C2, C3 DIY Four Wheel Alignment

[Greg L.]

I've been reading up a bit on the best way to perform a 4 wheel alignment and for the most part have all my answers.

Finding the centerline of the car will be the most trying issue but a while back someone posted that they use a method of running some fishing line from the back wheel to the front wheel. Basicaly set it up so that the front wheel is straight enough so that the line just touches the sidewall fore and aft of the vertical center and the AFT sidewall of the rear tire, then adjust for 1/16" toe-in and repeat for the opposite side. This in theory will give you 1/8" total toe-in and be centered.

This all sounds fine IF the tread width is the same for front and rear but(for 69 anyways) the rear tread is about .7" wider than the front. I was wondering if anyone has tried this method and could give me some insight on if this .7" is something to be concerned about or if there is some way to compensate for it.

[Timothy B.]

Re: C2, C3 DIY Four Wheel Alignment

The tires are the same size correct? I think what they are referring to is the negative camber for the rear and the slightly positive camber in the front. I did mine the way you mentioned in your post but you can also stringline the frame side rail and set front/rear toe. If the steering linkage is all straight from the steering wheel thru the pitman arm you will know right away if the front toe is not straight because the wheel will be off center as the car drives straight down the road. Then you pull it into the garage and adjust both sides the same amount to turn the wheels the proper direction while maintaining the correct tow.

Nothing will be as accurate as the frame centerline but I don't know how to do the with the body on the frame.

[Dick W.]

Re: C2, C3 DIY Four Wheel Alignment

The tires are the same size correct? I think what they are referring to is the negative camber for the rear and the slightly positive camber in the front. I did mine the way you mentioned in your post but you can also stringline the frame side rail and set front/rear toe. If the steering linkage is all straight from the steering wheel thru the pitman arm you will know right away if the front toe is not straight because the wheel will be off center as the car drives straight down the road. Then you pull it into the garage and adjust both sides the same amount to turn the wheels the proper direction while maintaining the correct tow.

Nothing will be as accurate as the frame centerline but I don't know how to do the with the body on the frame.

To correctly perform a four wheel alignment you have to establish a datum line as a reference.

[Terry M.]

Re: C2, C3 DIY Four Wheel Alignment

I was surprised to see the Prototype cars at Daytona using string down the side of the car for wheel alignment. They have holes int he body (maybe 1/4-inch dia) and a pre-made wire stand-off to hold the string. If it is good enough for them, it ought to be good enough for us.

[Dick W.]

Re: C2, C3 DIY Four Wheel Alignment

I was surprised to see the Prototype cars at Daytona using string down the side of the car for wheel alignment. They have holes int he body (maybe 1/4-inch dia) and a pre-made wire stand-off to hold the string. If it is good enough for them, it ought to be good enough for us.

I have used the string for toe settings over the years but for a true four wheel alignment you have to start of with a known C/L. Then work off that point

[Bill H.]

Re: C2, C3 DIY Four Wheel Alignment

I was surprised to see the Prototype cars at Daytona using string down the side of the car for wheel alignment. They have holes int he body (maybe 1/4-inch dia) and a pre-made wire stand-off to hold the string. If it is good enough for them, it ought to be good enough for us.

So do Indy Cars. While they do use an alignment rack in the shop, at the track, the strings take less than 5 minutes to set up, much less time than a laser setup.

[Bill H.]

Re: C2, C3 DIY Four Wheel Alignment

This all sounds fine IF the tread width is the same for front and rear but(for 69 anyways) the rear tread is about .7" wider than the front. I was wondering if anyone has tried this method and could give me some insight on if this .7" is something to be concerned about or if there is some way to compensate for it.

That's part of the problem Greg. And you can be way off using the tires to set up strings (I've seen guys get the strings uneven many times).

There's 2 thing to be concerned with: 1. The centerline - between the suspension pick up points. And 2. The strings must be as close to parallel as possible.

The centerline is easy to measure but hard to use (you can't pull a string line down the middle of the car, too many things are in the way).
So, I would go off the frame side rails. Stretch a small diameter string (fishing line) down each side of the car (hooked to heavy jack stands at each end). Measure from the frame side rails to the string and get the string parallel to the rail. The height of the string must be at the centerline of the wheels. Since the frame will be at a different height, you can use a carpenter's square to take the measurement, slide the square up to the string and measure from the square to the frame.

Once you have the strings stretched and measured to the frame, double check by measuring string to string at the front and rear. If the measurements are the same, the strings are parallel and you can measure your toe-in.

Note: I build the alignment bars that Terry mentioned, on the racecars, my strings are within 1/32 in. to the centerlines of the cars.
Done right, this is an accurate method to do an alignment.

[Duke W.]

Re: C2, C3 DIY Four Wheel Alignment

Carefully measure the center point of the frame cross members. Then set a string with plumbobs as required to get it to the proper height to measure rear toe in.

You don't absolutely need a string for front toe. Front toe will always equalize while driving on a flat road, but the steering wheel may not be centered. The string can help, but you can also tweak the tie rods and equal amount in the proper direction to center the steering wheel.

Duke

[Bill H.]

Re: C2, C3 DIY Four Wheel Alignment

And the toe measurements need to be taken while the car is on the ground (except centering the steering wheel) because the toe can change as the car is jacked up.

[Duke W.]

Re: C2, C3 DIY Four Wheel Alignment

Yes the car absolutely has to be at normal ride height.

The best way is to have a drive-on lift with enough length to roll the car at least half the tire circumference - about four feet - to measure track or half track to the centerline string at the same tire datums. Mark the measurement points on the rear face of the tires as high as possible to get the tape across without interfering with chassis components. Measure at the rear of the tread, then roll the car forward and measure from the same datums when they are on the front side. The difference is toe.

On modern cars with cam bolts on the control arms you can do the whole job from underneath.

On a C2/3 do the front caster camber with the lift on the ground, so you can access the engine compartment to change shims. Then raise it to do rear camber and set up your centerline string to do front and rear toe.

If you use the string to measure front toe and the steering wheel is straight driving down a flat road, then you can be resonably confident that your toe per wheel measurements are acceptably accurate. Another reference check is tie rod length. They should be essentially the same.

Duke

[Terry M.]

[Greg L.]

Re: C2, C3 DIY Four Wheel Alignment

Thanks Guys and I'm sorry that I forgot to make it clear that I'm mostly interested in figuring out how to set just the rear toe. I have the camber/caster and front toe method figured out and it's pretty straight forward however it's been about 20 years since I've done a 4 wheel alignment and back then it was with the latest alignment machine so it was a pretty simple task.
Since I'll be doing this without a fancy machine I appreciate everyone's thoughts but first I'd like to understand why using the string method with the frame rail as reference point requires the string to be set at the centerline of the wheels?
Also, should running the string from front wheel to rear wheel while just touching the sidewalls work IF I added enough, say "shimmed" the front string away from the front tire .35" to essentially make the tread width the same for both front and rears?

[Craig H.]

Re: C2, C3 DIY Four Wheel Alignment

I had always had some wander in my 71 and had done the front alignment etc but wanted to ensure the rear was correct.

The method I used was ......

With a piece of aluminium running along the side of the frame and one on the hub I aligned them parrallel adjusting the inner shims.








Then using a laser align tool I checked it in relation to the front tires and the beam hits in the middle of the font tire.





So if this is my baseline

I then removed 2 thin shims from the inside of trailing arms and measured the effect it had on the aluminium - allowed me to determine how much effect each shim would have (You need to remember your measuring half the wheel and one side only at a time)

Getting the rear properly aligned (Parallel to frame) first then doing toe is critical. My 71 has never driven as well as it did after this basic setup.

String method seemed too fiddly to to me and the centreline of the frame is parallel to frame sides so this made sense to me anyway.

I will take it to the alignment shop and get it tweaked shortly but am 100% happy with the changes so far.

[Dick W.]

Re: C2, C3 DIY Four Wheel Alignment

String method seemed too fiddly to to me and the centreline of the frame is parallel to frame sides so this made sense to me anyway.

.

You are making the assumption that the frame has never been damaged. A know, unhit car, this would work, but if unknowing to you the car had suffered damage in prior ownerships hands, this might not be the best way.

[Gene M.]

Re: C2, C3 DIY Four Wheel Alignment

String method works for toe. And a level is good indicator of camber. But what about front end caster? One would need to have a way of measuring tilt of the spindle casting pivoting on the ball joints. I would assume it would be important for both sides to be equal as possible. More caster making more steering effort but better centering. Any ideas for home set up?