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Old 09-05-2014, 04:36 PM   #1
GTdriver
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1997 SC2
Default Manual Transmission Driveline Noise - Accel Decel

I have a 97 SC2 with a little under 60k miles.

My problem arose a few weeks after a shift cable replacement.

Within the past year I have also replaced both half shafts.

On to my issue:

When i am driving, at any speed, i can hear what sounds like grinding or roaring groaning moaning gear type noise. It happens in any gear, but is most pronounced at highway speed in 5th. If i am driving 60 and shift to 4th the noise will diminish somewhat but not go away.

If at any time i depress the clutch the noise will be completely gone. The noise is also substantially reduced when only enough power is applied to remove accel/decel torque from the driveline.

In an attempt to troubleshoot this issue I have engaged in many many internet and forum searches. I've taken the car to a trusted mechanic, who pointed out my engine mounts were shot and to bring the car back when i had them fixed. I replaced all 4 mounts with OEM Saturn genuine GM parts and the noise persists. I have taken the car to a transmission shop that has been in business for many decades and is a reputable establishment. Both co-owners agreed there is a 99% chance that a torsion spring is cracked or broken on the clutch plate.

While I may have my answer written above I thought it best to put this query out to the Saturn community and see if there can be some consensus with the diagnosis. I know many of the users in this community are former Saturn techs and there are many quite passionate and knowledgeable about the S series. It's very possible my symptoms are something someone here has experienced and asking now may end up saving me the $400 or so i'd have spent on OEM clutch parts just to end up being wrong.

Thanks for sticking with this long read; I hope someone is able to provide some insight.

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Old 09-05-2014, 05:53 PM   #2
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Location: Madison, WI USA
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1996 SW2
Default Re: Manual Transmission Driveline Noise - Accel Decel

After you replaced the powertrain mounts, did you do the "unload" procedure with the two studs/nuts on the lower engine dog-bone bracket? There's a thread in our How-To Library about the procedure. Usually not associated with this kind of issue, but worth doing just to rule it out (or in).

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Old 09-06-2014, 10:25 PM   #3
GTdriver
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1997 SC2
Default Re: Manual Transmission Driveline Noise - Accel Decel

Yes I did unload the mounts. The mounts were replaced in an effort to fix the sound. After replacement the drive line was most certainly smoother and more refined, however the noise persisted unchanged.

I should also note that the fluid has been changed with Mobil synthetic. This was also done in an effort to quiet the noise.

Gears shift smoothly. There is not any binding or rough spots to be found. The car drives perfect except for this noise. Its not paranoia as my wife and father hear it too.

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Old 09-06-2014, 10:38 PM   #4
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Location: Far Southwestern Iowa
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1998 SC2
Default Re: Manual Transmission Driveline Noise - Accel Decel

Exhaust system and hangers.

OEM top mount, trans mount, late 97 or newer torque axis struts and the polly inserts. Engine must have an even smooth idle. That means good even compression. Clean flow balanced injectors. The 3 rubber exhaust mounts should not be stretched when the car is at rest, just supporting the exhaust. These 3 suspension pieces will be what couples the exhaust vibration into the floor pan so the stretchiness and thickness of these is how you tune them to not appear solid at some inconvenient RPM. The Walker 35119 isolator is thicker than the original OEM. They are cheap so modifying them is not a big deal. They thin nicely on a belt sander but if too thin they break and you will be buying a new exhaust.

If you have an uneven idle you will never reduce the vibration to zero. Setting the torque axis struts to zero tension/compression at rest is critical.

The torque axis struts are of 3 different designs and the 3rd design, late 97 production, have replaceable inserts. These are the stamped and welded design. There are 2 pictures in my gallery. What you are attempting to accomplish is restrain the engine free motion as much as possible without going solid. The main axis of rotation is on a line between the top mount and transaxle mount. The torque axis struts are positioned to restrain the normal torque reaction and drive axle wind up. The poly inserts allow enough motion to not act as a solid link but do not transmit vibration well either. The idea is to keep large excursions of the engine/transmission and exhaust to a minimum. Small displacement of the power train transmits to large displacement in the exhaust. The rubber hangers will deftly transmit this exhaust motion into the floor pan which simulates the head on a large kettle drum, with you inside of it. You can get a buzz in the floor that does not transmit into the upper frame or seats but the large low frequency pan displacement is pushed up to a higher frequency. the characteristics of the rubber mounts determines where this buzz occurs. The trick is to get it somewhere you do not care. By minimizing the powertrain displacement you minimize the magnitude of the exhaust displacement you have to deal with. You can slightly change the static exhaust position to take all the stress off of the flex connector and have the mass of the exhaust evenly spread over the 3 mount points. The muffler hanger basically controls axial twist on the exhaust. I used the Walker 35119 isolators and just stuck them on. Ended up with the buzz from about 50 to 57mph and this is a speed range that is only passed through so I did not pursue any further elimination. the bed liner should kill this 50-57 mph buzz all by itself. The OEM isolators are a softer rubber and thinner and would possibly isolate the floor better but as they were 10+ years old and I am adverse to dragging the exhaust down the road I decided to replace them. The harder-thicker isolator appears as a solid at given frequencies.

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Old 09-07-2014, 12:38 AM   #5
GTdriver
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1997 SC2
Default Re: Manual Transmission Driveline Noise - Accel Decel

Before this issue cropped up I had the entire exhaust system replaced. From the header all the way up to the muffler is OEM Saturn parts, yes that includes a brand new resonater. The muffler was the walker ss muffler and after the install the car was smooth and quiet as when I bought it. The sound I am experiencing is most certainly under the hood. The car has been run through the gears on a lift and the sound is present when listening outside the vehicle.

I would love to believe the trans shop guys and just go for the clutch but something in my gut tells me that might not be the solution.

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Old 09-07-2014, 09:24 AM   #6
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1998 SC2
Default Re: Manual Transmission Driveline Noise - Accel Decel

Well, as you are semi-convinced it is the clutch then either pull it out yourself or send the crystal ball out for cleaning and recalibration so you can make another guess.

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