[a67]

Have a caster question of a different kind, I'd like to verify that I am doing the actual measuring of the caster properly. I am doing a front end alignment on my '67.

This is what I did:

driver side wheel

turn 20 deg to the left (out), camber measures +1.0 deg.

turn 20 deg to right (in), camber measures +0.25 deg.

The difference in the measurements gives 0.75 degrees of positive caster, correct? (I hope).


IOW, the caster is just the difference between the two camber readings, no funny or new math involved here? [img]smile.gif[/img]

After dancing with the shims it is currently at +0.66 deg turned out, and -2.0 deg turned in, if I am doing this correctly that would be +2.66 caster.


In a previous post I mentioned having obtained and then rebuilt some turntables. This is the first I've ever used some and they do make it easier and repeatable. I don't have much room to be rolling a car forward and back between shims adjustments, so the turntables really help out.

For measuring the angle I am currently using a Howe bubble gauge on the hub.

Bob.

[davidpozzi]

IF, the bubble gage has a caster scale on it, you can do it the way you are doing it.

If you are just reading the camber scale, it won't work right, the angle built into the spindle, the "steering axis inclination" will interfere with a simple reading like that unless you have a special scale on your gage.

I believe the angle of turn is "usually" 22.5 deg but verify which spec the gage manufacturer has calibrated it for. 22.5 deg is half of 45 deg, which is the total for your turn-in and turn-out comparison.

There is another method to calculate caster by comparing two camber scale readings. If your gage only has camber scales, I can provide the info you need.
Does your gage have an adjustable bubble in the center with small allen screw?
David
David

[davidpozzi]

There is some good info here: http://www.smartracingproducts.com/P.../alsutools.htm
Download and read the smartlevel manual, it shows how to measure caster if you don't have the special caster bubble on your gage. I think there are some handy charts too.
David

[a67]

lol, I am so glad that I asked. Yes the gauge has an adjustable caster bubble and the instructions say to use the 20 deg in/out.

Now, why the laughter? The caster bubble doesn't measure true degrees of angle. It is way off from the camber bubble. I thought that it was bad and wasn't using it!

I'll hit the link you posted and read up. Then I'll be able to double double-check my work.

Thank you.

Bob.

[davidpozzi]

On my gage I turn the wheel in and set zero on the caster gage, turn out and read the caster. The caster scale is made for a particular turn angle and no other.
If you could turn your front wheel ninety degrees, the simple subtraction method of the two readings would work, but only turning part-way is why it requires compensation.
David

[ 04-27-2004, 06:26 PM: Message edited by: davidpozzi ]

[Everett#2390]

Thanks, Dave for the instructions. I picked up a three-point machine very similar to the digital one shown. This one marketed by Snap-On in the early '60's.

I wrote Snap-On for instructions as the previous owner didn't remember how to use it. Snap-On replied they had no instructions.

Now, all I need are a set of turntables and a scuff bar. I could use a tape measure and white paint.

[a67]

OK, read the caster info at the link provided (good info) and worked on the alignment again last night.

The gauge has three bubbles, one at the user end parallel to the side of the car. This one is used to level the gauge in that direction (seems logical as the only instructions that came with it is a sticker on the side giving the turn in/out degrees for the caster measurement).

The camber bubble is fixed and is as accurate as I can read it. I checked this against a Starret angle measuring device (not sure of the correct name for it).

The caster bubble is adjustable to allow for zeroing. I do not believe that this bubble is accurate.

When I did the caster measurements I wrote down both the camber bubble values and used the caster bubble. The caster bubble will read +5.5 degrees while the camber method calculates out to +3.0 degrees of caster.

So I am going with the camber bubble reading difference and multipling by 1.5 for caster.

Down the road sometime I am also going to get a SmartLevel module. It is too easy to make a mistake reading the bubble. I actually did this last night and was off by 1 full degree on camber. Wasn't at the zero mark, but the -1 mark. The clue was that the turntable plate was moved out quite a bit and just didn't look right.

With the SmartModule I'll be looking at a number instead of trying to figure out where the center of a bubble is (my eyes are getting weary for this kind of stuff [img]smile.gif[/img] ). Probably set it up with a hub adaptor.

All in all it is working out.

Bob.

[davidpozzi]

Bob,
Here is some info I had saved for doing the caster calc using only camber readings.
I'm not so much posting it for you, but for others who may read this when it is in the archives.

"To calculate caster angle.
Turn wheel 20 deg ea way, multiply difference by 1.5
Turn wheel 15 deg, ea way, multiply by 2
Turn wheel 10 deg ea way, multiply by 3
If turn in reading is larger neg, the caster is positive."

The only thing to watch with the smartlevel is, verify it is zeroed, allways watch if it's showing a positive or neg reading, the only indication is a up arrow or down arrow pointing toward zero deg, so it's easy to read .3 deg pos as a .3 deg neg if you don't watch out. If you are just placing a smartlevel against the tire side it reads .87 deg instead of .3 like it would if level, and the arrows point left/right toward 90 deg.

placing the level vertical against the tire is not as accurate as gaging off the rim. The tire will bulge on the bottom, you can stay off to one side but the sidewall is still a little distorted, probably close enough for most of us.
David

[davidpozzi]

found bubble gage instructions here: http://www.longacreracing.com/instru...t.asp?instid=5

also helpful instructions here: http://www.longacreracing.com/articl...at.asp?CATID=2

Try to keep the turtable center at the tire turn center, to keep the tire from rolling off the turntable when you turn the wheel.
David

[a67]

Finished the alignment last night and was hoping to have a driving report, alas it is raining this morning. I'll have one later.

Another tip for the 'too clever' folks, like me [img]smile.gif[/img]

When doing caster measurements and the wheel is turned 20 degrees (in or out), the opposite wheel is not also at 20 degrees. Mr. Ackerman thanks you.

So be sure to set the 20 degrees in/out separately for each side.

Got a good laugh when setting up to do the toe setting. Set up the parallel strings using 20lb test monofilament fishing line. Then did the calculation for the 1/32" toe over the diameter of the 16" rim (outer bead). And came up with 18 thousands of an inch! OK, dial calipers and measure the diameter of the fishing line: 19 thousands of an inch.

OK, toe setting will be one fishing line diameter. . .

Final settings:

Camber is 0.0° both sides.
Caster is +3.75° drv, +4.2° pass
Toe is 1/32" in drv, 3/64" in pass

Couldn't quite get that passenger side toe, will see how it drives first then adjust from there.

Bob.

[davidpozzi]

Why so little camber? I'd use .5 neg camber minimum.
David

[a67]

Basically I used Guldstrands touring specs with a little extra caster. With power steering and the camber change that comes with the caster I figured that it would be a good place to start.

Doing this alignment was a great learning experience. I actually have quite a bit of time into it. Next time will be much easier and faster.

On top of everything else I also discovered that the alignment shims are not the thickness they are supposed to be. So removing an 1/8" shim and placing two 1/16" shims in its place actually changes the alignment, lol.

Once I drive the car I'll see how it is and go from there.

Bob.

[Everett#2390]

It'll be interesting to read of the driving test with caster settings, 3.75* & 4.2*

I would think if the car pulls to the right, one might want to decrease pass caster to closer match driver caster.....just thinking out loud.

[CarlC]

Even with the Guldstrand mod I agree with David, -0.5* as a minimum, and if you drive agressively on the street -1*. Try putting a bit of white shoe polish on the outside edge of the tire to monitor wear.

[a67]

Just wanted to post a quick update. After a week of rain, traffic, & work I finally (!) drove the car this morning. For about 50 minutes at that.

Nice, it really is nice. The previous alignment was a tad cockeye, - camber on one side, + camber on the other, caster all askew. Didn't even bother to read the original toe.

With the current alignment it rides, handles and steers in a smooth predictable manner. I am going to keep an eye on front tire wear and adjust the camber from there. Although I can feel where at least a -1/4° or -1/3° would be welcome.

Lol, I didn't get the steering wheel dead on. I knew it would be off too, only a couple of degrees, but enough to notice. I need to create a setup to use a level on the spokes in order to set the steering wheel dead straight.

I even tried to look through the back light to see where it was clamped, high back seats prevented that. . . I'll get it.

Thanks,

Bob.