PorscheAddict

Someone asked for a DIY on how to change gear oil on the 981, so here goes. No guarantees this is right, or that you won't mess something up/DIY'er beware/other disclaimer crap. Rely on the below at your own risk.

The PDK has two reservoirs, one for clutch fluid (which is NOT DIY-able due to needing PIWIS) and one for gear oil that lubricates the diff and transmission gears. This DIY covers only the latter. Service interval is allegedly 120k, but that's insane. The car sees track time, but the fluid was black, very thin for 75w90, and had some metal flakes already at 26k miles.

You'll need a torque wrench, M6 socket, M8 socket, fluid pump, 3/8 socket wrench, and extensions. Plus fluid and a drain pan, of course. Service at no more than 40 degrees C fluid temp per Porsche. Took me 1.5 hours without rushing, including jacking and lowering.

Step 1: make sure you have the right fluid. Cars with LSD need fluid with LSD additive. Cars without do not. My car is open diff so I used Driven 75w90 sans LSD (they also have a LS version, which LNE sells).


Step 2: raise car (level), remove rear wheels for easy access unless you have a lift.
Step 3: remove fill plug with pan under it. You want to start with the fill plug because you'll be pretty SOL if you drain the fluid only to find out the fill plug is jammed or you break something. It also gives you an idea of your current level. I had zero fluid coming out of the fill plug, which tells me the level was probably a tad low.

Step 4: remove rear drain plug under diff. This should release 2 quarts or so of fluid.

Step 5: remove small drain under trans (make 100% sure NOT to remove the clutch fluid drain, which is within the black plastic cover on 981's).

Step 6: Fill through fill hole using pump, after capping the drains of course. It should hold around 3 liters if you got everything out. Torque values should be around 20 ft/lb for the diff drain and fill, and 7 or 8 ft/lb for the small (m6) trans drain. Don't over tighten. It would probably be a good idea to replace the sealing rings, but I did not and so far so good.

conceptDawg

Thanks for this write up. I appreciate the effort.

Do you fill until you get overflow or did you just stop at the recommended amount?

PorscheAddict

Definitely get it to overflow, which is what the workshop manual specs. I'm even thinking of trying to top it off again (while cool) to ensure it's 100% full. FWIW, mine only held 2.5 liters or so. I guess that means I didn't get all of the old out, or it was .5 low!

KBell

Thank you, Thank you, Thank you for doing this.

Noah Fect

Good info, thanks! Any difference in shifting feel/response time?

PorscheAddict

It's hard to be certain because I also changed the PDK mapping to Cobb Sport, which firms up the shifts a bit, but it shifts great. I just got back from a HPDE at VIR, where the transmission worked great. On another note, the center radiator lowered my oil temp from 270-275 to 240-245. That can't hurt either.

okie981

Sounds like the problems you were having with clutch slippage have been solved. What was it that resolved the issue?

I also see indicated engine oil temps in the 240-245 range on a hot day. Was at Barber Motorsports on 7-8 July a few weeks ago. I have PDK also but no Cobb PDK tune.

PorscheAddict

Charles Navarro

When Driven was developing the DCT fluid, they had SWRI do a KRL test on shear stability - test is based on ASTM standard tests OEMs use. The Driven product has the lowest amount of shear after the test.



Based on our initial testing and Driven's, here was their recommendation on intervals. I believe the slippage you were experiencing was due to the fluid being beyond its service life.

okie981

I forgot in my post above to mention that I did the 3rd radiator install as you have, and engine oil temps on hot days are similar between our cars with PDK.

okie981

Can't paste in the embedded text from your post for some reason but , changing DCT after every track weekend?? Is this a typo? By DCT, you mean the PDK clutch pack oil? This is a PITA service requiring a Durametric or PIWIS or similar tool during the fill process. Color me skeptical about this recommendation to change after each track weekend. If that's true, I have two choices, sell my car and get one that doesn't require this or stop doing track weekends. BTW, BGB Motorsports didn't have this recommendation when I consulted them about 981 PDK track use reliability.

Charles Navarro

I can't comment on BGBs recommendations, but we do have a ton of experience with track PDK cars and all I can tell you is that we never had any PDK problems and had boxes with hundreds of race hours on them. Only exception is when we saw a used race car come in and it had an unknown service history on the PDK and were street cars before being turned into race cars. In those two instances, the cars both ended up needing new transmissions, likely due to the PDK not being serviced earlier in its life.

We have since stretched that interval out a bit, but doing used fluid analysis would probably be the best indicator of when to change it. You technically don't need the PIWIS for a simple fluid change - we would drain them and re-fill them using graduated cylinders to make sure we put in what we take out to ensure the total fill quantity doesn't change. But still, we advise fluid changes every other event (I'm talking longer multi-day Club Racing events) and gear fluid changes every three events in cars with LSD.

We would do the re-calibration when doing the filter change, which would be every other or third fluid change, again depending on how much/hard the car was actually driven on the fill.

As Lake said, the PDK side of the box is dirty and it's hell on fluid, but there has to be a happy ground between the factory interval and our severe service intervals.

okie981

First, I should clarify my reference to BGB Motorsports. They didn't make any specific recommendations on how often to change the PDK clutch fluid in my car, and I never discussed that with them. I discussed HPDE track use (no racing) of my 981 car with the 3rd radiator installed on hot days in the Southern states. It was essentially just a conversation on durability of the PDK being used in these conditions, and them stating that no additional PDK cooling would be required. So in my earlier post, I jumped from commenting on PDK fluid change intervals to commenting on durability of the PDK without explaining I had done that.

I respect your expertise and Lake's at Driven as well. I've exchanged several emails with Lake after meeting him at the Porsche Parade in 2016 and also after I switched to DT40 for engine oil. I've shared several UOA reports with him and I'm happy with my DT40 results and the support from Lake. BTW, I usually purchase my DT40 from your website.

Your points about putting a street car into racing service are well taken. My car has never been raced, and as of this post it has 12 HPDE track days on it and 32,700 total miles. The first track day was at about 24k miles. I've owned the car since brand new. I've never done a launch control start, FWIW. I suppose a typical race weekend puts about 2 to 3 times the hours on a car compared to a HPDE weekend (??), and at maximum stress where a DE is certainly less stress. Having said that, I'm changing both PDK fluids before my next DE and will do UOA of the clutch fluid. I'll also get an analysis of a new clutch fluid sample for comparison. As you said in your post, UOA is the best way to determine change interval in a given application and use case.

Good to know about not needing PIWIS for simple drain/refill. Now if I can get my hands on a good fill pump and some graduated cylinders.....

PorscheAddict

My only concern DIY'ing the clutch side would be if the level was not correct in the first place. Then, you would simply fill it back to the incorrect level. If it had been changed with PIWIS fairly recently, probably not a big risk. Would like to see the UOA on it.

okie981

I'm doing the gear oil myself. Having dealer do the clutch fluid this first time so I know level is correct, then will do drain/refill myself for later ones. I will have the dealer get fluid samples of old and new for UOA. Will post results here. BTW, the shop foreman at the dealer who used to do the GT car work there (a very large dealer) recommended I only do the clutch fluid drain/refill this time and he is familiar with my car and how I've used it. Down the road, I may do the pan/filter myself and just make sure I put back in the amount that comes out. I replaced the brace under the pan with the 718 part a few months ago when I installed the dog bone reinforcement the 718 cars have between the rear sway bar mounts. Removing the brace under the pan isn't a big deal, there are 2 bolts for the long diagonal braces you have to buy new because of single use requirements. Just make sure all weight is off the wheels and be aware a wheel alignment is recommended by Porsche after removing/replacing that brace structure. I was going to do a new track alignment anyway afterwards, so the alignment was no additional cost for me at the time.

Car goes in Friday this week for the PDK fluid transfusion. I've got 7 track days lined up between now and end of September. Most will be hot weather.