joc4s

Hi I'm fairly new to this discussion group and 993's. I have done a search but cannot find much information relevant to my problem.

My car is a 97, C4S, with 14000 miles with standard ROW suspension. The car pulls down even a very slight road camber (to the left here in the UK) thus pulling on the steering wheel and causing it to be slightly misaligned from the straight ahead position (about 5 degrees clockwise) to keep it in a straight line.

I have had the car aligned and rechecked (including the rear kinematic toe) at two separate Porsche dealerships and everything is well within spec. The OPC dealer I purchased the car from seems to be passing this off as normal but I haven't detected it whilst driving other wide body 993's.

In all other respects the car is 'as new' but this fault IS DRIVING ME NUTS!!!

With new tyres(at the correct pressure all round) making no differance and wear in the suspension seeming improbable on such a low mileage car, has anyone suggestions of where to look for the cause or experienced this slight pulling

Jo .

Jeff96-993

I had a similar problem when I purchased my car. The pulling was even worse under acceleration, and when deceling it pulled in the opposite direction. Do you notice anything similar?

I had the car at two dealerships... no luck there, they were stumped. Luckily an independent with extensive racing experience finally figured out that one rear tire was about 1/2 in rolling circumference larger than the other. That in combination with LSD caused the rear wheels to push the car.

The tires on the car were not N-rated tires, so they were the wrong ones for the car. I purchased a proper set of N-rated rubber and the problem was eliminated.

I can also tell when the tire pressures in the rears get different by a few pounds... the car begins to wander again.

Good luck,

joc4s

Jeff

No, acceleration and braking don't make a difference. Other than the gentle pull on the steering wheel and hence misalignment to keep the car from wandering towards the kerb, everything feels fine.

Any more suggestions from anyone - PLEASE.

SundayDriver

Jo,

I am assuming the alignment was done by a competent shop AND they checked to make sure there are no loose parts, such as tie rod ends, etc.

I suspect tires (or tyres in your case). What pressures are you running? I would set to 32/34 cold and see if the problem is still there (better/worse). These cars will pull on a crown and it is pretty stong with the factory pressures, in my experience.

If if still exists, then start with some measurements. Carefully measure the circumference of the tires. Make sure they are the same across each axle.

Then check the squareness of the car. Measure the distance from the front wheel to rear on each side. You will need to pick a repeatable point on the wheel (perhaps an edge of where the center cap mounts).

Post your alignment specs and we can see how they look.

Hope this helps.

joc4s

Mark - thanks for your interest and help with my problem - much appreciated but when will you Americans learn to spell English correctly? It's tyre and colour not tire and color etc (hope you have a sense of humour - this problem is resulting in me quickly losing mine).

Alignment done properly at independent Porsche specialists and then checked by OPC dealer few days later - both readings near identical (except where indicated below).

Tyres are at factory spec so will try your suggested pressures tomorrow (it evening here in the UK). As the tyres are all new and the fault was the same on the original tyres I don't expect the circumference to be making a significantly difference - unless you know different.

Will also try measurements between axles on both sides, as you suggested.

When you say 'pull on the crown' what do you mean?

Alignment readings are within factory spec posted on Robin Sun's P-Car.com site but are as follow:

Front left caster - 5deg 16min (5deg 24min at recheck)
Front right caster - 5deg 16min
Front left camber - minus 0deg 20min
Front right camber - minus 0deg 17min
front left toe in - 0deg 2min
front right toe in - 0deg 2min

Rear left camber - minus 1deg 7min (minus 1deg 17min at recheck)
Rear right camber - minus 1deg 8min
Rear left toe - 0deg 8min
Rear right toe - 0deg 10min
Left

Thrust angle - minus 0deg 1min

Apparently, the first alignment technician had difficulty in bringing the left rear camber and kinetic toe within spec (originally the car was out of spec on nearly every count).

Will post again as soon as I can check your suggestions out.

Thanks again - Jo

Steve Weiner-Rennsport Systems

Hi Jo:

You've gotten some good input here and I'd just add and reinforce some points.

Pulling problems are usually tires and/or alignment. I'd swap front wheels and see if things change.

I would also suggest that you add some additional front toe-in to assist the car in going straight on the road. Another thing,....sometimes, one can add some caster stagger to help keep a car from "falling" off a crowned (cambered) road. .25 to .5 deg would be plenty.

Final alignment setup really depends upon the local road conditions and how you drive the car. I find the factory specs are only a guideline and starting point.

joc4s

Hi Steve

I was hoping I would receive an input from you. I wish I could bring the car to you!!!

I can only swap the front wheels side to side temporary as they are directional tyres.

Would the caster be added to both fronts say 5deg 45min

Anyone else have anything to add?

Regards - Jo

SundayDriver

Jo,

By crown, I meant camber on the road. I find these cars to be very sensitive to this when the tire pressures are high (factory spec). Steve is, of course, giving you good advice about alignment, swapping wheels, etc. Tire direction is not particularly important unless it is wet, and we all know you never get any rain over there.

BTW - What colour is your car? And do you keep your rubbers and garters in the boot? LOL
Be careful about making fun of our spelling or JimBob might join in.

Steve Weiner-Rennsport Systems

Hi Jo:

I too, wish I could align your car here and straighten this out, once and for all. As Mark indicated, these cars are VERY sensitive to alignment and tire pressures and everything must be spot-on to drive as well as they are capable of.

Swapping the front tires side-to-side will show whether its an alignment or a tire problem.

I'd add more caster to the "downside" of the car; right in the US and L in the UK. This helps keep a car centered on roads that are not flat.

joc4s

Thanks again for your interest and help Mark and Steve.

The car is Ocean Blue Metallic exterior/ Cashmere leather and midnight blue interior with white gauges, RSR's and Motorsound airbox and a C2S engine cover, otherwise the car is pretty much standard.

Hope I can get this sorted. Will come back with a posting when I've checked your suggestions out.

Mark. You ask what I keep in the 'boot' - well its a six cylinder 3.6 boxer engine. What do you keep in your boot or should I say 'trunk'?

Jo

SundayDriver

I don't have a boot or even a trunk in my car (check out the avatar). They built it in Peterborough - even put the steering wheel on the wrong side - I can barely reach it when I sit in the left hand seat.

MJR911

Has the car ever had an frame damage? Wouldn't this impact the car quite sevearly if it was repaired in a botched up way?

Mitch
....who is from the states and studying abroad in Edinburgh. Just figured out the whole MOT thing last week and was a bit slow on the uptake when a "mate" told me to get my helmet out of the boot today after some kart racing.

Ray Calvo

I'll go along with Steve from 27 years of one or another 911 ownership; get a competent alignment. Did they adjust it to the factory specs, or some "race" specs. Many independents dial in more negative camber than stock to improve track handling.

joc4s

Mark and Steve - you experts are the greatest!

(Ray - I think the specs I posted above comply completely with the factory specs and tolerances.)

Things are looking much better after todays experiments based on your suggestions!

First I measured the wheel base and compared side to side = exactly the same distance.

Next I reduced the tire pressures to 32/34 as Mark suggested = a marked improvement in riding down the camber.

Next I removed both front wheels and measured the circumference = same circumference (after all they are both brand new and only done 500 miles)

I then swopped the front wheels onto opposite sides (they are Continental Sportcontact 2 N2 and therefore not directional - yipee) = car drives perfectly straight and with straight steering wheel on major highways (almost no camber) - YIPEE!! Car only pulls a little on high camber roads and mainly after hitting a road depression causing bump steer down the camber and then the necessary correction on the steering wheel, resulting in temporary slight misalignment of the steering wheel.

Now for the questions based on the above:

1) Is it OK to run the car at 32/34 pressures on a permanent basis?

2) Why has changing the front wheels onto opposite sides of the car made such a marked difference bearing in mind both tires are brand new and the same fault was present on the old tires (tough one this - eh!)?

3) Is this the closest I'm going to achieve (I'm a perfectionist) on high cambered roads or should I still apply more caster on the downside as Steve suggested or will the car then pull the opposite way on major highways?

4) Should I still apply more toe in for directional stability?

5) Finally, would changing the left rear camber closer to that of the right wheel improve things?

Thanks again for your help so far guys (You'll soon be talking with an American accent!)

Regards - Jo

joc4s

Correction to the last ling of the above post

'Thanks again for your help so far guys (You'll soon have me talking with an American accent!)'

Jo