Questions about Possible Suspension Issue...

[Laneco]

I did my first autocross on Sunday - WHOO HOO!!! - with Butters. Great fun! When I was driving back from the event, I noticed that Butters felt rather unstable. The rear-end felt "loose" just driving in a straight line. Very odd sensation. Not terrible, just somewhat disconcerting and definately different than it was on the way to the event that morning.

When I got home, I checked for obvious loose things (wheel fasteners, CV-bolts, etc). Can't feel any issues with the bearings. I didn't go crazy jacking the car up and prying on stuff, but there is nothing obviously wrong.

My right rear tire is surprisingly worn. The tires have about 2,000 miles on them. The righ rear has a distinctive wear pattern on the outside of the tread blocks beginning at the middle of the tread (and going across all blocks to the outer edge). Tire pressures were 32 psi front and 36 psi rear - no change.

Then I saw the pictures my husband shot during the event. Here are two of them. One is after a couple of runs and the other is during a run (obviously). Is it my imagination - or is that right rear tire cambered out?

The car is going to the alignment shop tomorrow. What should I have the guys down there check in addition to the standard alignment? They've done quite a few porsche's - they're "familiar". Something worn? A bushing? What the heck have I done?

thank you,
angela

[911pcars]

I couldn't tell if there was a definitive amount of camber (+ or -) from the pics. You could perform a rough test by holding a short carpenter's
level vertically against the sidewall on each side, then compare. If the RR has excessive camber, you'll see the difference in the bubble.

The tread wear you describe does sound like positive camber wear. Could also be the RR tire has excessive toe in. Does the tread have a "scalloped" wear pattern like progressively worn and feathered steps? The alignment shop can easily determine this. Make sure they disconnect the rear sway bar before they realign it. Also check the rear wheel bearings. You didn't say you heard any low pitched growling in the back so this may not apply.

Also check tire/wheel runout.

Hope this helps,
Sherwood

[Eagledriver]

Check the sway bar brackets where the rear bar is attached to the chassis, these break often.

-Andy

[Steve@Rennsport]

Hey Angela,

Just glancing at the top picture, it looks like you are missing some rear negative camber that these cars MUST have to handle properly. The second picture suggests insufficient negative camber as well.

Get 1.5 deg neg camber in the back of that thing and it will feel FAR more settled.

[Laneco]

Thank you everyone!

Steve - Butters will be in the alignment shop today. I'll record the before and after. I'll have them set the rear at 1.5 negative. Very very curious to see what it is at right now.

Also can't wait to GET IT BACK ON THE TRACK!!! The slippery slope begins!

angela

[RWebb]

Butters?

What is the name of the 550?

[Laneco]

Usually just "the spyder" but it has been referred to by other far less politically correct names...

Technically the spyder is Steve's car even though about 11,800 of the 12,000 miles are mine. Steve doesn't "name" cars. That seems to be one of my peculiar habits.

angela

[RWebb]

Yes, that naming syndrome is caused by having too many X chromosomes....

[911st]

Some times the bolts on the rear arm that is used for alignment can slip.

[Laneco]

Picked up the car yesterday. Good news and bad news. The good news is that they were able to correct the alignment. The bad news is that the car drives terrible and needs to go back... You know something is wrong when you go to pick up the car and the alignment specialist says, "Hey, we weren't able to get rid of that drift-to-the-right...can you bring the car back later?"

Hmmm... The car didn't drift to the right at all when I dropped it off. Definately loose feeling before, but nothing like now. Now the car feels very planted, but if you let go of the steering wheel, the car makes an right turn...

At any rate here's before and after:

Front - BEFORE: Camber left -1.2, right -1.0. Caster left 4.7, right 4.8, Toe left -1/8, toe right -1/8.

Rear - BEFORE: Camber left -.5, Camber Right +.5, Toe left 1/8, Toe right 7/32.

Front - AFTER: Camber left -.9, right -1.0, Caster left 4.7, right 4.8, Toe left 1/32, Toe right 1/32.

Rear - AFTER: Camber left -1.4, right -1.4, Toe left 0, right 1/16.

Long and short, pulled the front tires inward as they were toe-out and changed the right rear camber a full two degrees. They need to figure out why the car wanders strongly right, but they already said it was an issue and they would fix it. Hopefully real soon as I was planning on driving the car to Tahoe on Monday.

angela

[David in VA]

Angela, please post what they end up finding. I have what sounds like the same thing. Feels loose at speed, changing lanes on the freeway is a bit scary. Nothing obvious that I could see, swaybar brackets are solid and no play in the wheels.

Thanks
David

[rfn026]

Before you take the car back to the alignment shop paint a white stripe on every bolt that relates to the alignment. Then when you pick the car up check to see if they actually did anything. You may have gotten what's called a toe-and-go alignment.

They set the front toe and then charge you for a 4-wheel alignment.

I don't put too much faith in before and after numbers since I can get the machine to read anything I want. The little print outs are too often just a smoke and mirrors type of thing. I'm a little concerned that the shop obviously never test drove the car after the alignment. If they had driven it they would have experienced the pull to one side.

Richard Newton

Autocross Performance Handbook

[Laneco]

These are good guys, they'll make it right. I only drop cars off when the owner is there as his worker does not always get the message straight. The owner was busy getting ready for a Vegas trip so I missed him on drop-off. That got the miscommunication started.

When the owner got back, nearly all the work was done (alignment, new brake rotors, new pads, flush brake lines). He hopped in for the test drive and was "wow! this definately pulls to the right" and assumed it must have been just awful beforehand. In fact it didn't pull at all before.

This is a minor screwup. They'll fix it. It's the first time they've erred on anything they have ever done for us. Good guys get another chance.

By the way, that Autocross book looks like a good one. I just bought a copy from Amazon! If you are the author, that makes it all the better - thanks for the advice!

angela

[911pcars]

Angela,
After they complete the adjustments, confirm the car also stays straight under hard braking. Since you're autocrossing, you may want to consider corner balancing it to confirm each corner is sharing the correct proportional load. However, that will necessitate re-aligning the suspension.

Sherwood