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Discussion Starter · #1 ·
Alright, I've been working on this car for quite some time chasing what i thought was a drive line vibration. This started early 2020 and has been getting worse, yet more refined as of late.

As a reference, the modifications necessary to follow this post are as follows:
  • GForce 9" IRS kit w/ Outlaw axles
    • 4" Aluminum one-piece driveshaft
    • Strange aluminum 3rd member
    • GForce IRS housing w/ plate front mount
    • Red poly bushings
  • VMR V810 wheels (19X10.5 R / 19x8.5 F)
  • Monster Triple Disk Clutch
  • Stock manual trans

It's a higher-frequency vibration which does not correlate with engine speed nor whatever gear i am in - it is solely affected by ground speed, and appears at approximately 80mph on-wards.

As always, I started with the simple checks: tightened lug nuts, loose body panels, wheel imbalances, etc. etc. etc. Balanced, re-balanced, and balanced again. Not the issue. Frequency of wheel imbalance is much lower than what I experience.

Messing around one day, i noticed the tone generator app on my phone and it gave me an idea: see what frequency the vibration is at speed. Turns out to be around 75Hz at 80mph. This got me thinking and I then did some math to attempt to figure out what may be spinning at that frequency, and it turns out the driveshaft spins at ~4500rpm (or 75Hz) and climbs with the ground speed.

Aha! This must be the problem.

I pulled the driveshaft and had a shop take a look. They found bad u-joints (only in one axis somehow?) and put it on the balancer. Threw the driveshaft back in the car...and the vibration was still there. So i took the driveshaft back and had them inspect it again; this time, the driveshaft took weight to balance (weird).

Still didn't fix the vibration.

From there, i decided to check out the rear end because it was making noise on accel (a sign of a bad pinion bearing?) and drained the gear oil. That oil was on-par with the black diamond tri-coat which was NOT good. On top of that, the diff housing was effectively wedged against the rear subframe, potentially making the vibration transfer even worse! Luckily, GForce willingly took the housing back and redesigned it with new hardware to make it fit just right. I also got a new gear-set with bearings and seals from Strange. Threw everything together to-spec.

This still didn't fix the vibration.

I am getting fed up and more annoyed. The car makes north of 700 whp on corn and i am limited by this vibration which gets worse after 80mph!!!

I had my driveshaft shop build me a custom 4" one-piece which has billet 6-bolt flange to 1350 u-joint coming off the trans, and a 1350 yoke for the Strange 3rd member. I know that thing is silky smooth, but i still get the high frequency vibration.

As of last weekend, I have replaced all four hub bearings and completed a rotor and pad job (thanks for the 2-piece rotor posts!). I found during this job that the inboard CV on the passenger side had a severely ripped boot and the grease was like clay...

GForce had me send the axles back for inspection and confirmed my concerns about the bad CV, and are currently RMA'ing both axles.

Could this be the culprit? I am in no way familiar with how CV's behave on our cars.

I also have a set of BC Forged wheels which were delivered yesterday, so that will be a fresh slate to drive on.

After replacing the differential parts and installing the new driveshaft, the vibration seemed to be more refined - as in, extremely repeatable. When cold, it comes in at 85mph and gets progressively worse, with the vibration intensity being more severe in between the engine driving the wheels and the wheels driving the engine (almost like in between gear lash). But it doesn't dissipate when decelerating. Only below 80mph.
When the car is warm (having been driven around for ~30 minutes), the vibration creeps in around 78mph and the intensity is worse from then on. Definitely affected by component temperature(s), whatever that's worth. The vibration does not show anywhere else in lower ground speeds, only at and above the speeds mentioned prior.

So, to recap, I have
  • Balanced, re-balanced, and balanced my wheels
  • Had the original one-piece DS inspected and balanced twice
  • Had a new one-piece DS made (bitchin' job AZDS!)
  • Replaced the subframe bushings with black poly (much more planted rear end w/ minimal noise intrusion)
  • Rebuilt my entire 9" with new gears, seals and bearings
    • Had GForce inspect the diff housing and correct improper housing placement within the subframe
  • Replaced all four wheel bearings
  • Installed all new rotors and pads
  • Ordered new wheels
  • Sent axles back to GForce and am awaiting their return

If the axles do not solve the issue, I'm really not sure where else to look next. I would hate to have to tear into my transmission, but it seems unlikely due to the nature of the vibration itself.

If there is any one on here that can shed some light on something i may have not thought of, PLEASE let me know. I want to get back to doing freeway pulls the speed limit!
 

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Discussion Starter · #5 ·

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Describe the noise more. Does it sound like something grinding or is it almost like an electrical frequency in the cabin?



Sent from my SM-G991U1 using Tapatalk
 

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Discussion Starter · #9 ·
Describe the noise more. Does it sound like something grinding or is it almost like an electrical frequency in the cabin?



Sent from my SM-G991U1 using Tapatalk
It sounds like an unbalanced driveshaft, effectively. But it’s not because I’ve replaced it with a known good shaft. It’s almost like bearings hitting a flat spot.
 

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I have a very similar issue with mine, have been throwing parts at it over a year trying to fix. Have tried most of what you have. The only things I can recommend not already mentioned: 1. Confirm the torque spec on driveshaft is correct with a good torque wrench, not under or over tightened. 2. If possible, try swapping back to a stock diff/driveshaft/clutch. That is exactly where I'm at now in my situation, just waiting for one more part to get in. 12 Vagon here also, 74k miles, 690 rwhp. My vibration is a rolling vibration between 78-94mph approximately, evident every 4 seconds at those speeds with 3 seconds of smoothness in between.
 

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I have a very similar issue with mine, have been throwing parts at it over a year trying to fix... My vibration is a rolling vibration between 78-94mph approximately, evident every 4 seconds at those speeds with 3 seconds of smoothness in between.
Xanax is cheaper, Brah! :p
 

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Driveshaft torque was good. Then I replaced the aluminum driveshaft with stock as well as the differential, also stock. Then I swapped the front tires with each other. NO CHANGE whatsoever. Same vibration, same frequency, same speed range. I'm swapping rear tires with each other tomorrow but don't expect anything to change. So frustrating, and it seems no one else has this same issue that I can find. I assume if it was a bent wheel, something would change when swapping wheels left to right...maybe not. Next up on diagnostics:

1. Have someone sit in the car when it is going 85 mph on a dyno, and have someone else underneath the car looking for the vibration.
2. 4 wheel alignment / road force balance.
3. Replace the clutch with another stock clutch.
4. Motor mounts? I know the previous owner replaced them not long before I bought it.
5. FInd someone local with a V who would be kind enough to let me install their 4 wheels with tires and drive around for 15 minutes to eliminate them as a possibility.
6. Replace all suspension.
7. Xanax (haha just kidding). It's severe enough where I don't think it would help.
8. Sell the car. I love this thing but with the way it is now, if I can't eliminate the bad vibes and take it on road trips not sure what else to do.

Any more suggestions would be greatly appreciated.
 

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Discussion Starter · #17 ·
Driveshaft torque was good. Then I replaced the aluminum driveshaft with stock as well as the differential, also stock. Then I swapped the front tires with each other. NO CHANGE whatsoever. Same vibration, same frequency, same speed range. I'm swapping rear tires with each other tomorrow but don't expect anything to change. So frustrating, and it seems no one else has this same issue that I can find. I assume if it was a bent wheel, something would change when swapping wheels left to right...maybe not. Next up on diagnostics:

1. Have someone sit in the car when it is going 85 mph on a dyno, and have someone else underneath the car looking for the vibration.
2. 4 wheel alignment / road force balance.
3. Replace the clutch with another stock clutch.
4. Motor mounts? I know the previous owner replaced them not long before I bought it.
5. FInd someone local with a V who would be kind enough to let me install their 4 wheels with tires and drive around for 15 minutes to eliminate them as a possibility.
6. Replace all suspension.
7. Xanax (haha just kidding). It's severe enough where I don't think it would help.
8. Sell the car. I love this thing but with the way it is now, if I can't eliminate the bad vibes and take it on road trips not sure what else to do.

Any more suggestions would be greatly appreciated.
I’m pulling the trans here soon and doing a refresh, I’m thinking it may have to do with some endplay or bearings going out. Mine has a temperature aspect, too. When it’s cold (sitting overnight or longer), the vibration is more of a hum at 80 before getting severe; once the car warms up, the vibration comes in earlier - around 75. I’m thinking something in the trans on the output-side is going out and taking parts along with it.

Just my input as to where this is going.
 

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I’m pulling the trans here soon and doing a refresh, I’m thinking it may have to do with some endplay or bearings going out. Mine has a temperature aspect, too. When it’s cold (sitting overnight or longer), the vibration is more of a hum at 80 before getting severe; once the car warms up, the vibration comes in earlier - around 75. I’m thinking something in the trans on the output-side is going out and taking parts along with it.

Just my input as to where this is going.
What are you doing to refresh it? I'm pretty ignorant as far as manual transmissions...not familiar with any components other than clutch, flywheel, shifter, etc.
 

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Discussion Starter · #19 ·
What are you doing to refresh it? I'm pretty ignorant as far as manual transmissions...not familiar with any components other than clutch, flywheel, shifter, etc.
First, I’m going to drain and replace the fluid and see if there are any significant chunks not picked up by the case magnets.

Then I’ll probably have it built up a bit to withstand the car’s power. Bronze shifter fork pads, carbon blocker rings, new seals and bearings/bushings throughout, and new gears (maybe cryo-treated). Will also have the shop look at the shafts and check runout, to verify everything looks ok.

At this point, I have nowhere else to throw money at which is related to the problem. If the new trans doesn’t fix the issue, y’all will be seeing it on the classifieds
 

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First, I’m going to drain and replace the fluid and see if there are any significant chunks not picked up by the case magnets.

Then I’ll probably have it built up a bit to withstand the car’s power. Bronze shifter fork pads, carbon blocker rings, new seals and bearings/bushings throughout, and new gears (maybe cryo-treated). Will also have the shop look at the shafts and check runout, to verify everything looks ok.

At this point, I have nowhere else to throw money at which is related to the problem. If the new trans doesn’t fix the issue, y’all will be seeing it on the classifieds
Please let us know if the trans rebuild helps in any way! I just re-read your posts and saw where your issue is primarily a noise-type of vibration. Mine is a shudder felt throughout the car, but not constant, just recurring at an interval not consistent with the speed of 79-90 mph as one would expect. Sorry to hijack your thread, but I thought it might be helpful even if our vibrations are different... would be great if we found someone who had our issue and chimed in with a positive fix.

Where are you located by the way? I'm in Charlotte NC.
 
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