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T56 noise/vibration issue - help identify possible causes

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Old 02-25-2017, 03:07 PM   #1
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Default T56 noise/vibration issue - help identify possible causes

Vehicle details: '05 CTS-V, stock T56 w/134k miles, RPS twin disk clutch and flywheel, Creative Steel 8.8" diff conversion

This is a bit of a long story, but this problem has developed over time and I'm still trying to put the pieces together. I wanted to be thorough in explaining the chain of events in the hopes that will help others tell me what the hell is wrong with my car!

I've been having some driveline noise and vibration issues with my CTS-V. I think I initially noticed an issue back in the September/October time frame. I thought it was a wheel bearing (based on it sounding/behaving like bad wheel bearings I've had on my other cars), so I was working on that premise for to start out with. By the December time frame, the noise and vibration had gotten quite a bit worse, to the point I was somewhat worried about driving the car home for the holidays (~800mi round trip). At certain speeds the vibration would "set off" various vibrations in the car, and it was quite loud. Around New Year's I swapped the driveshaft with a spare one I had on hand (thinking I had a bad CV in the driveshaft), and while the car was up on the life I found the boot on the inner CV of the driver side axle was torn about 3/4 of the way around, and the grease had spewed all over.

I swapped out the CV on the axle and took the car for a spin but still had the vibration/noise. So, I jacked up the rear end and let the car idle in 2nd gear, then listened to the wheel bearings and diff bearings with a mechanic's stethoscope. I heard noise from the driver side rear wheel bearing, so I replaced that wheel bearing.

After finishing up that job, while the car was on the lift I repeated the 2nd gear idle test to see if the rear sounded better. Sure enough, it did, but then I heard a different noise coming from the transmission / clutch area. I got a couple quick videos under the car with my digital camera. In person, the sound had a more metallic character to it than comes across in the video.

(very short, realized I couldn't see anything without a light)
[I apologize for the poor video/audio quality, but that was all I got on my first attempt.]

I shot those videos a week ago, then left the car sitting at the auto hobby shop on the local military base. Today I went back to the shop to fiddle with the car again. I took it out for a spin and shot some video from inside the car, but the noise/vibration didn't come through very well on the video, so I won't bother posting it. I did test a couple things: the noise/vibration did not change when I put the clutch it, nor did it change when I downshifted (but maintained the same speed).

I put the car back up on the lift and shot another video, this time with my ReplayXD and good mic (rather than the point-n-shoot digital camera in video mode). Audio quality isn't much better than with the digital camera; oh well.


I listened all along the transmission with my mechanic's stethoscope, but couldn't really localize the noise - it's so damn loud that it sounded pretty much the same regardless of where I was on the transmission.

I also checked for play at the tranny output. Didn't get any movement trying to push straight up and down, but got some when I grabbed from the side and was kind of pushing diagonally (up and towards the passenger side, then pulling down and towards the driver side). And even that play was more felt/heard than actually seen - I couldn't really see any movement, but I could hear/feel a clunk clunk as I forced it back-and-forth.

Any thoughts on what we're hearing? The noise was loud and the car was actually rocking a bit with the noise. The driveshaft seemed to be rolling smoothly the whole time.

My thinking at this point is that the noise/vibration was initially due to some combination of the driveshaft CVs, the driver side axle CV, and the driver side rear wheel bearing. However, at some point in the November/December time frame, something went wrong in the transmission, and that's what caused the progressively worsening/increased noise and vibrations.
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Old 02-26-2017, 09:42 PM   #2
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Drop the driveline, does the noise continue?
If no, reinstall and drop the CV shafts.

This isn't perfect; noises can and do change under load.

"Something went wrong in The transmission" doesn't say much.
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Old 02-26-2017, 10:55 PM   #3
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Quote:
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"Something went wrong in The transmission" doesn't say much.
Uhhh, I know. That's why I started the thread - I don't know what went wrong, so I'm asking for help.
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Old 02-27-2017, 12:40 AM   #4
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Is it way worse in fifth or sixth vs other gears? Is it RPM or vehicle speed dependent? Meaning does it change if its in different gears at the same speed? Does it do it in neutral? Is it an audible hum or more something you can feel in your gut rather than hear?
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Old 02-27-2017, 05:56 AM   #5
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It's speed dependent. Shifting from 6th to 4th at highway speed made no difference, nor did putting the clutch in while at ~65mph. It's definitely audible, gets louder the faster I go. It's got a deep tone to it (not high pitched).

Edit: As mentioned in the first post, I do have some in-car video. I didn't upload it to youtube because I didn't think it did a good job of conveying what the noise sounds like while driving, but it's better than nothing, so after work this afternoon I'll upload it and post the link.

Last edited by AAIIIC; 02-27-2017 at 07:25 AM.
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Old 02-27-2017, 08:49 AM   #6
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Quote:
Originally Posted by AAIIIC View Post
It's speed dependent. Shifting from 6th to 4th at highway speed made no difference, nor did putting the clutch in while at ~65mph. It's definitely audible, gets louder the faster I go. It's got a deep tone to it (not high pitched).

Edit: As mentioned in the first post, I do have some in-car video. I didn't upload it to youtube because I didn't think it did a good job of conveying what the noise sounds like while driving, but it's better than nothing, so after work this afternoon I'll upload it and post the link.
You actually gave some very good diagnostic information int his post. That it is not RPM dependent rules out tons of engine issues - you'd be amazed how engine vibes can translate throughout the car. That it is not GEAR dependent pretty much rules out the transmission itself.

That it is an audible drone tells you it is likely on the driveline side and not the wheel side. If it's on the wheel side of the diff, you generally feel it but can't hear it. Since the driveline is rotating approximately 4x the wheel, this puts the vibrations into audible range.

I know you've got a CV axle in your driveshaft, so that changes alot of the driveline angle rules. SO, I'd recommend checking motor and tranny mounts if you haven't already. I know you said you swapped driveshafts, but did you also swap the U joints out?
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Old 02-27-2017, 12:38 PM   #7
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The CTS-V's driveshaft has 2 CVs, so no U-joints.

What I'm confused about at this point is whether the noise/vibration I hear/feel while driving is related to the noise heard in the videos posted above with the car on the lift? I realize the drivetrain can make some different noises when it's rolling along unloaded, as jmd alluded to, but I've never heard anything like what I'm hearing on the lift now.
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Old 02-27-2017, 02:05 PM   #8
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I hear what you're talking about. At first, it sounded to me just like mine does when I jack the rear up and let it idle in gear. the clunking/banging thing i my case was just cam surge combined with lack of rolling momentum to overcome the surge. So, I ignored it and tried to hear a drone int he background. Since you're still stock, thats different. Also, in my case you could hear it at the rear as the diff loaded and unloaded.

but that sound, you're saying it does it on the jackstands, in the air, with the clutch in? Or going down the highway, there is no change with clutch, but in the air there is?

I'm also not sure that the clunking/banging is related to the drone/vibration on the highway. Are you hearing that banging going down the road? What about sitting still in gear, in neutral?

Sorry to be a PITA with the questions. Internet diagnoses are difficult sometimes.
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Old 02-27-2017, 05:55 PM   #9
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You're not being a PITA at all, I appreciate the help trying to figure out what I'm dealing with!

Quote:
Originally Posted by Darth_V8r View Post
I hear what you're talking about. At first, it sounded to me just like mine does when I jack the rear up and let it idle in gear. the clunking/banging thing i my case was just cam surge combined with lack of rolling momentum to overcome the surge. So, I ignored it and tried to hear a drone int he background. Since you're still stock, thats different.
The engine is mildly built - stock LS6 short block, TEA ported heads, mild EPS cam, FAST intake.

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but that sound, you're saying it does it on the jackstands, in the air, with the clutch in? Or going down the highway, there is no change with clutch, but in the air there is?
Driving down the road there is no change if I put the clutch in. On the jack stands / lift, I've only rolled it along at idle in 2nd or 3rd gear, so putting the clutch in means the drivetrain immediately starts coasting down to a stop.

Quote:
Originally Posted by Darth_V8r View Post
I'm also not sure that the clunking/banging is related to the drone/vibration on the highway. Are you hearing that banging going down the road? What about sitting still in gear, in neutral?
The clunking/banging sound is only present when the car is on the lift. I've tried 2nd and 3rd gear, both just rolling along at idle, both do the same thing.

On the road, I don't get the clunking/banging. I get a low, rhythmic drone that is speed related, with very pronounced vibration. Here's the interior clip:


About 40sec in, as I say I'm at 54mph, I accelerate gradually up to about 65mph, and you can hear the rhythmic drone speed up a bit. Later in the video, about 2:10, I slow down to 45mph, and you can hear it slow down as I do that.

No noise when I'm stationary, in gear or out of gear.
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Old 02-27-2017, 05:56 PM   #10
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Quote:
Originally Posted by AAIIIC View Post
It's speed dependent. Shifting from 6th to 4th at highway speed made no difference, nor did putting the clutch in while at ~65mph. It's definitely audible, gets louder the faster I go. It's got a deep tone to it (not high pitched).

Edit: As mentioned in the first post, I do have some in-car video. I didn't upload it to youtube because I didn't think it did a good job of conveying what the noise sounds like while driving, but it's better than nothing, so after work this afternoon I'll upload it and post the link.
Have your rear tires balanced and report back.
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Old 02-27-2017, 05:59 PM   #11
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I'll feel pretty damn silly (but very thankful!) if that's all it is. Can't hurt to give that a shot.
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Old 02-27-2017, 10:35 PM   #12
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That clunking is most likely just the cam then. It lopes even a little, its loading and unloading the driveline.

I hope balancing the rears works. If you didn't have a CV driveshaft, I'd swear your pinion angles were off
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Old 02-28-2017, 02:50 PM   #13
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With 134k miles there's a good chance the 5-6 gear is loose on the mainshaft. If you feel confident it's something in the trans, they are not hard to pull apart. With the trans out of the car you can get to the 5-6 gear to see if it's loose in 10 minutes with just a set of lock ring pliers and snap ring pliers. A simple/cheap puller also for your yoke since it's a ctsv.

Fwiw, on jack stands mine does that knocking also from being unloaded.
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Old 02-28-2017, 04:52 PM   #14
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OK, good to know the knocking sound while unloaded isn't abnormal.

On Thursday after work I should be able to get over to work on the car again, will try putting a different set of wheels/tires on it to see if that fixes it. I've had tires go out of balance before (lost sticky weights) and have never felt vibration like this, but can't hurt to try the free fix!

I have another used T56 sitting at home in a shipping crate, bought it last year to rebuild it and swap out the tranny. I've never messed with a transmission before, but there's plenty of good "how to" info and vids, so I thought it would be interesting to give that a shot. Might have to get off my *** and actually get to work on that plan!
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Old 02-28-2017, 05:39 PM   #15
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I never messed with a t56 before the last month or so, I just rebuilt mine and had the main shaft repair done. If your mechanically inclined it's not that difficult. If you run into a snag, you just need to get on the internet. I laid all the parts out on a table in the order I removed them to help with re assembly.
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Old 03-02-2017, 06:04 AM   #16
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Have your rear tires balanced and report back.
Swapped out the wheels and tires last night, no change.
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Old 03-02-2017, 08:46 AM   #17
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Originally Posted by AAIIIC View Post
Swapped out the wheels and tires last night, no change.
That audible drone is telling you the noise is driveline speeds. At 65 mph, assuming gearing anywhere from 3.23 to 4.11, your tires are making 17 revolutions per second. That's inaudible, but you'll fell it in your gut. You'll feel every pulse.

However, times the gear ratio, and now you're anywhere from 54 to 65 hertz, which is right in the wheelhouse of your stereo subwoofers or the cones on 6x9 speakers. Not that your speakers are picking it up, but making the point that it becomes an audible, bassy drone.

That it doesn't change with gear or even with the clutch in and out is pretty much isolating it from the output shaft of the transmission through the rear yoke. Again, if you had a U-joint driveshaft, I'd be swearing it was pinion angle-related.

I suggest checking your transmission mount for being loose, worn, or deformed. It should be easy enough to swap that mount with the car in the air to a stock replacement mount.

That said, I have experienced a bent transmission output shaft, and you DO get that drone, and you get some pretty violent vibrations in the car. But, That was getting my car to dead hook on the street without a properly built up chassis, so I did all kinds of damage that day. Twisted the yoke, bent the trans output shaft, destroyed the rear, and had to drive 300 miles home like that. Only you would know if you've been that abusive to your car.
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Old 03-02-2017, 12:50 PM   #18
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Quote:
Originally Posted by AAIIIC View Post
Swapped out the wheels and tires last night, no change.


Sorry. I had a 55mph+ vibration from one if my cars that felt like drive line but turned out to be a missing wheel weight that fell off.

Other things:

Inspect motor mounts and transmission mount. I've seen a really bad motor mount really mess with vibration, a buddy couldn't even install a pro 5.0 shifter because his passengers side motor mount was so bad it made the trans sit crooked

Check the exhaust to make sure it is well away from the drive shaft. My wife's bone stock trans am would have a bad vibration under load caused by worn motor mounts and the exhaust hitting the drive shaft

The next thing I can think to trouble shoot would be to pull the drive shaft and wind the car up to it normal vibration point without a drives haft in it to see if it is indeed located in the transmission. You could also pull the diff cover and change the fluid and inspect for damage

If none of that helps or shows any damage, and the car has a vibration without the drive shaft installed, it may be time to drop the trans and inspect the main shaft and pilot bearing. I would plan it as a job to replace the slave throw out bearing and pilot bearing and inspect the main t56 shaft for any wiggle

Last edited by chrysler kid; 03-02-2017 at 01:03 PM.
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Old 03-09-2017, 10:07 PM   #19
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Quote:
Originally Posted by chrysler kid View Post


Sorry. I had a 55mph+ vibration from one if my cars that felt like drive line but turned out to be a missing wheel weight that fell off.

Other things:

Inspect motor mounts and transmission mount. I've seen a really bad motor mount really mess with vibration, a buddy couldn't even install a pro 5.0 shifter because his passengers side motor mount was so bad it made the trans sit crooked

Check the exhaust to make sure it is well away from the drive shaft. My wife's bone stock trans am would have a bad vibration under load caused by worn motor mounts and the exhaust hitting the drive shaft

The next thing I can think to trouble shoot would be to pull the drive shaft and wind the car up to it normal vibration point without a drives haft in it to see if it is indeed located in the transmission. You could also pull the diff cover and change the fluid and inspect for damage

If none of that helps or shows any damage, and the car has a vibration without the drive shaft installed, it may be time to drop the trans and inspect the main shaft and pilot bearing. I would plan it as a job to replace the slave throw out bearing and pilot bearing and inspect the main t56 shaft for any wiggle
I was about to make a thread as im having a similar issue with my t56 making a noise and a vibration at 55mph and up gets worse.

I dont doubt my 02 fbody t56 needs to be rebuilt but my concern was how to tell if the output shaft is bent and the noise is coming strictly from the trans..or my diff and driveshaft. I do notice the kinda rattling sound does come from the shifter area..only under heavy load at lower rpm.The vibration itself is present 55+mph.

You mentioned to pull the driveshaft out and running the car upto highway speeds and see if there is any noise or vibration.is there any downsides to trying this in my driveway...losing trans fluid or anything that could go wrong..and would the clutch alone be enough load to be an accurate way to diagnose the issues. I can afford a basic stage 2 rebuild kit but if i need to add a mainshaft..bearings etc.it goes from a mid $500 kit to $1000.

Thanks
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Old 03-09-2017, 11:08 PM   #20
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Quote:
Originally Posted by Redbull87 View Post
I was about to make a thread as im having a similar issue with my t56 making a noise and a vibration at 55mph and up gets worse.

I dont doubt my 02 fbody t56 needs to be rebuilt but my concern was how to tell if the output shaft is bent and the noise is coming strictly from the trans..or my diff and driveshaft. I do notice the kinda rattling sound does come from the shifter area..only under heavy load at lower rpm.The vibration itself is present 55+mph.

You mentioned to pull the driveshaft out and running the car upto highway speeds and see if there is any noise or vibration.is there any downsides to trying this in my driveway...losing trans fluid or anything that could go wrong..and would the clutch alone be enough load to be an accurate way to diagnose the issues. I can afford a basic stage 2 rebuild kit but if i need to add a mainshaft..bearings etc.it goes from a mid $500 kit to $1000.

Thanks
When testing for the loose 5-6 vibration on my car, I ran it through the gears with no driveshaft, just a plastic tailshaft plug. That test was inconclusive for me because you couldnt really feel much vibration with no load on the trans.

How many miles are on your trans? Ive come across some t56's in my searching that were under 100k miles and had the loose gear. Not saying thats your problem. Do you get vibrations in 4th gear or just 5-6?

Jason at Texas Drivetrain Performance just repaired my mainshaft for $100, so not as expensive as you might think.
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