hmd

Rod,

You can think of caster as 'dynamic camber' it gives you more camber when turning yet not affecting tyre wear from straight line drivings. Pete is spot on on the 911 you want somewhere between 5-6 deg caster, having too much caster would just increase the steering efforts required.

Are you saying 'not feeling planted' in straight line, braking or turning? Toe and camber settings would have more to do with this than caster settings. But like Pete said you need to get a baseline go to a good alignment shop with optical/laser equipment and get your current setting now, then play around with it.

I would suggest running more cambers allround and more toe in at the rear. My car spend more time on the track than on the street and I have
caster +5.5 FL +4.92 FR
-3 deg camber fronts
0 toe front
-2.5 camber rear
+6mm toe in rears (about 3mm each side).

Hope this help.

Ron_H

May I join in this discussion?

I am a 928 driver with what I regard as the worst steering Porsche I have ever owned. I also have a Rabbit that tracks better than my 928. Steering rack and bushings are OK. Tie rods are OK. Bearings are OK. New tires. Though car is very sensitive to pressure variations, pressure is OK. All suspension bushings are either new or OK. Ball joints are new. Shock dampers are good.(Koni). 928s are extremely sensitive to ride height, but this height is correct.

The problem is wander. The car will not go in a straight line for more than a few feet at low (below 50 mph) speeds. Constant corrections back and forth are necessary and if someone spits in the road, the car wil react by changing directions. Back and forth, back and forth, constanly. I can't find a straight ahead position that will work for more than a few yards. Drives me up the wall.

At speed, the car is solid up to the speedometer peg, but I am not so preoccupied with the minor variations in direction and more concerned with other things at those speeds. Around town and on the boulevard, I am constantly annoyed with this machine's wandering. Freeway is OK but still some wander occurs.

I have argued and argued with the shop that aligns the car. It has been aligned bout 4 times and it is getting expensive. Give me more caster I say. The shop says no caster is necessary and will simply make the car less manageable at speed. Currently, there is zero degrees of caster in the front wheels; factory specs call for 3 degrees. I have always thought caster aided straightline steering stability and self centering. The shop disagrees. I am disagreeing with this shop.

Anyone care to comment? I could use the education.

rnln

basic understanding on all car/bike, the more cast = the better the handling. Unless there is a problem.

hmd

too much will increase steering efforts.
You will need gym membership as well

rnln

hmd,
well, how much is too much. If too much to the point you need more muscular, your wheel might hit the fender already

I don't really know how much is the stock spec but if it is 3, why alignment tech call for 0 and disagree to give it a bit? WHY?
I had similar problem in the past with a BMW. Returning to the same shop 7 times with the same "jerking" result. This was a recommended shop, kind of well known. Finally, I came to a wheel shop in the corner of the street. The guy would not called himself a pro on German car since most cars come to this shop for big wheels was Japanese cars, but he worked on German cars. Less than an hour later, the car drove perfect.
Try another shop.

hmd

rnln,

more than 6 is too much, as Peter Z said somewhere between 5-6 is ideal on these car. I had 7.5 on and it was too heavy have just dialed it back to 5.5 deg.

Ron_H

The reason the shop claims zero is right is to give better handling at triple digit speeds and above. This guy does a lot of open road racing, and has his personal preferences for alignment specs. His don't coincide with mine or the factory. I shall try another shop, but it gets pricey at $350 a pop.

911 Rod

$350 for an alignment?

Ron_H

Yes, at the shop to which I take my 928, $350 is the rate for an alignment. 928s are somewhat different animals; during the alignment, and after the ride height is set, the car's wheels may not be raised off of the ground, or the whole procedure must be repeated after having driven at least 50 miles to settle the suspension. Or a cable may be used to pull the car back down to proper ride height before continuing. So after a change of shocks or springs, it is alignment time all over again. Another shop that wants to do 928 work is "willing" to do it at around the same rate, but would be exploring virgin territory until they complete their learning curve. For that experience, they will charge around $50 less the first time. It sometimes takes more than once to "get it" right. Mine has never been right. I have driven SUVs and trucks that tracked better at low speeds than this car. At high speeds, it is a different matter (anything above 80 up to the peg). Then it is Smile City all day long.

Edward

Different animal, the 928, as is the 993 (also an expensive alignment). But a T-bar 911 should be in the $150 neighborhood (depending on your region, I suppose) for a quality alignment performed by a knowlegable Porsche guy who really knows these cars AND their handling characteristics. Alignment is not about the high-tech rack that's used; it is all about the human tech performing the time-consuming adjustments and setting all the parameters to just the right specs. Any of the garden-variety alignment shops get your specs within a wide range, then take the next customer. Fine for my Odyssey, but not for a sports car (any sports car), IMHO anyway.

Edward

911 Rod

Before I bought my 911 I looked at the other models.
I came to the conclusion that if I'm buying a 15 year car the up keep on a 911 will make up for the extra money pretty quick.
The water cooled seam to need constant attention.

Ron_H

Shortly after I bought my 928, I did a thorough rehab of the hoses, vacuum system, fuel system, ignition and timing belt. The car now has 180,000 miles.
I have driven it across country and back. I rarely need to change or adjust anything. It leaks a tiny bit of oil from somewhere in the "valley" necessitating about 1/4 qt of oil every month. It consumes zero oil. It will pin me in the seat until triple digits. It will cruise all day long at those speeds comfortably, and beats my 911s for comfort and ergonomics. I could take my grandmother to church in it. And it swallows my camping equipment and food for a week and has room to spare. If I could simply get the steering to function properly I would be hard pressed to find fault with this P car. I think I'll keep it forever.
Oh yeah, I forgot that I needed to rebuild the transmission around 8000 miles ago. But after that many miles, I think a rebuild is understandable, considering it is probably the best transmission I have ever experienced. At 140,000 miles, when I replaced the water hoses, the tech said some of them were original and still functioning properly. Don't ever drive a well maintained 928. You will regret it.