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Old 05-08-2014, 12:04 PM   #1
gsrcrxsi
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Default Clutch master cylinder failure. 2010 WRX

2010 WRX (121,000mi)
Exedy Stage 1 clutch (~17k miles ago)

So after stopping to get coffee this morning, I hopped back in my car, pressed the clutch in to start it and thought i heard/felt a slight pop from the clutch pedal. car started up fine. clutch still depressed, i moved the gear lever to neutral. pressed the clutch in again, and a more noticeable pop and the clutch pedal stuck to the floor. can be pulled up by hand.

opened the hood to have a look.
pressing the clutch does not actuate the clutch slave cylinder.
visual check shows fluid around the clutch master cylinder, but not coming from the lines.
further inspection shows signs of fluid leaking from the bottom of the clutch MC itself.
Verdict: blown MC, lines and slave appear fine

called around to some Subaru dealers for a replacement, and no one stocks it. had one rush ordered from my local dealer so i can get it tomorrow.

so i've been reading some threads, and it seems that this kind of failure is pretty rare. and a lot of people talk about bleeding the slave cylinder, but not much info about bleeding the master cylinder.

does the clutch MC need to be "bench bled" before installing into the car?
is there any specific procedure that makes this significantly different than say bleeding brakes? from what i've read, it seems like my plan of action will be the following:

1. remove old MC
2. install new MC
3. re-connect hardline to MC
4. properly adjust new MC to clutch pedal
5. "bench bleed" new MC on the car via the bleed nipped on the MC itself
6. remove slave cylinder from transmission
7. clamp slave cylinder plunger with C-Clamp
8. bleed slave cylinder while holding it above the level of the MC
9. reinstall the slave cylinder
10. drive

are there obvious flaws in this procedure?
please no snarky self righteous comments. i want to make sure i do this right and get it done properly.

thanks for the help
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Old 05-08-2014, 07:52 PM   #2
gsrcrxsi
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Oh I just thought of something else.

Is it possible that the slave cylinder is causing some resistance and extra strain on the master? Like if the piston is binding up or something.

Or does that never happen?

Just trying to be cautious. Wondering if I should replace the slave too.
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Old 05-08-2014, 08:09 PM   #3
gsrcrxsi
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And I'm looking through the FSM about the clutch master cylinder replacement. It says to bleed the clutch. But in the bleeding section, it mentions nothing about the master cylinder. Only the bleed procedure for the slave cylinder.

I don't have to bleed the master?
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Old 05-09-2014, 09:41 AM   #4
gsrcrxsi
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I must be the only person who's had to replace a master cylinder lol.

Really no one knows?
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Old 05-09-2014, 10:42 AM   #5
slatere17
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While you have the fluid emptied out, it might be a smart move to pull the slave cylinder and at least disassemble it to make sure that it is still in good shape and there isn't any visible corrosion/damage. Somebody makes rebuild kits for them if something is wrong with it, if you want to go that route. Just some peace of mind that you aren't missing anything. The fluid in my clutch lines was pretty nasty and I was only at 70k ('10 WRX).

You could also check the clutch delay valve and see if it's clogged up which might cause extra resistance. I removed it when I did my clutch swap because I couldn't remember how it went in and it made the clutch feel completely different. But I did put it back in later when I found a picture of the assembly.

As far as bleeding the MC, I only bled the slave after the clutch swap and it seems to be just fine although I could have a little bit of air in the system, hard to say. I also didn't replace the MC, just emptied it.
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Old 05-09-2014, 10:53 AM   #6
gsrcrxsi
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what is the clutch delay valve? is that a part of the slave cylinder assembly? in the FSM (and looking at the car) i dont see anything between the clutch master and the slave besides the hard/flex lines.

thanks for the reply. i understand that you didnt replace the MC, and hence didnt bleed it. but you might not have needed too since it probably still had some fluid in it. im wondering what will be necessary for a brand new master.

and yes, my fluid looks pretty black, itll get a complete flush
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Old 05-09-2014, 11:02 AM   #7
slatere17
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As I understand it, the clutch delay valve is intended to reduce the shock to the tranny in the case where the clutch is dropped so the clutch engagement is slightly prolonged. It is part of the slave cylinder. It's behind the large "bolt" on the front end of the slave, opposite side from the piston. Some of the people who have aggressive setups and upgraded clutches discuss this "mod" a lot. But I would guess it can probably destroy a tranny in a heartbeat, especially our supposedly weak 5spds.

Here's a link to a thread about it:
http://www.wrxforums.com/forums/11-s...-clutches.html
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Old 05-09-2014, 01:58 PM   #8
gsrcrxsi
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Thanks.

I'll disassemble and inspect the slave. Picked up a stainless clutch line also from IAG because why not. Lol.
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Old 05-09-2014, 08:39 PM   #9
gsrcrxsi
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Got the new master in with the new line. Not too bad in all honesty. Separating the hard line from the old flex line was a bit of a pain.

Also. One of the most stupid things I've ever seen. The ****ing pin that holds the master cylinder piston to the pedal assembly. The pin goes through then there's a retaining clip that keeps it from coming out. Then the head of the pin has this ****ing plastic arrow push pin like tip. Where you have to squeeze the wings to remove it. Problem is there's no ****ing room to get in there to squeeze them together to remove the pin.

Luckily, that portion of the pin is plastic so I just broke it off. Totally unnecessary when there's already a retaining clip that will keep it from sliding out.

Just need to bleed the clutch and I'm all good. I asked the guys at IAG about bleeding the master. They say you don't have to. And that you just bleed through the slave so I guess that's why the FSM doesn't mention anything about bleeding the master and just the slave. Just weird that the master has a bleed nipple if it's never used.
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Old 05-12-2014, 11:03 AM   #10
Kuros
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I have had SIX fail in the last 5 months

SIX.


If you want, you can pm me and i can tell you some things you can do. I have machined a new piece to replace the hardened steel plate, the spring, and the outer cap all as one piece. It's holding up pretty well for now, but with these stupid exedy clutches anything you do will fail. If the master cant fail, the slave will.


best hope is to replace the clutch itself.
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Old 05-12-2014, 11:16 AM   #11
gsrcrxsi
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well i just replaced the master cylinder and all is well now.

i sincerely hope i dont have the same kind of recurring failure youre seeing. thats a bit ridiculous.
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Old 11-03-2014, 11:03 AM   #12
Uncle Bumpy
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Default same issue

I just experienced the same failure. Exedy Stage 1 Organic clutch, installed 6 months ago. pressed the clutch in and heard/felt a slight "click", pedal came back and on next press another "click" and pedal stayed on the floor. Found that there was a failure in the metal disc in the master cylinder body. A crack right through the disc. Replacement part not available, only option is replacement of the master cylinder assembly.
Kuros: What is it about the Exedy clutch? Any specific issue that you can comment?
I have elected to prematurely replace mine with an ACT HD.

Last edited by Uncle Bumpy; 11-03-2014 at 11:13 AM.
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Old 11-03-2014, 01:01 PM   #13
gsrcrxsi
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I dont think it's an issue with the Clutch itself. I think is an issue with miles and the part that failed in the master.

I havent had any issues with mine since I replaced it.
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Old 06-16-2015, 03:15 PM   #14
gsrcrxsi
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Welp a little over a year, and the clutch master popped again -_-
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Old 07-25-2015, 10:19 AM   #15
rhinotech
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I just had this same exact issue with my 09 STi. I have a triple carbon-carbon clutch with 10k miles on it. Was in a drive thru at Wendy's and pushed the clutch to put it in 1st and heard a pop, clutch stuck to the floor, had to get towed home

Put it on the air in the garage and had a buddy push the clutch. Fluid coming from bottom of master cylinder around the snap ring in the bottom. I guess there's a seal in there?
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Old 07-26-2015, 05:36 PM   #16
gsrcrxsi
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Yup. There's a thin metal plate that breaks of bends from the fluid pressure. And it causes the seal to fail.

I replaced my master cylinder and just replaced my clutch. Now my pedal isn't so stiff and hopefully this solves my problem for good.

My theory is: clutch wears or overheats, causes the pedal to become very stiff. This means that you have to exert more force on the clutch pedal and generate more pressure in the clutch hydraulic system to actuate to clutch. The increased pressure breaks the plate internal to the master cylinder, breaking the seal. The root of the problem is usually the clutch pressure plate itself.
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Old 08-26-2015, 04:45 PM   #17
Mercvt
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I went through 2 master cylinders in my 09 wrx (within 15k miles). Ive an act stage 2 (not the 6 luck) clutch. I didn't know why at first that ikept popping my master cylinders but then I had the issue discovered that my clutch support bracket located on the firewall has failed. The tac welds were broken (all 6). I made a claim with SOA (with 110k miles on my car) an they decided to cover the repair ($1200). It works way better and feels much more solid. No more pops or squeaks either. I hope this is relevant to your situation.
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Old 08-26-2015, 05:04 PM   #18
Stretch18
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I hadn't seen this thread before, but this happened to my 2010 wrx last year. Getting up to speed on the highway, when to shift into fourth and the clutch just went to the floor. Just barely made it over to the shoulder, got her towed to my place and they did the repair.

I kind of lucked out, actually, as I was about 2 miles into a 150 mile drive up to go camping. It would have been much worse if I were stuck in the middle of nowhere and needed a 125 mile tow...

Anyway, I had it repaired at my mechanic, so I can't comment on anything regarding the actual mechanical repair. I can say that the failure was with the stock clutch at about 100k miles.
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