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TheRedGlacier
03-31-2016, 08:44 AM
Hey guys, I have an interesting issue if you will.

Last summer, I picked up a 1994 Trans Am GT from my uncle. 49k miles. 360 HP, T56, 4.10.

So, I have realized (JUST prior to putting her back on the road this year) that there is a quiet rattling noise in the background of idling.. And it stops when the clutch is disengaged. There is a little scraping/scratching noise when accelerating from a stop, and the noise only is apparent when engaging the clutch with less than 2000 or so RPM.

My final issue that I believe to be related is that intermittently, if you push in the clutch pedal too fast/hard at low speeds, there is a moderate bang from under the car. Most of these signs would suggest a dying throwout bearing, correct? Although, the bang would make me think it would be a Trans mount maybe..( if it is a Throwout, how long would I be able to drive on it without damage?) I'm only seventeen, so my ability to diagnose issues is limited, as is my wallet.. But I wanted some advice or suggestions from people who are more experience than I am.

I doubt it has anything to do with it, but driving beyond 75 MPH emits a vibration, but this is most likely the tires.. I'm putting a new set on this week, since these old ones practically have no tread remaining. I figured I would post this just in case, as my friend suggested a possible broken rear end, but she never got a lot of hard launches, although the tires have been spun quite a bit. Besides that, the car drives fine.

Dan
03-31-2016, 09:05 AM
Sounds like trans mount or torque arm mount for the banging,
Throwout bearing for the rattling noise sounds like.

Camaro96
03-31-2016, 09:36 AM
Sounds like trans mount or torque arm mount for the banging,
Throwout bearing for the rattling noise sounds like.
I would agree with Dan . How long can you drive it with out causing damage. There already damage but there is no way to say how much damage. If you continue to drive the car the more damage may occur to the cluch and pressure plate. As for the vibration is it in the steering wheel or whole car?

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TheRedGlacier
03-31-2016, 10:19 AM
Thanks for the hasty responses guys!

How can I check the torque arm or trans mount? Just a visual inspection?

I'm not too concerned with damage to the clutch, as I planned on replacing it along with the rest of the main components. My only concern is potential damage to the T56 or the LT1.

and to Camaro96, the whole car vibrates, including the steering wheel. It is most apparent beyond 80mph, while in neutral. It feels like a large massage chair on high, which leads me to believe the tires are the culprit, but I figured I should mention it just in case.

Injuneer
03-31-2016, 10:27 AM
Not unusual for the T56 input shaft to rattle a bit, from my experience. Did it from new in 1994.

With 4.10 gears, the vibration above 75 MPH could be due to a harmonic frequency problem with the steel driveshaft. Very common problem when you go 3.73's or 4.10's. The problem was so common that GM issued a TSB "back in the day" that allowed some to get a free aluminum DS replacement.

To check the trans mount, jack gently under the trans to see if you can lift it, exposing a cracked rubber mount. The TA bushing in the bracket on the tailshaft of the trans is in a clamshell, and serious bushing rot should be visible externally.

TheRedGlacier
03-31-2016, 12:25 PM
Oh alright then, that makes sense then. So long as it is just an issue of harmonic balance, and not a safety issue then I'll leave the steel one in for now. I just got home, so I'll jack up the car and post back after I inspect the mounts and arms.

Injuneer
03-31-2016, 05:30 PM
Well.... it is a problem. It's hitting the critical frequency and trying to self destruct. Not good for the trans or rear.

TheRedGlacier
03-31-2016, 09:31 PM
So basically no going above 75ish until I get the money for a new driveshaft? I mean I can live with that, I have no reason to go above 65.. But that's still disappointing.

I forgot to post, both the trans mounts and torque arm are good. Not too sure.. The banging before was minimum, and you could feel it through the clutch pedal.