Clutch Master Cylinder DIY

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.

Nice write up.

To avoid spilling fluid all over the place when removing the cylinder, remove it with a turkey baster first.
http://www.nsxprime.com/forums/showthread.php?s=&threadid=20258

Excellent, thank you!

ADD THIS TO THE FAQ PLEASE.

How long did it take you?

D'Ecosse:

Thanks for the link (and the advice). Somehow I missed that thread when I did a search before my install. Awsome that you have pictures of the slave replacement! I'll do that sooner or later.

White94:

It took me an afternoon, maybe four hours. That's for someone with no real experiance working on cars, if I had to do it again I could probably do it in an hour. I also had some issues with a SpeedBleeder I tried to install on the slave, which ate up some time.

Cool, thanks.

FWIW, I have seen where several model speedbleeders have been recommended for the slave. I used SB8125 with great results.

White94 said:

FWIW, I have seen where several model speedbleeders have been recommended for the slave. I used SB8125 with great results.

Click to expand...

Oh I'm pretty certain it was me, not the speedbleeder. At the time I had never bled anything so I had no instinct for how it should work, and there was a lot of air in the system. It was probably good for me to have to do it the traditional way.

I've since used speedbleeders on the brakes and they worked like a charm. Next time I touch the clutch system I'll try the speedbleeder again, I'm sure it will work fine now that I have a better idea of what I'm doing.

dgaetano said:

...... The procedure goes like this: Make certain the reservoir is full and the clutch pedal is in the "up" (disengaged) position.
...... Make certain the clutch is fully disengaged: 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.

Click to expand...

Not to be picky Daniele (just to be sure of accuracy of terminology for the FAQ):
When the pedal is in the "up" position, clutch will be engaged; depressing the pedal will dis-engage the clutch (unless of course it isn't bled or working properly!)

D'Ecosse:

OK, you cought me. I've edited the post. Which is not to say that it's correct now, just different

I also took the liberty of adding the brake fluid removal trick you mentioned. Thanks again!

-Daniele

FYI, Daniele's writeup is on the money. I did not have a wobble, and got one before starting. It was a lifesaver. I might offer a coupe more tips.

#10 is MUUUUUUUCH easier if you undo both ends of the fitting coming out the of the MC. That is NOT how it is written up in the service manual, but TRUST ME.

You can do this without taking the seat out, but it isn't comfy. Prepare your vocabulary with some very colorful words.

Order a speedbleeder and get a vacuum pump to bleed the system. You'll thank me.

White94 said:

You can do this without taking the seat out, but it isn't comfy. Prepare your vocabulary with some very colorful words

Click to expand...

The added work in removing/re-installing the seat is nothing compared to the inconvenience (uner-statement) of trying to do it in-place. Anyone contemplating this, do yourself a favour & just take it out - only 4 bolts & a couple of electrical connectors to unplug. It's just not worth NOT doing!

Great write up! This was spot on and a big help!!!

I just did this today and thought I'd add a few things that made it even a little easier... for me.

When removing the clutch pipe, I loosened it first with a line wrench (looked like a good nut to round off with a regular end wrench) and then used a 1/2 length shorty wrench which allows you to get almost 1/2 turn at a time!

Definitely loosen the other end of the tube to aid in getting the end positioned and started at the master (I didn't take it completely off though)

When installing the master cyl., I used a short bolt (~8mm X 2-3cm) as a drift and inserted it going from right to left to temporarily attach the pistonrod to the pedal. This holds the master and two thru bolts in place and allows you to get the two mounting nuts started w/o someone pushing on the master from the outside. Also, wrapping about 2-3 layers of teflon tape on the nuts will make a tighter fit in the socket so no chance of falling off.

Bleeding was no issue. Pump the pedal slowly (with the cap off of the reservoir) until no bubbles come out of the master and you begin to feel pressue. Attach a piece of clear tubing to the slave bleeder and proceed with the pump, open /close valve method. Then leave the bleeder valve open and pump slowly while someone adds brake flluid. Not sure what a speed bleeder is, but I bled the syslem very quickly once I got pressure on the master cyl., which takes a little while.

I did not remove the seat. It's a bit tight, but I'm 6' 2", 210 lb and 46 y.o. and I had no problem doing this job with the seat in place.

I did the Master and slave two days ago. It took about 1.5 hours for the master about 30 minutes for the slave and 1.5 hours for the bleed. Now I am 6'1 275lbs and found it challenging to get the job done due to the small space under the dash but was able to get done with just a samll amount of frustration.

I did take the seat out. Took less than 5 minutes to do so and well worth it. Hardest parts was getting the cotter pin out from the clutch petal. spent about 15 minutes trying to pull it out then took a small saw (hacksaw blade would work) and cut the cotter pin right at the base and was able to knock the pin out with a long screwdriver. I did remove the clutch pipe form the MC and the block it goes into and this made it really easy. Second hardest part was getting the pin that attaches the MC to the pedal through the hole. Took about 10 minutes.

I then moved on to the slave cylinder. I was able to do it all from the top. (I have an after market air cleaner assembly). This was really quick and removing the hose from the slave was the hardest part. I did replace the gasket on the hose portion. I cut the old off with xacto blade and slid the new one on.

Now for bleeding I could not get any pressure into the system. I tried both the two person method and single person with a speedbleeder. I ended up putting a small bottle of brake fluid near the slave cyclinder filled with fluid then opened the bleeder valve and ran a tube form the bleeder to the bottle of brake fluid. I pumped several times and then felt some very light resistance and then closed the bleeder. This sucked up some of the brake fluid and "primed the system somehow) I then changed the stock bleeder to a speed bleeder and was able to bleed the system. I ran about 10 reservor fulls of brake fluid through the system to make sure it was nice and clean. Bleeding took about 1.5 hours but if I would have done it they way I got it to work would ahve taken about 15 minutes.

I was vaccuuming leaves from the NSX driver's side carpet on Monday and found a spot on the mat. I looked up & surprise! - The clutch master is leaking. So, I ordered a new master that arrives Friday. This is the first replacement, car has 66,000 miles.

Thinking ahead, I've noticed comments in this string on the mess made from fluid spilling during removal of the old unit.
Question: Why not just open the bleeder on the slave and pump the fluid out? Would that remove enough to reduce the mess under the hood?

If your master still has fluid in it - opening the bleeder should drain it fairly quickly. Should make for a neater replacement.

I suggest you this is easier to do from "above" than below unless it is really easy for you get under the car. Remove the airbox and the slave is visible and easily reached.

I think I won't be the only one who suggests you replace the slave too. It could fail in 10K miles and you'll have to drain/flush again.

My master failed a month ago - 65K miles. Although the slave gave no signs of a problem, I replaced it. The old unit looked "ok" at removal, though some of the rubber didn't look great.

In step #7 make sure you swap the rubber seal(that meets the body) from the old to the new MC.

Also if you have a stock clutch the MC come preset for the rod depth.

Regards,
LarryB

The part arrived late yesterday, and I did the install this morning.
Comments from my experience per the step numbers:
0. Open the bleeder at the slave cylinder and drain the fluid. Doing that, I didn't spill a drop.
1. I didn't remove the driver's seat. I put a piece of carpet on the garage floor, sat on it, and was able to reach everything. (I'm 6' and 185 lbs and never found myself bumping into the seat.)
2. Disconnect the brake MC level sensor wires and move them out of the way. This seemed an obvious thing to do and made access to everything else a little easier.
I undid the clutch pipe at the block, removing it with the MC. Hint: loosen the pipe at the MC a tiny bit before removing the MC; its easier than removing the pipe with the MC out & on the bench. My 12 mm flare nut wrench bumped up against the brake MC reservoir such that I had no room to turn the wrench to loosen the pipe nuts. I loosened the two mounting nuts on the brake MC about 3 turns each, which allowed just enough movment of the brake MC for turning the flare nut wrench.
7. Larry covered transferring the rubber body seal to the new MC. I found a lot of "black dirt" (probably rubber or oxidized aluminum) in my reservoir, and therefore flushed that with clean brake fluid before mounting it on the new MC. This was far more "dirt" than I saw in the reservoir in previous routine flushings.

Note that I purchased a Wagner # CM140593 MC from Rock Auto - $112.94 including shipping. Well, its the OEM device - same casting marks (NISSIN 5/8, etc), same length adjustment on the push-rod, "Made in Japan" on the box label.

I know this is an old thread, but I came across it before I completed and Master/Slave replacement this morning. I hope this may be useful to a future user.

Note that some people say they took hours bleeding the clutch, and others did it so fast it isn't even mentioned. I was in the first category and getting frustrated. What could be wrong? I gravity bled this line, vacuum bled it, and used the up/down, close/open methods by myself. Couldn't get a pedal.

While waiting for a friend to do a better up/down bleed this morning, I noticed the back of the car was higher than the front. I had simply jacked up the left side of the car and put it on jack stands. The rear was lower than the front, 4 notches to 5 for the front, but even so when looking at the car the butt was higher. I lowered the back to 2 notches (carefully!) and noted the flow during a gravity bleed was significantly more robust. My friend arrived, five or so up/down pumps and we were done; the pedal was strong and all was well -- and finished.

Was it the more vigorous pump at the master, or reorienting the car? Don't know, but I suspect it was lowering the rear.

If this helps a future DIYer, great. It sure helped me.