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I'm baffled. Another phantom knocking

This is a discussion on I'm baffled. Another phantom knocking within the Firebird / WS6 forums, part of the Vehicle Specific category; Iv'e been plagued by a "comes and goes" knocking noise, not really loud but just loud enough to hear, for ...

  1. #1
    Member Redrokit8's Avatar
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    I'm baffled. Another phantom knocking



    Iv'e been plagued by a "comes and goes" knocking noise, not really loud but just loud enough to hear, for over a year now. I can't record it for you because it appears when I am braking to a stop and it starts at maybe 15-20 mph down to zero. You can see from my signature that I have installed a decent amount of UMI products for the suspension and it's interesting because after an install of a part, the knocking won't show itself for about 1/2 hour or so. I think the knocking comes around after taking corners like off an expressway and then decelerating to a stop. I had the occasion to carry a heavy item in the back boot, 75 lbs, and that noise didn't show it's head until I took the item out of the boot and drove just about 20 minutes, went to brake for a light and sure enough that old reliable knock, knock, knock was back. To me it sounds like the sound is coming from either the drive shaft or rear end. The knocking mimics the sound you would have with a large rock or nail in your tire but it's deeper and more solid of a sound. Yes, it slows down as the car does so. I had a '07 Corvette that made weird noises like this and it was the rear posi clutches sticking and not releasing. I added two slip enhancers instead of one and that remedied the problem there. I'll end this crazy long post by saying you could compare it to a sound that a ball peen hammer would make if lightly tapped on rear axle shaft. Before I go and have a running gear specialist go over it I was hoping that one of the forum members had a similar or same problem.

  2. #2
    Moderator 98TransAmWs-6's Avatar
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    Does it do it at all when turning, if so hard or light turning?
    Last edited by 98TransAmWs-6; 07-07-2012 at 06:30 AM.
    1998 Trans Am WS6 - Phantom
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  3. #3
    Member Redrokit8's Avatar
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    No, it is noticeable braking when you get to 20 mph and under. But it is noticeable after you have taken a corner and then slow down to a stop. I guess I could say that if I don't take any corners then I don't hear it. You do not hear it while in the corner. MY interpretation is that the knocking is in time with the driveshaft revolutions. Not to throw a monkey wrench into this whole thing but I have found two extremely small ball bearings on my garage floor. Just two and no more. Could have come from anywhere like shop vac etc. (I hope).
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  4. #4
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    Driveshaft u-joints have needle bearings, so that's not what the ball bearing came from. I would start by checking everything under the car to ensure that all suspension bolts are properly tightened. Also, check you brake caliper mounting bolts just for fun. Do you feel any pulsation in your brake pedal that corresponds with the noise?

  5. #5
    Member Redrokit8's Avatar
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    No pulsating at all. As far as the brakes go, I recently put on all new rotors and pads wishfully thinking the noise would have to go away. Most of the suspension is all new UMI stuff and when putting on the LTH's everything was torqued down underneath.
    I did some research and found out that a good number of Camaro SS and Trans AM's came with a Torsen rear end. There were a lot of complaints about the same noise as I have now. I'm told that the Torsen has a different posi set up and it is, or was, known for this quirky noise. Apparently the factory replaced a number of them before realizing that nothing is wrong, it's just that way. Old internet posts from 2001-2002, mostly Camaro sites, talk about this. What I can't understand is why aren't there any Forum members reading my post and replying that they have been through this and don't sweat it. Torsen seems to be a reputable manufacturer of pretty durable rear end assemblies.
    I can't be the only one who hears this. Based on what I have learned, I'll just drive it and hopefully I'll get to not hearing it. Love to hear more if anyone recalls the 2001-2002 complaints.

  6. #6
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    I have read that the Torsen can make a "rusty screw" noise, but that it was remedied with the use of positraction additive (even though there are no clutches).

  7. #7
    Member Redrokit8's Avatar
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    Quote Originally Posted by pajeff02 View Post
    I have read that the Torsen can make a "rusty screw" noise, but that it was remedied with the use of positraction additive (even though there are no clutches).
    Ok Jeff, I'll bite and say I never had a "rusty screw" ! (not that I would mind one)
    I'm tempted to go for another drain, refill and add two slip enhancer packs. I had a similar situation with the posi rear end clutches in a Corvette. Two slip enhancers did the trick but this is a totally different sound. Can't lose anything by trying it.

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    Quote straight from Torsen's site:

    Is it true that the Torsen unit in the production Camaro needs the GM modifier added?

    GM issued a technical bulletin adding modifier to the rear axle oil. This was done to quiet what we call a "Rusty Screw" noise that we heard in a very small percentage of vehicles. This does not happen in all cases, however to address owner's concerns we asked that the modifier be used in all instances to insure that the driver would not get this noise. When replacing the fluid it is at the owner's discretion whether or not to add the modifier. Elimination of the modifier does not affect durability of the differential.

  9. #9
    Member Redrokit8's Avatar
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    Quote Originally Posted by pajeff02 View Post
    Quote straight from Torsen's site:

    Is it true that the Torsen unit in the production Camaro needs the GM modifier added?

    GM issued a technical bulletin adding modifier to the rear axle oil. This was done to quiet what we call a "Rusty Screw" noise that we heard in a very small percentage of vehicles. This does not happen in all cases, however to address owner's concerns we asked that the modifier be used in all instances to insure that the driver would not get this noise. When replacing the fluid it is at the owner's discretion whether or not to add the modifier. Elimination of the modifier does not affect durability of the differential.
    Well, ok the "rusty screw" is for real !!! I'll give it a shot when I can. It already doesn't sound so bad knowing it is not a self destructive noise.

  10. #10
    Former Mopar Man 2002ssslp's Avatar
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    Quote Originally Posted by Redrokit8 View Post

    Iv'e been plagued by a "comes and goes" knocking noise, not really loud but just loud enough to hear, for over a year now. I can't record it for you because it appears when I am braking to a stop and it starts at maybe 15-20 mph down to zero. You can see from my signature that I have installed a decent amount of UMI products for the suspension and it's interesting because after an install of a part, the knocking won't show itself for about 1/2 hour or so. I think the knocking comes around after taking corners like off an expressway and then decelerating to a stop. I had the occasion to carry a heavy item in the back boot, 75 lbs, and that noise didn't show it's head until I took the item out of the boot and drove just about 20 minutes, went to brake for a light and sure enough that old reliable knock, knock, knock was back. To me it sounds like the sound is coming from either the drive shaft or rear end. The knocking mimics the sound you would have with a large rock or nail in your tire but it's deeper and more solid of a sound. Yes, it slows down as the car does so. I had a '07 Corvette that made weird noises like this and it was the rear posi clutches sticking and not releasing. I added two slip enhancers instead of one and that remedied the problem there. I'll end this crazy long post by saying you could compare it to a sound that a ball peen hammer would make if lightly tapped on rear axle shaft. Before I go and have a running gear specialist go over it I was hoping that one of the forum members had a similar or same problem.
    Just go under the car and check everything to make sure all the bolts are tight and all your bushings are in place.
    My ride is a 2002 Camaro SS SLP #3296 with 30k, LTH, 3" Y, CME, Frost tune, K&N, ported TB, Blackwing lid, Bellows, MSD, Denso Iridium, and 85mm MAF, Bilsteins, Eibach springs, SLP strut brace, Adj. Panhard, TA Girdle, UMI, Pro 5.0, Nitto NT555
    My wife has a 2004 GTO with the rare SAP, 18" wheels, K&N Cold Air System, MSD, Ported TB, Frost tune, Denso Iridium, Flowmaster cat-back, 3200 Yank, 75k

  11. #11
    Moderator 98TransAmWs-6's Avatar
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    I did have the rusty screw problem and I just used Vavoline differential fluid with the additive and it went away. The sound would be when making sharp and hard turns though. It was also more of a whine.

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    Member Redrokit8's Avatar
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    Thanks to those who commented. Last night I was at a Cruise In at Jimmy Johnson's in Roseland, NJ. Met someone who has same car as mine except for color and miles. She said that she has always had the knocking, that I described, since day one when bought new. After many visits GM brass said it was a result of the Torsen rear drive assembly and the sound should be classified as normal. It isn't going to go away, so just drive it and after a period of time it just becomes another quirky, non-invasive noise.

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    Member Redrokit8's Avatar
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    Alright, enough already about this noise !!!!!

    Ok, one last experience with this noise and its disappearance. This past weekend I pulled over to the side of the road to let my friend pull ahead and lead the way to a cruise in. When I pulled out in back of him I was on a small amount of gravel and was pulling out to the left. Naturally I gave it quite a bit of throttle and the trac control kicked in. When it activated I felt a few small shutters or shakes that almost felt like the drive shaft was made of rubber. I could feel the rear wheels deciding what axle to pick. All I can explain is that something happened (?) and the differential became quieter and the knocking noise is gone, at least for the time being. So, my question is did something finally absorb enough slip enhancer ?
    Don't forget the car was most likely driven for a year in 2002 and then again in 2011 with 8K on the clock.

  14. #14
    Moderator 98TransAmWs-6's Avatar
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    If it is the "rusty screw" or just another normal noise I don't think miles have anything to do with it. I am inclined to say yes but the noises from my rear I have had were fixed immediately with a differential fluid change with the limited slip additive. It is hard to say. Wish you could record.the sound so I could hear exactly how it sounds. That is really strange it would stop then, that would make me want to take a look under there.

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    Billy -- make the trip over to Green Lane, PA for our Spazapalooza event on August 4th. You will have several very experienced die hard car guys on hand that can assist you in diagnosing and resolving this issue, myself included.

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    Member Redrokit8's Avatar
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    I'm working on it. Thanks.

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    Member SuperSSguy's Avatar
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    I used the GM additive---Does anyone have an opinion on this? Do you HAVE to use the GM specifically? What other brands do you think are comprable?

  18. #18
    Moderator 98TransAmWs-6's Avatar
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    Quote Originally Posted by SuperSSguy View Post
    I used the GM additive---Does anyone have an opinion on this? Do you HAVE to use the GM specifically? What other brands do you think are comprable?
    No you don't HAVE to use the GM additive. I know the additive in Vavoline and Royal Purple differential fluid works well. Those are the two I have used and the sound hasn't come back. I am sure Amsoil and any other big brands would work fine too.

  19. #19
    Member Redrokit8's Avatar
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    [QUOTE=98TransAmWs-6;2791812]No you don't HAVE to use the GM additive. I know the additive in Vavoline and Royal Purple differential fluid works well. Those are the two I have used and the sound hasn't come back. I am sure Amsoil and any other big brands would work fine too.[/QUOTE

    Good advice.
    Thanks.

  20. #20
    Member SuperSSguy's Avatar
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    Quote Originally Posted by 98TransAmWs-6 View Post
    No you don't HAVE to use the GM additive. I know the additive in Vavoline and Royal Purple differential fluid works well. Those are the two I have used and the sound hasn't come back. I am sure Amsoil and any other big brands would work fine too.
    Thats good to hear! `cause last i remember it wasnt that cheap @GM...Thankfully i dont have a problem with my rear end...HUH?... that sounded funny...

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