What is my favorite kind of repair? It is a repair that replaces a good but worn out part with a upgraded part. And that is exactly what brought us here to adding a carbon fiber driveshaft. After I had removed my 6 speed transmission to replace the gears and upgrade the dccd, I found that the u-joints were very worn and sticky. Which can cause issues when leaving a stop light, you will notice this as taking off from a stop light is quite jerky.

Old crusty u-joints aren’t beneficial in any way. So why not upgrade them by replacing the driveshaft as well.

Now I think a new driveshaft would remedy this issue, why not add something with some performance benefits to it. Another reason to upgrade to a carbon fiber driveshaft was to reduce the amount of NVH that can travel from the rear diff to the rest of the car. Now let’s see what it takes to remove the old driveshaft and install the new unit.

New u-joints have arrived with a nice new lightweight carbon fiber driveshaft attached to it.

Timeframe

This should be pretty straight forward as long as your undercarriage isn’t rusted over. I think with 2 hours this should be very easy, but I think 1 hour is very doable. Especially if this is your second time doing this…. It was for me.

Tools

Not too many tools here. We will need to remove just a few bolts and nuts around the exhaust, rear diff and original driveshaft. Here is a small list of what I used.

Parts

DSS 04-07 STI carbon fiber driveshaft (find it on eBay)
DSS 04-07 STi aluminum driveshaft (Find it on eBay)

How to

As with any repairs that reside below the car, our first step is properly lifting the vehicle and getting it supported safely and correctly. I put together a write up for this and you can find it here.

As with so many replacement parts guides, we start right off by properly supporting your vehicle on jack stands before getting underneath it. How to properly put your Subaru on Jack stands

With the car well supported on jack stands or a lift you can start with the removal of parts to access the driveshaft. My first step was to disconnect the exhaust at the connection of the midpipe and downpipe. For my Cobb titanium this is two bolts and nuts at the downpipe connection. And a clamp at the midpipe to axle back connection. Then I was able to undo the single exhaust hanger and set it aside.

Next up is removing the rear diff lower cover to gain access to the rear bolts that connect the driveshaft flange to the differential pinion. This will be 6 bolts.

Now you have access to the rear driveshaft pinion and can start removing the bolts.

Now you will have access to the four nuts on the differential pinion. I prefer to use a prybar slid into the u-joint to hold it steady while you break the nuts free. As you are removing the four bolts, washers and nuts from the flange be careful as it could fall down on you. I would recommend placing a support item below it incase it falls.

We can move on to the middle of the driveshaft to remove the two bolts that support the center driveshaft bearing. Again be aware that removal these bolts will free another portion of the driveshaft which will try and fall on you.

Before removing the driveshaft you can place a a couple rags or absorbent mats on the downpipe. When we pull the driveshaft out it is highly likely that transmission fluid will come out. And we don’t want it to land on the exhaust to be burned off later. With that complete we can do one of two things, we can have a friend ready with the carbon fiber driveshaft to install after you slide out the old driveshaft. Or you can use a plug or old driveshaft to keep the fluid from spilling out in between replacing it.

Once the new driveshaft is in you might notice that it looks different. Most of the carbon fiber driveshaft options out there don’t have the outer cover that is fitted to the factory driveshaft.

Moving back to the rear of the car you will now be to install driveshaft to the differential. I found on my DSS carbon fiber driveshaft that the flange wasn’t deep enough to allow for it to properly mount to the differential flange. I read that this issue effects some vehicles but not all. You can find more about this in my DSS carbon fiber driveshaft review. You can drill out your factory differential flange to use the supplied hardware. Or I found the proper sized shim spacers that you can utilize that will allow you to use factory or factory like hardware.

With it torqued and installed it is time to return the exhaust back on so that you can test out your new part. After everything is reinstalled and retorqued, you should lower the vehicle down and take a very slow test drive to make sure everything is happy.