I had my 86 951 aligned by an alignment shop and everything is great except the front caster seems way off. It is 4.2 and 5.0 left and right now. That is almost twice the max amount in the specs. I also noticed that my right shock bolt in the engine bay was completely loose when I got it back. I used the factory cut-away socket to tighten that shock down.

All of the suspension is brand new, bushings, caps, dust covers, Koni yellows, tie rods, rack directly from ZF themselves, etc. The car drives just about straight Like it always has. This car was driven so softly by my father for 25 years that he only had it aligned once, got 60K miles out of his tires, 100K from the rotors, and 80K from the clutch. The car has never seen rain or a pothole.

My question is what would cause the caster to be so high? I have read that there is very little adjustment available. And would the shock being so loose have caused it, and if so, how is the other side also set so high considering that on that side the shock was tight? The car should not have any real damage to it because we've had it since 87. Though the right front fender had a minor repair from the first owner who had it for just one year.

 

Caster should be about 3.0 to 3.5. Do you have the spec sheet that shows before and after? Might have been left as-is. There is quite a bit of caster adjustment range.

Porsche alignment shop? What did you pay for the alignment and how long did it take?

Top shock bolt would have been loose from when it was installed (said its brand new?).

 

How do you know this....from an after alignment spec sheet or are you measuring it yourself...?

If you really have 5 degrees of caster and the wheels in your avatar, you'd be getting close to rubbing paint off the bumper cover with the tire, if not already.

Put the 5.0 side to 4.2 and let it ride. On race or street, you want this symmetrical side to side. Unlikely you'd ever use advantages of extra caster on street tires.


It's not necessary to loosen this when aligning....don't know why anyone would.



T

 

Front shocks, along with about $5K worth of other work was done in the same visit by a well known independent Porsche shop, and they get it aligned at a performance truck shop next door who has a machine. It was aligned due to the new rack and tie rods. Per the computer printout, the car was started at 4.1 and 4.9 and came out at 4.2 and 5.0, and the sheet shows the acceptable range for the car as 2.3-2.8, which matches what I've seen online. To me the wheels appear to sit perfectly in the well right where they should. I'll take a photo tomorrow. Car is level on all corners measured from the center of the fender well. The steering effort seems harder than it used to me.

Yes it is the car in the avatar - my dad bought it in 87 and used it on nice days. I drove it a lot in college twenty years ago. Now I have it and trying to get it all back to perfection, though it was not bad. It is bone stock other than than the cup II's and K&N cone filter. It is a reliable car, and I drive it everyday.

 

That's a great story of the car between you and your dad.

I did the same thing with my son with a 944S.

I can understand you wanting it to be spot on and continued experience with the car just as your dad enjoyed.

If it concerns you that much, have the caster reset to the factory specs.

As the angle of the strut changes to a positive setting, more of the car's weight must be "jacked" as the steering turns back to center. This effect is what makes the steering effort harder and is the reason you want the left and right to be symmetrical no matter what the setting is. A difference between left and right makes one side "jack" more of the frontal weight than the other, detrimental to balanced handling.
A car with more + caster will a) be more stable in a straight line, b) turn initially into a corner faster, c) move the contact patch of the tire forward which improves braking stability, d) increase steering effort.

I see no ill effects of having a lot of caster on a street car other than the increased steering effort.

On our race cars, we run the maximum amount that the factory settings allow that we can achieve symmetrically side to side, i.e., +4.5 R & L using stock ZF power steering rack and pinion with the power assist deleted (pump and hoses deleted with metal lines capped and housing filled with Mercury outboard lower unit grease). The effort around paddock and grid is noticeably higher but once rolling at high speed, definitely not bothersome. You have to really control the steering wheel to avoid turning too much at entry as the wheels want to "fall over" and have to unwind the steering at exit because of the weight jacking effect.

I don't sublet any work on our cars, thus, do my own alignments and have experimented with all of the settings, this on a front running, track record setting 944. "Caster is faster" as the saying goes.

T

 

Completely agree, I run max caster on my mostly track 951.

 

Thanks for the great info everyone!