Background:
Excessive steering wheel vibration that comes and goes in exact intervals while driving on long curved part of a road at highway speeds. (Highways and ring roads with new uniform surface)

Example 1: Driving on a curved part of a road at 60mph. In the beginning no vibration in the steering wheel. After a certain distance while still driving at the same speed on the same long curved part of the road steering wheel starts to vibrate. Minimal vibration at first that slowly becomes excessive to the point I can feel the car shake, then becomes minimal again and finally no vibration. If I continue driving on the long curved road this will repeat.

Example 2: The same situation as in Example 1, but If I exit the curve on to a long straight portion of the road while the steering wheel is NOT vibrating, the vibration doesn't come back, until I enter another curve and the whole thing starts again.

Example 3: The same situation as in Example 1, but if I exit the curve on to a long straight portion of the road while the steering wheel IS vibrating, the vibration continues until I enter another curve and then it goes away, and then comes back and the whole thing starts again.

Based on that I figured it has to be both - left and right side of rotational assembly. Due to difference in wheel travel between left and right side of the car while on a curved part of a road the defect in rotational assembly is aligning and miss-aligning in set intervals.

In the last 2 months I have tried, replaced or re-checked the below items in the front suspension with no resolution to vibration.
- Brand new rims and tires. Checked and balanced twice by 2 different shops. (no faults found)
- Winter tires and rims
- Brand new balljoints
- Brand new brake discs
- Brand new brake pads
- Wheel alignment

Currently trying:
- New bearings (No click or play while compressed with axle nut. Old bearings were just couple of years old - *** brand).
- New Inner/outer tie rods (going back to stock, previously Elephant Racing)
- Serviced axles (one boot was torn (~ 0.5in tear, still plenty grease inside)

But...
I came across an interesting find with the front axles (axles were never serviced before I opened them). No pits or excessive wear on bearings or bearing surfaces. Grease was still OK looking. I assembled the axles in the exact same way they were before. I noticed it before and after rebuild - the inner CV were binding on both axles when the CV joint was compressed.

Is it normal?

 

Engine mounts and transmission carrier bracket/bushing?

 

All bushings, mounts all throughout are newer (max 4 years old). No play in lower front control arms or rear trailing arms. New steering rack bushings too. All Porsche parts.

 

I have experienced something similar. If there is a slight imbalance in both front tires, when going around corners, the imbalances can synch up and reinforce the the vibration or cancel it out. Since the outer wheel in the corner is going faster it causes the imbalance points to change position relative to each other.

 

Balanced the wheels twice. Checked for bends. Checked for rubber uniformity. Both times they balanced correctly and the rims are true.

 

It sounds as though you have been very thourough possibly check any movement at the strut bearings at this stage they could be very old...
Bert

 

All top mounts are new Porsche parts (1 year old).

I might do dynamic road force balance to be 300% sure it's not the wheels.
Also, another thing I can possibly try is to balance the wheels through lugs.

 

I had a similar problem and it turned out to be a faulty CV axle. It was one of the front. I had replace 3 of the 4 axles but my mechanic said the last one was serviceable, so he rebuilt it and we assumed it was ok. The problem persisted and went away when we replaced it. I have a thread about it. Let me see if I can find it.

Edit - My thread - https://rennlist.com/forums/964-foru...-bearings.html

 

Checking your thread.
Thanks!

Andrew

 

Hi Andrew - sorry for your troubles. Agree with Bert that you've been thorough in your analysis so far. You mention front axles - so assume you have a C4. Some rando thoughts/brain dump below:

Have you done any PDAS troubleshooting? Have you recently serviced, or otherwise checked the function of the related components - accelerometers, longitudinal/transverse locks, solenoid, wheel speed sensors, etc.? When was the last time you flushed and bled the system? Have you scanned (i.e. Durametric, etc.) for any system faults? Checked the ABS/PDAS control unit connectors (both on the harness side and the control unit side) for any corrosion?

 

PDAS last serviced about 2 years ago. Flushed together with brakes and clutch. A while ago had issue with ABS activating at low speeds going forward and in reverse. Run durametric. Found fault with ABS sensor (front). Replaced both with the updated sensors as per Porsche manual. Checked for signal continuity, all was good. Connectors clean. No issues with ABS since.

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Not sure if you are using OEM wheels or OEM lug nuts, but if so, the longest OEM nut (anti-theft nut) goes onto the red stud and this must be directly opposite the valve stem. If your mechanic does not know this, perhaps the wheels were not correctly installed?

 

Knowing it’s a C4, front differential comes to mind. If the differential is locked (or not allowing enough slip) then as you go through a long turn a rotational difference will build up, causing either differential bind/break or wheel chatter. The rotational difference will *have* to come out somewhere so if the differential holds it will turn into wheel hop/chatter as one rim snaps forward or backward and the tire gives.

Common for 4wd vehicles if someone forgets to unlock the diff when they go from dirt back to pavement.

Bind will show up only on longer turns. If you are making short turns, zigzags, or are going straight there will not be enough rotational difference built up to be a problem.

 

Aftermarket lug nuts, all 5 are the same kind.

 

Front diff in open state, 4WD not engaged. The vibrations happen in straight line too.

I can try to decouple the front driveshaft or remove the axles all together. Just need the C2 axle bolts to hold the wheel in the hub.