Front Suspension Vibration at Speed

[gt2993]

My 911 developes a front suspension vibration which starts to get noticeable from speeds above 70 mph and can be felt in the steering wheel. What is strange is that the vibration almost completely goes away on a very smooth road surface and re-appears if I go over a couple of bumps and/or uneven road surface or if I have to turn the steering wheel to change lanes or negotiate a turn. The severity of the vibration varies from almost unnoticeable to being able to notice the steering wheel shimy.

I have brand new tires, balanced by a respected tire shop, brand new brake rotors, brand new front wheel bearings and races. I checked for excessive run out on the hub without the rotors and it is fine, with the rotors attached and it is also fine. The car also has brand new Von struts and coil overs and brand new monoball bearing for the top of the strut. Finally, I installed brand new turbo style steering rod ends.

The only things in the front end I have not changed yet (I was hoping to make this a project for next fall) are the lower control arm bushings and ball joints. Anyone have any thoughts whether the ball joints and/or bushings could be causing this problem? Has anyone encountered something similar. I saw some of the other threads that discussed issues with the tire balance, but I am confident that is not an issue here. I would love to hear some thoughts from some of the suspension wizzards here who might have some ideas. Thanks.

[Daviboy]

You don't mention if wheel alignment was done? Had same problem before my suspension refresh cured it. Control arm bushings and ball joints could also be culprits why did you nt change them when doing all the other work?

[EMJ]

Originally Posted by Daviboy

You don't mention if wheel alignment was done?

This ^^^^ and corner balance...

[JAR0023]

Have another shop road force balance the tires on a Hunter machine before you spend crazy money on parts. My car did exactly what you are describing, albeit on older tires.

No amount of balancing could get them right even with multiple road force balancings. They were great except for a 10-15 mph window where the steering wheel would go from mild shimmy to wild gyration. Keep accelerating and it would go away. A little lateral pressure from turning and it went away. New tires and a proper balance resolved the problem.

There is a good thread here where a poster with tire industry experience explained the mechanics of the issue. -J

[gt2993]

I probably should have mentioned it in my original thread. The car has been alligned and corner balanced by a Porsche specialty shop. I am very confident that the allignment was done correctly.

When I was doing the struts, the ball joints and the bushings looked tight, without any visual signs of deterioration, so I took the lazy (and less costly) way out and decided I would do the bushings and ball joints when I am having my control arms powder coated.

[HawgRyder]

Another thing to check is the wheel bearings...for play...and wear.
A "loose" bearing can do all sorts of things....it will not be consistant.
Bob

[EMJ]

I had these exact vibrating symptoms recently and it turned out that the car had 2 slightly bent wheels and was just a fraction out of balance. Rebalanced, and even with the bent wheels, the drive was very much improved.

[pete3799]

First thing i'd do is jack the front end up (just high enough so you can spin the wheels) place an object (spray paint can etc.) against the tread so it just barely touches. Watch for any high or low spots as you rotate the tire. The faster you spin it the easier it is to see any deviations. Then do the same along the side of the tire and watch for a wobble.
My car had the same problem you describe when i bought it. By checking as above discovered the PO had locked up the brakes and flat spotted the tires.

[gt2993]

I just checked the bearings and they have less than 5,000 miles on them, so I think that they are O.K. The wheels spin nice and smooth, without any unexpected noises. However, the passenger side wheel seems to have a very small amount of shake or play when I grab the wheel at the 12 o'clock position and the 6 o'clock position. Essentially, what I tried to do is to grab the wheel at the top and the bottom and shake it back and forth and although I cannot see any movement, I can feel about .020" of movement back and forth. The driver side is not doing this, no matter how hard I pull and push on it.

What could be causing the wobble if the bearings are tight (and everything else is torqued down to proper torque settings)?

[pete3799]

Ball joint.

[lateapex911]

My fist thought was ball joint or tie rod bushings. 911 steering is VERY communicative, and the SLIGHTEST issues get through to the steering wheel.

IF you can, rotate the fronts to the rears. (Even if they don't REALLY fit or rub at the extremes), just to take it down the highway and see if it gets worse, or better, or stays the same.

Top to bottom play though is either bearings or ball joint.

(I had a similar issue, but mine cycled in and out depending on how the tires were phased to each other across the axle) ...it ended up being the belts, only new tires cured it)

[HawgRyder]

Second the idea of tires.
I had a belt shift on me once...and it was difficult to see.
It used to happen if you exchanged tires from one side to the other when rotating....with radials.
If you spin the tire slowly and watch the tread pattern...a shift appears as a sort of twich in the tread line...like a wiggle in the carcass.
If so...new tires.
Bob

[sled9146]

I had the same problem and did the same detective work. Finally got down to the spindle spacer on one side had worn down.

[gt2993]

FOUND THE PROBLEM!!!!!!!!!!!!!!!

After re-checking the bearings for the third time, checking the ball joint and the steering tie rod ends, and everything being up to spec, I started to do some visual checking of the rest of the passenger side suspension. With the wheel removed, I used a couple of old wheel spacers and torqued the wheel nuts to spec to simulate the wheel being mounted. Then I would hold the brake disk in the 12 o'clock and 6 o'clock position and push and pull on the disk to see if I had movement. I noticed that I was getting the strut insert moving back and forth (not up and down) in the strut housing. The amount of movement is about .020". Apparently there is excess play between the strut housing and the strut insert.

I repeated the same exact procedure on the driver side and that side was nice and play free.

What surprises me about it is that these are brand new struts. Does anyone know if Elephant Racing warranties their struts? I have less than 5,000 miles on the struts and only one autocross, so I cannot imagine that this is normal wear and tear. Oh well, at least I found the problem and I can call Chuck on Monday.

[lateapex911]

Good find. Maybe some shim stock is the easy button?