[KaiserN54]

I have always had some sort of hum from the rear of my car when running a tune and WOT in higher gears. (I have a Wavetrac LSD). I recently got my flex-fuel flash and all supporting mods done. (FBO). Now, 1-2 gear are scary fast, but 3-6 will violently vibrate under WOT after climbing about 2k or so. The timing of the onset of this vibration is very much a function of load, but as soon as I let off it stops. I don't have any codes except a shadow active front steering code and an intermittent IBS code (also shadow- no half engines)

The vibration FEELS like it is coming from the drivetrain, but I know it could be misfire/timing/fuel issues that I am feeling, but I never really know how to read the datalogs I capture.

I did some quick rolls in 4th gear @ 3200rpm- with sudden acceleration. Like CLOCKWORK, a few seconds in and the car feels like it is going to blow up. I am suspecting my LSD is f**ked and is failing under maximum torque, or something like that. Hopefully it is something else that I can fix with some optimization in procede.

Here are some screen captures. Can anyone help?

[HellsBells]

I had what sounds like the same issue, turned out to be carbon buildup.

[KaiserN54]

Originally Posted by HellsBells

I had what sounds like the same issue, turned out to be carbon buildup.

No, had walnut blasting done 10k ago.

[Wedge1967]

I don't think you have a tuning issue. Sounds like something is shifting under load and is out of balance causing the vibration. You need to get this into the shop and have the drivetrain pulled down to make sure everything is ok before it comes apart completely and breaks something else.

[ashmostro]

^agree

[Jeff@TopGearSolutions]

When was the last time you checked the torque spec on your lug bolts on all 4 wheels? Seriously. I've seen it on cars before. I dont think you have a tuning issue but a mechanical within the drivetrain.

[KaiserN54]

Originally Posted by Jeff@TopGearSolutions

When was the last time you checked the torque spec on your lug bolts on all 4 wheels? Seriously. I've seen it on cars before. I dont think you have a tuning issue but a mechanical within the drivetrain.

So fuel trims, timing look okay? I don't think its the lug nuts because it was doing this earlier in the day, went and got new rear tires...still acting exactly the same. Plus it only does it under a certain amount of load

[3-Serious]

Originally Posted by KaiserN54

I have always had some sort of hum from the rear of my car when running a tune and WOT in higher gears. (I have a Wavetrac LSD). I recently got my flex-fuel flash and all supporting mods done. (FBO). Now, 1-2 gear are scary fast, but 3-6 will violently vibrate under WOT after climbing about 2k or so. The timing of the onset of this vibration is very much a function of load, but as soon as I let off it stops. I don't have any codes except a shadow active front steering code and an intermittent IBS code (also shadow- no half engines)

The vibration FEELS like it is coming from the drivetrain, but I know it could be misfire/timing/fuel issues that I am feeling, but I never really know how to read the datalogs I capture.

I did some quick rolls in 4th gear @ 3200rpm- with sudden acceleration. Like CLOCKWORK, a few seconds in and the car feels like it is going to blow up. I am suspecting my LSD is f**ked and is failing under maximum torque, or something like that. Hopefully it is something else that I can fix with some optimization in procede.

Here are some screen captures. Can anyone help?




Attachment 863697





Attachment 863698

I have the same problem! Just installed my LSD like 3-weeks ago it started happening after about a week. It only happens when I shift into gear from 3rd-4th and up. I was at a local shop today everything in my rear seems to be nicely locked down and tight. Are you a 6spd? I also had VAC do my install and watched him do it, so i doubt its my diff. My shop told me It might be my tranny mounts. I also have the lock down kit as well and he said it could be the transmission moving around because it needs a place to send the shift.



On seconds thoughts I think I miss read your post you are having a vibration during acceleration? Not just during the shift? I wonder if it could still be you tranny mounts? On rouge engineering they have tranny mounts and said under load with weak mounts the transmission can wiggle back and forth.

[m_fife]

I've got the same issue with just JB4. I've done some research on n54tech.com and the general consensus is that it is the DM Flywheel. If you switch to a regular flywheel it goes away.

[Jeff@TopGearSolutions]

Originally Posted by KaiserN54

So fuel trims, timing look okay? I don't think its the lug nuts because it was doing this earlier in the day, went and got new rear tires...still acting exactly the same. Plus it only does it under a certain amount of load

Unless fuel trims exceed 30% they are not an issue.

[Dave W.]

Yes it could be the DMFW if it's getting old. How many miles on the flywheel? Your datalogs shows the rpm line is just a little wavy, can you post the csv or maybe just look at the csv yourself and see if the rpm jumps or rises steadily? If the DMFW is getting worn and loose it might show up in the rpm log.

[Dave W.]

I just had a few more ideas for you to consider.
I once saw a car that threw a code for steering sensor, and it was because the alignment of the rear wheels was bad. It threw the code because the rear end was tracking slightly sideways. Have you checked alignment lately? You just had the rear tires replaced, was the tread wearing unevenly on the old tires?

The driveshaft carrier bearing can cause vibration if it's installed upside-down. It's fairly common since it needs to be removed when installing a rear diff or when installing a clutch.
HTH

[KaiserN54]

Originally Posted by Dave W.

I just had a few more ideas for you to consider.
I once saw a car that threw a code for steering sensor, and it was because the alignment of the rear wheels was bad. It threw the code because the rear end was tracking slightly sideways. Have you checked alignment lately? You just had the rear tires replaced, was the tread wearing unevenly on the old tires?

The driveshaft carrier bearing can cause vibration if it's installed upside-down. It's fairly common since it needs to be removed when installing a rear diff or when installing a clutch.
HTH

I had an alignment done with the new tires. The rear diff was installed almost a year ago. I have a newish ACT clutch, but they resurfaced and reused my DWFW...I wonder if that's it? It only seems to happen under peak load, and I have honestly always some sort of hum/ vibration from the back, at least when running a tune.

[Jeff@TopGearSolutions]

Originally Posted by KaiserN54

I had an alignment done with the new tires. The rear diff was installed almost a year ago. I have a newish ACT clutch, but they resurfaced and reused my DWFW...I wonder if that's it? It only seems to happen under peak load, and I have honestly always some sort of hum/ vibration from the back, at least when running a tune.

BINGO

Resurfaced DMFW goes wrong about 90% of the time that's why we always recommend a NEW DMFW.

[Cripple]

Originally Posted by Jeff@TopGearSolutions

BINGO

Resurfaced DMFW goes wrong about 90% of the time that's we always recommend a NEW DMFW.

What he said - Porsche uses a DMFW on Manual applications in 911's and recommend only new DMFW's for this specific reasoning.

I would get this replaced ASAP!

[Jeff@TopGearSolutions]

Originally Posted by Cripple

What he said - Porsche uses a DMFW on Manual applications in 911's and recommend only new DMFW's for this specific reasoning.

I would get this replaced ASAP!

Not to be the bearer of bad news but it's possibly he may need a new clutch too. I've seen this happen a few times already when a customer gets the DMFW resurfaced it ends up messing up the clutch. I'm not 100% positive in this particular instance until the clutch is pulled out and a professional can examine it.

I'd also get rid of the ACT clutch and go for the Spec. The ACT clutches have a short life span and horrible drivability in comparison to the Spec Clutch Kits on this platform.

[Dark9T]

Same to me after LSD installed, I got a AT..

[KaiserN54]

Originally Posted by Jeff@TopGearSolutions

Not to be the bearer of bad news but it's possibly he may need a new clutch too. I've seen this happen a few times already when a customer gets the DMFW resurfaced it ends up messing up the clutch. I'm not 100% positive in this particular instance until the clutch is pulled out and a professional can examine it.

I'd also get rid of the ACT clutch and go for the Spec. The ACT clutches have a short life span and horrible drivability in comparison to the Spec Clutch Kits on this platform.

I kind of figured that. I would need to get a new clutch anyways if this is what is wrong b/c I would go with a SMF. The car is going to the LSD installer tonight to get looked at.

[KaiserN54]

Cars at the shop now, and it is confirmed to be internal from the diff. Thank goodness for warranties...

[KaiserN54]

Originally Posted by KaiserN54

Cars at the shop now, and it is confirmed to be internal from the diff. Thank goodness for warranties...

Okay, NOW they are saying the diff is fine, and that they suspect something with the driveshaft. Anyone had any experience with driveshaft failure on these cars before? All searches seem to only reveal old threads- nothing on point.

[KaiserN54]

WTF!! Now the garage is saying that the vibration they detected differs from the vibration I reported- which is "much worse than what we previously diagnosed." The garage maintains the the cv joint on my draftshaft is binding, but they aren't confident that this will fix the violent vibration! The mechanic said the car is definately f*** up, but he doesn't know what else it could be. He seems sceptical that it is the DMFW, because the rumble is intermittent.

I would really appreciate any other opinions others might have on this...

WTF is wrong with my car?!?! Please someone help!

[///Mposter]

I would say to put it on a lift and get the RPM up to see what was vibrating but that may cause other issues if only two tires ( rear) are moving . Maybe use a GO-PRO under to see if something looks off. Someone once told me that they had a neon with an issue . They kept replacing tires at the dealer, redoing balancing and could not find it. He asked them to put it on a lift and had the car in drive. The midshaft attached to the engine was bent from the factory. Once replaced , all vibration was gone. You have to visually see it to know what out of round, or it will be a costly trial and error process of elimination .