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Old 03-16-2011, 07:37 AM   #1
macvette63
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Member Since: Jul 2008
Default Trailing arm alignment and shims

Hi,
I'm in the UK coming to the end of rebuilding the rear end of my 63 split window. New wheel bearings, trailing arms rebushed, strut rods rebushed, ujs replaced all powder coated where needed. Car is on stands in my garage. Does anyone have a more detailed way of shimming the the control arm to get the alignment correct than the one in the assembley manual and the maintenance manual that I can use in my garage. Taking the car to a local shop would be a waste of time because the car is as rare as hens' teeth here.

Thanks Mac
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Old 03-16-2011, 09:16 AM   #2
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I saved this awhile back from the Forum. I think it was from Duntov but not sure. Hope it is a help to you. Dave

Rear Suspension
Alignment School






A lot of us would rather do it ourselves than take our Corvette to an alignment shop that hasnít seen a C2-C3 Corvette in 20 years. I have used this method for years, and it will put your car on the money.

All you need to align the rear end of your 63-82 Corvette is an hour or so, a short level, a pair of 2í by 4 x 4 wood blocks, two 3-foot aluminum straight edges, a framing square, some string, a measuring tape and a helper.

Your car needs to be on the garage floor, with all the trailing arm shims removed from the front trailing arm bushings.

First the ride height at the rear should be set. Your carís favorite ride height is where the half shafts are horizontal. In this position, the U-joints donít have to work much at all, but that may be too low for you. Adjust the ride height to your favorite position by tightening or loosening the spring bolts.

Next is track. We have to have the toe-in equal on both sides so the car will track straight down the road. Position the rear wheels as close to straight as possible. This is easy even with weight on the car, as you can use the trailing arm as a big lever to pull or push the front of each wheel in or out.

Make sure the front wheels are straight. Have your helper hold one end of an 8í string on the outside of the left rear tire behind the axle, at the height of the axle. Pull that string taught to the front of the car and move it in until the string just touches the front of the rear tire in the same position as your helper has the other end pinned at the rear.

With the taught string in your left hand, use your right hand to measure the distance between the string and the dust cover of the front spindle. If you have rally wheels, measure to the center of the cone.

All we are trying to do is get a relative measurement to which we can compare the other side. Repeat this procedure on the right side, and go back and adjust the tow by hand until both lines of alignment are equal when measured relative to the front axle reference.

At this point your Corvette is tracking straight, but we have not yet set the toe. We have set the track.

To set the toe, place the 2í 4X4 wood blocks on the floor outside, centered and up against the rear tires. Place the 3-foot aluminum straight edge on top of one of these blocks, centered on the tire. Have your helper hold the strap tangent to the outside of the tire. In case you are wondering, the purpose of the block is to elevate the aluminum straight edge above the bulge in the tire at the floor.

Now you go to the other side and place your block and aluminum strap in the same relative position and feed the end of your tape measure under the car to your helper on the other side. Measure the distance between the aluminum straight edges in front of the tire and behind the tire, again with both aluminum straight edges sitting on the reference blocks and tangent to the outsides of the tire.

Our target is 1/8-inch total toe. That means the distance between the front of the tires should be 1/8-inch less than it is at the back of the tires. It wonít be. You will have to torque the arms in or out to achieve this number, but the trick is to do it half on one side and half on the other. When you think you are there, go back and do the string trick again to make sure you are still tracking straight down the road. Adjust accordingly and repeat until it is both tracking straight and the total tow is 1/8-inch.

When you are there, put the spacers in and tighten up the trailing arm bolts. Check it again just to make sure, and then insert the cotter pins in the trailing arm bolts and in the shim packs and you are finished with the toe adjustment.

Last we adjust the camber, which is the angle the rear tire sits to the floor. The target is ľ to Ĺ degree negative camber, meaning we want the top of the tire to be tilted in just barely, like 1/8 to 3/16 inch from vertical. You adjust that with the strut rod cam bolts that are located under the differential. Loosen, twist, tighten, measure, and repeat as necessary until you get it right. You will have to roll the car between adjustments to allow the tire to move.

When you are all finished, if you are into self-abuse, you can drive the car around the block and measure the toe again. It will go much faster this time. Remember we need to have the toe-in right, but we must also have the tracking equal left and right.
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Old 03-16-2011, 10:16 AM   #3
dkleather
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Here's another I saved by MagicV8

Rear wheel alignment is easily divided between setting the camber (top and bottom of wheel tilted in or out) and toe-in/thrust-angle.

Camber first:

You need a (carpenter's) level. Oil up the adjustment cam on the inboard end of the original style strut rods, or clean and oil the threads on the (replacement) twist type aftermarket strut rods. Cut/buy 4 pieces of sheetmetal, smooth floor tiles, or heavy plastic about 1 foot square (larger doesn't matter, neither does shape, even round will do), and stack them in pairs with a film of grease between them, like grease sandwiches. Position the car on a spot that is fairly level across the car (left to right). It can run up or downhill a little (front to back).

Jack up the car at the frame in front of each rear wheel and insert the greased squares under the rear wheels, then lower the car. Push down on the bumpers a couple of times to reset the rear suspension. Put the carpenter's level vertically across the wheel or the tire (depending on the size of the level. Mine is 18 inches long. I put it on the tire. The rear wheels should be vertical. The car will squat with a load (wheels splayed out at the bottom). Since my wife rides with me on long trips, I throw 75 pounds of cat litter bags in the driver's seat to give a percentage more weight to the left side, and I like to align the car with a full tank of gas - which loads the suspension half way between an empty tank and 2 suitcases in the back with a full tank.

If the wheel is not vertical, Use the strut rod adjustment to make it so. Rest the car on the plates on the ground and push on the bumpers again, before checking the new alignment settings. Repeat as necessary.

Toe-in/thrust-angle:

With the camber set, measure the track width of the rear tires, about half way from the floor to the top of the tires, at the front of the tires and at the rear of the tires. For the factory spec 1/8 inch toe-in, the dimension across the rear of the tires should be 1/4 inch wider than at the front of the tires. If the toe is off by more than 1/16 (difference off by more than 1/8) the rear wheels need to be reset by moving shims at the front of the trailing arms (where they pivot at the cross bolt in the frame, in front of the rear wheels).

To determine which wheel has to be changed to point the wheels evenly toward the center of the front of the car, you need to draw a map of the wheels on the floor, I did it by making a tool to set in the wheel rim and scratch a mark on the floor in front of the wheels. In the attached picture, you can see the tool in the lower right corner, a piece of wood that fits in the wheel rim as shown, with a piece of angle iron screwed onto it to scratch the floor in front of the wheel. By scratching another mark behind the wheel and drawing a line between the two marks, I determined that my tool stuck out 1.5 inches outboard from the tire tread edge.

When I drew a line from a point 1.5 inches from the tire edge through the mark that the tool scratched in the floor, it points the direction that the rear wheel wants to roll. Since the front tread width is a little wider than the rear tread width (.375inch or .188 inch per wheel), I moved shims at the front of the trailing arms until each rear wheel pointed .45inch ( 7.2 times 1/16 inch) inward as measured at the front wheel tread center line. See the diagram on the attached picture. The reason for the 7.2 multiplier is to project the .0625 toe dimension of each rear wheel to the other end of the 97.75inch wheelbase. To determine the thickness of shims to move, divide the projected movement at the front by 5.5 (determined by dividing th e 97.75 wheelbase by the 17.375 dimension to the trailing arm pivot). The two multipliers a(7.2 and 5.5) are necessary because the alignment spec is noted at the front of the rear wheels, while the shim are farther forward at the front of the trailing arms.

It sounds complicated, but once you map the car to the ground, it's not bad. I find this produces repeatable results. I am able to get the alignment right this way the first time. If I let laser alignment shops do it, every one says the last one got it wrong, and they can't align my front end unless THEY fix it.
magicv8
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Old 03-16-2011, 10:50 AM   #4
magicv8
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Here's the diagram that goes with the text above:
Click the image to open in full size.

It can also be linked from the help section near the bottom of this web page: http://home.mchsi.com/~magicv8
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Old 03-16-2011, 04:16 PM   #5
macvette63
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Thanks for the advice

Mac
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Old 04-06-2013, 03:58 PM   #6
856666
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Hello,

I used the previous threads to set up the alignment on my 65 convertible, and someone asked for a starting point for the rear shims. Here is the alignment I currently run.

Thanks for your posts


Front
Toe Tire Tread Align Shims Camber
LF Zero * *9/32 * Zero to .25 Neg Deg
RF Zero * *9/32 * Zero to .25 Neg Deg

Rear
Toe In Tire Tread Align Shims Camber
LR .080"(in) *9/32 Out:.415"--In:.325" .25 Neg
RR .080"(in) *9/32 Out:.367"--In:.353" .25 Neg

The car had a frame off restoration 5 years ago - but had not been sorted out until now. It is a L79 with 4 speed and manual steering. It is completely stock

With this set up it goes where pointed but has body roll into a corner before the tires (205/75 R 15) bite and it turns. When driving on the express way it feels light/not connected in corners/turns until the springs are loaded in the turn. I would say it is not extremely responsive/tight at the steering wheel, but it is predictable.

I hopes this helps.

Phil
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Old 04-06-2013, 03:58 PM
 
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