I'm gathering stuff to try my hand at DIY alignment. So far have the gauge Wixey WR300 Type 1, CH47960-10 rear caster bracket. Made turn plates out of 2 12x12 floor tiles with talcum powder between. A 22" piece of 1/2" square tubing to fit across wheel. The face on the Z51 wheel is complete flat so no stand-off needed. I am going to make a couple of toe-plates.

The question:

I have no problem measuring camber front and rear. I get good repeatable readings. What about caster? I haven't tried yet.

So from what I have read:

Turn wheel 20 degrees (or some other # as long as they are the same) out, zero gauge, turn to 20 degrees in, reading is caster angle.

The plan is to set up front and rear about - 1.0. Front caster around +8.0, rear about +0.8. Front and rear toe 0.

I noticed in the photos that there appears to be a little oblong in the control arm mounting holes. Do y'all think I can get any caster adjustment by loosening the bolts and knocking the tops all the way back and the bottoms all the way forward or is that a waste of time?

 

Having dreams about alignment, up at 3 AM. Anyway lots of BS out there to sift through.

Checking camber is pretty straight forward read directly from angle gauge.

Caster is a different story. You see the old school bubble caster/camber gauges. Turn the wheel to right 20 degrees then to left 20 degrees, etc, etc. There is lots built into the guage. For one thing it only works for 20 degrees.

I you take a look at the front suspension imagine it is a gokart with old fashioned kingpin solid axle front end. If the kingpin was vertical, 90 degrees from horizontal front to rear and side to side, when the spindle rotated on the kingpin there would be no change in camber when the wheels are turned side to side. Now imagine kingpin angle slanted back 10 degrees. When the wheel is pointed straight ahead there would be 0 camber. Imagine that the wheel can be turned 90 degrees. Let's say it is the outside wheel, 90 degrees to the left would now give you 10 degrees of negative camber. Turn it 90 degrees to the right would give you 10 degrees positive camber. If you had a car where the wheels could be turned 90 degrees you could measure caster directly by measuring the difference in camber angle between wheels straight ahead and turned toward the middle of the car.

This is not possible on most/all cars. You can only measure a portion of the arc. The camber changes from 0 to full caster value from 0 to +90. The bigger the angle the more accurate the measurement. Unfortunately it ain't linear. The value turns out to be the sin x angle. On our gokart with +10 degrees caster I turn the right wheel 90 to the right and get a reading of +10 degrees. If I only turn it 20 degrees I will get a reading of 3.42 degrees (10 x sin 20). I can double the accuracy by going 20 degrees both sides of zero so that would be 3.42 x 2 = 6.84. Sin of 40 degrees give you 6.43, not the same. A 10 degree caster angle give me a reading of 6.84 degrees. To correct you need to multiply by inverse of 6.84/10 or 1.46.

So if you are trying to measure caster with a conventional angle gauge turn wheel to right 20 degrees zero gauge. Turn wheel to left 20 degrees and measure angle. Multiply by 1.46 to get caster. If you use 15 degrees left and right the correction factor will be 1.93, 25 degrees left and right 1.18.

 

Look up David Farmer Racing's DIY alignment tips ( https://dl.dropboxusercontent.com/u/1634366/align.pdf ). He has a calculation you can use to measure caster based on how far you turn the steering wheel (1/2 or full turn). No need to try and determine if you have turned the wheels 15 or 20 degrees.

Bill

 

Looked at it. Probably not accurate on his car or any other.

Anyway got my bracket (CH47960-10) from local at cost + tax, $137 + 11.31.

Measured rear caster R + 0.3, L + 1.5

Front camber L - 0.3, R - 0.5.

Rear camber L - 0.7, R - 0.8.

Reading are consistant/repeatable. I am measure on a section of my drive that is almost level in both planes and am zeroing the gauge to compensate.

 

Why do you say it probably isn't accurate? David has been a racer and a member of this forum for as long as I have been a member. He used to run in the SCCA World Challenge series with his C5 competing against people like Lou G. He has been providing alignment advice and doing alignments for other people for as long as I have known of him. I haven't heard of any complaints during that time. I don't imagine GM has changed the Corvette steering ratio from the C5/C6 16:1 ratio. No reason to change it.

Bill

 

Couple of reasons. I am more of a math guy than a car guy. I figured out the math and it didn't fit his method. To measure the caster indirectly you need to measure the arc from straight ahead to some angle, say 20 degrees. The change in camber divided by sin of 20 will give you caster. I you go 20 left and 20 right you will double the value. I said it probably isn't accurate. He might know something I don't know. Things that can throw off the reading, more than 20 degrees will give high reading, less low readings. You can use any degree turn but the adjustment must match. Any time you hear the angle doesn't really matter as long as it is the same left and right, that is pure horse hockey.

I just finished measure the caster on mine using home brew turning plates made for 12 x 12 vinyl tile inscribed with 20 degree marks.

Measured 4.6 and 4.7 and calculated caster at 6.7 and 6.9. Sounds about right.

 

Bottom line:

My '16 Z51 after a year 14,000 miles measures:

Front camber

Right -0.1 degree
Left -0.2

Front caster

Right +6.9
Left +6.7

Rear camber

Right -0.5
Left -0.5

Rear caster

Right +0.4
Left -1.2

I want -1.0 camber front and rear
+8.0 caster front or as close as I can get
rear caster +0.8

 

So did you compare it to his method where you don't need turn plates but know how much to turn the steering wheel? As you say you need to know the angle and have a formula based on that angle. Don't you think if you know the steering ratio that you may actually have a damned good approximation of how many degrees the wheels turn when the steering wheel is turned a half revolution one way and then a full revolution from there to the other side? From there a person can develop a formula for the amount of degrees traveled by the front wheels with that sweep of the steering wheel. For the people who are mathematically challenged all they need to know is turn the steering wheel X amount (and easily observed) take the differences in camber readings and apply the formula. As far as they are concerned they don't need to know the angle even though the value of the angle is inherent in how far they turn the steering wheel.

Bill

 

It is probably close. On thing, if you turn the steering wheel 1/2 turn to the right. The right wheel turns more than the left wheel. Accurate caster reading depend on equal movement left and right from straight ahead.

 

Got my Longacre to plates off Amazon about $60. Works good.
Rear toe = + 1/16" (Toe in) Front toe = - 1/32 (Toe out)



Front camber

Right -0.1 degree
Left -0.2

Front caster

Right +6.9
Left +6.7

Front toe - 1/32" (toe out)

Rear camber

Right -0.5
Left -0.5

Rear caster

Right +0.4
Left -1.2

Rear toe + 1/16" (toe in)

Everything was in spec except for rear caster


I want -1.0 camber front and rear
+8.0 caster front or as close as I can get
rear caster +0.8 front a rear to about 0.

 

The saga continues . . .

Talked to the local Firestone. They have a Hunter machine and a knowledgeable alignment guy. Bought lifetime alignment for $127.78

Went there on New Years Day and spent a couple hours screwin' with just rear using Bear machine and my CH47960-10 bracket and Wixey angle guage. The initial reading off his machine didn't match mine to begin with. Couldn't seem to get to get the -1.0 rear camber and +0.8 caster. Went home and removed 1 washer from each mounting point of upper control arms and tried to knock the mounting points as far toward the front of the car as far as possible since the hole in the mounting bracket is slightly larger than the bolt.

 

Post 11
Interesting ... in for the saga.

$100 home alignment "machine" versus $10,000 shop machine.

 

I think I finally figured out this caster thing. Moving both the front and rear cams doesn't change caster. Moving the front (of car) cam to push the arm out, make it longer increases caster.

I haven't been able to get the positive camber on the rear I want, around +0.8. As it stands I have -1.1 and -1.3 for camber with room to go both directions. I'm gonna move rear cam to the minimum position and try to get the caster I want by adjusting the front cam.

The holes in the upper A arm mounting points are slightly bigger than the bolts. When I removed the washers I tried to move all the brackets as far toward rear of the car as possible. Judging by the marks left by the bolt heads on the brackets, they did move slightly.

 

Removing washers from upper control arms is pretty simple. You need to remove wheel. You need 15mm socket and torque wrench. After you get the bolts out the washers will fall out. There were two washers at each point on mine, remove one.

 

Adjusting camber and caster ain't bad. The nut/bolt heads are 21mm. The nut probably needs a deep socket. You will probably need a 21 wrench to get at the bolt head.

Increasing the forward (toward front of car) decreasing the rearward increases caster.

 

Getting two machines to agree is difficult. Your camber gauge may not be attached the same way as his adapters. I find I can get several different camber readings on the same wheel by just moving the gauge around. Putting it on the upper left of the rotor gets one reading while putting on the lower right gets another. Using the hub gets another reading. Using the wheel itself gets another.

DO NOT Forget to check the level of his alignment rack. It may or may not be level. If isn't level his machine may be calibrated for that while your gauge isn't. That is one of the things the GM Rear Caster adjustment instructions point out is to check the level of the rack and zero the gauge before making any measurements.

Bill

 

I'm getting pretty close. Got - 1.0 negative camber on both sides rear by going minimum (shortest) on the front and about halfway on the rear. Maximum on the rear gave me too much negative camber all the way out. Both sides now have positive caster about 1.1 on one side but about 3.0 on the other. Toe is now way out about + 3/8.

 

I guess your definition of close is different than mine. Keep working at it. I found the best way to settle the suspension so I could get a good measurement after making an adjustment was to drive the car around the block at a minimum but a mile seemed better. Added a lot of tear down and setup time but gave me more accurate results. Makeshift sliders under the wheels never seemed to get the stiction out of the suspension like bouncing down a road.

Bill

 

....Don't want to hijack this thread but since we have some alignment experts chiming in I have an alignment question for you guys...

The rear end of my car has been torn out 2 times to get the transmission out once for a TC replacement and the second time for a full transmission replacement. ( 2015 C7 Coupe)
When the tech reinstalled the rear end would he have needed to do a rear end alignment to have the rear wheel Caster in spec or would it go back together in spec if it was in spec when it was torn out ??????

Thanks.

 

They would do a rear wheel alignment but the odds of a dealership being able to measure and set rear caster are between slim and none. Most do not have the tools to do the job. No tools no way to do it. The only way to know is to ask the mechanic who did the job. The Service Advisor/Writer will not know. If rear caster was set the mechanic may have just put the settings within spec which is 0 deg +/- .8 deg individually. There is no rear cross caster spec. Setting at both rear wheels at +.8 degrees as recommended by some members of the forum isn't something they would know about.

The odds of being able to get the rear caster set at any shop approach zero when you include independents shops in the mix. Independents will have even less info than the dealerships.

Bill