LOUD metallic screech on downshift
Thread Starter
Teching In
Joined: Aug 2005
Posts: 12
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From: OR
LOUD metallic screech on downshift I've had some drivetrain vibration issues (now with less than 1500 miles on an aftermarket clutch) and recently a new symptom has arisen.
Sometimes when letting off the clutch from a standstill, to get moving, the car will let out a LOUD metallic screech. It's brief but a very unsettling noise that seems to come from somewhere under the shifter. This also happens when downshifting and will happen every time I downshift if I let the clutch out too fast. The noise makes me think something which shouldn't be turning IS, or something that should turn doesn't want to and is being forced to turn. It seems torque transfer related, if I am stopped facing up an incline and try to get going the noise will present itself but on a flat surface may not. Downshifting at lower rpm also wont cause the noise.
The car generally has a hard time with getting power to the ground, hard to break the tires loose at any time (and its putting down 485rwtq). Also on hard shifts it just feels flat. This is with TM turned off and traction control off also.
If anyone has ideas on the screeching, violent whine I would sure appreciate any thoughts on what might be going on.
Thanks!
[oh, car is an 01z06, mn12, 3.73 gears, 418ci ls2.]
Sometimes when letting off the clutch from a standstill, to get moving, the car will let out a LOUD metallic screech. It's brief but a very unsettling noise that seems to come from somewhere under the shifter. This also happens when downshifting and will happen every time I downshift if I let the clutch out too fast. The noise makes me think something which shouldn't be turning IS, or something that should turn doesn't want to and is being forced to turn. It seems torque transfer related, if I am stopped facing up an incline and try to get going the noise will present itself but on a flat surface may not. Downshifting at lower rpm also wont cause the noise.
The car generally has a hard time with getting power to the ground, hard to break the tires loose at any time (and its putting down 485rwtq). Also on hard shifts it just feels flat. This is with TM turned off and traction control off also.
If anyone has ideas on the screeching, violent whine I would sure appreciate any thoughts on what might be going on.
Thanks!
[oh, car is an 01z06, mn12, 3.73 gears, 418ci ls2.]
TECH Addict
Joined: Dec 2001
Posts: 2,907
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From: Bergen County, NJ
When you let off the clutch in gear the pilot bearing and the throw out bearing are already spinning, the clutch disc engages with the pressure plate and flywheel through friction and the input shaft begins to rotate along with first gear and the output shaft. The likely cause then would be the clutch or the bearings on the input. I assume you did not have this before the new clutch and given that you have had vibration issues and what sounds like holding issues with the new clutch I would bet the problem is with your new clutch.
Thread Starter
Teching In
Joined: Aug 2005
Posts: 12
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From: OR
DaddySS- Yes the screeching is new and I can imagine it being the clutch. sometimes on slow clutch release theres an odd feeling vibration/wobble that I can feel through the peddle as the mating surfaces come together (like things are not grabbing right). So 1/3 of the time there's the metallic screech, 1/3 of the time the wobble and the rest it seems to work ok. Vibration has been there through 2 clutch replacements. Clutch seems to hold ok (doesnt slip) but i've had problems getting power down even prior to this clutch (low traps...ALWAYS 118, cant break tires loose etc).
AJ- can you provide more info on your thoughts wrt the tranny? This other symptom really low trap speeds regardless of power which has plagued me through engine swaps and clutch changes and I am curious about your transmission comment.
Thanks!
AJ- can you provide more info on your thoughts wrt the tranny? This other symptom really low trap speeds regardless of power which has plagued me through engine swaps and clutch changes and I am curious about your transmission comment.
Thanks!
TECH Addict
Joined: Dec 2001
Posts: 2,907
Likes: 1
From: Bergen County, NJ
You've got to tackle these things one at a time. To start with the putting down power issue, do you have the dyno graph? With that peak torque it should haul but what's the torque at 2500 to 3500?
Vibration issues are difficult but they just take time. Was the vibration there from the time the new engine went in?
Vibration issues are difficult but they just take time. Was the vibration there from the time the new engine went in?
Thread Starter
Teching In
Joined: Aug 2005
Posts: 12
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From: OR
Torque is actually over 400 from about 2500-5500, on the dyno. The car has been through H/C package, now a 418stroker and really everthing has been swapped (EXCEPT transmission, torque tube and diff). Car trapped 115-116 when I just had headers on it....with 70rwhp more (h/c) and now with 100rwhp more it will not break 118mph.
Vibrations have been present since the first clutch swap. Now has a different clutch and new engine, vibrations are worse and the metallic shriek is new.
Appreciate your insight here. I know its not an easy one...has everyone I have asked stumped and over on the CF no one seems to want to reply to my post!
Vibrations have been present since the first clutch swap. Now has a different clutch and new engine, vibrations are worse and the metallic shriek is new.
Appreciate your insight here. I know its not an easy one...has everyone I have asked stumped and over on the CF no one seems to want to reply to my post!
