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Transmission Whine

edited November -1 in Repair and Maintenance
I recently noticed a moderate whine while driving my 2001 Chevy Impala (100k miles) on the highway. I thought it was an engine bearing until I realized that it changed in pitch and volume as power changed, but not rpm per se. That is, as I accelerated or went up a hill, it got more pronounced, but went away when coasting, even if I put it in nuetral and revved it. Also, I discovered that if I put the shift column in '3' (forcing it into 3rd -- it is a 4 spd tranny, right?), it never whined?

So I'm concluding that it is the transmission, but I have no idea what the problem is, or what I can do about it. The tranny fluid is full, but I've never changed it or the filter. I'll start there, but need help to really figure this out.

What do you think

Comments

  • edited August 2007
    I know about a problem that occured on older 4T60 transmissions. An audible whine would issue from the transmission due to a faulty vacuum modulator valve.

    This transmission is a 4T60-E or a 4T65-E, if I remember correctly. If so, it may not even have a shift modulator. Try sticking your head into the engine compartment and listening for the sound while an assistant revs the engine in Neutral. You did say you could hear it in Neutral when revving from within the car so the same should be true if you have your ear next to the tranny.

    I am however inclined to think that this is actually NOT a tranny issue. You said you hear it with an increase in throttle. It may very well be in the intake setup. A leak at the air box, or even at vacuum, could make a whistling/whining noise. I've heard of old dirty air filters doing it too. Also, does it whine with the radio off? It could possibly be electrical; been there and done that.

    -Matt
  • edited August 2007
    Um... for saftey reasons, use PARK and not NEUTRAL while listening for the sound. =-/

    -Matt (again)
  • edited August 2007
    No,no. The sound goes away when in nuetral. The sound volume is basically proportional to power. When coasting there is very little noise, when accelerating or going up a hill there is a lot. Mostly it shows up above 50mph, but after driving a while it will show up at 30mph.
    I took it to a tranny shop and rode with them, it took about 20 minutes from a cold start before the noise showed up, and got louder over the next 10 minutes, but again, only as I applied power under load, not while coasting.
    He is going to test it again with a scanner hooked up to see if the noise only occurs when the torque converter locks. Evidently this might indicate the the converter is shot, actually he used the word 'shelled'.
    Anyone know what this all means?
  • edited August 2007
    I guess I should say its proportional to load, as opposed to rpm.
  • edited August 2007
    A shot TC on an 01' Impala? That sounds iffy. What he meant by lock is when the converter clutch is engaged. Torque Converters are fluid couplings. So they slip, and waste energy. But are necessary for automatics. But at cruise speeds, with no gear shifting happening, there's no reason for a TC anymore. So the two halves of the TC are locked together by a Torque Converter Clutch (TCC). This creates a direct link between transmission and engine, reducing slippage by between 5 and 8 percent, so I hear. That equates directly into fuel mileage.

    You can see if it is the clutch on your own. While driving, and hearing the noise, step lightly on the brake (just enough to turn on the brake lights) while maintaining the gas. This disengages the clutch. You should notice the tachometer needle jump up a little bit. If the noise abates (at least until the needle goes back down) then the diagnosis may be correct. If not, then the diagnosis is probably wrong.

    -Matt
  • edited August 2007
    I really appreciate the conversation about this, it is helpful.
    By shelled, he explained that he meant that the TC blades might be sluffing off material, probably due to the thrust bearings wearing out and sluffing off material themselves. I don't quite understand why this would create a whining noise, but to be fair, he mentioned this in relation to the need to check the condition of the whole tranny even in the event that only the TC needed replacement.
    Regarding the TC clutch as the source of the problem, I did engage the brakes while under load at 65mph, and the whine did not go away.
    He did mention that, in general, the Impala tranny can be expected to only last 100k or so on average. Is this true?
    If this doesn't sound like the TC or the TC clutch, what do you think it sounds like the problem is?
    Thanks for the help,
    Mike
  • edited August 2007
    Oh, yeah. I don't have a tach. I wish I did.
  • edited August 2007
    The comment about the tach made me remember that I have noticed recently that the cruise control shuts itself off occasionally for no reason. I have also noticed for years that I hear a light whirring noise when decelerating from 25mph or so to zero, such as at a stopsign. It sounds like what I have heard previously to be a speedometer cable problem.
    Could any of this be related?
    Keep in mind that when I put the gear shift in 3rd, the transmission whine always goes away. Also, the sound is always proportional to load, not rpm.
  • edited August 2007
    Actually, that would seem to tie the whine to your overdrive gear.

    My first reccomendation would be to change the fluid and filter. Maybe even have it flushed, and the filter changed, so that all the fluid is replaced. See what that does for the noise.

    It doesn't seem to be harming anything so you can probably ignore it for the time being. But I think a full transmission diagnosis will be the only way to determine what the problem is. Since it seems to be related to overdrive gear, I'd say that the TC is probably NOT the problem. But I could easilly be wrong.

    -Matt
This discussion has been closed.