Tuesday, September 3, 2013

Going Straight

Adjusting a Porsche to follow the track that you want while going down the road is not as simple as it is with almost any other car. Camber, caster, and toe adjustments are common with most cars.  But, with a Porsche you can adjust the height, the rake, the corner-balance, and you should adjust the car in order to take into account the weight of the driver. You will adjust to make sure the car is the same height side to side (with driver in there); that there is just about a 19mm slope in the body of the car (lower in front, called rake); whether or not you have adjusted to "Euro" height or North American height; and the like. If a parked vintage Porsche 911 has a notable tilt to it when empty, it either means that the driver needs to go on a diet, or it means that someone turned adjustment "C" when they should have been turning adjustment "G".

And almost every one of those adjustments affects one or more of the others. You could tear your hair out for a week trying to get the thing the way you want it, and it would still be wrong. For example, if the car pulls to the right, it means that there is more weight on the left front and the right rear tires than there is on the other corners. This is not the case with the run-of-the-mill minivan you see at Walmart, which is lopsided for other reasons having nothing to do with precision handling, but we won't get into that subject just now.

You need a computer controlled machine like this one to accomplish the job of exact alignment, but more importantly, you need someone running it who has a good amount of Porsche experience. And, by the way, everything done to the front of the car also has to be done to the rear, which then affects the front again. And, be sure to test drive it in between each new tweak, because the car's handling will change with each adjustment you make.  

My car has a 'clunk' in the front when going slowly over small bumps, plus the car pulls slightly to the right, plus the front tires have begun to wear on their inside edges and they have a slight 'feathering' of those edges. In other words, it needs work. Oh, and the steering wheel vibrates at speeds above 100kph or so. In investigating all of this I learned that the 'rake' of the car is twice what it should be, and that ill adjustment must have increased the negative camber, as well as the toe - in front.  The rear tires seem to be wearing normally with no indication of misdirection.  We'll fix that.

I ordered a batch of rubber bushings for the front anti-sway bar, since they appear to be the cause of the clunk, plus a set of 'bump steer' spacers to accommodate the too-low front of the car. The spacers lift the steering rack so that the tie rods are once again level after having been lowered. I'm not especially interested in raising the car back to 100% stock in the height department.

Anyway, lifting the steering rack will affect the negative camber and toe, once again. Maybe it will actually put the alignment almost right, but it won't fix the steering wheel vibration, nor the drift of the car to the right which likely is a corner balance issue. The mechanics you see here are competent and have aligned a number of Porsche 911s, so we'll see if they have a comprehension of all the subtleties in the bigger picture.

Naturally you have been wondering why there are so many adjustments to be made to the suspension of an older Porsche like mine - or yours. Today's Porsche cars may have even more complex adjustments; I don't know, but if so, they are there for somewhat different reasons.  What I do know is that when my car was built, in November of 1973, it was not produced on a modern production line, such as those pioneered by Henry Ford in 1913 - a century ago. Each Porsche was installed on a sort of large wheelbarrow device that allowed it to be moved along when it was ready for the next phase of its construction. I guess this was a 'production line' of a primitive sort, but it was not as smooth as the one Ford had in operation 60 years earlier, which manufactured cars in large numbers.

Porsches the age of mine were among the last of the handmade cars constructed by any surviving manufacturer to build cars in significant quantities. Each body was assembled using parts that had been stamped out, as is normal. They were then welded and soldered together without the same precision, identical alignment of typical modern cars built in huge numbers. Therefore, every body is different to a degree, and it is easy to see this if you compare a number of examples of this era - you can see hammer marks from the process of convincing various pieces to fit together. As well, one person might have assembled a transmission, or engine, and when it was finished it went into a certain car. There weren't dozens of people involved; these cars were pretty much hand built.

1974 production line. Notice all the workers and the frantic pace involved.
As a result, alignment has to take into account the fact that no two car bodies are alike and so infinite adjustments are needed to bring all of these varying vehicles into a reasonable relationship with one another. Porsche obviously wanted a standard of handling and even appearance for its cars, and to accomplish this alignment of everything had to be precise in the end. In addition to this, various owners had an interest in racing, or touring, or hill climb competitions, or going to buy groceries. The adjustments can accommodate all of these interests, as well as the variations in the actuality of each car.

Naturally, this makes for complication 40 years after the car was built. Some components might have been replaced, but not others. Possibly a previous owner made changes to suit his interests, and he might have botched the job. Parts will have been damaged from the years of vigorous use the cars have endured. I found evidence of vigorous use in my car when I removed the gas pedal. It was bent into a curve from having been mashed hard to the floor repeatedly over time. Also, other abuse was possible, even expertly repaired and concealed accident damage. All of this makes solving the issues my car now suffers a test of resolve and creativity - as well it is necessary to read competent books on the subject.    

Continuing this story later, all the parts I ordered arrived and have been installed, and so the wheels were aligned again. I think. Every movement up or down of the car (i.e. push up on the bumper, or pull down while it is on the alignment rack) changes all the settings. So, when is it correct? Everything will change as you bounce down the road, therefore, there is no apparent absolute alignment, except for momentary serendipity when you hit the right bump or slope in the pavement. I guess you get it in the ballpark. That, or I find a more experienced Porsche aligner.  


PRebordao said...

Maybe in 73 they didn't had any robots yet, but the panels were soldered while being fixed to precision jigs, so I don't think this introduced any significant dimensional variations between cars.
I believe most of the manual work was in removing small dents made in some previous step and/or finishing the appearance of the welds... but I'm no expert.

PS - Mine was built in October 93

J911 said...

Your comments are interesting and thanks for posting them, but to my knowledge jigs used were not very precise at the time my car was made. Professional restorers I have spoken with point out differences in the fit of various identical parts on cars of this vintage. I'm no expert either, but I am reporting the situation as it has been shown to me.