dcbrooks3

Hey Guys,

I have been lurking since I bought an '02 C32 four years ago. Your threads have helped me keep it running with my own wrenches, but I've got an issue that I just can't figure out.

I have a vibration that is coming from the rear of the car and felt through the steering wheel (mainly) and frame. I know that it is from the back end because I set the rear end on jack stands and ran it up to 47 mph indicated without the wheels on. There was no change from being on the road.

The attached file details my findings, and I would really appreciate any help. (I had a wonderful write-up, but it was too many characters (embeded pictures?) and the system deleted it. Ouch!)

Without going into all the details, here is what I know:

1. The vibration starts at ~40 mph, peaks at 47 mph, and diminishes until 60 mph. However, from an accelerometer, it is still present at 80 mph but cannot be felt.
2. The vibration is the same under power or in neutral while at speed.
3. The peaks at ~10 Hz and ~34 Hz correspond with the half-shaft and drive-shaft rotations.
4. The vibration is present with the rear end off the ground and wheels removed.
5. Removing the 4mm Vertical Differential Mount Shim had no effect.
6. The Differential Mounts "look" okay.
7. The Rear Flex Disc has some micro-cracking.
8. The vibration may diminish with driving time, but I don't have any real data to support this.

I am ready to replace the Differential Mounts, Differential Oil, Differential Shim, and Rear Flex Disc but don't really want to troubleshoot by parts replacement. Due to the accelerometer data, I am convinced that it has something to do with the Differential. However, it could be something else (Half-Shaft Universals, Drive-Shaft Center Bearing, too much exposure to the Solar Eclipse).

Please take a look at the attaced Word document. Any help or advice would be greatly appreciated.

-dcbrooks3

TL/DR: Vibration in the steering wheel at the same frequency as the Half-Shafts and Drive-Shaft.

mars-red

Very interesting! I'm pretty new to C32 ownership, but have a few mechanical bones in my body. Off the top of my head, I can think of a couple tests you could try to help narrow down the cause. The easier of the two would be to set it up with the rear wheels off the ground, like you had, and put a jack underneath the rear diff to really load up the diff mounts. If the problem is sloppy diff mounts, then I think that would greatly reduce or eliminate the vibration. Then what about the same test with the rear half shafts removed?

Regarding the driveshaft support bearing (center bearing), you should be able to feel if it has excessive play by grabbing the driveshaft tight and applying abrupt radial force to it. The human body is able to detect amazingly minute amounts of movement.

I wonder also if the transmission mounts should be something to consider.

I can't think of anything internal to the diff that would cause this, without causing other much more severe and noticeable symptoms.

I'm drawing a blank trying to come up with a way to test the flex couplings on the driveshaft. Are you familiar with using dial indicators? You might be able to set up a dial indicator on a mag base, and observe runout of the driveshaft at either end. If you had much worse runout at one end versus the other, that could indicate a flex coupling problem. The problem with that approach is that I think you'd first need to somehow rule out any excessive misalignment between the transmission output and the diff input. A brand new flex coupling trying to compensate for too much misalignment isn't much better than an old, worn flex coupling trying to compensate for the same misalignment.

Anyway, maybe my brainstorming will spark some ideas that help you out.

Morphh

dcbrooks3

I'll have to give some thought to loading-up the Differential mounts with a jack while under power. (I was nervous enough running it with the rear end lifted. The computer did not appreciate the rear wheels turning with the front wheels stationary.)

Would transmission mounts come into play when the car is coasting in neutral? The vibration is just as strong in neutral.

I am very familiar with dial indicators but would expect a mis-alignment to get far worse with shaft speed.

I guess the big question is why I have the high (~34 Hz) and low (~10 Hz) vibrations. The ratios pretty much match the Differential ratio. What can cause both of those?

dcbrooks3

The Control Arms were replaced at Christmas due to normal wear. The Rear Flex Disc has some microcracking, and the Front Disc looks okay from what I can see. Since the vibration was still there with the Rear End lifted and running, the Front End is pretty much eliminated as a source.

Yesterday was warmer, and the vibration seemed to be less. This morning was cold again, and the vibration was stronger. We will see in the next few weeks what this does.

I noticed that this thread has a lot more views than the attached document. The verbage of it (without the cool accelerometer shots or car pictures) is shown below.

Troubleshooting Steps

New Tires
1/19/17 – Rear
4/11/17 – Front
Evaluation: No Change from Before

New Front Brakes
11/18/17 – Discs
11/18/17 – Pads
Evaluation: Not Measured

Checked Wheel Bearings
11/18/17 – Front
Evaluation: No Change from Before

New Control Arms
12/22/17 – Front Upper
12/22/17 – Front Lower
Evaluation: Not Measured

New Tie Rods
12/29/17 – Inner & Outer; Both Sides
Evaluation: Not Measured

4-Wheel Alignment
1/2/18
Evaluation: No Change from Before

Balanced Tires
2/1/18
Evaluation: No Change from Before

Swapped Each Tire with the Full-Sized Spare
2/9/18
Evaluation: Possible Lighter Vibration when Left Rear Swapped – Last Tire Checked

Tested for Vibration @ ~47 mph in Neutral
2/12/18
Evaluation: No Change from “Under Power”

Raised Rear End on Jack Stands; ~47+ mph
2/16/18
Evaluation: No Change from Normal Driving

Raised Rear End on Jack Stands & Removed Wheels; ~47 mph
2/23/18
Evaluation: No Change from Normal Driving

Removed 4mm Shim from Differential Mount; Road Test @ ~47 mph
3/2/18
Evaluation: May be more sensitive to Temperature

Road Test @ ~47 mph for 15 miles, ~80 mph for 10 miles, ~47 mph for 1 mile
3/7/18
Evaluation: Higher Frequency Vibration too High for Measurement
Bad Vibration @ ~47 mph;
Measured Vibration @ ~80 mph;
Low Vibration at @ ~47 mph

Inspected Rubber Components
3/16/18
Evaluation: Some Component Wear

Exclusions:
Not Front End Related (Vibration present when the rear end is in the air with power)
Not Engine Related or Engine Mount Related (Vibration present in neutral at speed)
Not Tire or Wheel Related (Vibration present when the rear end is in the air with power)

Inclusions:
Vibration is always there (47 & 80 mph measurements)
Temperature may be a Factor

Unknowns:
Driveshaft Alignment (4mm Shim removal was inconclusive)

Conclusions:
Drivetrain Related (Rear End lifted with power)

To-Do:
Replace Differential Oil
Replace Rear Flex Disc
Replace Differential Rubber Mounts
Check Center Support

Morphh

PJmak

Was the car ever in an accident??

Morphh

dcbrooks3

The vibration is there with the car stationary, the rear end lifted on stands, the rear wheels removed, and at an indicated speed of 47 mph. The wheels cannot be the issue.

dcbrooks3

I've known the original owner since he bought the car in '02. Never in an accident, and all work performed at the dealer.

Morphh

PJmak

Its gotta be a driveshaft.

Sounds like you narrowed it down to that yourself.

Either that or maybe the diff??

c32jet

Hello dcbrooks3, did you ever figure it out? I have long had this issue and worked through many of the potential solutions you mention with no success of getting to root cause.

Morphh

I went through this and it was the front upper back control arm bushing was gone replaced all 4 of them and everything is perfect bow

c32jet

Thanks Morphh... any chance you have the part number for the control arms?
I am at 147K and figure for sure there would be no harm is putting some new ones on.
I may do the control arms for fun if it turns out an axle replacement is a much bigger job.

I saw your post on the bent axle and remembered that I did blow out a rim around the time this started... spent time today looking at how much and how easy an axle is to replace... I had never considered it might be a bent axle. Also the issues seems to be getting sloooowly worse. The issue is not terrible, just annoying. One item that did seem to make a bit of a difference in the vibration was the 4MM (Stock?) differential spacer. I have a 1MM in there now.

Below are pics of the rim. I still had in the garage. I hit a piece of concrete on the freeway. It popped up just perfectly when a truck hit a pot hole and rolled under me to instantly take out the rim and tire.

c32jet

Morphh... any chance you have the part numbers? Or can you drop of a pic of which control arm and bushing this is?
I should probably be able to figure this out ... just that unsure if 'front upper back control arm' is in the front of the car or the back of the car.. weekend mechanic working to save a few bucks. thanks for your help.

Also is the fix two control arms on each side (2 for passenger side / 2 for driver side)

Morphh

I bought mine from fcp euro u need front upper lower back febi is brand name which Is oem
I thought vibration was wheels got brand new wheels and road forced balanced and vibration was still there I did sway bar bushings and links vibration was still there once I did control arms 2 per side vibration went away I will check for part number
same i do all work myself
front upper u have to loosen shock tower connected to knuckle u need thin wall sockets to loosen it I forget size

c32jet

Thanks Morphh... how do you get to this bolt? See pic. Also is there a special torx or something to get the bolts out?
Yes, big fan of FCPEuro - looking at this kit... is this one that would cover what you replaced?
Not sure they offer one for the c32... this kit below wont fit a c32 from what I can tell...
https://www.fcpeuro.com/products/mer...PrQQAvD_BwE#qa

To get to the bolt it almost look like the frame has to drop or something... seems these things are never as easy as you would hope. Thanks for your help.

Morphh

That is rear of car
I thought u had vibration in steering wheel front of car
go get rear wheels and tires road forced balanced they will print out sheet to see if wheels are warped bent etc.
Most common issue in rear would be sway bar bushings and links then lower control arm

c32jet

Yes, you are correct, this is a photo of my driver side rear... which is where I thought you had fixed your issue.. ;- )
To be honest, I am not sure where the vibration is coming from... I have changed motor mounts, trans mounts, checked my center bearing and replaced both flex disks. Also sent my trans fluid off to see if I had contamination as I still have the valeo radiator... came back good (no glycol contamination). So now I am reviewing possible fixes - suspension / bent axel / drive shaft (not sure why it would 'get' out of balance).
I've tried new tires, alignment, etcs... was open to digging into the suspension as the car has 150K on it and runs like a champ. Just this little vibration around 40 mph bugs me.. it feels like something is 'rubbing'... like a bearing. I have put on new front bearings... vibration is still there... bough new rear bearings.. then had to punt as that will be a bigger job for me. Thinking due to my rim blow out (above in thread) that this is a real possibility. Also, I am running the 1MM spacer in the differential and this 'did' help but did not remove the vibration entirely. And... was considering a full refresh on the front suspension, easier than the back as I have now found... at 150K I cant go wrong doing suspension both front and back. Thanks for your help.

c32jet

Now re reading some of this thread and your comments... sway bar... I do recall that way back when I took it to the dealer to replace the front lower bushings (had the funky 'THUNK' sound) that they stripped out one of the front sway bar bolts on the passenger side.... will have to go back and check that.
Thanks.

Morphh

U run spacers on wheels? I bet that is your problem
check brakes emergency brake shoe etc

c32jet

Hi, no on the wheel spaces... everything 100% stock. Yes, I will check on the emergency brake and brake shoes as well.
So on the front control arms you replaced.... can you share some pics or part numbers? Thanks.

c32jet

Update - I think I have finally found it... went back and checked the control arms and sway bars and bits... I was running the 1MM spacer in the differential... I took it out and am running with no spacer now and I believe this is it! Just took her for a test run and silky smooth.... wanted to share. Hope this helps someone.

c32jet

DCBrooks did you get this figured out? I am still chasing it... I thought I had it figured out... was wrong. I did your experiment today by putting the back end on jack stands. First run with rear wheels on the car... around 45-47 got the vibration. Car is cold and has been sitting for a day. Second run rear wheels off, car still cold... same result. Got the vibration around the 45-47 MPH mark. I had to clear the No ESP / No ABS lights after each run as the car did not like the rears at different speeds than the fronts.

I should also mention that I too notice a 'temperature' difference. What I mean is that when I take it out cold.. (not driven in a day or so) I feel the vibration much more initially than later when the car is warmed up and has been driven 10 min or so. At the 10 minute mark the car is actually pretty good and likely only I would notice the slight vibration. Also I have gone back to the 4 MM spacer on the differential. I've checked the parking brake and lubed it up fresh and all looked in working order there. Also checked all my rims, all good there. Almost new tires all the way around.

I think we can eliminate the wheels being the issue. I've swapped the fronts side to side and now also the rears today. Just took it for a spin and see no difference and again confirmed the vibration is heaviest on the first or second 45 MPH run. Then seems to diminish after a few minutes of driving but does not entirely go away. I can feel the vibration most during deceleration.

Interested in the experts thoughts here... thanks. Thinking about the front suspension refresh again... Have not done the front upper control arm bushings yet...