OK. I am new to this car. It is a 96 LT-4. A Chevy dealership put a new clutch in it 1,500 miles ago. Yet I'm detecting clutch chatter today. Talked to Chevy's mechanic and he said it sounded to him like the previous owner slipped the clutch a lot and created "hot spots" on the flywheel.

I will contact the Chevy dealer that put in the clutch. In the meantime, what is recommended? I've never been down this "road" before.

 

I wish you good luck finding a Dual Mass Flywheel. Let's hope the dealer finds one for you.

 

Assuming the fly wheel has "hot spots" what does that mean? What's happening between the flywheel and the clutch?

If, in fact, the clutch is new, it has 900 miles on it. Still waiting for the dealer to reply.

 

I found this web page:

http://www.ecklerscorvette.com/catal...0-_-9421573763

Anything here apply?

 

I would think the dealer that replaced the clutch would have inspected the flywheel ... but you never know.

A hotspot is an area on the flywheel that may not grab the clutch well (the flywheel is discolored differently at a hotspot caused by overheating - this could be caused by a slipping clutch or improper installation or ...)

What this means, if true, is that you need to have the flywheel inspected. If not too severe, cutting the flywheel may eliminate the hotspots.

Did you have the clutch replaced, or was it the PO?

 

It was done by Chevy dealer prior to putting the car on the lot. PO bought it from the dealer. The dealer will not respond to my inquiries.

Anyone have advice as to best solution(s)? I only want to do this job once.

 

Well, I guess that makes sense. The dealer might tell the PO what they did and found, but most dealers won't talk to "others" about repairs.

Does the clutch slip on you? Or, is it "just" noisy?

 

He didn't say it was noisy, he said that it chatters. That generally means that it doesn't engage smoothy; it grabs, slips repeatedly until fully engaged (usually with a final "grab"/jerk) and you're off. Annoying.

Can be caused by the aforementioned hot spots (hardened spots) in the flywheel, oil contamination, improper installation, bad disk or pressure plate, improper break in of the new clutch (900 miles ago)...lots of things.

How do you fix it ONCE? Take it out, install a new flywheel, new, quality brand clutch, slave, TOB, and disk. Install it correctly, and break it in correctly.

 

I can hear, but not feel, the chatter. It lasts about 2 seconds (almost as if the engine was faintly lugging). I see new flywheels are hard to find and resurfacing is not recommended. I only came up with Fidanza with ths link:

http://www.summitracing.com/search/m...?Ns=Rank%7cAsc

Mine is a 96 LT-4. I'm open to suggestions on a flywheel. Thanks to all.

 

Does this mean that it is engaging smoothly?

It is possible to find original dual-mass flywheels. Talk with Jim http://www.powertorquesystems.com/index.htm (but after he gets back from fishing )

 

chatter is something you normally "feel" as much or more than "hear." Chatter typically is the clutch disk "grabbing" on the flywheel before it completely makes a complete "hold." Generally, the car will "shutter" or "shake" when letting out the clutch upon leaving from a dead stop. This can be from a number of things other than a "bad clutch." In fact with new high performance clutch parts, it is not uncommon to have clutch chatter since the disk and pressure plate may be made with a higher friction surface and a higher clamping load. It is really pronounced when going to an aluminum FW with a cammed car and high performance clutch material, trust me I know; especially in reverse gear with a ZF.

 

I think what your hearing is a worn out DM flywheel.

When you let the clutch out, the 2 peices of the flywheel rotate around and bang into each other because the springs are worn out in it.

The best option for DM replacement is the SPEC "extra mass" flywheel, PN SC05S-2.

http://www.lmperformance.com/40428/25.html

Make sure to click in the box and select "extra mass".
Will

 

The clutch is very smooth. The noise is very faint (almost like octane pinging) and very short but I hear it after the shift and no other time. A Chevy garage mechanic ID'd it as clutch chatter due to "hot spot" when he pulled it out of the service bay.



Thanks for the tip on Jim.

I see where his are resurfaced. I have read that resurfacing a GM dual mass flywheel is not recommended (Not that I have much choice when they are discontinued.).

 

The link is to a single mass flywheel. I'm not married to dual mass if they are interchangeable but don't know if they are.

 

I Totally Agree

 

I am beginning to doubt the Chevy mechanic's diagnosis that I have clutch chatter. Two poster's raised the question of how it should shift if it has "hot spots". The clutch should intermitently grab on those hot (high) spots for an uneven, jerky engagement.

In reality, 90% of my shifts are as smooth as glass.

So today I put it through some tests:

1) There is no noise (chatter) when releasing the clutch in 1st or in reverse.
2) There is in all other gears.
3) Shifting down and releasing the clutch to use the engine as a compression brake produces no noise in ANY gear.
4) I could reproduce the noise by slowing down to 20 mph in 4th gear and trying to accelerate from there. It won't make the noise at 21 mph.

So I don't think it's my flywheel. I think it's either lugging or pinging. Keep in mind I'm new to the car but my first thought was lugging when I originally heard it.

But I can't exclude pinging (or main bearings). Before I took it to the Chevy garage, I added a bottle of Heet to the gas tank. The car has had 16 years to condense water in the tank. I figured it was wise to get rid of it now (If it was there) before rust occured. Googling Heet afterwards, I found that, if you have water in your gas and dissolve it in alcohol, the water passing through your engine will reduce your octane by 3 points. So, if water WAS in my tank, my 91 octane gas becomes 88. This is no problem for an LT1 but an LT4? It's close. The car is supposed to detect pinging and retard the spark but this feature has had 16 years to go wrong and it has 10.5 compression which it may not be able to compensate for like the LT1.

I also have a slightly uneven idle which is to be expected if GM cam'd the LT4. If they didn't, then a vacuum leak is highly probable which could be leading to a power loss which produces the lug.

Comments or opinions?

I'll start an "I'm stupid" thread in the General Section on the shifting speeds of an LT4 in case it's me.

 

NO! Two (or more) posters have tried to clarify that you problem is clutch chatter, which is most prominent while starting from a stop. In first gear. You can have a clutch that "chatters" badly, but still shift seamlessly. Shifting smoothness is more a function of driving skill. Not clutch performance.

Seems like we need to further clarify the symptoms here.

 

What in the world are you doing driving 20 in 4'th? Buy a Prius or some other boring car. My 91 automatic will not shift into 4'th until 47 mph. Just because you have the torque to do something does not make it a good idea.

Take it out and drive it like a Corvette on a back road and see if you have any 'chatter' I suspect not.
Dave

 

21 mph in 4th? really? I'm still in first gear at 21mph. Drive it like a Vette.

 

I did it to recreate the noise. The clutch was fully engaged and I slowed down to see if I got the same noise. That's the only reason I did it. To get the same noise suggests to me lugging or knocking versus clutch chatter. Of course, I'm not a mechanic and another poster just disagreed with me and that I have not ruled clutch chatter out.

I afterwards did exactly as you suggested and took it out on a back road and went through the gears at a much higher speed. Of course, the engine is now roaring and that noise is very faint and hard to hear. I only detected it twice. Shifted down on one and it instantly went away and that made me think "lug" (was going uphill). The other one time made me think "chatter". So I remain undecided.

I figure I need to rid of the gas that has Heet in it, refill with fresh 91 octane, and see if it goes away (That's when it started.). If not, to a trusted transmission shop it goes and I'll let them drive it.

All thoughts or suggestions are welcome.