Speedtoys

Took the 18s off, put on the winter wheels..

And instantly I felt the alignment was off..but didn't notice it at all on the 18s.

The worst of it was the car jumped right on acceleration, to then dive left on decel a decent amount...plus it just felt squirley over highway rises and bumps...

In the attached, it had issues, and im looking at being time to replace some worn bits to get things fully straight again, but even after alignment, it will still go some (less than before) right on acceleration on the road, and left on decel.

Where should I be looking, this is new to me.

hacker-pschorr

Years ago had the same issue with a local 928. The two front bolts for a front lower control arm were not torqued properly. It's a long shot, doesn't hurt to check.

Speedtoys

Hmm..ok, I can see that..

FredR

I would class that alignment as somewhat "sloppy". The rear right camber is not even within spec range yet alone good side to side agreement that I put a lot of emphasis on but then most of the time I make the adjustments on the rig I use. Whether or not those side to side differences are having any impact with respect to what you are sensing I do not know but you might also wonder what caused those errors in your pre- alignment setup- I suspect with those pre-alignment toe numbers the steering wheel must have been off centre when driving in a straight line.

As to what alignment numbers you should use I would use the 91 S4 or the GTS data spec and set the caster in the range 4.5 to 5. I would also set the front camber at 1.0 degrees and ensure that front and rear toe are set mid range and exactly the same both sides. Rear camber I would set to the max allowable assuming you are running stock rubber sizes.

As Eric says if the mounting bolts are not correctly torqued then the alignment settings are somewhat academic but then one might expect they would pick up and signs of "slop" in the suspension. Settings can change slightly if the shop doors are open and it is windy- they are that sensitive.

Speedtoys

Alignment numbers are to the limit of available adjustment _somewhere_ for camber front & rear, so effort was made to make them even where adjustment existed.

I need to replace the upper dog bones in the rear, eccentrics in the front..and someone has rear-cradle inserts to repair worn eccentric range issues, lots of places where .01 of an inch is missing.

But in the end, my thrust angle was wack..I knew that, but seems still there, kinda...

FredR

If you were out of range adjustment then you have a problem [or problems] that needs solving

Carl makes a kit to rectify the rear cam adjuster pocket problem that I can highly recommend. I have a thread about that if of interest to you.

Your rear camber problem is strange to me. The issue I had was not being able to get the camber down to the values I wanted which were a bit higher than spec range to start with. The rear camber adjustment rectification helped as did new upper arm bushes. I also reckon that part of my problem was in running at the low end of ride height and possibly wear deformation of the rear lower arm bushes but at least I have alignment where I want it which is non stock to start with.

Speedtoys

Ya..I know, if I cant be 'right', then at least be even.....the car tracks straight, its the on and off the gas that is interesting.

If I had toe issues, then I can see the front and rear ends as they rise & fall doing odd things..

Speedtoys

"Carl makes a kit to rectify the rear cam adjuster pocket.."

Yes, thats where I read this,

Was just on his site and a quick scan didnt see it, will check again later.

STRIKEMASTER

Just a thought;
Is the car "Dog Tracking"?? You are going in a straight line but the rear wheels don't track the same path as the front?? What you describe is almost like "Toque Yaw" that you get with single engine, tail-dragger prop planes on takeoff. A Dog tracking car does that...Because the body-frame and /or suspension is twisted...
When a car "Dog tracks" a diagram drawn thru the tire contact centers is not a rectangle when centered on the body/frame C/L, it's a Rhomboid...That makes the car 'dance around' as you go on and off the throttle......
There IS floor pan diagram in the WSM that shows measurement points for the body, but it doesn't show the suspension fits to the body...It would be nice to know the distance from the car C/L to each wheel hub, for example...

Speedtoys

You mean thrust angle, no, it tracks straight..it does not on acceleration, it pulls not-so-subtly right.

Hasnt felt like this in the last 4yrs, so its new.

Mrmerlin

based on your report the eccentric on the rear cross member is loose and moving back and forth .

In the rear I would suggest that the two fat bushing that the eccentrics go through be replaced,this required LCA removal
as well as the 4 dog bone bushings.

NOTE also verify that the lower link pin bolts are tight and that the beveled washers are both in place

GregBBRD

Also:

The front lower control arms, with their rubber bushings that are vulcanized to the control arms and must twist (instead of rotating) are a MAJOR part of the front spring rate on a 928. If one side fails, there will be a HUGE change in spring rate on that side of the car, making the car go in different directions under acceleration and deacceleration.

Failed limited slips (friction material galled, radically increasing the lock percentage) can also cause this problem.

Speedtoys

The LSD was rebuilt 2yrs ago..so _shoooould_ be ok?

The LCS bushes, how does one diagnose them?

And rear pin bolts and washers, I know they're there, I did the last maint on them in the spring and the paint on the hardware still lines up, but I can check it. No odd noises back there that Im used to when hearing those rotate incorrectly.

hacker-pschorr

This is why I'm always so adamant about following the procedure in the WSM for doing an alignment.
A proper alignment the vehicle is lifted off the ground, wheels removed and all the suspension parts inspected. A trained alignment tech will easily and quickly figure out if something is loose or worn out.

This "drive on no lift" mentality we drive home around here is only going to lead to people having half-assed alignments done with worn out suspension parts.

Sorry for the rant......

dr bob

My nickel goes to Stan's recommendation to verify the assembly and tension on the rear LCA pins and washers. This rear-steps-out phenomena is a known result of a loose lower pin, and relates conveniently to the camber you are seeing.

For those who have Carl's rear tie-down brackets on their cars, mke sure you have his updated pieces. The original pieces caused the rear nut to slowly come loose from normal suspension and pin movement. Contact Carl for more info.

Know that Porsche recommends replacement of the rear pin locknuts after disassembly. The locking component is less and less effective with each removal. I'm loath to try to add thread locker becuase it can make removal impossible with the floating pin design. The nuts are cheap and easy to replace. Contact your favorite parts supplier for new.