Starting from no shims, putting an equal number of shims in the front and rear positions on the upper "a" arms cross shaft adjusts the camber. What does installing a different number of shims in the front and rear adjust, or is this an indication of a problem with the frame?
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
it's not unusual for there to be different shim thicknesses for and aft. mike -
Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
What exactly does that adjust that the tie rod adjustment would not take care of?Comment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
"What does installing a different number of shims in the front and rear adjust"
Caster
So long as the amount removed from the front is added to the rear the caster will change with minimal change to the camber. Same thing applies to shims removed from the rear and added to the front -- just moves the caster the other direction.TerryComment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
Terry,
I have been reading a little about the alignment thing (front and rear). I understand how to adjust caster, camber and toe....sort of that is. I have read a few peoples comments about where they should be set to. Do you have an opinion? Should all 63 to 82 corvettes have the same alignment settings if being set for regular street driving? How does having +/- camber effect drivability? How does toe-in effect drivability? How does caster affect drivability?
What makes the car twitchy? Personally, I would like a car that drives staight and does not grab every crack in the road. I am not interested in seeing how many G's I can pull in a turn.
Any ideas on how to find a true center line on the underside of the car? Were is a good place to measure from?
Sorry for all the questions. I have been reading some of the archives. Anyone should feel free to speak up. I would like as much input on this. Thanks, TerryComment
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TerryComment
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Re: ALIGNMENT
Thanks for the responce. I believe I read that radial tires can get by with next to zero camber. I hope more people chime in. I will look into the hot rod magazine thing. If someone had a copy of the exact issue that would be great, I could zip over to the library and check it out. Thanks, TerryComment
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Re: ALIGNMENT
Duke will probably chime in later, but the following are good settings for normal street driving with radial tires:
Front Camber - Zero
Front Caster - +2.5 deg with power steering, +1.5 deg with manual (the +2.5 will also work with manual steering, but parking steering effort will increase).
Front Toe-In - Zero-to-1/16" TOTAL toe-in (bias tires want 1/8"-1/4")
Rear Camber - Zero to 1/2 deg. negative
Rear Toe-In - 1/16" TOTAL, split equally, 1/32" per side across the thrust centerline.Comment
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Re: ALIGNMENT
Terry,
I believe the article is in the November Hot Rod magazine. It's very informative as it describes stringing the car from the side to set toe for the front and rear. This article also mentions using floor tile under the tires so when adjusting angles the tires will slide easily while supporting the weight of the car. I think (but not sure) the thrust angle is determined by setting the rear toe exactly the same on both sides so stringing the car for at home alignment is very important. I would also like to know how to best determine the centerline for the frame as this is probably the best way to string the car and set toe.
I have set camber with a 24" level in front and rear but I am not sure how to check caster and I keep reading Duke's post because I want to try and accomplish this at home.Comment
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Re: ALIGNMENT
Thank you for the update on the month of the article.
As far as caster adjustment is concerned, I think you do it this way. I am not sure if this is a direct measuremnt or indirect measurement of caster angle. Any how, you turn your wheels 20 degrees to the left then 20 degrees to the right. This must be exact so most people just turn the wheels untill they stop which is very close to 20 degrees. When you have the wheel turned to the left, you measure the vertical angle on the right wheel and visa versa. I stand to be corrected on this. I have thought about it and I think that caster is engineered into the steering geometry to cause the wheels to naturally want to return to center. Also, the more caster the greater force required to turn the steering wheel. Just my thoughts. Both sides of the car should be symetrical with regards to caster. Thanks, TerryComment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
Here is what I wrote in response to your question in a thread on another topic on Dec. 30. It's as good as I can do without writing a book.
On most cars there is some interaction between camber and caster adjustments. On C2/3 Corvettes, the best way is to shim for camber while keeping the
caster in the ball park. Start by measuring both camber and caster to see where you need to go to get to your objective. Camber is changed by adding or
subtracting shims to both studs. Adding shims changes camber in the negative direction since it moves the upper ball joint inboard. Caster is affected by
adding/subtracting shims to just one stud, which moves the upper ball joint forward or backward, and moving it backward increases caster. Once camber is
about right you can fine tune caster by removing a shim from one stud and placing it on the other, which will change the caster with little effect on camber.
Your understanding of measuring caster is basically correct. Caster can be estimated by the arithmetic difference between camber readings with the wheels
turned. I just turn them to the limit of steering travel. The important issue is to get the side to side difference as close to zero as possible.
For cars that have near zero caster, getting the sign correct can be tricky, but should not be a problem on C2/3 Corvettes since their nominal caster specs
are in the range of 1.5 to 2 degrees.
As an example say you are measuring left side caster and the camber is zero degrees. You turn the wheel full left and the camber is plus one, and minus
one with the wheel turned to the RH stop.
Caster = 1 - (-1) = 2 degrees.
The RH side caster measurements and computation is a mirror image.
Another way to look at this is that positive caster creates negative camber gain on the outside wheel. Zero camber results in no gain and negative caster
yields negative gain. The negative camber gain created by positive caster is good since it tends to offset body roll to keep the tire more vertical relative to the
pavement.
Once camber and caster are set, set the toe. With the steering wheel centered, I adjust the tie rod sleeves until each tire has just a hint of toe-in by
eyeballing down the edge of the tires from the front of the car. Then I measure and adjust the sleeves equally to 1/16" total-toe in. This usually results in the
steering wheel being nearly straight on a level straight road, but I sometimes have to tweak one or both tie rods once or twice to get it dead straight with
about 1-2 32nds total toe-in before I'm satisfied.
If the tire has a center groove, use this to measure toe. If it has four grooves pick either the second from the inside, or second from the outside, on both
sides. If the groove is a zig zag, measure from the outside apex. On the back side of the tire mark these references with a tire crayon as high as possible
without a straight line between them (your tape measure) interfering with chassis components. Measure the distance, then roll the car forward to the limit of
where a straight line will not interfere with the chassis and take the measurement between the same reference marks. You want this measurement to be
about 1/16" less than the first measurement.
Once set up, the car should hold alignment well if the suspension is in good shape and you don't bang any curbs.
DukeComment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
The light bulb may have come on a little bit brighter. So caster improves handling by slightly changing the angle of the wheel in turns thus improving the contact of the tire tread surface with the road surface. Correct? But it seems that it would also have a secondary effect of wanting to return the wheels to a neutral/center position out of a turn.
So to measure caster, you can measure one wheel at a time in both full stop positions and subtact the angle difference (each angle converted to degrees)?
Toe-in helps prevent wondering and helps prevent the tire from grabing cracks and ruts in the road? I will keep rereading your posts. Thanks, TerryComment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
Yes, positive caster increases negative camber gain on the outside tire, and increases steering wheel returnability and on center feel.
Many modern cars with power steering run caster in the range of 5-10 degrees, but you can't run this much with manual steering, so older cars that don't have P/S standard typically specify no more than about 2 degrees.
Tire shelf aligning torque combined with a little toe will cause either tension or compression of the steering linkage, which will make it feel "tight". The natural drag force on the front tires tends to force them rearward,which will tend to reduce toe from slight toe-in to zero toe. On FWD cars the drive forces tend to pull the tire forward, so they often specify a small amount of toe-out, and some RWD cars with front mounted steering linkage specify a little toe-out.
Radial tires require less toe than bias ply tires, because radial tires have greater self aligning torque due to a longer contact patch than bias ply tires. Also, low profile tires tend to have less self aligning torque, so installing low profile tires on a car designed for higher profiles can cause a loss of steering feel unless caster is increased.
The really important parameter is "caster trail", which is the distance between the contact patch center and point where the steering axis intersects the ground. As this dimension is increased due to increased caster, the self-centering effect is increased, and for this reason the self centering effect will be decreased if tire radius is reduced.
DukeComment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
Interesting. I am afraid to say that I understand but it seems a little clearer. Sorry to rehash this but....If I take one wheel (say the drivers side) and turn it all the way to the right and measure caster of 3 degrees negative then turn that same wheel all the way to the left and measure a 5 1/2 degree negative caster. I effectively have a positive 2 1/2 degrees caster on that wheel? Because -3 - (-5 1/2) = 2 1/2 . I am making these numbers up in my head. I have never attempted to measure cast on a car yet. But, is this essentially correct. I am going to purchase a bubble gauge and play with it.
When I was looking at some of the charts for alignment, I noticed the caster numbers were larger for the power steering cars. That was my clue that the caster angle effected the force it took to steer the car. Increased caster also gives more feedback to the steering wheel and may be more comforting to the driver? I seem to recall people complaining that they couldn't feel the road with PS equiped corvettes.Comment
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Re: '67 UPPER "A"-ARM ALIGNMENT SHIMS
Reread my post. You measure the CAMBER with the wheel and right lock and left lock, and the differences in measured CAMBER angles is the caster.
I use an inclinometer, which you can buy at Sears or any hardware store.
DukeComment
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