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Full PDF with Photos attached below along with Service Manual extract

Clutch Fluid and Trans Axle Fluid and Filter Change

I am making this write up for Clutch Fluid and Filter Replacement to help owners of 12c’s and other McLaren’s more comfortable working on their own cars. As the price of a 12C has fallen in recent years especially when compared to the later 650’s and 675’s there is an opportunity for people to own truly amazing cars for somewhat ordinary budgets. As owners of these cars we hear it again and again that the cars are amazing, but no one can do maintenance or the parts cost too much etc.. or they have problems. While there are parts of that statement that are true much of it is truly just a myth. They use readily obtainable fluids, Filters etc. and tons of the maintenance and repairs on these cars can be completed by an owner with just basic tools and a little bit of review.

I recommend this service be combined with the transaxle service as well as the air filter service as most of the steps are exactly the same and if done concurrently will save 4-5 hours of repetitive work overall.

I will try as hard as I can to capture every step but I may miss one if I do tough… I took my time, money, and own car to produce the following write up use it at your own risk. Others may say you need a McLaren computer for this, or only the factory techs have that … Blah blah blah. I tend to follow factory service procedures whenever possible and practical until one of two things happens. The parts or procedure is unreasonable or unavailable or THERE IS A BETTER WAY or a BETTER PART. In considering my better way I may or may not have considered the secondary issues feel free to let me know what you think but don’t get your feelings hurt if I don’t listen. As far as the training and quality of the dealer and factory techs see for yourself. If you pay close attention to the photos you can see several SINS committed by the factory techs some of which I call out but at least two hidden ones only a few of you will notice. The car was under warranty until this October and was serviced at one of two Texas dealerships since new and I have the service records to verify that. There was no reason for the shortcuts, and downright bad workmanship present. But at the same time take solace that even with the redneck engineering by the previous technicians the car has been reliable and rock solid through 6000 miles of road use, three full track days, 2 driving schools and 4 autocross competitions since Jan 21st, 2018. All with nothing more than a ruptured hose that happen prior to any of the flogging.

On With The Show.
The factory maintenance manual starts the description of the process on page 170 and again on page 175 for the clutch filter . I will include the PDF of this section as an attachment. Ignore sections 1-2 as most of us don’t have a lift in our garage and or can figure out how to take the wheels off. Always be safe and use good jacking and blocking practices.
To start the project beat the ever-living crap out of the car use manual mode, use the air brake, cycle the gears etc. get the trans temp nice and high. I am not saying this because I’m a mosaicist but because the fluid will flow much easier and drain much more completely when its warm. The various bolts and plugs may also be a little easier to loosen even if they are scalding hot.

You will need to Jack the car up and remove the rear wheels. As some of the only available locations for jack stands are bound to be occupied by your jack you will also need to be creative about your jack and stand placement. Only jack the car from one of the 4 locations marked with the green sticker. Use a hockey puck or a rubber pad to save yourself from jack rash to the rockers. Chock the front wheels to prevent any unexpected movement of rolling forward. Once one side if up and the wheel is off place a jack stand under the rear control arm near the wheel hub being sure to not place any undo loads on ball joints or other moving components. There is a convenient bulge or notch that may be on the lower control arm to serve just this purpose. Go to the other side of the car and repeat. Leave the jack under the passenger side fully locked just below or slightly touching the jack point. In this configuration there will still be some minimal suspension action for the car and the movements could cause a jack stand to slip. Always do this with two people especially in this scenario. You cannot use ramps of blocks under the wheels because you need access to the driver’s inner fender to complete this task. It is also important to note that this creates a scenario in which the gearbox is tilted slightly down hill try to only go as high as you need to minimize the guesswork associated with the fluid filling later.
One the car is up start by removing the inner fender there are about 2000 bolts all of which are 10mm but 2. These two “other” bolts are stainless 4mm Allen head. Do these last. They hold the Tire pressure monitoring sensor in place to the inner fender. I chose to leave the sensor plugged in and simply unbolted it from the inner fender.

his was done to minimize the chances of a service light or similar issue that could only be remedied by a 6-hour one way trip to the dealer. Probably overly cautious but I like to minimize risk in that department. The sensor has two small crews with plastic spacers and two 10mm nuts. The wire is short, so you will need to reach behind the loosened inner fender to detach them.

While you’re at it repeat the process for the other side. You will see why below but trust me its worth the extra 5 min for peace of mind. Once the inner fenders are out its time to take off the lower valance. This piece is held on with 30,000 10mm bolts that are hex head like my car or possibly Torx like the service manual says. There are four that are hidden behind the small plastic caps just below the license plate/valance area. To remove those caps pry gently from the underside of the car , the retaining portions of the caps clip into the sides and are remarkably stubborn in that direction. Once you have the bolts out the 3rd brake light can be disconnected as well as the backup camera. (do not turn the car back on or even go near it with your keys or lock the doors etc. as the self-check in the cars computer could conceivably through a code (again just being cautious).

One the Rear valance is off take off the rear under tray made of aluminum. This only has like 20 10mm bolts with standard hex heads and washers. Remember the order in which you take off the valanve and undertray. The undertray needs to sit flush to the crossmembers so it should go first if not you will need to flex and wiggle it under the valance when you reinstall it is possible either way just way easier the right way.

No you have full view of two different areas of your transmission/transaxle assembly. Hope fully you will see something that is pretty clean and not oily… I wasn’t so lucky. As I mentioned earlier my transmission was subjected to some questionable technical interaction at some point in the past. (I’m looking at you McLaren Dallas on 4-21-15 when you did the clutch cooler service with 23,970 miles)
There is also a small TPM sensor on the small metal under tray unbolt this sensor with a combination of 8mm and 10mm bolts and tuck out of the way.

No that you can see what your working with its time to start the real work.

Clutch Fluid and Filter
The first thing you need to do at this point is remove the fill plug on your clutch housing. This plug is an inverted Allen plug with an 8mm hex. It features either a soft aluminum or copper washer. It is located on the driver’s side between the axle and the trans control module. It is approximately even with the large round plug of the TCU. You must ensure that you can remove this plug before anything else because if you can’t get new fluid into the case then you should seriously reconsider your plan to remove the existing fluid. This is where you will be refilling the clutch fluid from take note of the tight quarters.

Unlike most cars but Exactly like most modern Ferrari’s our cars have a clutch fluid filter (because the vaulted Ferrari transmission is basically the same unit in or cars- Graziano Made McLaren and Ferrari branded). This filter is located behind a small cast aluminum cap and is held in with 4 small 10mm bolts. This cover contains a machined inner surface that has a thin O-ring that protrudes into the filter housing creating a good seal. Above this cap he filter is inserted and orientated vertically there is an open and a closed end. Pull this out and set aside.

Item of Note this cap and its 4 screws are generally pretty easy to get to UNLESS your rear Z-Bar bushings are heavily worn like mine. The problem is that the z bar runs across one edge of the cap and the bolt will still have maybe one or two turns of thread left engaged when you bottom out on the z bar. This is not a huge problem if it happen to you just loosen the z bar bushing mount bolts 10mm again and gently pry the offending bushing down. Remember you are acting against the weight of the car and on the suspension in which the car on top of you is resting GENTLY is the operative word. In all likely hood you won’t have this problem unless you beat your car like it owes you money.

Take a small clean container and fill with ½ a quart of the FFL-4 fluid and place the replacement filter into it and let it soak. Leave the hole end up and fill with fluid. The purpose of this is to minimize the risk of air bubbles or dry spots in the filter as we as at home mechanics don’t have a reliable way to bleed air from the system. Let the filter soak until fully saturated.

At this time take a small pick tool and remove the O-ring from the cover and replace the O-ring with a new one. The original may look fine but beware it’s a trap it! is not fine and it will start to leak the second you reuse it. In the case of my car someone decided to reuse the original O-ring the first time and tried to mitigate the problem by applying silicone sealant around both the O-ring area and face of the filter cavity. That or they are just extra dumb and put a new O-ring on and added silicone failing to appreciate how the silicone would bind he O-ring and prevent it from expanding and contracting as it was designed to do. It may have been a dealer tech who couldn’t get the replacement ring and was being pressured by the service manager to get the customer his car back. Regardless of the circumstances its never cool just don’t do it.

Reinsert the new fully saturated filter and replace the cap being careful to not cross and threads and to tighten in a cross pattern to ensure easy sealing of the part. The torque spec is 10 MN it converts to approximately 88 Inch pounds I believe but trust my math at your own risk. Either way it does not need to be tight. Tighter bolts will not reduce leaking as all the sealing is actually in the inner diameter of the cap by over tightening all you will do is rack, strip, bend ,distort or otherwise screw up a otherwise good transmission.

Now that the filter fill plug has been removed and the filter removed and replaced let’s drain the remaining fluid from the case. There is an inverted 8mm Allen plug on the bottom of the case. Remove this plug and drain the case. In the case of my car I was unsure of its prior maintenance especially after seeing the mess on the clutch filter. I deceived I wanted to measure the exact amount of fluid that I removed as a reference point for what I needed to put back in. I drained both the filter housing and the drain plug into a large bucket with graduations and found that I had removed exactly 8 liters from the car.

Now it was time to replace the precious 37.00 a liter fluid. The only question was how much to put back and how to get it into the car. In regard to volume I only had 7 liters on hand which based on my removal was not enough. I had to scramble, and it was amazon to the rescue. I bought two extra liters and I’m glad I did as it took almost the full 8 liters to fully fill the case until fluid trickled out the fill hole. It is my understanding that the factory fill can be closer to 10 liters but that includes coolers and airbrake/wing hoses and lines so well go with the 8 I used. Plus, at some point in the past my car had obviously had this service and a cooler replacement completed so who knows what actually made it back in from the original factory fill. In my opinion and after looking in the case with a small camera there is plenty of room for more clutch fluid. If you are a few ounces over full because of the tilt of the car then I’ll accept that. I’d rather the fluid get warm and it find a vent tube than for me to be at a track and smoke the clutches due to low fluid. The fluid from McLaren of Boston came packaged in a weird container with the Pentison ffl-4 label and the stuff from amazon came in a retail ready grey bottle. The price was nearly identical, and McLaren of Boston has everything else you need when you order the parts get a liter or two extra its 40.00 worth of insurance well spent.

In terms of installation of the replacement fluid this is the method that worked for me. I took a 3-4’ piece of 3/8 fuel line and attached one end to my funnel the other was snaked through the driver side wheel well past the suspension and subframe into the fill hole. I then had my wife (friends all abandoned me) slowly pour the fluid into the funnel. As the fuel hose fits the hole very tightly there is no venting making the filling process very slow. After what felt like an hour all the fluid was in and there was a tiny trickle of the excess fluid down the side of the case.

But wait we are not done yet. As you may have gathered the car had a chance to cool completely off between when the order for the extra fluid was placed and when the magic amazon guy dropped it off to me. This meant that while probably accurate the level was not perfect. There could have been voids in the lines that had settled out during the service trapped air and of course thermal expansion. The reason you always check transmissions running and warm is that the fluid needs to be pumped into all the nooks and crannies as well as any expansion that will be happening needs to have happened. This meant that I had t reassemble the rear valence to avoid warning lights and tire wrap the TPM sensors and reinstall the wheels and drive to get everything up to temperature…. What was the lesson absolutely positively don’t waste your time from dead cold to surface of the sun the fluid didn’t change much maybe a cup or possibly a full pint. Not sue what the inner workings of the transmission are precisely but I know that along with operation of the clutches the fluid serves a second more important function and that is cooling and if were talking about cooling more is better. With all of that considered just roll with it. Better yet have enough fluid on hand when you start so that its still relatively warm when your done but if not make sure it is at least full its hard to overfill something that leaks out and take solace in this. when I watched the McLaren and Ferrari documentaries on how they were built no one at the factory get its up to temperature cycles the wing blah blah blah and check the level for ML precision. The see the spec it says 8 liters the put in 8 liters all is well with the world. Take your time try to be accurate but don’t sweat the nerd stuff. Fresh fluid whether it is a small amount over or under is way way better than the junk I pulled out after only 15k miles since its last service.

Transaxle Fluid and Filter

The first step once you have everything uncovered is to remove the transaxle fill plug. Like many of the other plugs it’s an inverted 8mm Allen with an aluminum of copper washer the fill plug is located toward the upper left of the rear case. Open this plug and set aside for later. Now that you have ensured that you can indeed fill your case if you happen to accidently drain it let locate the drain plug. The drain plug is exactly the same as the fill plug with the exception of its location. The drain Plug is on the bottom of the case near the center. Make sure you have a container to catch the fluid and lots of rags and soap as the stuff that comes out is nasty. It is by far the stickiest, worst smelling fluid in any modern car. To quote the labyrinth this stuff has a stick that won’t wash off.

I was able to collect exactly 1 gallon of fluid out of my transaxle. your mileage/quantity may vary as we will discuss later.

The next step is to locate the Transaxle fluid filter. It is located on the driver’s side of the case near the bottom. It is close to the clutch fluid housing but oriented horizontally vs vertically. There is a single 10mm bolt that holds it in. If you’re lucky which I never am it will come out easily with just the most minimal amount of prying at the edge. Did I mention that I wasn’t lucky? Mine happened to be glued into place with black silicone in much the same was my clutch filter was. After a few minutes of struggling I was able to remove the filter 99% of the way out. This is where it gets interesting much as the Z bar offer obstacles for the clutch fluid the trans cradle and subframe offers obstacles to the Transaxle filter. It will come out but just barely you may need to flex the filter ever so slightly to do this. Just try to not scratch the internal surfaces of the housing as they need to be smooth to seal with the O-rings

Once the filter is out inspecting the surfaces for major nicks scratches and dirt. Reinstall the replacement filter and tighten the bolt to the specified torque. At this time, be a nice guy and put the date on the bottom of the filter so the next guy knows. Even better do that before you put it in so it doesn’t look like you have palsy when you write. You may have noticed that I didn’t presoak this filter like the clutch. The reason is twofold.
1. This filter is a fine stainless mesh that doesn’t seem like it would hold much fluid.
2. This stuff stinks. I mean smells like burnt hair mixed with garbage. I try to touch as little gear oil as humanly possible I keep that as a rule through my life. If my child was drowning in gear oil I would probably just chalk it up to evolution. That’s how much I hate this stuff.
Speaking of this stuff, gear oil. Our cars take a unique and special version that is either available from the dealer ship or via mail order from mars with a selling price of about 60.00 a liter of which you need at least 4 plus shipping. The factory specified fluid is not widely available and lucky for us its not necessary. Instead you should use Mobil Delvac 75w-90 synthetic gear oil. This is also rare just not as crazy rare as the real stuff. Our cars do not have limited slip differentials so it’s important that we use fluid without the friction modifier added or built in. This fluid is about the only one I can find that meets the specs, is synthetic, and does have the friction modifier. If you search amazon you can find it rea the review it is the go to fluid for many Porsche enthusiast and racers as the right stuff. If you want to send me 5 quarts of the real stuff for free, then fine if not I’m “running what I brung.” The astute among us may have noticed the 5 quarts reference. I’m not sure what up with my car but on level ground at moderate temperature it took very close to a full 5 quarts to get it full. Maybe if you don’t do the transaxle filter the small sump and filter may make 1-gallon work but it would have not been enough for my car on this day in this situation while I was doing it. Use your own judgment. Below are photos of the old vs new fluid for comparison.
Reinstall everything in the reverse of how it came out. And your done
The fluid that came out as well as the filter were decidedly darker than what went in. as seen in the photo below. I took apart the filter looking for any metal fragments etc. and found nothing to note. Driving the car felt very similar,possibly except for slightly harsher sounds when manually toggling the shifter at low speed it seems the same. But looking at the junk that came out I’m still happy it was changed. The word on the street is that the filter was actually meant to be cleaned which based on its stainless steel construction would seem possible I’m not sure it’s a worth the effort most people will be in a position to do this job once maybe twice the entire time the own the car I don’t know if I would worry about keeping around a used smelly filter that may be able to be cleaned all in an effort to save $176.76.

My experience is that the transmission feels smoother, but it may be placebo effect but ill take it every time.

Onto a few of the SINS that I noticed on my car. One the Fill plug was so tight that a properly inserted and seated Allen socket had no chance at getting it out. In the end it was a 18” pipe wrench grabbing the sides that did it. That one issue alone cost me an hour of time.
The issue wit the silicone was messy but not terrible I had to clean everything with solvent and a bristle brush including the residue inside the filter housing. I don’t know why or how it happened but its not cool. As you will see in the next write up on the Gear case oil the same thing was present on that filter as well.
The last and worst SIN was the state of the air filters in the car. The car had received its last two-yearly services at McLaren Dallas 1-8-16 and 8-15-17 approximate 6k miles apart from each other. The cars air filters were dated 11/4/16 and were factory parts. this means they were installed in all likely hood at the last service in August of 2017. Since that service the car has traveled 6001 miles. How is it possible that the foam lining present in each of the airboxes was in perfect condition prior to that service despite having covered 34k miles but now in the last 6k mile shad deteriorated to a point that it was completely blocking the air filters. Not saying it wasn’t possible just not likely. That is why you take both inner fenders out, so you can change/check/clean the air filters. Its only 3 8mm bolts per side and your car will thankyou

How long did it take?
The total project took approximately 4 hours for the air filters, the clutch fluid, and the transaxle fluid. (excludes amazon waiting time) Each part would have taken nearly as long on its own as much of the work can and was completed concurrently. Do your self a favor and treat the Clutch, Transaxle and Air filters as a single project. The dealer would likely charge in the neighborhood of 1,200.00 for parts and at least 8 hours in labor which means that you would have likely gotten a bill for 3,500.00 by the time it was done and that doesn’t include transport. The dealer may have done a better job than I did. The service would be in the system which can be a huge plus, the wing hydraulics would have been flushed/cycled hopefully and if they happened to make a mistake they would probably make good on it. But do those factors outweigh your saving, that’s a personal call. Will you get some satisfaction and real car culture street credit for doing your own oil and transmission services on your McLaren hell yes you will.

Tools Needed:
10mm ratchet wrench with flex head preferably
10mm socket and ratchet
4mm Allen socket or wrench
8mm socket with 4” extension
Pick tool to remove O-Rings
Flat head screw driver to pry with (Be Careful Cletus)
8mm Allen key or socket
NM or Inch pound Torque wrench from harbor freight 8.99
Bucket or another suitable container.
Shop vac if your airboxes are disintegrating


Parts Needed
11G0017CP Filter Clutch Oil- 126.52
MOBIL TRANS PTX 75/90W (OEM STUFF) [email protected] 60.21

I would like to give a special Thanks to Corbin Olson
at McLaren Boston for helping me get the right parts etc.
Call him at 781-347-3950 or email at [email protected] or visit their online store at

I would also like to thank McLaren Life Member Valentin for posting the service manual some time ago.
Authored By Justin White as a service to anyone with a McLaren who wants to try for themselves. Don’t put this in a book you can do way better without stealing from me.
May 23rd 2018
McLaren Owner #1687
McLaren Life Username: JTWHITE312


104 Posts
Wow, thanks so much for taking the time and effort!

But am I the only person for whom the photos did not load?



98 Posts
Ive done this three times.... I have encountered some differences than the write up. Not saying right vs wrong just noting what's been different in my experience.

The fill and drain plugs on my 2012 12C were T50 Torx plugs not 8mm Allens. When draining the clutch fluid I have two drain plugs the one shown in this write up drains approx 2/3 of the fluid this is is plug toward the rear of the clutch housing near the torsion bar. The second is about 10" further forward on the same centerline. This one drains the the remaining 1/3 of the clutch fluid. They both need to be drained. The one in rear is for the electronic section and the one in the front is for the wet clutch assembly cavity. Per McLaren as of the Feb 2020 the factory revised method of fill has changed. Previously McLaren had said to fill it until it runs out the fill hole. That was later revised in 2015 to say fill it to the fill hoe then remove 0.4L. That has now ben revised to indicate drain it and refill it with 6.6 Liters and be done with it.... McLaren has said in not so many words these transmission were overfilled from the factory and had a maintenance procedure that also overfilled them.... Whether this had anything to do with leaking history who knows....
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