Please help me figure out steering vibration!!!

[FirstGen]

Car is a 1977 911S. With 18" wheels.

This has me absolutly stumped. I have a vibration that only occurs between speeds of 52ish - 65ish. Slower or faster than that window of mph the car is smooth... not glass a higher speeds but not what I would call a vibration.

The vibration that happens is also pretty bad where if I am not gripping the steering wheel firmly it will shake almost 3/8" from side to side!

Every blue moon the car will be completely smooth for a short period of time in that mph range.

So far I have aligned the car several times. I have replaced all four tires with new rubber. I have not noticed any excessive movement in the wheel bearings (I can barely move the wheel ever so slightly with the car on jack stands).
I have inspected the ball joints and the rack and they look ok and there doesn't seem to be any play in any of those componets.

I don't think this is brake related because it doesn't happen when I brake and only occurs between the magic 52-65mph. It does continue when I hit the brakes within that range until I fall below that range.

Please help me out here before I get stuck throwing MORE money at it to try to fix the problem.

Thanks guys!

[Jack Olsen]

I had the exact same issue and it was wheel balancing problem. It doesn't take much to throw it off, since the two wheels' frequencies can play against each other -- at least that's my theory. I think it goes away sometimes because the two front wheels' orientation will change if you're turning more left than right over a given stretch of time.

Again, that's my non-engineer's theory. I suppose you could jack the front of the car up when it's doing it, rotate one of the wheels 2/3 of a turn, lower it back down and see if the vibration changes.

When I got my two front wheels balanced at the track recently, the problem immediately disappeared.

[FirstGen]

That totally makes sense except that I have had all four tires balanced twice by a good shop with a road force balancing machine... any other ideas?

[Emission]

Have you moved the wheels across positions, so they are now rotating "backwards" compared to their original orientations?

I only drive my car about once a week, so I get "flat spots" that disappear after about ten minutes of driving. Does this happen after the tires are warmed?

[Jack Olsen]

Try a different shop?

It could also be a steering rack problem.

[Kroggers]

Originally posted by Emission
Have you moved the wheels across positions, so they are now rotating "backwards" compared to their original orientations?

I only drive my car about once a week, so I get "flat spots" that disappear after about ten minutes of driving. Does this happen after the tires are warmed?

You get flat spots after just a week I am running on R tyres, and use my car mostly at the weekends, so it can sit for up to two weeks between drives. I did notice a small (new) vibration the last time I drove the car - do the R rated tyres flat spot faster than normal rated tyres??

FirstGen, I have found that the 911 is very sensitive when it comes to wheels that are out of balance. I had problems with the Fuchs when I had them on the car. After having them balanced several times I ended up going direct to Porsche who did the job properly for me, and the problem was gone

[lateapex911]

I hate to say it, but it is definately similar to Jacks first suggestion.

I had the same issue with mine...I knew it was a tire issue because it came and went, dependant on curves! If I hit it right, a curve before a long straight would ""line them up" correctly, and all was bliss. But..if not, it was a long straight.!

In my case, it was tires...a belt was slightly shifted, and the most sensitive steering on a production car in the world, picked it up.

Triple check wheel balance, tire belt runout, and wheel runout, esp lateral.

Finally, a slight bit of slop in the tie rods, bearings, and bushings can exacerbate such issues.

[FirstGen]

Originally posted by Emission
Have you moved the wheels across positions, so they are now rotating "backwards" compared to their original orientations?

I only drive my car about once a week, so I get "flat spots" that disappear after about ten minutes of driving. Does this happen after the tires are warmed?

Yes, I drive the car daily...

[Jon Merck]

I experience the same problem.

In my quest to resolve it, the latest has been to retorque every bolt and nut in my front suspension. This seemed to help a little.

One thing I have noticed is after a track event steering is perfect for a week or two and then slowly it returns.

Must be something to do with the tire wear and balancing as stated above.

[Dueller]

I had this exact problem and chased it for weeks...rebalance tires 4 or 5 times, checked wheels for bends, everything in the front end, etc etc etc.

Ultimately turned out to be broken belts in tjhe front tires. Tires were Kuhmo's which apparently have a tendency to do this especially when run at lower tire pressures. Not visisble on inside or outside inspection...tires would balance perfectly. Replaced the two fronts (dealer replaced free since they had less than 5000 miles). VOILA...no more vibration.

Try "borrowing" a front set of someone who doesn't have this problem to verify that its the wheels/tires.

[Huh]

have you taken your rims to a repair place and have them check for truness? Even if you have your wheels balanced you still may have a slightly oblong rim or something. I know a guy who had that problem with a couple of rims.

[Jon Merck]

Originally posted by Dueller

Ultimately turned out to be broken belts in tjhe front tires. Tires were Kuhmo's which apparently have a tendency to do this especially when run at lower tire pressures.

I had Suminitos (sp?) and presently have Kumhos. Same problem with the Suminitos and now the Kumhos. Could be...

[Dueller]

Hey Jon...just noticed you're running 18's. I assume with adapters/spacesr? If the adapters are the same front and rear, you may try switching them....I've seen the adapters getting out of whack and causing an intermittent vibration.

[Paulporsche]

Just checking:

When the car was up on jackstands, did you try moving the road wheels both N/S (wheel bearings) and E/W (suspension/steering)?

Also how old are your brake rotors? I wonder if they could be out of balance somehow?

And how about your front strut mounts? Could be some wear/play there.

[Emission]

You can always mount someone else's front wheels/tires for a spin around the block. That would isolate the vibration to your vehicle, or your wheels.

[FirstGen]

Originally posted by Paulporsche
Just checking:

When the car was up on jackstands, did you try moving the road wheels both N/S (wheel bearings) and E/W (suspension/steering)?

Also how old are your brake rotors? I wonder if they could be out of balance somehow?

And how about your front strut mounts? Could be some wear/play there.

I did check all of that and everything seemed tight.

Strut mounts are new.

I'm stumped.

[FirstGen]

Originally posted by Emission
You can always mount someone else's front wheels/tires for a spin around the block. That would isolate the vibration to your vehicle, or your wheels.

This is exactly what I would like to try however I don't even know any fellow 911 owners in the area yet.

[ianc]

You probably know this already, but there is a paint mark on one of the studs on each of your hubs. When mounting the road wheels, you should orient the wheel so the valve stem is aligned with this paint-marked stud for correct balance. Just hadn't seen it mentioned so far, so I thought I'd add it...

ianc

[carrera1975]

Go to a different shop that has the latest wheel balance machine, My 75 had the same problem went to place called Custom Alignment here in the SF bay area.

You need to run your tires on a "Hunter Gsp 9700" this is state of the art Bang bang (robo cop)

This machine will find your problem

[72doug2,2S]

Ianc, I didn't know that.
First Gen, is it worse under braking?