Originally posted this in another discussion, figured the DIY section was a better idea...
To determine if this BBI slave cylinder conversion is for you (as installed on a stock 996 turbo), consider this:
1) it is about as stiff as the OEM system without the accumulator working...so, if you're finding the clutch very stiff on cold start after sitting overnight, your accumulator is shot and this slave feels similar, or perhaps 15-20% less. If you want to replicate that feeling, with the car off, pump the clutch about 20+ times to drain the accumulator and pay attention as it begins to stiffen up.
2) the take-up feel is MUCH MUCH better. it engages closer to the floor than the OEM slave, but with a lot more control, but it sure takes some getting used to for the spring-back on the pedal. I'm considering the GT3 spring, but as the others have mentioned, you can get used to it, so perhaps i'll try it for awhile and see if i acclimatize before spending more money and time on it.
3) the power steering lines are plumbed separately through the BBi slave, but simply ported through an orficen, so it has the proper pressure drop, etc expected by the steering pump without removing lines and plugging holes, etc as in the GT2 mod. the bonus with this is there's no way for the clutch and steering hydraulics to mix anymore, but its as simple as installing a new slave (easier actually, since you're not screwing around with the accumulator).
So, in summary, the BBI slave is a very high quality part - well machined, anodized and fits perfectly, though it requires a fair bit more effort to actuate the clutch, but its waaay simpler to install than the GT2 mod, which costs about the same and has similar pedal feel, and you never have to worry about squeezing oil out of the clutch reservoir or having the accumulator fail as you do with the OEM step.
If BBI is reading this, the only two changes i would like to see are the bleed nipple rotated 90deg, for better access, and a larger diameter piston to reduce the effort to actuate the clutch
Supposedly you can change the clutch pedal assist spring to a GT3 spring to reduce the pedal effort, but I haven't found any review on that with the BBI conversion installed yet.
So, without further adieu, here's how I swapped out my OEM slave and accumulator to a BBI unit, after cobbling together the DIY from a couple sources and past experience:
1. chock the front tires and raise the rear end as high as you can (or use hoist) and block the rear tires
2. prep for lowering the engine by removing the airbox and disconnecting the y-pipe hoses
3. set up blocking and a bottle jack under the engine block, at the crash bracket, just in front of the cross-bar.
4. get a bit of weight on the bottle jack and then use a long extension and a deep 18mm (i think) socket to loosen the engine mount nuts until the nut is about flush with the end of the stud - this is your backup in case the bottle jack craps out, so don't load it up with the full engine weight as you only have a few turns of thread engaged. lower the bottle jack until the engine is barely resting on the nuts. now you have room to work on top of the transmission.
5. follow the up to step 12 in the following DIY, but remove the bracket too (15mm for the cylinder bolts, 13mm for the bracket). one note - i never was able to get that red plastic connection out of the cylinder, so i ended up cutting the band off of the hose and then hack-sawed the old cylinder housing apart once out of the car to retrieve the aluminum fitting, hose clamped the fitting back on the hose (which is the power steering low-pressure return) under the car. a bodge job, but it worked
. also, clamp that low-pressure hose before removing it from the cylinder housing - mine pissed oil everywhere until i got a clamp on it. super awesome. http://www.rmeuropean.com/porsche-99...placement.aspx
6. flush the system - i used a power-bleeder - push the clutch in with a block of wood (this evacuates all the fluid from the master cylinder), and push through 4 liters of Dot 4. if you want to flush some through the master cylinder, don't push it in and out with the bleeder pressurized, its likely to cause damage...release the pressure, then pump and keep the reservoir topped up.
7. now the fun bit, installing the new slave cylinder - i zip-tied the rubber boot onto the actuation rod, then stretched the boot out so it was able press back into the cylinder, keeping the rod seated in the cylinder and not flopping around. this made it way easier to position the rod into the clutch fork. Also, make sure the allen key grub screw on the slave block is tight before installing....mine wasn't and it leaked.
8. connect the lines *** follow-up, i ended up taking the slave off again due to the grub nut leaking, when reinstalling it the second time, it was waaay easier to push the piston in and get the bolts lined up without the lines connected...ie: do steps 7, 9, 10 and then 8. ****
9. rather than removing the starter i was able to get the feel around until the rod was seated in the fork (you can move it around slightly and feel that the end is captive in the divot, then gently move the cylinder ahead until its sitting in-line, it will be positioned about 0.5in back from the bolt holes
10. put the bolt in the hole furthest from clutch, at the slave bleed nipple end, and position your hand so you can push on the end of the cylinder while holding the bolt in place (with palm of your hand). push slow and steady (about 0.5in), and ensure the cylinder is lined up, if the rod is at an angle you won`t likely be able to push the cylinder. this will likely take you a few tries. you may cry. keep trying until you feel the bolt catch the hole. get it finger tight, then put in the other bolt. you won`t be able to get your fingers inside the bell housing (unless you removed the starter and took a look with a mirror or something - remember to disconnect the battery, if you do this) but you should be able to tell if the rod is still in the fork when you start to tighten the two bolts - there should be a fair bit of tension in the cylinder, pushing back towards you - if the cylinder is loose on the bolts, the rod slipped off the fork. cry. try again.
11. tighten the two bolts, and then bleed the system (the bleeder is 8mm - you`ll need a short wrench) - i used another 2 liters of DOT4 for this, again, while pumping the clutch to work out any stuff, etc in the lines. it may take a few bleeds to get good resistance in the clutch pedal and not have to pull it back up by hand.
*** follow-up to this: first time around I didn't follow the procedure in the manual...short story long, my master cylinder popped shortly thereafter. soooo, new master cylinder installed, i then bled the system properly, namely: connect the bleed bottle to the nipple, have the clutch pressed in with a board or something propped up to the seat, fill the reservoir with dot 4 and pump up the power-bleeder to 10psi, crack the bleed valve and push a liter or two of dot 4 through the system total. i stopped every 200mL, closed the bleed nipple, released the pressure on the power-bleeder, then brought the clutch pedal back up fully, and pumped it a few times by hand (without the power-bleeder pressurized), then pushed the clutched back in with a block of wood, applied 10psi with the power-bleeder and then cracked the bleed nipple again. i put through about 2L of dot 4 this way and got a fair bit of air out, without cooking my master cylinder again.
12. raise the engine back up and tighten the engine mount nuts, reconnect the axle, and reinstall the airbox, then lower the car to test the clutch by running the car and pumping the clutch - try to engage 1st - VERY gently as it feels WAY different and has a totally different engagement point than the old system (at least mine felt that way). if it doesn`t go in gear it probably means you have air in the lines - raise it up and bleed it again. if the pedal doesn`t return after pushing it in, pump it a quite a few times by hand until it gets resistance, then rebleed if its not actuating the clutch still (can`t get it in gear).
13. if it works, raise the car back up, fit the hoses, brackets, under trays back where they belong and button it all back up.
note: the power steering system doesn`t need to be bleed manually, simply run the car and turn the steering lock to lock a few times and it will work the air out.
All in, this may take you about 6-8 hours if you're a confident wrench. Its tricky to be working above the transmission, but its not a complicated job since you're simply pulling the accumulator and old slave off, flushing the system, installing a new slave and then bleeding it. After a few days i'm getting used to the pedal weight and wouldn't think twice about installing it again, since i should never have to worry about it breaking, unlike the OEM unit.