Speedtoys

79 manual..

Bringing my kid's BF's project car to another location today, it rolls down the road smooth, but as I neared the highway it developed what felt/sounded like a realllly out of balance wheel, pretty bad.

Goes up and down with road RPM, not driveline/engine, etc.

Hard braking it goes away...smooth.

A good kick/push on wheels shows up lose lugnuts, they were torqued last weekend.

Recent work done:
Snug front wheel bearings per WSM
New front lower ball joints (were Al and really ****ed up)
New inner/outer tie rods

Everything was torqued...

The Forgotten On

Probably a warped rotor knocking away at the caliper. My 81 had the exact same issue before I replaced all front brake components when going to 993 calipers.

I would recommend doing a brake job on it anyway just for safety's sake.

Another thing it could be even though it is rare is that the spindle has been worn or damaged and braking centers the hub on it.

You never know until you really dig into it with these older 928s.

OTR18WHEELER

Could be tires?, I have a set of aged goodrich tires that make a walking Kardashian look good, if you know what I mean.

wpgshark

Could be wheel bearing. Jack up that corner, the back if you have LSD and spin the wheel, try to move it out of plane, you might get a better ides.

Good luck

Speedtoys

The front bearings are...tight, they were a tad off, but they took about a 1/16 hand turn and they feel good.

How would braking make bad tires feel smooth?

I mean, everything shakes a little in the car with this vibration..throttle position/speed doesnt matter, but hard braking it goes away

pumpedTSI

I vote tires.....put the wheels on a balancer......it will show up real quick....

Randy V

I suspect you have many chem-trails in your area...

Explains everything.

Billu

Are you saying you had loose lug nuts?

wpgshark

Are you sure the vibration is coming from the front?

If it could be coming from the back possibly a CV.

It has been my experience that vibrations from the braking system get worse when the brakes are applied, this may change with hard braking, what happens on light braking? If the vibrations get worse I'd look at the brakes.

Balance almost always changes with speed, there will be sympathetic frequencies with the suspension which make it worse, hard braking could possibly reduce vibrations because the loading of the suspension would change these frequencies, but I don't think it's likely that that is the case.

By hand tightening the bearing 1/16 turn what did you mean? was that with a tool? I haven't done a Porsche bearing but bearings that I have done require very particular torque, either an applied torque to the fastener, or a resultant torque in the rotation. Even if the bearing is properly tight that doesn't mean that it isn't the source of the problem, a damaged or worn bearing component can still make a lot of noise. When rotating the wheel by hand trying pulling pushing and torquing the wheel to feel for anything that isn't perfectly smooth. Any sensation at all that isn't perfectly smooth is an issue.

Check your CV boots, if any are cracked and foreign material was allowed to enter, then deterioration can occur very quickly.

Wheel nuts are a good source as well, they can cause issues by being under torque or over torque, and especially with being unevenly torqued.

I've had to go as far as putting a car up on jack stands and running it to find vibrations, fortunately it was an AWD.

Good luck.

Speedtoys

Braking doesnt change it, other than when you brake hard, it all goes away.

I dont know which end it comes from.

"By hand tightening the bearing 1/16 turn what did you mean? was that with a tool?"

Yes, my hand, per the instructions/WSM.

This was beyond a lug nut...vibration, things vibrate IN the car..its a fairly large strong vibration.

wpgshark

Put it up on jack stands and run it it might, just might eliminate half the car.

I looked up the procedure for tightening the front bearings here is some alternative methods worthy of a look. http://www.nichols.nu/tip235.htm

If you're unsure of corner have you checked the rear bearings?

Speedtoys

Have not checked rear...but in 2 miles, it went from smooooth, to w-t-h....

FredR

That sounds typical of when a wheel bearing fails spectacularly - happened to me once but not in the 928 - it was so bad it felt like something was about to fall off the car. Pulled over, called a tow truck and sure enough it was a huge and sudden front wheel bearing failure.

wpgshark

I have more experience with failed volvo bearing, I swear they tuned the car to resonate to the bearing failure, amazing amount of noise.

Good news, constant extreme problems tend to be easier to diagnose than intermittent irritants.

Speedtoys

And there was no vibration in the steering wheel for this?