Help with diagnosis: noise coming from left rear wheel well area...
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2004-2007 Cadillac CTS-V General Discussion Discussion, Help with diagnosis: noise coming from left rear wheel well area... in Cadillac CTS-V Series Forum - 2004 - 2007; Since my last track event at Sebring I've noticed a humming noise coming from the left rear wheel area (driver's ...
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    smbstyle is offline Cadillac Owners Fanatic
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    Help with diagnosis: noise coming from left rear wheel well area...

    Since my last track event at Sebring I've noticed a humming noise coming from the left rear wheel area (driver's side) that I can hear from 40mph and up; almost sounds like it could be a wheel bearing. The noise sounds like a mud-tire on a truck. I've swapped wheels/tires around and the sound is still on the driver's side rear, so its not the tire tread, although the tread is low on all tires.

    Also, when turning the car right at low speeds like in a parking lot, I hear almost a grinding sound coming from the area, but it only does this when turning right, and at low speeds. I put the car in the air yesterday to check for a bad wheel bearing (rocked the wheel side to side, up and down) and there was no play at all, so I'm wondering if the outer CV joint on the axle could be bad because of the noise when at speeds over 40, and the grinding sound when there is a load being put on it by turning right? Any ideas?

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    darkman's Avatar
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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    The "mud-tire" sound sounds like the characteristic whine that these differentials tend to develop. If it is it will be louder with the rear-seat trunk access door open. It will also vary with very light aceleration/deceleration.

    The grinding in very slow turns sounds like you need more friction modifier in the differential fluid. A fluid change with the friction modifier additive will cure this condition if that is what it is.

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    smbstyle is offline Cadillac Owners Fanatic
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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    Quote Originally Posted by darkman View Post
    The "mud-tire" sound sounds like the characteristic whine that these differentials tend to develop. If it is it will be louder with the rear-seat trunk access door open. It will also vary with very light aceleration/deceleration.

    The grinding in very slow turns sounds like you need more friction modifier in the differential fluid. A fluid change with the friction modifier additive will cure this condition if that is what it is.
    yeah the pitch of the sound gets higher as i increase speed, but it clearly comes from the left rear wheel well area which is why I kinda ruled out the diff. Shouldnt it come from the center if it was the diff whine?

    also, if its an issue of needing more friction modifier, shouldnt it make that sound turning both directions, not just turning right? and why would it start making that sound now; why not after I changed the diff fluid months ago? FYI I am running AMSOIL SVG 75w90 without adding anything else.

    Thanks for the response!

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    darkman's Avatar
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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    Quote Originally Posted by smbstyle View Post
    yeah the pitch of the sound gets higher as i increase speed, but it clearly comes from the left rear wheel well area which is why I kinda ruled out the diff. Shouldnt it come from the center if it was the diff whine?

    also, if its an issue of needing more friction modifier, shouldnt it make that sound turning both directions, not just turning right? and why would it start making that sound now; why not after I changed the diff fluid months ago? FYI I am running AMSOIL SVG 75w90 without adding anything else.

    Thanks for the response!
    Yes the differential noise comes from the center, but it can reach the driver's seat (ears) from the cradle/frame and be hard, therefore to isolate. If you sure its is only from one side, then the differential is not the problem.

    On the slow speed grinding, if the friction coeffeicient is close, but imperfect one set of clutch packs could be sticking while the other is not. Although Amsoil does not always require the additive it does sometimes. You might want to add some additive and see - it would at least eliminate the cheapest possiblity.

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    smbstyle is offline Cadillac Owners Fanatic
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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    Quote Originally Posted by darkman View Post
    Yes the differential noise comes from the center, but it can reach the driver's seat (ears) from the cradle/frame and be hard, therefore to isolate. If you sure its is only from one side, then the differential is not the problem.

    On the slow speed grinding, if the friction coeffeicient is close, but imperfect one set of clutch packs could be sticking while the other is not. Although Amsoil does not always require the additive it does sometimes. You might want to add some additive and see - it would at least eliminate the cheapest possiblity.
    Good point; I'll add the friction modifier; it cant hurt!

    I'll keep an eye on the sound; see if I can have a passenger sit on both sides in the back and see if it is just me hearing it from the drivers side.

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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    If it was a wheel bearing, it would be making the noise from 1 mph and up and get louder with speed.

    When you changed the diff fluid, did you do some tight figure eights? That helps get the new fluid into the clutch packs.

    FWIW, when the delear replaced my diff under CPO to the gen4 version, they used that newer stuff....DEXRON LS fluid that has the modifier in it. Not to jack your thread, but how often are people changing fluid? I haven't changed the trans yet (33k) and was going to do both before V day...not liking that you're hearing diff noises with Amsoil....might just stick with the GM stuff.

    And...did you get a chance to take pics of the pads? ...thanks.

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    darkman's Avatar
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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    Quote Originally Posted by JDB View Post
    If it was a wheel bearing, it would be making the noise from 1 mph and up and get louder with speed.

    When you changed the diff fluid, did you do some tight figure eights? That helps get the new fluid into the clutch packs.

    FWIW, when the delear replaced my diff under CPO to the gen4 version, they used that newer stuff....DEXRON LS fluid that has the modifier in it. Not to jack your thread, but how often are people changing fluid? I haven't changed the trans yet (33k) and was going to do both before V day...not liking that you're hearing diff noises with Amsoil....might just stick with the GM stuff.

    And...did you get a chance to take pics of the pads? ...thanks.
    I like to change out the original transmission and differential fluids as soon as the car (or the replacement part) is broken in because all gears put metal in the fluid during break-in. After that the frequency is pretty subjective unless the unit (trans or diff) is exposed to high temperature operation. I change my differential fluid with almost every oil change (paranoia) and my transmission fluid every couple of years. I stil use GM fluids but believe Amsoil is also a good choice. (I run Amsoil filters everywhere I can.)

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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    Quote Originally Posted by darkman View Post
    I like to change out the original transmission and differential fluids as soon as the car (or the replacement part) is broken in because all gears put metal in the fluid during break-in. After that the frequency is pretty subjective unless the unit (trans or diff) is exposed to high temperature operation. I change my differential fluid with almost every oil change (paranoia) and my transmission fluid every couple of years. I stil use GM fluids but believe Amsoil is also a good choice. (I run Amsoil filters everywhere I can.)
    My diff was flushed about 1k after install since the dealer put in the grape scented stuff thinking it was the DEXRON LS stuff with an additive...but wheni verified the part numbers from my invoice...it showed the grape stuff and there was no part listed for an additive....but the tech said he thought he used the stuff with additive in it. So just to be safe, they flushed it and I was in the shop with the tech watching him put in the Dexron LS.

    Definitely can't hurt to flush after breakin but I didn't have that opportunity with the trans since I just bought the car last year with 24k on it. In my Audi, I switched to Redline fluids in trans and diff, and 30-50k is fine ...lots of people with 100k-200k on original oem fluid and run fine. (Not auto though ) I think the trans should be fine with 30-50k intervals, but I'll probably do the diff more often. ...maybe every other oil change/10k/once per year.ish.

    It's interesting how there's not much of a consensus of maintenance intervals for fluids, filters, plugs, etc. Everyone does their own thing and stands behind it without any scientific basis. These cars are 4-7 years old and you'd think people would see real world results by now.

    I took a sample of my last oil change and plan to send it to Blackstone...plan to do the same for trans and diff.

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    andyb119 is offline Cadillac Owners Member
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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    I had noise coming from the right (passenger) side that didn't manifest itself until over 20mph and thought it might be the diff. However, it turned out to be the wheel bearing. Only had 60k on the car so I was a bit surprised it failed but it was a cheaper fix than the diff.

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    Re: Help with diagnosis: noise coming from left rear wheel well area...

    From the description it sounds like a wheel bearing...

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