DIY - Swap clutch slave cylinder and hydraulic line for improved feel and control
 

The stock setup of the clutch is frustratingly vague because there is too much leverage between the clutch pedal and the pressure plate. I started looking for ways to change the diameter ratio between clutch and master cylinders when I stumbled into the no-brainer solution. The stock slave cylinder has a 13/16" bore. Subaru has another clutch slave cylinder with a slightly narrower bore of 3/4". It is otherwise identical to stock but decreases the leverage by 17%. Here is the original thread leading up to this DIY. Enjoy.

Update 07/27/15: Added links to parts from NAPA and Autozone

Update 05/13/15: ck-GT86 generously added his procedure to upgrade the hydraulic line in concert with this swap. Skip forward to his post here. The link is also repeated below. Thanks, @ck-GT86.

Update 12/15/14: Drain, plug, and save your original slave cylinder. It will come in handy if you ever boost enough to require a heavier clutch. Thanks, @Koa.

Update 12/11/14: Added table of manufacturer's torque specifications. Thanks, @JB86'd.

Update 11/26/14: Corrected references to socket size. 14 mm was 12 mm. Thanks, @Phantobe.

Update 11/14/14: On discussing with some fellow members, if you are already running an aftermarket clutch with a stiffer pressure plate this may not be the hot ticket. This mod increases pedal stiffness. It's comfortable on the stock pressure plate but might be too much for a big-boy clutch.


Precautions:

1. Brake fluid will eat paint. Be very careful to avoid spillage onto any finished surfaces. If any is spilled, stop working. Immediately wash and rinse all contaminated surfaces.
2. Brake fluid is toxic. Use nitrile gloves and/or wash hands immediately after contact. Dispose of used fluid and any contaminated items in accordance with local, state, and federal law.
3. Inspect your clothing. Zippers, buttons, rivets, etc. will scratch your car. Consider using a fender cover while working.
4. Cleanliness is key. The slightest particle of grit or schmutz will settle to the bottom of the cylinder and cause premature failure by grinding back and forth with each operation of the clutch.

Tools:

socket driver
14 mm socket
6 in extension
8 mm combination wrench
torque wrench (recommended and easily rented)
1/2"female-to-3/8"male adapter (if needed for torque wrench)

something to tie the loose end of the hydraulic line to the strut brace

a partner to operate the clutch pedal when bleeding the new cylinder

Consumables:

1 pint DOT-3 brake fluid
Shop towels or rag big enough to absorb 1-2 oz brake fluid.

Parts:

1 ea. Subaru 30620AA111 (or equiv.) slave cylinder

NAPA Altrom atm p3038 (Nabco just like OEM)
Autozone Duralast 900061

2 ea. Subaru 114130151 (or equiv.) gaskets (crush washers) for 10 mm banjo fitting

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Torque specifications:

http://www.ft86club.com/forums/pictu...pictureid=8688

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Preliminary steps:

1. If not already adjusted for minimum usable height, perform the Clutch Engagement Adjustment.
Although not required, be prepared to perform a second adjustment after installing the new cylinder. The smaller diameter of the new cylinder will slightly raise the touch point.

2. Inspect the new cylinder for any obvious defects. Do not remove the rubber stopper from the new cylinder. It will be transferred to the old cylinder just prior to removal.

3. To minimize the possibility of particulate contamination, before disassembly, thoroughly clean the hose, banjo fitting, AND the 14 mm socket.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Procedure:


To prevent fluid loss, be prepared to lift the loose end of the hose above the fluid level in the reservoir immediately after unscrewing the banjo bolt.

http://www.ft86club.com/forums/pictu...pictureid=8582




http://www.ft86club.com/forums/pictu...pictureid=8581

http://www.ft86club.com/forums/pictu...pictureid=8583


Now we're ready to disconnect the banjo fitting.

Place another towel within reach. Use the ratchet only to loosen the bolt. Use your fingers to unscrew the bolt most of the way.

With towel in free hand, prepare to cover the end of the banjo bolt and fitting.

Remember, there is a gasket (washer) both above and below the banjo fitting. Be aware of the lower one. It should stay with the cylinder.

Leaving the bolt inserted in the banjo fitting, immediately lift both up and away from the cylinder.

Observe how slowly the fluid oozes on its own. This knowledge will come in handy when reassembling the fitting.

Separate and set aside the bolt and old gasket.

Tie off the hose.

Inspect the area for, and remove any spilled fluid.


http://www.ft86club.com/forums/pictu...pictureid=8646

http://www.ft86club.com/forums/pictu...pictureid=8585


***Ignore the removal of the reservoir cap at this point. It is vented and therefore will allow the fluid level to equalize.***

http://www.ft86club.com/forums/pictu...pictureid=8587



Remove and set aside the remaining gasket.

http://www.ft86club.com/forums/pictu...pictureid=8586

http://www.ft86club.com/forums/pictu...pictureid=8592


Using a rag to prevent spillage, set the cap into the old cylinder.

Note for working without a torque wrench: The mount bolts will feel especially tight and may first come loose with a "snap." Do not use this as a gauge for torquing the bolt upon assembly. Try to feel for where it's good and snug but doesn't stretch the threads. It can help to get a feel for that sweet spot by repeatedly tightening and loosening the bolt each time increasing the torque a smidge. The fastener will settle in over time but if you're not sure, keep the ratchet in the car and check it the next time it's cold.

Remove the 2 mount bolts and remove the old cylinder.

http://www.ft86club.com/forums/pictu...pictureid=8593


Mount the new cylinder and if upgrading the clutch hydraulic line, follow ck-GT86's procedure here.

Quickly, using 2 new gaskets, mount the banjo fitting.

Tighten the banjo bolt only until snug. Then continue turning the bolt 1/2 turn to set the gaskets. [service manual specifies 13 lb-ft torque]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Bleeding the system
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note: The clutch pedal will not return on its own if the assist spring remains installed. This is normal.

Caution: Monitor the fluid level in the reservoir carefully. If the master cylinder is allowed to suck air, bench bleeding will be required to restore function.

1. Have your partner prepare to press and hold the clutch pedal.

2. Establish a clear method to communicate with your partner. This may seem odd but with the repetitive nature of this task, an "oops" moment is a very real risk. It's not a big deal, just a little frustrating when "Arrrgh!" You almost had it.

3. I bleed the clutch fluid into a rag because there's less risk of spillage and it's easier to feel presence of air that way.

Procedure is as follows:

1. Press clutch pedal.
2. Slowly open bleed valve. (listen/feel for air bubbles)
3. Close bleed valve.
4. Lift or release clutch pedal.
5. Check fluid in reservoir and add if required.

Repeat this cycle until all air is eliminated from the system. It will be easy to feel this. Yay! Enjoy the new sporty feel of your clutch.

https://www.youtube.com/watch?v=uLj-qA25EXM

1 ea. Subaru 30620AA111 (or equiv.) slave cylinder

Is this a larger or smaller diameter cylinder than our factory slave? For "feel and control" would that be a larger diameter cylinder which would take more pedal movement?

The factory BRZ/FRS slave is 13/16". The 30620AA111 is 3/4" and 1/16" smaller than stock (approximately 15%).

By shrinking the slave you reduce the amount of distance that the master needs to travel to create the same amount of motion. This allows pedal movement to be reduced. That reduction creates a more tactile range of motion during said pedal movement, returning the "feel" that many of us miss having in this clutch system.

Oh I cant wait for this :thumbup:

I hate the feel of the clutch in this car (even after I adjusted the position)

Finished. Go for it.

so is the crush washer just a standard 10mm? I am picking up my new slave today.

Yup. nothing special. I got mine off of the rack at a generic parts shop.

You the man, Ultra. Trying this during the weekend. Parts just came in :)

Thanks for the help earlier last week as well

Thanks for the DIY post. Interested in hearing from guys who have done the pedal adjustment, and removed the helper spring and how this compares.

My pleasure!



Can't tell you how excited I am for you all.

Well i just finished mine. I have a little bit of adjustment on the pedal still but man is it better. There is an engagement point now. It is so much less vague. Thanks for figuring this out. I wanted to add a few more part numbers for everyone.

I got my part from autozone
part # 90028
Subaru part # 30620-aa041

Still 3/4 and fit perfectly

Great now you get it posted! After the snow is on the ground. It will just have to wait till spring now I guess.

How much was it?

like 21$. it was a good deal