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958 Cayenne DIY: Replacing the Power Steering and PDCC Reservoirs


958 Cayenne DIY: Replacing the Power Steering and PDCC Reservoirs

Old 01-20-2019, 10:28 PM
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Location: calimesa ca.
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Default 958 Cayenne DIY: Replacing the Power Steering and PDCC Reservoirs

Our CTT just clicked over the 60k mile mark. Porsche recommends the PDCC reservoir be replaced. The reason it needs to be replaced is that there is a filter built into the reservoir. The power steering system uses the same reservoir (same part number). So for the price of an extra reservoir, $68 each, I replaced both reservoirs.

Armed with a six-pack of Pentosin and three feet of 3/8 hose I dove in.

The power steering and PDCC system share the same pump. Its a two-stage pump with 2 halves independent from each other. I did one system at a time.

I started with the power steering system. With the hood open and standing in front of the car it is the first reservoir on your right, against the driver's side fender. The PDCC reservoir is the one against the bulkhead a little higher in elevation.

The first step is to suck every bit of fluid out of the reservoir as possible. Then remove the reservoir from its mount. It is mounted in three places. One nut at the base of the mount, one bracket holding the top of the reservoir and one mount holding the back of the reservoir. After you remove the nut at the base and the bracket on the top, the reservoir lifts off of the back mount.

Now that the reservoir is detached, its time to stuff a bunch of rags under the reservoir and under the hoses we will be detaching. Apparently, Pentosin is not good for rubber hoses. But it flows through rubber hoses go figure. I heeded the warnings and tried to protect things from the Pentosin as best as I could. The return line from the pump to the reservoir is the smaller of the two hoses and is held on with a one-time use hose clamp. I cut it off with a pair of diagonal cutters and will replace it with a regular 3/8 worm type hose clamp.

With the smaller hose clamp cut off the return hose and the bigger feed hose, spring clamp moved out of the way, I removed the reservoir. It's messy and sucks but it has to be done. So have a bunch of rags available. With the old reservoir out of the way, you have room to work. Take your 3-foot chunk of 3/8 hose and hose clamp it to the smaller of the two pipes like the picture shows.

The other end of the 3/8 hose goes into a suitable catch basin.

Both of my new reservoirs came with yellow caps on the inlet and outlet nipples. Remove and discard the big cap. It's trash, but on the little cap slip a 3/8 hose clamp over it. It will keep the new fluid from pouring out. With the cap in place, we are going to install the new reservoir. This is only temporary so no need to bolt it in place. Push the big nipple on the reservoir onto the big hose that goes to the pump and clamp it with its spring clamp. This is how it should look:

It's time to fill the new reservoir with new fluid. I filled mine to the top because we are going to pump this new fluid through the system and at the same time it will push the black nasty into your catch basin. Now is the time to get your trusted helper to get behind the wheel, roll down the window and wait for your commands.

What your helper needs to understand is that we are just bumping the engine....

He/she is going to start the car and immediately shut it off. The power steering/PDCC pump pumps a lot of fluid very fast. It is not unmanageable but just be aware. My pump pumped about 1/2 the reservoir with each bump of the engine. I never even came close to pumping the reservoir dry. After each engine bump, I re-topped off the reservoir.

I have a pretty good helper who understood what we were doing. I was able to explain that during the engine bump if she was able to rotate the steering wheel at the same time we would get the best results. We could push the new fluid from the reservoir, through the pump, and down to the steering rack and then into the catch basin. You can't flush the whole system in one shot like the trans flush. I think it took us 3-4 engine bumps to get the black nasty out and get clear emerald green into the catch basin. This is what you should see.

When you see clean emerald green pentosin flowing into the catch basin the flush is done, but you're not finished. Now you need to suck out all of the fluid out reservoir again. Ty to get out as much as you can because we have to remove it again. Once you have the new reservoir out you can loosen the hose clamp from the 3/8 flushing hose and let it slide down. No need to remove it we will be reusing it. Pinch the end of the flushing hose and take it off the return pipe. But set it aside in a safe place because we are gonna use it again for the PDCC reservoir and we don't want it to get contaminated. Leave your rags in place because when you go to install the new reservoir again you will have spillage.

Install the new reservoir again. This time it will be for good. With the reservoir in your right hand push it on to both the big feed hose and the smaller return hose at the same time. Side the factory spring clamp back up into its final position on the big hose and then slide up your worm type hose clamp onto the smaller return hose and tighten it up.

Now you can get all of those oily rags out of there and finally mount the reservoir. Lift the reservoir and slide the back of it over the mount and push it into place. then put the nut on the base of the reservoir and tighten it down. Then put the top clamp into place and tighten it up.

After the new reservoir is secure, fill it up about 2/3 full and have your helper start the engine again. This time leave the engine running but have the pentosin bottle in your hand just in case.

Watch the fluid level in the reservoir and have your helper turn the steering wheel lock to lock a few times to work any bubbles out of the system. There shouldn't be much if any air in the system if you followed directions. When satisfied bring the fluid to the proper level by using the dipstick in the cap. I have found that the bottom line is when the system is cold and the top line is when the system is hot. I took a sharpie and marked the full mark on the outside of the rezzy so I can do a quick visual check whenever I open the hood.

While you have all your tools out might as well do the PDCC. For those of you who opt to only do the PDCC reservoir, this is where you will begin.

The procedure is basically the same so I won't go through all the steps again. But there are some differences and I will point them out now.

The PDCC systems hoses attach to the reservoir a little different than the PS system. The return hose is compression/swaged on to the pipe so you are going to have to make an adapter. The hose has an ID of about a 1/2 inch. I had a little chunk of 3/8 steel pipe and pushed about 3/4 of an inch long piece of my 3/8 hose on it. To make a sort of shim. The picture may explain better than my words:

See how end of the tube has the little piece of clear hose on it? That is the end that will fit into the smaller PDCC hose coming from the pump. The other end of the tube will have the 3/8 hose you saved previously, and it will go to your catch basin.

Then just follow the same steps as the PS procedure bumping the engine. You won't be able to cycle the PDCC system like you cycled the steering rack during your engine bumps. I guess with the Porsche tool its possible.
Pump out the black nasty.

And pump in the clean green. When the emerald green is flowing stop bumping the engine, remove the reservoir, remove your flushing hose, reinstall your reservoir, secure your hose clamps, top off with fluid, make sure you have all the air out the system (shouldn't be any), top off again.

Once you have everything back together, and all of your oily rags removed, give that area a good hosing down with simple green and a good thorough rinse. JOB DONE

Out of curiosity, I cut up one reservoir to have a look at the filter. I don't remember if it was the PDCC or the PS. It looked clean to me. The white plastic fuzz is from the band saw cutting the reservoir apart.

Last edited by deilenberger; 01-28-2019 at 07:53 PM.
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Old 01-23-2019, 05:27 PM
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Join Date: Mar 2014
Location: calimesa ca.
Posts: 180

The reservoir part number is955-314-015-30

Last edited by deilenberger; 01-28-2019 at 07:56 PM.
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