Here's a step by step how to replace the clutch master cylinder. I wrote it up mostly in response to a joking dare from Mark Johnson, but also to give back some for all the fabulous advice I get off this forum.
From what I've noticed, if you own an older NSX you're going to be doing this sooner or later. Keep in mind that if I can do this, so can your average chimpanzee. Your above average chimpanzee would have replaced the slave as well
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Replacing the Clutch Master Cylinder
Overview: Before you start this job make certain you have a decent socket set that includes a wobble extension. This should be a one person job, though I ran into a snag in step 8 that required two people to get around. I'm going to assume you have a copy of the service manual for your NSX which has all the diagrams. If by chance you don't have one use the one on NSX prime.
1: Remove the driver's side seat. If you've never done this before: move the seat all the way forward. Pry off the (2) plastic coverings for the bolts behind the seat and remove the bolts. Move the seat all the way back and removed the (2) bolts under the front of the seat. Place a towel over the door lip (so you won't scratch anything). Pry the plastic cap covering the bolt on the seat belt and remove the bolt. Tilt the seat and unplug the wiring beneath the seat. There's a place to push on the plastic connector that will allow it to slide off. Carefully remove the seat without scratching the interior.
2: Under the hood: remove the metal hydraulic line (clutch pipe) from the Master Cylinder (12mm wrench). You can only get about 1/16th of a turn at a time, so it's going to take a while. Alternately you could undue the clutch pipe at the other end and remove it with the MC. I didn't, but if I ever do this again I will try it that way. To prevent making a mess you may wish to suction out as much of the brake fluid as you can from the reservior (you can use a turkey baster) before hand.
3: Under the hood undue the (2) bolts attaching the clutch fluid reservoir to the car.
4: In the cabin of the car, at the clutch pedal, remove the cotter pin that holds the bolt which connects the master cylinder to the pedal. You're supposed to throw this pin away and replace it. A new pin does not come with the MC, but you can get them at any auto store. After removing the pin remove the bolt itself.
5: In the cabin of the car remove the (2) bolts that hold the MC in place. You're never going to manage this without a wobble extension. The bolts are 12mm.
6: Remove the MC from under the hood. It's no doubt theoretically possible to do this without getting brake fluid all over the place. I wouldn't know, I spilled it everywhere. If you find that you have to rinse everything off use water in a big glass and pour carefully. Remember there is a big hole leading into the interior of your car.
7: Now that you have the MC out, remove the reservoir and attach it to the new one. If you removed the metal hydraulic line with the MC as mentioned in step 2 then attach it to the new MC as well. Also verify that the locknut which will connect the MC to your pedal is set the same on the new one as it was on the old one.
8: Put the new MC in. This is the only step which required two people for me. The mounting brackets for the clutch pedal shifted once the MC bolts had been removed and partially blocked the bolt holes. One person had to push them back into place in the cabin while the other pushed the MC from the other side.
9: Get the (2) bolts that hold the MC in place on. Just on and threaded, don't tighten them up yet, you'll need the play to get everything else together. If you have trouble getting the bolts on use some tape around the socket (as in the socket on the socket wrench) to lightly tape the bolts to the socket. This should keep them in place in the socket long enough for you to thread them.
10: Attach the metal hydraulic line. Attaching it to the MC was a pain, which is why next time I'm going to try using the other end of the line.
11. Attach the MC to the pedal, replacing the cotter pin.
12. Tighten everything up.
13. Reattach the clutch fluid reservoir.
14. Put the seat back (just do everything in the opposite order as step1). You're done with the mechanical part! It won't work though, you're going to have to bleed the air out of the system...
Flushing/Bleeding the Clutch Hydraulics
Overview: Without specialized equipment this is a two person job. If you have a third person you can put them to work as well. Technically all you have to do is bleed the air out of the system, but if your MC installation went anything like mine you got so much air in that you're going to flush the entire system anyway
1: Jack up the rear driver's side wheel and remove it. You will have to stick your head under the car, so have at least 2 supports (the jack and a jack stand for instance).
2: Locate the bleed screw, it is on the slave cylinder. The slave cylinder is to the left of the wheel about 30 cm back.
3: Attach a small piece of plastic tubing (the same stuff you use in fish tanks) to the bleed screw, place the other end in a catch bottle. I used an empty 12oz coke bottle.
4: Bleed the system. This takes two people. The procedure goes like this: Make certain the reservoir is full and the clutch pedal is in the "up" (transmission engaged) position. The first person will unscrew the bleed screw by about a quarter of a turn. The second person then presses the clutch pedal to the floor and holds it there. Each time the clutch is pressed air and/or fluid will be pushed out of the bleed screw. The first person then screws the bleed screw back tight, after which the second person pulls the clutch pedal back up. If the bleed screw is not fully closed when the clutch is brought back in the air/fluid that was just expelled will be sucked back into the system (instead of clean fluid being sucked in from the reservoir). Repeat this a few (no more than five) times before checking the reservoir, filling it as required.
Repeat 4 until done: When no more air comes out of the system, and there is pressure to push the clutch back up (test this by pushing it with the bleed screw closed) then you're done. Unless your intent was to flush the system. If so you'll probably be able to see when the dirty fluid is finished coming out and only the clean fluid that you've been putting into the reservoir is coming out.
Once everything is back together (but before you put the wheel back on) have someone pump the clutch while you visually inspect everything you've touched to make certain there are no leaks. You should do the same when bleeding your brakes by the way. Ask me how I know.
That's it. Put the tire back on and you're good to go. Make certain the transmission is fully disengaging: push in the clutch, put the car in gear, gently release the clutch. There should be some play before the transmission engages. If it engages immediately then it's possible that it never fully disengaged.
From what I've noticed, if you own an older NSX you're going to be doing this sooner or later. Keep in mind that if I can do this, so can your average chimpanzee. Your above average chimpanzee would have replaced the slave as well
--------------------------------------------------------
Replacing the Clutch Master Cylinder
Overview: Before you start this job make certain you have a decent socket set that includes a wobble extension. This should be a one person job, though I ran into a snag in step 8 that required two people to get around. I'm going to assume you have a copy of the service manual for your NSX which has all the diagrams. If by chance you don't have one use the one on NSX prime.
1: Remove the driver's side seat. If you've never done this before: move the seat all the way forward. Pry off the (2) plastic coverings for the bolts behind the seat and remove the bolts. Move the seat all the way back and removed the (2) bolts under the front of the seat. Place a towel over the door lip (so you won't scratch anything). Pry the plastic cap covering the bolt on the seat belt and remove the bolt. Tilt the seat and unplug the wiring beneath the seat. There's a place to push on the plastic connector that will allow it to slide off. Carefully remove the seat without scratching the interior.
2: Under the hood: remove the metal hydraulic line (clutch pipe) from the Master Cylinder (12mm wrench). You can only get about 1/16th of a turn at a time, so it's going to take a while. Alternately you could undue the clutch pipe at the other end and remove it with the MC. I didn't, but if I ever do this again I will try it that way. To prevent making a mess you may wish to suction out as much of the brake fluid as you can from the reservior (you can use a turkey baster) before hand.
3: Under the hood undue the (2) bolts attaching the clutch fluid reservoir to the car.
4: In the cabin of the car, at the clutch pedal, remove the cotter pin that holds the bolt which connects the master cylinder to the pedal. You're supposed to throw this pin away and replace it. A new pin does not come with the MC, but you can get them at any auto store. After removing the pin remove the bolt itself.
5: In the cabin of the car remove the (2) bolts that hold the MC in place. You're never going to manage this without a wobble extension. The bolts are 12mm.
6: Remove the MC from under the hood. It's no doubt theoretically possible to do this without getting brake fluid all over the place. I wouldn't know, I spilled it everywhere. If you find that you have to rinse everything off use water in a big glass and pour carefully. Remember there is a big hole leading into the interior of your car.
7: Now that you have the MC out, remove the reservoir and attach it to the new one. If you removed the metal hydraulic line with the MC as mentioned in step 2 then attach it to the new MC as well. Also verify that the locknut which will connect the MC to your pedal is set the same on the new one as it was on the old one.
8: Put the new MC in. This is the only step which required two people for me. The mounting brackets for the clutch pedal shifted once the MC bolts had been removed and partially blocked the bolt holes. One person had to push them back into place in the cabin while the other pushed the MC from the other side.
9: Get the (2) bolts that hold the MC in place on. Just on and threaded, don't tighten them up yet, you'll need the play to get everything else together. If you have trouble getting the bolts on use some tape around the socket (as in the socket on the socket wrench) to lightly tape the bolts to the socket. This should keep them in place in the socket long enough for you to thread them.
10: Attach the metal hydraulic line. Attaching it to the MC was a pain, which is why next time I'm going to try using the other end of the line.
11. Attach the MC to the pedal, replacing the cotter pin.
12. Tighten everything up.
13. Reattach the clutch fluid reservoir.
14. Put the seat back (just do everything in the opposite order as step1). You're done with the mechanical part! It won't work though, you're going to have to bleed the air out of the system...
Flushing/Bleeding the Clutch Hydraulics
Overview: Without specialized equipment this is a two person job. If you have a third person you can put them to work as well. Technically all you have to do is bleed the air out of the system, but if your MC installation went anything like mine you got so much air in that you're going to flush the entire system anyway
1: Jack up the rear driver's side wheel and remove it. You will have to stick your head under the car, so have at least 2 supports (the jack and a jack stand for instance).
2: Locate the bleed screw, it is on the slave cylinder. The slave cylinder is to the left of the wheel about 30 cm back.
3: Attach a small piece of plastic tubing (the same stuff you use in fish tanks) to the bleed screw, place the other end in a catch bottle. I used an empty 12oz coke bottle.
4: Bleed the system. This takes two people. The procedure goes like this: Make certain the reservoir is full and the clutch pedal is in the "up" (transmission engaged) position. The first person will unscrew the bleed screw by about a quarter of a turn. The second person then presses the clutch pedal to the floor and holds it there. Each time the clutch is pressed air and/or fluid will be pushed out of the bleed screw. The first person then screws the bleed screw back tight, after which the second person pulls the clutch pedal back up. If the bleed screw is not fully closed when the clutch is brought back in the air/fluid that was just expelled will be sucked back into the system (instead of clean fluid being sucked in from the reservoir). Repeat this a few (no more than five) times before checking the reservoir, filling it as required.
Repeat 4 until done: When no more air comes out of the system, and there is pressure to push the clutch back up (test this by pushing it with the bleed screw closed) then you're done. Unless your intent was to flush the system. If so you'll probably be able to see when the dirty fluid is finished coming out and only the clean fluid that you've been putting into the reservoir is coming out.
Once everything is back together (but before you put the wheel back on) have someone pump the clutch while you visually inspect everything you've touched to make certain there are no leaks. You should do the same when bleeding your brakes by the way. Ask me how I know.
That's it. Put the tire back on and you're good to go. Make certain the transmission is fully disengaging: push in the clutch, put the car in gear, gently release the clutch. There should be some play before the transmission engages. If it engages immediately then it's possible that it never fully disengaged.
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