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Old 11-10-2018, 07:11 AM   #1
viper_crazy
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Default (Long read) Clutch slip.......when cold?

Right, so interesting issue that I'm gonna have a poke around today. Been trying to find any topic or thread on something similar and have been coming up empty handed.

Relevant info:
2008 WRX w/ Factory 5mt (~120,000/~75,000 km's/miles on trans)
New Exedy Stage 2 Cerametallic w/ Streetlight flywheel (~20,000/12,000 km's/miles)
Stock clutch Master and slave
Firewall bracket fixed and secured
New fluid and bleed 20,000 km ago (almost 2 years now)
Solid transmission mount

Not sure if it's relevant:
Weather/temps the last few days have been below freezing, even at the warmest it's below freezing, with snow fall.

About 2 or 3 days ago, on my commute to work, I attempt to accelerat at a quick pace (half throttle, say) as I am straightening up from a u-turn (a legal one) and as I do so, I realize I've misplaced my gear. I realize I was in third as the clutch was roughly half way engaged. Quick downshift, and I WOT out of my mistake in second gear and my clutch slips while my foot is completely off the clutch pedal. I immediately back off and try partial throttle and I can feel it slip again. Shift up to 3rd and try partial throttle @ ~8-10psi boost around 3k rpm and starts to slip again, but not quickly, so I drive like a normal person and as I'm 2 minutes from work, I try another 3rd gear pull at 3k and no slip.....what gives? This has been consistent for the last few days, and I haven't driven aggressively (I mean, it's rush hour traffic, there's not much chance to). Of course, no slip when I drive like a grandma.

I'm super conscious about resting my foot on the clutch and I take it off when I'm not accelerating to speed or slowing down, even then I pull my foot off to hover over the pedal.

Odd thing is, this seems to happen when when my engine temp is around 1/4 warm. Fully warm and I cannot....and I mean, CANNOT get it to slip in any gear under any load.

Since my u-turn, I've also noticed a shutter worse than before. It's stage 2 clutch so it's been a bit chattery from the get go but it's been worse last few days. Been driving rather gingerly.

Last thing to add, and I don't know why I haven't noticed before if it's changed or not, but the clutch pedal has like an inch or so of freeplay (hard to see the travel in the drivers seat so it's a guess) at the top before it starts to disengage the clutch.

Any ideas on what to check check first? I really hope it's nothing expensive as I'm flat broke at the moment. I'm thinking clutch delay valve issue, if not clutch slave or master cylinder issue (fluid level has remained constant so I'm confident there are no leaks), maybe even a broken engine mount to cause shudder?

There was no slip before my u-turn. Again, I'll be checking things out today, but thought I'd get some feedback from anyone who's experienced anything like this. Only fluids that leak is from the power steering line under the car but I doubt (hope) any got in to the clutch.
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Old 11-10-2018, 07:23 PM   #2
viper_crazy
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Well, short from taking my trans/engine out to inspect clutch things (which I inspected last June when I replaced the clutch fork), the only thing I could find was the clutch slave may have been pushing against the clutch fork enough to cause the slip.



I have a Verus Engineering clutch fork as I have an Exedy Stage 2 clutch, I wanted a beefier clutch fork. Back in June, when I installed the clutch fork, I remember one bore on the slave didn't line up with the threads on the trans. You could get one bolt in, but not the other. A bit of muscle, leverage from a screw driver, and holding your tongue the right way, got the other one in. No issues until it got cold, maybe?



So, I took the slave out, drained the fluid, did the slave delay valve delete, put it all back together, filled with a brand new, freshly sealed brake fluid and bled and no change in slip.



So, the old ticker got to thinking. Since the slave push rod isn't fixed in place, I trimmed off a bit of the slave end of the cylinder, little by little, enough until the slave could be put in place without having to muscle it in or use screw drivers hold it in place.



So far, no slipping, but I'll keep an eye on it over the next few days. I may have to do some clutch deglazing.....still a little unsure why the increase in clutch shudder, but hopefully that goes away with some normal use.



Back of my head says something happened with that u-turn to cause excessive shudder, but had a look at mounts and nothing obvious is standing out.
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Old 11-11-2018, 05:24 PM   #3
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Shortening the clutch slave rod help only a little. The slippage isn't as bad, but it's still slipping. Will have to investigate in a few weeks, but I'll report back.
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Old 11-11-2018, 08:58 PM   #4
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Back when I had my VW I had an issue with it slipping when cold. It started after taking off in 2nd (couldn't shift to first unless all the planets aligned properly). It continued to slip for a few days of gentle driving until it stopped. I would just drive it as if you were bedding in a new clutch in case it ended up glazing.
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Old 11-11-2018, 09:16 PM   #5
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I've had that same thought so I've been doing just that the last few days.

Came across this TSB, not sure if it applies to my car, but I'm going to investigate this next weekend.

https://forums.nasioc.com/forums/sho...3#post36011693

Quote:
Originally Posted by fire_chimp View Post
SOURCE: Subaru Tech Tips
TITLE: Clutch Appears to Be Slipping
APPLIES TO: Impreza WRX
SERVICE TIP:
If you encounter an Impreza WRX with a customer concern that the vehicle's clutch slips under hard acceleration but drives normally under light acceleration, it might not be the clutch that's the problem. Before you yank the transmission to get to the clutch, put the car on the lift. Start the engine and put it in gear. Release the clutch and see if all four wheels are turning. If they are not, inspect the one that is not turning. The Technical Support Line has received a couple of calls with the above concern and in both cases the retaining clip on the inner end of the rear axle shaft has come off. This allows the axle shaft to move outward slightly to disengage from the side gear of the rear differential but, the wheel bearing retainer assembly will not allow the axle to come out completely. Since these vehicles have a limited slip rear differential, there is enough drag on the axle to move the car under light acceleration but not under heavy acceleration.
The repair is simple. Just push the axle inward and it should reengage the retaining clip. If this procedure does not work, then you will need to remove the rear differential cover to re-install the clip and/or examine the axle. If the vehicle is an Impreza WRX STi, you might find that the vehicle won't move unless the DCCD is in the 'Manual' mode. In this case the cause may be a failed rear axle shaft or joint assembly
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Old 12-09-2018, 01:29 PM   #6
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To update, ask axels are fine. I haven't been able to inspect the clutch, but it's been slowly getting worse. RPM's rise while speed does not. I guess some how a brand new clutch is goosed within 12,000 miles.
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Old 12-19-2018, 10:18 PM   #7
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Any chance your rear main seal is leaking? Exedy makes a pretty darn good clutch in my experience so 12K seems way too soon, but maybe the case. Anyhow, a leaky rear main could cause some slipping, but there really is no good way to check without pulling the motor.
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Old 12-20-2018, 01:39 AM   #8
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I've thought of that. I haven't been able to properly check. I did have a peek down the top inspection hole and didn't see much out of the ordinary, but it's on the list. I don't think it's the rear main as it has as much mileage as the clutch though.

Last edited by viper_crazy; 12-22-2018 at 09:43 PM.
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Old 12-22-2018, 08:00 PM   #9
bp05obxt
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Default (Long read) Clutch slip.......when cold?

Throw out bearing may be getting hung up on the snout of the transmission and not allowing the clutch to fully engage. This also causes the transmission shudder you speak of. The best fix is a snout repair kit and throw out bearing from TSK; if this is a relevant issue.
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Old 12-22-2018, 09:34 PM   #10
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That's the most logical explanation I've read so far. Since I'm planning on taking the trans out anyways, might as well get all that and replace it regardless.
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Old 12-23-2018, 10:57 AM   #11
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Quote:
Originally Posted by viper_crazy View Post
That's the most logical explanation I've read so far. Since I'm planning on taking the trans out anyways, might as well get all that and replace it regardless.


Keep in mind to inspect the clutch it may have been glazed and damaged too much from the slipping that it may warrant needing changed regardless of other issues present. Good luck!
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Old 12-30-2018, 12:27 PM   #12
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That's my worst fear. Can't exactly drop the money on a new clutch kit at the moment. It grabs fine any other time.

To update, I'm thinking the u-turn may have been more so coincidence.

Took the slave cylinder off and not sure why I'd didn't notice before, but the Verus clutch fork is butted right up against the transmission housing where it comes through the fork opening when clutch is fully engaged. I took the boot off to allow any extra millimeters and any difference may have been in my head, but any little bit helps, I guess.

Which leads me to believe that maybe the stack height between OEM flywheel and clutch kit is a smidgen shorter than my current Exedy LWFW and Stage 2 clutch.
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Old 12-30-2018, 02:43 PM   #13
CarmelValleyWRX
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to me it sounds like your on the right track looking at the fork/slave assembly. it should all float/rattle freely when the clutch is out. it sounds like its being held in tension by something which is casing your clutch to slip. the fact that you trimmed something and the slip got better means you found a problem aria there. it could be that the clutch disk has gotten thinner over time and its now exposing this issue of the fork/slave components hitting and interfering.
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Old 01-14-2019, 10:18 PM   #14
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So, couple of things I've learned so far:

1) I'm apparently a lot lazier than I gave myself credit for.

2) I may have prematurely ruled out the axle issue.

3) You can successfully space the bell housing surfaces 1/8" without breaking anything or having anything go catastrophically wrong.....I'll get to that.

So, I have not been able to inspect any clutch or bell housing internals. Been super busy and I'm slightly afraid that the only vehicle is gonna be put out of commission.

To get my mind off of other anxieties, I decided I'm going to look up what's all needed to swap a 6mt into my car, both as an upgrade and solution to this problem (expensive fix, I realize, but worst-case-scenario me is preparing for the worst even though I can't afford a 6mt swap.... Moving on...). I came across some info that said the speed sensor on the 2008+ (aka "GR" series) is on the wheel, not the trans. Which got me thinking about the signs to determine axle slip vs clutch slip, and that is basically that if the speedometer increases with tachometer, it's probably axle slip.......but with the speed sensor being in the wheel, the wheel isn't slipping so the speed would never increase. That said, when the car was on the lift, all the axles seemed fine, but I'll be honest, I don't think I have a clue what I'm looking for. No excessive play or wriggling about but I don't know.

I have a funky feeling my motor mounts may be at play. I have the round fluid filled ones and at 122,000 km's (~75,000 miles), I doubt they've ever been replaced, as I'm getting a bit of chatter when engaging the clutch and excessive vibration at idle along with the odd clunk over some bumps. I'm thinking theres some amount of torque lift pulling an axle out once boost climbs up a bit. Considering 'Booki' on this forum had axles break due to bad mounts....see where I'm going with this logic (even though I asked him already).

To cure the top of the clutch fork from bottoming out on the bell housing, I spaced the mating surfaces 1/8". I now have a bit of play and can even compress the slave a bit, so I've relieved any pressure that may have been at play on the pressure plate, which still leaves the possibility of a broken throw out bearing with a piece stuck in the fingers of the pressure plate? But I did it to test and problem still exists so, I guess it's a set of Group N motor mounts.

If that don't fix it, I think some gasoline and a lighter will do the trick.
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Old 01-15-2019, 07:31 AM   #15
bp05obxt
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There is a rubber grommet on the opening where the fork comes out of the trans. Pull that an look in. You donít need to separate the trans to see in there. Donít make this too complicated for yourself..
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Old 01-15-2019, 09:10 AM   #16
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Quote:
Originally Posted by bp05obxt View Post
There is a rubber grommet on the opening where the fork comes out of the trans. Pull that an look in. You donít need to separate the trans to see in there. Donít make this too complicated for yourself..
Tried it and can't see a thing aside from the fork pivot.
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Old 01-15-2019, 09:41 AM   #17
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Quote:
Originally Posted by bp05obxt View Post
There is a rubber grommet on the opening where the fork comes out of the trans. Pull that an look in. You donít need to separate the trans to see in there. Donít make this too complicated for yourself..
Quote:
Originally Posted by viper_crazy View Post
Tried it and can't see a thing aside from the fork pivot.
I have a cheap ($15US) lipstick camera on a long USB cord. For things like checking a fork or ToB, you plug the camera in a Windows laptop, and lower the camera down through the boot. It has LED's on it to light the area.
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Old 01-15-2019, 10:09 AM   #18
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Quote:
Originally Posted by Charlie-III View Post
I have a cheap ($15US) lipstick camera on a long USB cord. For things like checking a fork or ToB, you plug the camera in a Windows laptop, and lower the camera down through the boot. It has LED's on it to light the area.
I know someone who has one, actually. Ima steal it....for a day or two.
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Old 01-15-2019, 02:34 PM   #19
Charlie-III
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Quote:
Originally Posted by viper_crazy View Post
I know someone who has one, actually. Ima steal it....for a day or two.
Great!

I have looked at some clutch assemblies to have an idea on what is wrong before pulling parts.
Did some MacGuyver work until parts showed up......helps to know needed parts BEFORE yanking big bits and then waiting on parts.


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Old 01-15-2019, 04:00 PM   #20
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i have a feeling that the WRX transmission/rear end doesn't have aggressive enough diffs to drive the car forward very fast at all if one of the axles were to be loose. its really easy to one tire fire the WRX around tight turns.

i am still leaning toward TOB/fork issues since you had no play and then gained play by spacing the bell housing.
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Old 01-15-2019, 09:14 PM   #21
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Quote:
Originally Posted by CarmelValleyWRX View Post
i have a feeling that the WRX transmission/rear end doesn't have aggressive enough diffs to drive the car forward very fast at all if one of the axles were to be loose. its really easy to one tire fire the WRX around tight turns.

i am still leaning toward TOB/fork issues since you had no play and then gained play by spacing the bell housing.
I guess I'll be finding out. I doubt it's the clutch fork, though, as the current fork is a Verus Engineering fork. My stocker broke last June and after a bunch of digging around I found out OEM forks don't like upgraded pressure plates.
Quote:
Originally Posted by Charlie-III View Post
Great!

I have looked at some clutch assemblies to have an idea on what is wrong before pulling parts.
Did some MacGuyver work until parts showed up......helps to know needed parts BEFORE yanking big bits and then waiting on parts.


Exactly! And the mystery of it all is also what's holding me back. 'What parts do I need? Do I just order everything and hope for the best? What if it's something simple?' and so on.....
I'll find that endoscope camera. Apparently, it was left in my garage, so Ima have to dig around.
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Old 01-15-2019, 09:23 PM   #22
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I've scheduled this Saturday afternoon to checking out what I can see. Maybe one of these evenings if I can swing it. I rent a small garage and it's not really close to me that I can just run out to the garage for a few minutes.

Related or not, engine mounts are definitely shot.
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Old 01-19-2019, 06:32 PM   #23
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Well, that was basically a useless endeavor. Couldn't really see anything. I took some vids with the endoscope if anyone is interested but nothing obvious (to me) stood out.

But I guess just call it for what it probably is. Clutch slip.

Car is practically not drivable now. I can barely accelerate in any gear without some funny business of some kind.

I'll keep this post updated just to close it off for any future readers.
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Old 02-17-2019, 06:03 PM   #24
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Quote:
Originally Posted by CarmelValleyWRX View Post
...it could be that the clutch disk has gotten thinner over time and its now exposing this issue of the fork/slave components hitting and interfering.
I believe this is exactly what happened, but why? Not sure. Exedy says the stack height of their LWFW and Stage 2 kit is the same as OEM, but I didn't have any spacing issues with the OEM flywheel, clutch kit, and fork before the spun rod bearing and motor build.

After the build:
New EJ25 case halves, new STi crank, Exedy LWFW and Stage 2 kit, and OEM clutch fork. Shortening the slave push rod and spacing the bell housing helped marginally but the clutch was likely too far gone to save, unfortunately. Only 15,000 miles...

The OEM clutch fork was also bottoming out as well with the Exedy setup. There's a rub line at the slave end where it was hitting the bell housing, which lead to it's failure. Which is why I decided to upgrade to the Verus fork. My theory is the OEM fork flexed enough to allow full engagement, which is why it lasted nearly a near and a half before the pivot burst through the fork. Not too much flex with the stronger Verus unit causing partial disengagement.

I have since purchased an Exedy Stage 1 kit and will be test fitting it a few days to see if the same clearance issues exist and I plan on taking some measurements to see differences, if any, between the two Staged kits.
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Old 02-26-2019, 08:35 PM   #25
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Left is old Exedy Stage 2, right is new Stage 1.



Did a test fit with new clutch before prep and cleaning and everything is as it should be.



So that pretty much closes this thread. Thanks all for your help and feedback.
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