dying TC symptoms and you're doing this preemptively)
- 1 Liter Transfer Case Fluid. Many have reported best results using
This Ravenol Fluid This Ravenol Fluid
(I ordered 2 liters because "stuff" can happen... in my particular case it did)
- Drain Pan (any size should suffice, capacity is under 1 liter)

Tools:
- 3/8" Ratchet
- 8mm hex bit. I used the same stubby one that was already in my hand from doing the differential fluid at the same time, but any should do. An 8mm Allen wrench will get the job done, but that's not advisable as you can't use a torque wrench that way
- 3/8" Torque Wrench. Be sure it's properly calibrated and you set the correct torque value (15 ft/lb OR 20Nm... do NOT get those values mixed up) I cannot even begin to stress the importance of this

Other
- New drain and fill plugs. I'd recommend using new for this due to the thread sealant that comes on the bolts. Trust me, that stuff's important.
- Good Music (to individual taste)

*A means of lifting the car while keeping it level is highly recommended. Many have mentioned raising the air suspension to it's highest level for servicing. Mine has standard suspension and I was able to do this all on the ground.

*Performing service when cold is recommended. Sticking your hands and face in the hot underbelly of the beast is not pleasant. ATF is bad enough, hot ATF oil is miserable. Additionally, aluminum housings and steel bolts have different expansion rates when hot, taking that variable away allows this to go more smoothly.

What To Do:

Photo of transfer case. Taken facing towards the front of the vehicle, from the passenger side:

(GREEN = FILL / BLUE = DRAIN)

1. Slip on under the passenger side, roughly near the gap between the front and rear doors. Nothing in the way to remove.

2. Remove the FILL PLUG FIRST. Not only does this aid in fluid flowing out the unit easier/quicker, but if you can't get the fill plug off, and have drained the fluid, you'll have gotten into a sticky predicament.

3. With the pan underneath, remove the drain plug. The fluid in mine shot back an unexpected amount, so maybe have the front edge of the pan directly underneath the drain hole.

4. Clean as much fluid and debris from the threading of the holes as possible

5. When fluid finishes draining, carefully hand start the replacement new drain plug. The sealant will add a fair bit of resistance. Using your properly-calibrated torque wrench, set to 15 ft/lb OR 20Nm (again, do NOT mix those figures up) finish tightening the the drain plug (at the bottom of this write-up, read where it all went wrong for me and you'll understand why I'm being so adamant about proper reinstallation)

6. Fill the Transfer Case. You'll probably want to keep the pan under the unit for this step, as it's a fill-to-overflow unit. This is also why it's important that the vehicle is level when this is performed. Take your bottle of Ravenol, and pop the top up and a tube will reveal itself. With this tube fully extended, you'll be able to use this without the need of a pump to fill the transfer case. It should take the better part of that liter. When it starts overflowing, stop, let it do it's thing and clean up the remains.

7. Installing the new replacement fill plug is the exact same as step 5.

8. When you've done all this properly, be VERY glad that you're not me. Here's why:

With all of my torque wrenches missing that day, I grabbed my father's 1/2" drive torque wrench that he had been improperly storing (locked on the highest setting, not all the way off) and a 1/2F-3/8M adapter. I then set it to 20 ft/lb..... I'm an idiot, DO NOT DO THAT. 15ft/lb OR 20Nm is the correct way... I got them backwards. Upon torquing it down and beginning to add fluid I noticed a small drip off the bottom of the unit, when it was nowhere near full. I then noticed the little hairline crack in the housing.



After some time, and me losing my bananas, the sealant (this is why buying new ones of these is a GOOD idea) had worked it's way into the areas of the crack allowing fluid passage and stopping it.



Seeing that had stopped the leak, but still left a crack exposed, I turned to my good ol' friend JB Weld. After some extensive cleaning with a wire brush and acetone around the affected area, using the tip of a safety pin I worked it into the crack as much as possible, then proceeded to give the entire area a healthy coating.



Now, this might seem like a hack fix. It kinda is, but I've seen this stuff hold transmissions and differentials together for a VERY long time, and those see much higher loads, temperatures, and more shock than this Transfer case will. Either way, I intend to replace it when these units, or even just parts like the rear cover, are more easily and affordably attainable. I've driven it, heat cycled it and check it repeatedly, and has shown to be holding up perfectly fine.

At this point you could be reading this thinking "why the hell would I listen to anything this guy has to say, especially when it comes to working on cars" or learn from my mistakes. I found out the hard way, and told you about it, so now you don't have to.

Standard DIY Disclaimer: (borrowed from deilenberger, and modified in this case) "You may be an ape with a wrench (like I apparently am). It's possible you should never be in the same garage as a car when you're holding a wrench (OK, Im not that bad). Therefore - what I just described is what I would do - not what I'm suggesting that you do. If you break it, bend it, pork it up, kill yourself doing it - I never told you to do it. I just told you how I'd do it. You're a big boy - man up if you screw up."

As always when servicing a motor vehicle, follow all safety precautions possible
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Old 08-18-2017, 03:08 AM
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Thanks much again - for the writeup that includes a "don't do this.." and I guess my disclaimer applies. Folks - be gentle tightening the fill and drain plugs. Snug and no tighter.
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Old 08-19-2017, 01:19 PM
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BTW - I doubt if the extra 5-ft/lbs was what cracked the case. The problem was the size of the torque wrench. Most 1/2" are not accurate at their lowest settings, plus the lever arm they provide is such that it's way too easy to overtorque small fasteners with them. The right wrench - an extra 5 probably wouldn't have mattered. I use a 3/8" electronic for most work, and for small values I'll dig out the 1/4" one, or the 3/8" dial one (an ancient SnapOn a neighbor gave me.. nice tool..) And then I'll try to sneak up on the value (set the clicker or beeper ones to 5 ft/lbs less than the required torque.. then when it beeps you'll probably find you're right where you wanted to be.)
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Old 09-22-2017, 02:14 PM
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So is it a myth that you have to fill the fluid in the Transfer case and Diffs only when they are at a specific temp and the only way to measure the temp is via hookup into a computer with a special cable and program?

Last edited by bcheney; 09-23-2017 at 12:30 PM. Reason: Typo
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Old 09-24-2017, 11:53 PM
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I used this as a guide today, thanks for taking the time to write up and share!
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Old 09-29-2017, 02:45 AM
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Originally Posted by bcheney View Post
So is it a myth that you have to fill the fluid in the Transfer case and Diffs only when they are at a specific temp and the only way to measure the temp is via hookup into a computer with a special cable and program?
You're thinking of the transmission - and that can be done just using a laser-digital thermometer. No need for a hookup or computer (although an iCarScan diagnostics tool will do this - to your smartphone..)

The diffs and transfer case are fill until oil comes out the fill plug. Install plug (gently in the case of the transfer case) and you're done.
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Old 11-15-2017, 02:04 PM
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You mentioned highly recommending new drain and fill plugs. Are these a standard sized item? Can they be purchased at an auto-supply store or do we need to go through Porsche?

(Asking as one of those apes who probably shouldn't be in the same garage as his car...)

Thanks for the write-up!
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Old 11-16-2017, 12:24 PM
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Originally Posted by EpiKAC View Post
You mentioned highly recommending new drain and fill plugs. Are these a standard sized item? Can they be purchased at an auto-supply store or do we need to go through Porsche?

(Asking as one of those apes who probably shouldn't be in the same garage as his car...)

Thanks for the write-up!
Get them from Porsche.
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Old 11-16-2017, 12:49 PM
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Originally Posted by deilenberger View Post
Get them from Porsche.
This.

it's not a common size, or even design. It's a fat, short, hex recess with no flange and a hefty amount of sealant (thank goodness for that)

I think I ordered mine from pelican.
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