Here is some information on aligning a 911. It started with a specific question, then I added to it. Hope it answers more questions than it generates! Someone asked about adjusting rear camber on his 911 to a more negative setting without changing toe, to decrease oversteer in autocrossing. This is what most people want to to to their camber, so the answer is useful.
If you adjust the rear camber more negative, you will need to pull the wheel forward with the toe adjusting bolt to toe it back in again. I have found that there is a simple and pretty accurate way to do this with only a tape measure. There are plenty of home alignment methods- here is my personal method which has been proven effective on the autocross course and race track.
It is much easier to adjust camber if you can get under the car in an inspection pit or on a lift, then you can loosen the 19mm bolts slightly and adjust the camber and toe from below without removing the wheels, and get an idea of the changes by measuring the camber directly with the method explained below. But most of us don't have access to a pit or lift, but we can use this method of adjusting :
Before adjusting anything, support the car on jack stands, remove the rear wheels and make sure that both rear suspension arms are at full droop. Then measure from a convenient point on the torsion bar cover (I make a dot in the center of the round end), to the hub of the rear brake (to the closest point on the hub). Both sides of the car (left and right) should measure about the same if your wheels are aligned correctly and your car is symmetrical. Now you can loosen the two 19mm bolts at the rear of the spring plate, and the two 19mm eccentric (cam) bolts. Turn the rear-most eccentric bolt with a hex wrench from behind to adjust camber more negative. You will want the eccentric part of the bolt to be at it's lowermost position for maximum negative camber. I find it useful to remove the eccentric bolt and mark the bolt at it's most eccentric part so I know when that part is down I have maximum negative camber and will not turn it further which reduces the camber.
It is hard to measure camber while you are adjusting it, but you can use a modified version of the camber measurement method below to get an idea of how much you are changing it.
To set the toe back in, pull the wheel forward a bit with the forward eccentric bolt to get the same toe measurement as before. After doing this, drive the car over some bumps and check the camber to see if it is set where you want it. If not, you can repeat the procedure above and move it a bit more or less. When the camber is OK, you must check the toe-in to see if the toe is still OK. The following method was suggested by Pete Albrecht and seems to work fine, and is easier than most methods. It works great on front or rear wheels.
An easy method of measuring toe can be done by sticking a thumb tack into your tire in a full tread area near the center of the tread, at the frontmost point of the tire (not too deep!). Hang a string from the tack with a weight such as a plumber's bob which almost reaches the ground. Make a mark on the ground (an X with a pencil is good) where the weight rests. Repeat this a few times to make sure it is correct and repeatable. Use another tack and do the same on the wheel on the opposite side. Now push the car backwards until the tacks are at the most rearward positions of the tires. Make the marks at the current positions on both wheels. Now you have two sets of marks, one is the WIDTH of the front of the tires, the other is the WIDTH of the rears. Measure between the two front marks, then between the two rear marks. If the two distances are the same, you have 0 toe. If the front distance is less than the rear distance, you have toe-in. If more, you have toe-out. Usually about 1/16" to 1/8" of toe in is desirable. For autocrossing, you may want to toe-out the front wheels by this amount, especially if your car is understeering or turning in sluggishly.
You can measure the camber accurately and easily with a good bubble level. You must first make sure the car is on perfectly level ground. You can check this with the bubble level on your garage floor and a long straight rod. If it is not level, you can use some cardboard or something under the low wheels to make it level.
First drive the car to settle the suspension. Now check the distance the top of the level is away from the top of the wheel, when the bottom of the level is touching the bottom of the wheel. Don't measure from the tire, as it is very distorted. Choose a nice flat spot on the wheel rim to measure from. You will probably have to fabricate something that you can hold the bubble level against, that will fit against the wheel without hitting the tire. I sawed-off a bubble level to fit the wheel's diameter, and inserted a thumb-screw into the top which presses against the top of the rim. I adjust the thumb screw until the bubble is level, then measure the length of the screw sticking out, and calculate the camber.
Use some math : camber = inverse sin (measured distance / vertical length). Vertical Length is usually about 1" more than wheel diameter, so 9/32" at the top of a 15" wheel is about one degree negative. I run about 9/16 (2 degrees negative) at the front and .7" (2.5 degrees) at the rear for autocrossing. For the street this will wear out the insides of the tires quickly, so you should try for about 1 to 1.5 degrees negative in the rear, and ' degree less negative in the front (more if you're serious about handling). If you don't have a scientific calculator handy, you can approximate the measurements for a 15" or 16" wheel by using 4.5 / 32" for each one-half degree. (For our metric friends, about 3.5 mm per half-degree camber).
The front of a 911 (or most Porsches) is fairly easy to adjust. Loosen the hex bolts at the top of the strut and mark the position of the plates so you know where you started. You may have to remove some of the goop around the plates. Then pry the strut towards the center of the car to get more negative camber. For competition, I think you should push the top of the struts as far back towards the rear of the car as you can to increase caster. This is not very scientific, but it works well, just make sure your car does not pull left or right which would indicate castor is not equal from left to right. It may be difficult to move the tops of the struts, you may need to pry against the metal or use a piece of wood against the mounting of the strut and hit the wood with a large hammer. It should help to jack up the car to remove pressure from the strut.
Front toe is not too difficult to adjust. But on older cars, the tie rod adjusting threads are often seized-up from rust. You may need to heat up the tube between the tie rod and tie rod end with a torch. First soak both ends with a good penetrating oil, this may be enough to get them loose. Then loosen the clamps on each end of the adjusting tube. When loose, turn the tube to change toe, you can use a "vice grip" in the center. You will be able to see which way to turn the tube for toe-in or toe-out by watching the wheel as you move the tube back and forth. You should adjust both left and right sides by the same amount, but if you are making a very small change (for example 1/8") you really need to adjust only one side (and it is much easier!).
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I know I should just pay $ and have it done right, but assuming it's out of adjustment anyway, I'd rather fiddle with it myself and learn something along the way before paying someone to set it right.
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Don't think that when you pay $$ to get it done that it will be better than doing it yourself. I've heard plenty of horror stories about alignment shops with equipment that was uselessly out of calibration. If you can DIY, you can check it occasionally and will always know it is right. Peter Gabriel says "If you want some control, you've got to keep it small- DIY".
CORNER BALANCING :
Juha Vane Vane@compuserve.com> asked :
- It is a stock -85 Carrera Coupe. What alignment spec is recommended, I am somewhat concerned about tire wear and would not like to go extreme here but again handling is priority.
I'd go with 1 degree front and 1.5 rear as a compromise of handling/tire wear.
>> I tried also to get corner weight adjusted, did not do too good.
Had my weight on driver seat, tank full.
I used following principle from Bruce's book, Porsche 911 Performance Handbook 1 stedition, page 174, I quote Bruce;
"Assuming the 911 has a weight distribution of 40/60 front to rear, forty percent of the left side weight should be on the left front wheel, and sixty on the left rear" end quote. Thanks Bruce, hope You don't mind me quoting You.
Mike Piera wrote some time ago, I quote Mike;
" When you find which diagonally opposite corners have too much weight (they will each be heavy by the same amount if you calculated right!) you should lower the 2 heavy corners, and raise the two light corners slightly, all by the same amount, then drive the car and measure again." end quote. Thanks Mike, hope You don't mind me quoting You.
I was not able to get weight transferred to right front and keeping car level. After I leveled the car, and 8 hours of adjusting, the car is level, but the weights are way off. LF 718, RF 561, LR 903, RR 933 (lbs) I did not drive the car after adjustment, adjusted with wheels on ground, rears hard, but it can be done with 2 people. After adjustment, bounced the suspension and the HEIGHT adjustment was logical. I adjusted a little, car HEIGHT changed in proportion.
Mike, I don't completely understand Your wording; "they will each be high by the same amount", please clarify.
<< Your weights are accurate, I can tell because the diagonal corners are all off by + or - 52 pounds. Here is your car (front of car is top)
718 1279 561 (LF, Front, RF) 1621 3115 1494 (Left, total, right) 903 1836 933 (LR, rear, RR)
Here is your car's weight distribution :
41% 52% 48% 59%
To calculate the desired corner weights, multiply the front or rear percentage times that side's weight, i.e. for left front 41% (front) x 1621 (left) = 665 pounds. You have 718 on LF so you need to reduce weight on the left front by 53 pounds.
When you calculate the other corners you will see that EACH corner is off by 53 (or so) pounds - and the diagonals are the same, i.e. right rear (diagonally opposite of left front) is also 53 pounds heavy : 59% (rear) x 1494 (right) = 881. 933 - 881 = 52.
In order to KEEP YOUR CAR LEVEL and at the current ride HEIGHT, and change all four corners to the correct weight, you need to LOWER the left front and right rear a bit (reduce weight on a wheel by lowering/loosening the torsion bar), and RAISE the right front and left rear by the same relative amounts. By doing so the car will stay level and at the current ride HEIGHT.
You can also change the corner weights by just adjusting two diagonals, i.e. just lower the LF and RR and then drive the car to settle it in and weigh it again to see if you did enough. This will lower the entire car however. But if you did want it a bit lower then this is just the trick to do! Likewise if you want to raise the whole car a bit then just raise the RF and LR. If you need to keep the ride HEIGHT the same then do all four corners.
Then if you do everything right you should have a perfectly balanced, level car that weighs:
665 613 956 881
Of course this is easier said than done and may take a few trials but if you are within 10 pounds or so you've got it! Good luck and let me know how it turns out!
'72 911S Targa, '73 911 RS lightweight clone
2 time SCCA SCCA Solo-II A-Stock national champion,
2 time Porsche Parade fastest of any stock "P" class