A Simple and Accurate Suspension Alignment Method for a Porsche 996, Part 1
|Part 1: Introduction|
|Part 2: Preliminaries|
|Part 3: Camber measurement|
|Part 4: Toe measurement|
|Part 5: Calculate adjustments|
|Part 6: Front adjustments|
|Part 7: Rear adjustments|
Am I Nuts? Doing My Own Suspension Alignment?
Doing your own Porsche 996 (1999-2005 911-based models) suspension alignment might sound crazy.
All the methods I have seen (and done on previous cars) are either expensive or tedious, iterative and error prone. For good accuracy on toe adjustments, specialized tools or equipment are often required (toe plates, camber gauges, complicated laser setups) and low cost methods (strings) are tedious to set up, hard to use accurately, and easy for the dog or an errant wrench to knock out of line.
The method described in this series of posts is a significant departure from other methods I am aware of and cheaper, simpler, and more predictable. It does not require any specialized tools or equipment. Total tool cost should be under $75: two cheap laser levels (specific model linked to below), a basic bubble level, a tape measure, a flat plate that fits across the wheel rim without touching the tires, and a bungee cord. A set of feeler gauges is needed while making precise adjustments on the rear wheels. And 996 alignment is really quite simple compared to most other cars although it demands high precision. I am not familiar with other car models but the same or similar method should work on many coil-spring based Porsches.
This alignment method does not need any trial and error. It does not require moving the car or rocking it back and forth to settle the suspension. It can be done in under 2 hours when well practiced; maybe 4 hours the first time.
If your car doesn’t result in near perfect alignment after this procedure, it probably has suspension damage, bent wheels, or excessively worn components. Wheel and suspension condition should be checked before attempting an alignment, in fact these along with brakes should always be in top condition before even getting out on the road.
Update 03/27/2015: it has been 2 years and 15k miles including one track day since I developed this alignment method on my 996. 15k miles from the rear tires of a 911 is respectable, and tread was past the wear bars. So today I had the rear tires replaced at a highly regarded local alignment shop (they had a Ferrari and 2 Porsches in the parking lot) and asked the manager to look at the old tires. His words: “Looks like some under inflation because the center is worn more, but the wear bars inside and outside are even, there is no other wear, so it looks like a very good alignment. You got your money’s worth out of these tires.”
The outline of this method is:
- Mark level tire locations on the floor of your garage and drive the car on them
- Make the camber and toe measurements at each wheel while the suspension is fully set
- Calculate all the adjustments using a spreadsheet that understands the car’s suspension geometry
- Make all the adjustments, jacking up and removing wheels if you prefer
The magic is the spreadsheet which calculates the interaction between toe and camber adjustments. It will tell you how to adjust camber (easy), and then uses the camber adjustment, the toe measurement, and knowledge of the geometry of the suspension to tell you the total toe adjustment to make.
Although the method is general and can apply to many cars, the spreadsheet is specific to the geometry of the 996 suspension. Additional cars can be supported by modifying the geometry description.
Why This Method Works
Measure Everything When the Suspension is Set
When the car is driven onto level ground and gently stopped, the suspension is set in its neutral condition. This is the ideal condition for making all the measurements. The problem is that when adjustments are made while the suspension is loaded with the car’s weight on it, we can’t tell if the adjustment is compressing a bushing or play in a ball joint, or it’s actually moving the wheel. The result is usually an overadjustment that we won’t find until bringing the car back down, resetting the suspension, and measuring again. Partial solutions include toe plates, low friction plates under the tires, and so on. We will not need any of these.
Instead, we start with this assumption: once even a single adjustment on a wheel is made, the suspension is no longer set, and all measurements from then on are suspect. So we never make an adjustment until all measurements have been made, and then we make all the adjustments without any further measuring.
Calculate and Make All the Adjustments
The problem with all the other methods I’ve seen is that they seem to assume that the interaction between the camber and toe adjustments is complicated and requires making adjustments, testing the result, making more adjustments, and so on. This new method takes all the measurements with suspension correctly set and uses a spreadsheet (maintained at Google Docs) to calculate all the adjustments to align the wheels correctly when the suspension is again loaded. The spreadsheet understands the geometry of the suspension and calculates how the camber adjustment affects the toe and how to compensate for it.
Once these adjustments are calculated, you are free to jack up the car and make the adjustments at your leisure without any remeasuring, or trial and error.
Toe Measurements and Car Center Line
Toe measurements are made from each wheel rim against the car’s center line. Some methods measure toe between left and right rims but this is an attempt to avoid the problem of finding the car’s center line. When each wheel is correctly toed against the car’s center line, the toe relationships between all of the wheels are correct. So we will concentrate on finding the car’s center line accurately and, maybe even more importantly, very easy to find when measuring each wheel’s toe.
The 996’s rear toe spec is 5 minutes in (a minute is 1/60 of a degree), with a tolerance of +/- 5 minutes. In other words, any toe between zero and 10 minutes toe in is within spec. Across an 18″ wheel rim, which is about 19″ in diameter, this entire tolerance range is a distance of a little under 1/16 of an inch, or 1.4 mm. How well will we be able to measure toe of hopefully less than 5 minutes, 1/32 of an inch across the wheel, against the chassis center line? We won’t: we will measure the toe over a much longer distance than a wheel diameter.
There are two keys to accurate toe measurement:
- Finding the center line of the car
- Accurately measuring small angles of the wheels from the center line
For this we use the two laser levels. One of them will have the laser beam turned into a line (this is why you need this specific level). The level will be placed on the ground at one end of the car just under its bumper. It shines a “fan” of light underneath the car and you will see a thin line of light all along the undercarriage of the car. We simply move the level until the line of light hits all the center reference points we can find underneath the car (there are several good ones). We now have a very accurate, narrow center line marker that we can see on a tape measure we slide under the car.
The second laser level is placed on the flat plate and bungeed to the wheel. Its pencil beam shines onto the tape measure, whose tape end is just touching the laser line marking the car’s center line, to accurately measure the distance of the beam from the center line. If the tape measure is 3 meters from the wheel, a 5 minute (1/12 degree) toe angle is 4 mm distance on the tape measure. This is probably about the range of accuracy of this method, and should be sufficient for just about any needs. If you have room and can put the tape measure 5 meters from the laser, 5 minutes gives 7 mm of distance, which is very easily seen.
That’s the Basic Outline
That’s the basic outline of the method. I have used it on my own 996 and it took me pretty much a whole day to think through (and I did the calculations manually). In the end it worked so well that I put together the spreadsheet and am happy to share it with fellow ‘ligners. It can certainly be improved because I’ve assumed a very simple suspension geometry, and it’s a little more complicated than I’ve modeled, particularly the rear wheel suspensions.
Here are links to or information on the tools I use in this method.
The laser levels are TradesPro 835082 16-Inch Two Position Laser Level, at Amazon.com currently for $18 but price can vary. You need two of these and they have to be this specific model.
I used a digital caliper for a few random things, but it’s not necessary. This one: Capri Tools 6-Inch Digital Caliper with Fractional Display/MM/SAE & Extra Large LED Screen is currently $19.
Any basic 2-foot bubble level will work, such as this one: http://www.amazon.com/Stanley-42-324-24-Inch-I-Beam-Level/dp/B000NIFC7K for under $12.
Any basic tape measure with a blade wide enough to hit easily with the laser from 6-15 feet away will work. A 3/4″ wide blade was good enough for me.
The plate I referenced above and will show one idea of its construction in Part 2 is an aluminum angle that is light, sturdy, and inexpensive (I used an aluminum sill nosing, $7). It should be about 24″ long to extend well past the wheel rims. It will need to have some bumpers or hard rubber “feet” on the flat side that will rest on the outside edges of the rims and separate the plate from the tires.
Total tool cost: about $75.
To adjust the suspension, you will need the following if you don’t already have them:
- Front tie rod: 21 mm open-ended wrench, 13 mm open-ended wrench, adjustable wrench to counterhold tie rod end
- Front camber: 15 mm socket
- Rear eccentric bolts: 18mm open-ended wrench to loosen nut, 17 mm socket or wrench to adjust eccentric bolt
- Measuring rear adjustments: feeler gauges, a 2″ clamp, and a block of metal or plastic to clamp onto the toe or camber control rod
- And of course a torque wrench, jack and stands, shop light, etc.
Actually to do this right, you should have 18 mm and 21 mm torque wrench adapters with 2″ center-to-center to torque the nuts when done, instead of using wrenches.
One Important Caveat
Cars with ABS and/or PSM (Porsche Stability Management) have a steering angle sensor that tells the computer where the car is supposed to be pointed. This is one of numerous inputs used to calculate the brake pulsing applied to individual wheels that ABS and PSM do. If the toe adjustment changes the steering wheel angle when the car is moving straight ahead, this sensor must be recalibrated. This requires access to the internal computer with a tool such as Durametric or the Porsche PIMIS, PWISI or other factory tool. If you do significant DIY work on your 996 you really need a Durametric in order to read out and reset computer codes, recalibrate the steering angle sensor, open the ABS/PSM valves to flush brake fluid, and numerous other operations. If you save just 2 hours of shop labor time, Durametric has paid for itself.