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Discussion Starter · #1 ·
OK, so I'm a scientist (like, uh.. literally) so I'll post this one in "Science Report" format.

Background: I had cold clutch judder/shudder last winter, cold days.. Usually went away after a while, but on particularly bad days it would linger longer, and start up even if it wasn't that cold. Ask the dealership guys to look at it, when the CD player tried to hork my discs. I parked the car there overnight.

The Tech drove with me in the car. It wasn't that cold. "Oh yeah, any car will stammer when it's cold!" He drove it really slow until it was warm, then of course it was fine. (ASSIDE: As I am a scientist, I convinced myself not to be embarassed, or pissed about the mild weather that day.)

Background, part 2: As we all know, cold starts suck. Also, as we all know, there's nothing we can do about it. Some people like to wait until the idle goes all the way down to 750rpm, some just drive it off. Generally I'm in between.

Hypothesis: The engine is just plain weak when cold. Like, pitiful, hamster running around the wheel, Model-T weak.

Method: I have performed a set of tests over the past few cold months: A) Start the car like normal. (ie, cause judder). B) Try to minimize clutch slip. C) Try to go a little faster than B cause an a$$hole in a SUV is behind you.

(A little more detail about B: basically I try to rev match from nearly idle. After starting, waiting ~1-2 min for pre-warm-up, rev up to 2k and get the wheels moving with 1-2 seconds of clutch rub. After that, clutch out completely, engine idles. Enter ULTRA GRANNY MODE, drive around the block until engine is warm, press on gas as little as possible. Ignore cars behind you, drive slow as hel... h3ll?... heck. {Grannies don't say hell.} Go from 1st to 2nd, but not to 3rd.)

Results: Method A) gives clutch judder/shudder. Method B) gives no clutch judder/shudder. (Note: I have the light flywheel.) Method C) gives a little bit of judder. Flip off SUV in repeated thrusting motion, return to Method B until engine is warmed up.

Possibilities for Future Research: 1. Were I a multi-millionaire scientist (uh.. I mean, if those existed) I'd suggest putting the car on a dyno to measure the power as a function of block and clutch temperature. I'm thinking it's really really low, like lower than a I-4 of similar displacement. I'm also guessing that noone in their right mind has ever tried to measure this before. 2. Does a bad juddering episode make future juddering events more probable? Does a "just juddered" clutch or pressure plate have any visible problems? Just curious. 3. A psychological study on the effect on aggressive drivers as to bird flipping as a function of slow driving speed. Does the repeated thrusting motion make a difference?

... just thought I'd share. :wiggles:
 

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Take this with a grain of salt because I spend hours on this site, and a Factory Five cobra site each night...but....You have way to much free time....
 

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Scientist!! ::cough:: NERD ::cough:: j/k :)

You bring up a good point about the cold engine and lack of power. I dont have this problem because Subaru gave me the heavy flywheel. No my question is, if I were to do a lighter flywheel and new clutch with same clamping force as stock, would I get teh judder?
 

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I'm in the same boat, Subaru can never reproduce the judder. I'm positive it's because they slip the clutch like noobs. They told me that the "WRX's performance clutch" is going to engage a little rougher than other clutches :rolleyes: I've found that if I let the car warm up for a loooooong time, say over 5 minutes, it doesn't judder. If I don't have time for the warm up, and it's juddering, it goes away if I slip the clutch moderately.

I've learned to live with it, and I have 3 documented (I hope) trips to the service dept. for the issue, so if it ever comes down to replacement post-warranty, I have some ammo to fight them with.
 

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Have you shown them the TSB? It's a known problem.....

With my car it's definitely NOT due to a lack of power. First, the engine has plenty of power when cold (though of course I don't really get on it). Second, if I start the car and let it idle and get up to temperature I still get the clutch judder if I'm not careful. Conversely, if I just take off with it cold and slip the clutch a couple of times to warm it up, the issue goes away.

C
 

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I've found that 1 good, big, intentional slip of the clutch will keep the shudder at bay for up to 8-9 thousand miles, at least in my case. I'm not letting any dealership butchers near my car. When this clutch goes, I will put a good one in.
 

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GV27 said:
Have you shown them the TSB? It's a known problem.....
Yeah, they know about it, but say that SOA requires them to reproduce ANY problem before they will fix/replace under warranty. They gave me the same BS about my windshield which I finally got them to replace. I just filled out the Customer Satisfaction survey 2 nights ago, and let's just say they earned a D- from me :mad:
 

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GV27 said:
if I just take off with it cold and slip the clutch a couple of times to warm it up, the issue goes away.

C
Same here.

I just live with it because the fix involves installing a weak, pu$$y clutch. :D :p
 

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bdoug said:
Same here.

I just live with it because the fix involves installing a weak, pu$$y clutch. :D :p
They don't change the clutch, just the pressure plate, my performance was not affected in any way.

I would DEFINETLY do it again...
 

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My dealer replaced the disc, pressure plate, throw-out bearing and flywheel under the TSB warranty [email protected] miles, no less.

The clutch had a little lighter feel, but better clamping force.

Unfortunately, the tech forgot to re-land the main grounding cable to the bell housing, which they suspect introduced a spike on the electrical system. End result: 3 tow-ins cuz the car would not start.

On the first trip in, they re-landed the ground cable. A week later, it was towed in again and they replaced the crank sensor (from code). On the third trip (2 weeks later), after having the car for a week and witnessing the symptoms repeatedly, I pushed them to replace the ECU. Problem solved.

All for a warranty clutch replacement.

:mad:

Curtis
 

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It's stories like yours that have kept me from pursuing the replacement further. I can live with it, and when/if it goes, I'll just replace it with something better.
 

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I had mine done at CARR subaru and have had no problems. The clutch is easier to push in and it seems like the flywheel is lighter than the previous one. They even gave me a loaner car (new legacy wagon) for trhe day while they fixed it.


- Peter
 

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Discussion Starter · #13 ·
Wade-0 said:
<SNIP--> I've found that if I let the car warm up for a loooooong time, say over 5 minutes, it doesn't judder. If I don't have time for the warm up, and it's juddering, it goes away if I slip the clutch moderately. <--PINS>
Just wanted to clearly state: the opposite works too. Meaning, if you can't wait, and/or you don't want to do a moderate to 10-second super-slip maneuver, you can rev match at idle and go real slow.

Either way, still seems like the engine's just weak. Letting it slip or going super-slow, we're compensating for having a fraction (half?) the power we're used to. Explains why the heavy flywheel works too--the extra momentum would have a more dramatic effect when the engine's cold than warm. At running temperature you probably wouldn't notice the heavier flywheel at all. (Unless you're at the track, maybe)

chevyeater: About the periodic big-slip fix, couldn't that be glazing the clutch? That would do it--just another way to make it slip more when cold. And I don't know, maybe the slip isn't noticable when hot. :confused: Anyone know why this fix works?

.. oh, and by the way, yes I do have too much time. But as long as something enlightening and educational appears on the forum now and then, my job is done. :D
 

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I couldn't tell you what actually makes the shudder go away when I do that. Your theory seems to fit klancek. There isn't much info on the actual cause of the shudder, just that it is a known problem. I figure that I am exposing a fresh layer of friction material. It still holds great after I do the big slip and let it cool off properly. Kind of similar to "burning in" a set of brake pads except I find myself having to repeat the process occasionally.

I'm sure my little trick is shortening the life of my clutch but, i'd rather enjoy a short time with it than suffer thru a long relationship. :)
 

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klancek said:

Either way, still seems like the engine's just weak.
Well sure it's a little weak when first started. All cars are. You need some temperature in the heads for efficient fuel burning. If you get into the boost though you'll have most of your power. Of course that's a really stupid thing to do with a cold engine. But it has nothing at all to do with the clutch shudder.

You don't need a huge slip to get the clutch up to temperature.
 

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PolarisSnT said:
Scientist!! ::cough:: NERD ::cough:: j/k :)

You bring up a good point about the cold engine and lack of power. I dont have this problem because Subaru gave me the heavy flywheel. No my question is, if I were to do a lighter flywheel and new clutch with same clamping force as stock, would I get teh judder?
do you know where I can get this heavy flywheel?
 

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klancek:
How long do you typically warm up your car before hitting the road? I'm fairly anal about letting the engine idle for a couple of minutes before I go anywhere. I've never noticed any weakness. I would assume that since you're some sort of scientist that you'd also know better than to flog a cold engine.

I'm pretty sure the ECU pulls timing a bit (or does something to limit engine output) until a certain water temp is attained.

Someone correct me if I'm wrong...:wiggles:
 

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Discussion Starter · #18 ·
RayfieldsWRX said:
klancek:
How long do you typically warm up your car before hitting the road?
Usually, a minute, or 2. More if it's BF-in cold. I don't see the point of letting it idle after the revs start falling past 1k--I like oil to flow over my engine. :D About the timing, uh, I dunno the mystical inner truths of our ECU, either. ..maybe? About the flogging, word up my sibling! Glad you got the point of my post. ;)

myton78: If you have a car Jan 2003 era, you probably already have the heavier flywheel. Check around the forum for a copy of the relavent TSB and check if your VIN.

SO FAR Driving slow seems to work. I get judder if I try to go too fast, before it's warm. I live too close to the damned highway, so I have to take the long way to the on-ramp. :(
 

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next week on subaru science... we will be review the WRX's ability to time travel... its a known problem and we should fix it... i hate getting to where i need to go so fast...
 

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klancek said:
Usually, a minute, or 2. More if it's BF-in cold. I don't see the point of letting it idle after the revs start falling past 1k--I like oil to flow over my engine
This is an unresolved issue to me. I've heard it said before that idling your engine unnecessarily is running it with inadequate oil flow, but don't we do this anyway, when in very heavy traffic, or at stoplights? Seems to me like Subie engineers would design an engine that's able to run in place without self-destructing.

word up my sibling
You could make a case that we are professional "siblings", since I work as an engineer. I'm like you, but I have to live in the real world. :p :)
 
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