STi Clutch Line Upgrade

Changing the clutch line on the car replaces the rubber hose that comes on the car stock. Much like brake lines, the idea is that replacing rubber lines with steel lines should improve pedal feel and firmness. However, unlike brake lines, the clutch doesn’t have something to bind to because pusing the clutch pedal separates the clutch, where stepping on the brake pedal clamps the pads to the rotors. Based on that, the difference in the feeling should be minimal compared to changing brake lines, but I figured the clutch line looks better than the stock line. The new clutch line was fairly inexpensive, so why not?

The clutch line is located under the intercooler and connects the clutch slave cylinder (the hyrdraulic assembly that engages your clutch) to the clutch master cylinder (the hydraulic assemply that is directly connected to the clutch pedal in the car. It uses standard DOT 3/4 brake fluid, and operates in much the same way as the brake system. You bleed it the same way, and you top off the fluid in the same way.

Parts needed:
  • Rubber mallet
  • Locking Pliers
  • Large adjustable pliers
  • 1/4 inch socket wrench (8mm)
  • 3/8th inch Socket wrench (14mm)
  • Socket wrench extensions for 1/4 and 3/8 inch
  • Turkey baster or syringe
  • Flare wrench or box wrench
  • Long flat head screwdriver
  • Bottle of DOT 3/4 brake fluid
  • Short Piece of rubber tubing
  • Empty bottle for dirty clutch fluid

First step is to take off the intercooler. This step is fairly easy. First, find the 3 hose clamps that hold the inlet and outlet of the intercooler on, There are 2 hose clamps on the outlet, and 1 on the inlet. Just get the 8mm socket wrench and loosen them. You will probably need the extension for the intercooler inlet hose, it’s more or less under the intercooler.

Next, find the vacuum hoses that run along the bottom edge of the intercooler. There should be three hoses to undo. They’re not on tight at all so a firm tug should pop them off.

Now find the two 14mm bolts on either side of your BPV or BOV and remove those. Pull the BPV off the intercooler, making sure the seal and gasket are somewhere safe. They ususally stick to the intercooler, so you can just leave it there. Look to the left and right of the intercooler, there should be 2 bolts total that bolt the intercooler to the car. On the right side, follow the black bracket down and there should be 2 more bolts that hold the bracket to the engine. Loosen, but don’t remove these bolts.

You should have removed 4 bolts total (2 for intercooler, 2 for BPV) and loosened 2 more (2 for the intercooler bracket on the right) as well as loosened the 3 hose clamps (1 on intercooler inlet, 2 on intercooler outlet)

Now, grab the intercooler firmly with both hands on either side. Pull the top of the intercooler so the top edge clears the A/C lines, then pull sharply straight up. With a pop, it should come out. There are two rubber isolaters on either side of the intercooler where it bolts into the car. Don’t lose those, make sure they stay on the intercooler. Also keep track of the hose clamps. You can remove the short length of tubing on the throttle body and reattach it to the intercooler so you don’t lose it. Set the intercooler somewhere safe. If you have a significant amount of blowby oil in the intercooler, you can get an aerosol can of intake or carb cleaner and spray the intercooler out.

You should now be able to see the clutch line. The clutch line is held into the body of the car with a metal clip that clips onto a steel plate. This is the same method for a brake line, so if you’ve done brake lines this should be familiar. You will need to get a large flat bladed screwdriver to pop the clip off. The clip needs to move up to release the brake line.

I was able to do this by getting a set of locking pliars and pulling the clip out. You may find it easiar to get a long flat blade screwdriver and tap it out from under the car, depending on how long your arms are.

After this metal plate is removed, you will now need to undo the fitting for the line to the master cylinder. To the left of the mounting clip there is a bolt that you can remove which removes the clutch line mounting assembly. If this is removed, your clutch line has a little more freedom to move around in the engine bay, and is only restricted by the hardline. I removed this to get easier access to the line.

Shove a wad of paper towels under the clutch line. The next few steps can get messy and you don’t want to ruin any paint by getting brake fluid on it.

Theoritically, you should be able to get a flare wrench on the line to remove it. However, in my experience, using a flare wrench almost always rounds off the fitting. You will want to skip the four letter words and yelling and go straight for the locking pliers. Lock them nice and firm around the small nut, and get your other set of adjustable pliers around the larger side on the clutch line itself. It will take a bit of fidgiting, but you should be able to loosen the clutch line fitting without much drama. Don’t remove it yet, just get it loose and remove the locking pliars.

Now, move on to the banjo bolt attaching the line to the slave cylinder. This should be a standard 14mm bolt head. Just loosen it and put the socket wrench away.

Make sure you have your replacement clutch line ready. You shold have the replacement clutch line, the banjo bolt, and the two copper washers that go on either end of the banjo bolt.

Quickly undo the clutch line fitting and banjo bolt. Get a paper towel and wipe off the mating surface on the slave cylinder, and quickly attach and hand-tighten the new clutch line on the car. Don’t let the clutch fluid reservoir get empty, if you do this quickly you should only have a small amount of brake fluid drip out.

Go ahead and use the tools to tighten both the banjo bolt and the fitting. Do not over-tighten the banjo bolt, it stretches very easily and you can break it. The washers on either end of the banjo bolt will do a good job of sealing. Re-attach the metal clip to secure the new clutch line to the body.

Now, get your turkey baster or srynge and open up the clutch resuivoiur. Suck out as much fluid as you can, and put the gross old fluid in your empty bottle for waste fluid. Grab your bottle of fresh brake fluid and fill up the reservoir.

The next step is to bleed the line and clutch cylinder so you get all the air bubbles out of the line. If you don’t have a vacuum or power bleeder, get your girlfriend / significant other / roommate / friend / whatever to help you out. You will need to find the bleeder bolt on the slave cylinder. Get your rubber tubing, slip it through your box wrench, and attach the tubing to the fitting on the bleeder and use the wrench to loosen the bleeder screw. Lightly tighten the screw and get your buddy. You will need good coordination to do the next part.

Get your buddy to push down on the clutch pedal when you yell “down”, and pull the pedal up with their hands when you yell “up”. Once your partner understands this, put the loose end of the hose into your empty catch bottle, and get ready to loosen the bleeder screw. Yell “DOWN”, and when the clutch line is down, open the bleeder for a moment, and close it. Once the screw is closed, yell “UP” and have your helper pull the pedal off the floor. When there is air in the line assembly, the clutch line will not return automatically and will need to be pulled up. Repeat this procedure until you get clear, clean, bubble free brake fluid from your clutch line. Keep a close eye on your reservoir and do not let it go dry, so keep it topped up with clear fluid. I had some pretty gross stuff in my lines so I went ahead and used up the complete bottle of fluid to make sure everything was clear in the lines. You do not want any bubbles in the line at all as this will affect the clutch pedal feel.

Once this is done, make sure the bleeder screw is nice and tight, remove your rubber hose, make sure your clutch pedal works normally and returns on it’s own, top off the brake fluid in the clutch resiovour, and off you go! Send you helper off to get you a case of beer.

Reattach your intercooler. If you have never done this before, this can easily be the most difficult part. It requires some coordination and muscle. Make sure the bracket on the right side of the engine bay is loose. Make sure the rubber isolators are on either side of the intercooler. Grab the short length of hose on the outlet side of the intercooler and put it on the throttle body, not on the intercooler. Get your hose clamps, and make sure they are on the hose, but don’t tighten them yet. Rest your intercooler in the general area on top in the engine bay. The easiest method I have had is to lubricate the inlet and outlet hoses up with a little oil from the dipstick, and tip the bottom edge of the intercooler so the hoses are touching the turbo outlet and the throttle body. Now press down on the top side of the intercooler towards the throttle body. With some coordination, pushing, shoving, yelling, and banging, you should be able to get both the inlet and outlet hose of the intercooler attached to their respective fittings. Don’t worry about getting it on 100%, just get them close. If you can’t get the throttle body hose on without crimping, focus on the turbo outlet/intercooler inlet and get that on. On STi’s, there is a metal nub on the intercooler y-pipe that you can grab to help shove the pipe on. For the WRX, I suggest liberal application of a flat-blade screwdriver. For the throttle body, again, get your flat blade screwdriver and run it along the edge of the outlet pipe to make sure you have a seal for the hose. If you have a set of radiator hose hooks, these will be a great help. Radiator hose hooks are a set of curved metal rods with a screwdriver handle that make it much easiar to manhandle the hose into position.

Once the intercooler is on, make sure that the hoses on on tight, and thread in the mounting bolts on the right and left of the intercooler. Make them finger-tight, and then on the right side, tighten the two intercooler bracket bolts to spec. Now go around and tighten the left and right intercooler mounting bolts. Once this is done, go get your 1/4 inch socket and extension and tighten all the hose clamps. You may need to get your flat blade and re-alighn the inlet and outlet hose if they squirmed a little.
Once the hose clamps are buttoned up, attach your BPV with the two bolts, and tighten. Re-attach your three vacuum hoses. Double check that everything looks, good, clean up and go for a drive! You’re done!

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