DIY: Clutch Master Cylinder (CMC) replacement and rebuild

fillerbunnie

Hey everyone,

After looking at the cost of a rebuild kit vs replacement kit for the CMC, I thought I would do a quick DIY for anyone thinking about replacing it. The rebuild kit is about the $20 mark (vs a replacement of $120), and the actual process of rebuilding takes less than 20 minutes, requires no specialty tools and is dead simple. Unless you value 20 minutes of your weekend at more than $100 or your CMC has been cut in half by a stray flywheel, I highly recommend giving this a go!

The master cylinder & rebuild kit are not stocked anywhere in Australia (Where I'm from) - The dealer said 6 weeks lead from Japan, and while I'm at it quick props to Nick @ Concept Z for getting me one delivered within 72 hours!

Excuse the filthiness of my engine bay, my car travels on unsealed roads a lot (Or that's my excuse anyway!)

Now to it...

Parts you need:
Rebuild kit for the CMC (around $20, Nissan P/N#30611-JK025)
Rubber grease (Critical. I used Bosch RG17 as it is designed exactly for this, but any automotive rubber grease should be OK. Do not use a non-rubber grease!)
Silicone grease
Fresh Brake fluid

Tools you need:
2 x Jack stands & a jack
Oil drain tray for old brake fluid
10mm flare nut spanner (idealy, but you can make do with a normal open-ended one)
14mm open-ended spanner (if you have a ZSPEED CSC)
12mm socket wrench & extensions
Retaining ring pliers/snap ring pliers for a very small retaining ring hole. (If you don't have these, at a pinch you can use a cheap pair of needle-nose pliers and file the tips down.)
Bench vice for holding the CMC during the rebuild

Difficulty:
I would give this a 4/10 difficulty, only because of the tight working spaces. Even including the rebuild, nothing is particularly difficult in this job.

People required:
1 person, however a second person is useful to hold the CMC in place when you are trying to put the nuts back on, and maybe also to re-install the CMC retaining ring while you hold the piston down. This isn't a deal-breaker though.

Time required:
Allow up to 3 hours, but realistically you could do it in as little as 1 hour working quickly. The actual CMC rebuild only adds on about 20 minutes.

Steps!
1. Jack the front of the car up on stands
2. Slide underneath the car and locate the bleed valve. It is on the left-hand side of the transmission and will be mounted next to a rubber dust boot. With lines going into the transmission (See attached images).
3. Open the bleed valve a bit (requires a 14mm (to hold the fitting) & 10mm (to open the valve) spanners for the HD CSC, I think only need a 10mm for the OEM bleed valve) and let all the brake fluid drain out. This will take a few minutes – Give the clutch a few slow pumps if it does not start draining.
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4. While draining, remove the cowling from around the clutch and brake reservoir. This is only held in place by a few plastic press-studs. Once drained, remove the hose from the clutch reservoir to the master cylinder (See attached image, sorry I didn’t get a good shot of the hard line).
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5. Now remove the hard line from the master cylinder. This can be done with a 10mm (I think, may be 12mm?) flare nut spanner, but if you only have an open-ended spanner be careful you don’t strip it. Minimal fluid should leak out as the system is drained.
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6. Using your best Tetris skills, navigate into the driver’s floor well and remove the retaining pin and clevis pin from the master cylinder clevis (see image).
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7. Now remove the two 12mm nuts holding the CMC in place. These are not done up tightly, but the top one is a bit difficult to get to. I used an 8” extension + 4” extension + 12mm deep-socket on a ¾” drive socket wrench.
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8. At this point, you can slide the CMC out from the engine-bay side. Don’t lose the rubber gasket (unless you bought a replacement :lmao: )
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9. Set up a clean work space to rebuild the CMC.
10. Remove the clevis, retaining nut and rubber boot. You can discard the old rubber boot as this is being replaced.
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11. While applying pressure to the CMC actuator rod, use retaining ring pliers (or your home-made needle-nose pliers) to remove the snap ring/retaining ring from the CMC. Slowly release pressure on the rod or you will end up with brake fluid and CMC parts launching all over your garage. (I didn't get a photo of the CMC end pre-rebuild, but see step 20. for a photo of what it would look like minus the grease, showing where the retention ring is)
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12. Discard the old retaining ring and piston/spring assembly.Keep the washer and actuator rod.
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13. Clean any brake fluid out from the CMC bore with a cloth, then examine the bore for any scoring/marking/damage. It should be perfectly smooth. Use a finger to feel for any damage as well. (I imagine damage would be quite difficult unless you have a catastrophic spring failure, so is very unlikely, but if you have any bore damage your best bet is to buy a complete new CMC at this point).
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14. Apply a light coating of automotive rubber grease to the bore of the CMC. I used Bosch RG17, but any good quality automotive rubber grease will do. Rubber grease is NOT the same as lithium grease/silicone grease /bearing grease/WD-40/Shaver oil/dry-lube/PTFE/turtle wax/olive oil (you get my point) and if you use any of these you WILL destroy the seals very quickly. Go buy some rubber grease if you don’t have any!
15. Remove your new piston & spring assembly from its packaging, and apply a coating of automotive rubber grease to spring & piston assembly.
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16. Apply a small amount of silicone grease to the piston cup (where it meets the actuator rod)
17. Put the CMC body into a bench vice for reassembly.
18. Slide the new piston into the bore of the CMC and reassemble as per the picture (or your memory if you remember the order it was in before it sprung out and launched brake fluid all over your garage ). Note the washer is keyed (bent inward) so make sure you put it the right way around.
19. While applying pressure to the actuator rod to hold everything in place, install the new retention ring.
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20. Apply a small amount of silicon grease to the base of the actuator rod/where it meets the washer.
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21. Re-install the clevis retention nut and clevis arm. NOTE: I found if I screw the retention nut and clevis arm all the way in as far as they can go, it will drop the engagement point of the clutch to about half way up the pedal (as opposed to right at the top of the pedal) which gives a far more natural clutch engagement. I have attached the service manual spec which has the OEM position & tolerances anyway.
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22. Hand-operate the CMC a few times to make sure its action is nice and smooth.
23. You just saved yourself $100 (minus the $4 of rubber grease you bought)
24. At this point, re-assembly is just the reverse if what you have done so far.
25. Slide the CMC back into place and either have someone else hold it there or jam a rag behind it to hold it in place.
26. Jump back into the foot well and re-install the two nuts holding the CMC to the firewall. The top one will be annoying to seat.
27. Re-install the clevis pin and retaining pin
28. Head back to the engine bay and Re-attach the CMC hard-line (to 16.2nm/12 lb-ft for those of you with a flare-nut toque wrench ) and hose from the reservoir.

Bleeding the system:
Firstly, I have the ZSPEED HD CSC. General consensus is that this is miles easier to bleed the clutch system with the HD CSC than the OEM system. For the ZSPEED CSC, the bleeding process was basically a slightly more extensive version of the one used when replacing the CSC itself. I believe this is because when you replace the CMC you can’t have it gravity draining properly until all the air is evacuated from the CMC. Still, it is a simple process:

1. AT ALL TIMES DURING THE PROCEDURE, MAKE SURE THE RESERVOIR STAYS FULL. (So step one is fill the reservoir, and keep it full )
2. Open the bleed valve
3. Let it gravity bleed for 3-5 minutes, or until it stops draining.
4. With the bleed valve slightly open, operate the clutch pedal by hand slowly ~10 times, stopping for a couple of seconds between pumps of the pedal.
5. Let it gravity bleed for 2-3 minutes
6. Repeat steps 3 & 4 until the system gravity bleeds without stopping. I only had to do this twice.
7. Close the bleed valve
8. Operate the clutch pedal 10-15 times
9. Open the bleed valve
10. Let it gravity bleed for 2-3 minutes
11. Repeat steps 7 to 10 once more.
12. All done! Pump the clutch a few times to build up pressure in the system and you should be good to go.

I won’t comment on the bleeding process for the OEM CSC, but I have attached the service manual’s version. The one described above for the ZSPEED CSC may work as well, so feel free to try it and report back!
OEM Bleeding procedure:
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After rebuilding the CMC and adjusting the clevis & retaining nut as far down the CMC actuator rod as it could go, I now have a clutch engagement/take-up about half way down the pedal. The car is hugely more manageable now than it ever was with the OEM clutch and I highly recommend anyone with clutch issues going down this path (or at least trying it). For $20 and a couple hours of your time, it is well worth it!

Good luck!

Attached Images

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Kzonts

Nice work! Thank you...

I have the RJM clutch pedal so I would probably need to set the CMC to stock settings.

__________________
2019 Magnetic Black Roadster
FI Exhaust | EVO-R Rear Diffuser | Artwork Bodyshop Front Splitter | Tuned By Specialty Z

JARblue

Excellent write-up. Repped for that

Kzonts, I've done bleeding with two different RJM clutch pedals on my car and several on other vehicles with RJM clutch pedal (all rev2 or later). There is no need to mess with the pedal adjustments unless you have a rev1 pedal

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Kzonts

Thanks. That's what I was thinking as well. My clutch is nearly perfect at this time but I'll be replacing the CSC in a few weeks along with the CMC. But I'm taking it to SOHO Motorsports. :-)

__________________
2019 Magnetic Black Roadster
FI Exhaust | EVO-R Rear Diffuser | Artwork Bodyshop Front Splitter | Tuned By Specialty Z

TreeSemdyZee

Thanks for the write-up.

Question though. On the Zspeed bleeding technique, is the bleeder open during step 4?

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Borla S-Type | Motordyne | Z1 (lots) | South Bend | K&N | Nismo/Nismo S-Tune | Eibach | Aerojacket | Fujimara | Spl | ZSpeed Performance | Kenwood-Infinity-Sound Ordnance | Whiteline | Ecutek | Hotchkis | Clazzio | VQ Vortex |Morimoto XB |Dynosty Tune 329.64hp 265.73 ft/lb

fillerbunnie

Sorry, yes it is open slightly. I have updated the instructions

Jayhovah

Really great write-up!

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2013 Gun Metallic Sport - Gamma V3 Twin Turbogized
DIY Gamma V3 TT Install * Jayhovah's Gamma V3 TT Install Pic'Z and Vid'Z * DIY: Washer Reservoir for the Boosted

Akshaya

Great write up! saving this one!


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