Rear end toe-in revisted.....Help!

[Brandon K.]

Well, just spent the better part of the day trying to set the toe-in on my frame-off 67 project. I fabricated some metal bars to bolt onto the spindles, and measured everything with the trailing arms suspended at ride height. Everything looked fine, until I bolted on a set of wheels and measured the toe-in at the wheel rim itself. Boy was I off.... I played around with the shims and got it to about 3/16" toe-in measured at the wheel (with a tape measure). Will I be in trouble once I get the car back together? I know that its out of spec, so how much will this affect handling and tire wear? Is there a more accurate way to measure the toe setting?

Thanks!! Brandon

[Duke W.]

Re: Rear end toe-in revisted.....Help!

The toe in spec is based upon measuring at the outside circumference of the OEM tire, which is about 27.5 inches in diameter. If you have the body off, carefully measure the frame to determine the exact centerline. Run a string along the CL and hang plumb bobs near the front and rear plane of the tire OD. With the suspension supported ( and, of course the wheels/tires installed) at normal ride height set each wheel at 1/32 inch toe in, as close as you can measure. This is the difference between the measurement from the rear to centerline and front to center line. If the tire does not have a good smooth groove down the centerline you can use any circumferential groove, but you must be consistent. After it is set up let the suspension droop, then reset it to normal ride height and take new mesaurements. Keep iterating until you get consistent measurements. This is a tedious and time consuming process, and your're learning while doing. If you are careful and take your time you should get good results. It's best to get this done with the body off, whatever it takes, as setting the rear toe accurately with the body on is a lot tougher.

Duke

Duke

[Brandon K.]

Re: Rear end toe-in revisted.....Help!

Duke, thanks for all your help... I think I'm OK now, as far as the toe-in. Looks like about 1/8 inch, and should be squared to CL of vehicle. My frame was already checked and straightened by Sunshine Corvette. The variance I was referring to was really only the factory tolerance, which can vary by 1/8 to 1/4 inch from side to side.

As far as body-on rear toe setting, probably the best way is to use slotted shims. If the two hole shims are slotted then they can be mixed, and also wont be a giveaway at judging time.

Thanks again, Brandon

[Roberto L.]

Re: Rear end toe-in revisted.....Help!

I realized now that it was an error to buy non slotted shims. Adjust/install them, with trailing arm bolt difficulties, is a problem. Roberto, NCRS #30019, RMC

[John M.]

Re: Rear end toe-in revisted.....Help!

Duke, I'm going to be putting the trailing arms back on my 69 with the body on. I have slotted shims and a lot of patience. Any ideas on how to set the toe in with body on would be very helpful. The camber ideas were great and I'm not worried about that department.

Thanks for any help. John

[Duke W.]

Re: Rear end toe-in revisted.....Help!

I've never done the rear toe measurement on my'63 with the body on, just the body off, but I suppose you could use the same method, which is to find the true centerline of the car by locating the exact center point of each cross member. All five points should line up, but the rear cross member might be tough to access and then there's lots of hardware in the way underneath which will tend to throw off your string laid along the cross member center points. With the body off you draw the string on top of the frame.

Modern alignment equipment is capable of four wheel alignment, but I'm not sure how they do it because I haven't been to an alignment shop in 20 years. The one exception is my '88 MBZ 190E 2.6. I got the dealer to check alignment under warranty, Of course they wouldn't let me in the shop, but the computer output of the results was interesting. One of the outputs was "thrust angle" which is the angle between the car centerline and the center of thrust, but I don't know how they measured it. It's easy to get the total toe right on any IRS car. The key is to have it equal on both sides so the thrust angle is as close to zero as possible, because at some point the thrust angle can become great enought to cause the car to pull or have different right/left handling characteristics.

Of couse, the key to all of this is detemining the true centerline of the chassis, and that can be a tough task. It might be worth going to a couple of local alignment shops in your area to see if you can get an "education". Find out how they measure the centerline. The only IRS car that I've aligned is my '91 MR2, and I have reset the toe. This car has "toe-links" and the shop manual just said to insure that they are equal length at the final toe setting. This car, like many modern cars is so accurately fixtured when they weld up the unibody that the camber on all four wheels is "net build". There is no adjustment except for over-the-counter offset "crash" bolts. Because the chassis is so square you only have to get the rear toe links equal length to insure that the toe is equal on both wheels which results in essentially zero thrust angle. This eliminates the difficult task of measuring the true centerline.

I'm hoping that someone else on the Board who understands the geometry issues has worked out a good method to measure and adjust our Corvette's rear toe and will post a response.

Duke

[Terry M.]

Re: Rear end toe-in revisted.....Help!

Duke,

Sorry I can not tell you about how they get the thrust angle. I think it is calculated somehow from all the readings, but I am not sure. I learned alignment by the old light beam and mirror method.

I saw a demonstration of a 4 wheel rig with transmitters attached to each wheel and radio waves (or some transmitting means - no wires) to the main computer. The tech called up the vehicle by make and model, colored bars came up on the screen at four corners. Move adjustment until bars turn from red to green, press the button and you get a computer print out with all the settings, the spec and tolerances and thrust angle and all that. Major FM to me. They bought the system for the school I hang out at, but I have not had a chance to learn how to use it. I think the cost, without the alignment rack, was in the neighborhood of what I paid for my house 25 years ago. Less than a C5, however.

I expect this type machine is only one reason alignment shops will not touch a c-1 to c-3 Corvette. The machine doesn't have the settings programed into it for something so "old," so the tech has no idea where to start. There has got to be a way to make it work to the specs you program in, or just use it to read out the adjustment, but that might require more skill than most could muster.

I might add that in 1990 Bowling Green used a four wheel Bear rack - mirrors and light beams for audit purposes. One look and I knew what they were doing. Bet we will see FM there this summer.

Terry

[Dave, NCRS#24235]

Re: Rear end toe-in revisted.....Help!

I did my 66 at home. Thinking about the laser setups hooked to all four wheels (operators make sure they are not bent) made me try measuring (using wire) the diagonals between rear shock mounts (with equal camber on both wheels) and the front ball joints. Marking where the diagonals cross will tell you if the car has a "square" frame. Front and rear wire segment lengths should be equal. If they are, half the distance between ball joints is the center. To get the car to go down the road straight, the wheels have to be mounted with front and rear axes of rotation parallel and the centers perpendicular to each other. Whether the frame is "bowed", or the body is mounted square on the frame is the body shop's problem. - Dave

[Duke W.]

Excellent idea

If the two diagonals are equal length, then the four points are "square". Then lay a string between the ball joints and between the lower rear shock mounts and find the mid points. Last, lay a string across these two mid points. This is the true centerline. It's going to be a tedious and time consuming process,but you should only have to do it once. Once the rear toe is properly set, it will likely not change unless something gets bent. There's probably nothing you can't do with string and a little ingenuity than you can do with a laser, but the laser will be much quicker and more accurate. Properly executed, the "string method" will probably get the same results given the minimum change in toe allowed by the thinnest available shim. This sounds like the way to do the rear toe with the body on.

Duke

[Brandon K.]

Re: Excellent idea.....maybe

This gets real tricky..... because the position of the lower rear shock mounts will be affected by both the toe-in and camber in the rear, as well as the camber/ caster adjustments in the front. Therefore, the very thing that you are trying to adjust by finding the precise vehicle centerline will affect the centerline itself when it is adjusted. I've never taken a logic course, but that doesnt seem to have much logic to it.

[Duke W.]

Re: Excellent idea.....maybe

The lower ball joint point is fixed solely by the lower control arm. Only the upper ball joint moves with changes in caster and camber. You've got a point about the rear camber. It must be equalized before attempting to find the reference centerline, and it would be better to use the bottom point of the strut rod centered on the through bolt that holds the spindle carrier as this point will remain essentially fixed (within reason), regardless of toe. Also, there may be enough tolerance build up in all the components (frame, control arms, strut rod, the various bushings,etc.) to defeat the logic of this method. My '63 shop manual gives some reference frame dimensions along the longitudinal axis, but no diagonals, and no tolerances. My gut level feeling is that if the diagonals are within a quarter-inch, the method will work, but it will take a few people trying it out to find out the bottom line.

Duke

[Jack H.]

Re: Rear end toe-in revisted.....Help!

Texaco station and independent Goodyear dealer in small mountain town nearby has solid 4-W Bear machine that works with individual wheel transmitters. I had four major alignment shops in Denver work on 'Lil Red (my '71 SB) with POOR results and decided to give my local boys at the Texaco a try....

They let me climb into the pit, watch and ask questions. Spent 2 hours with 'er and charged me a whooping $80. Runs like a spotted ape. Here's what I learned:

(1) While some systems are limited to geometry under table lookup, all

can be 'spot programed' (OTHER) and fed mfgr's original data that's

available in the Chassis Service Manual.... (2) 'Trick' to getting good accurate results is two fold:

(a) Is alignment machine REALLY level? Pro shops pull factory

cal 2-3 times/year because foundations shift and cars going

on/off the rack will effect wear.

(b) Is alignment tech REALLY experienced in mounting sensors on

your wheels? (3) Item 2.b is REAL important. 'Acid' test is have 'em pull alignment,

get final report print out, take car off machine, put it back on

machine, re-mount sensors and run a 'beginning' sweep. If the 2nd

beginning readings aren't DEAD ON THE MONEY with your 1st pass final

readings, take your business elsewhere -- you've got poorly trained

alignment techs and/or suspect alignment machinery. A case of the

traditional computer fault syndrome -- garbage in = garbage out x

a bunch....

[Michael W.]

UJ- some thoughts

I am lucky to have a similar situation to yourself with my local Petrocan Garage.

Regarding your point of repeatability, I can't help but wonder if this test is truly fair to the garage, the guy or to the car for that matter. Or even if it's worth doing. Most of our cars are at least two, if not three or four decades old, and the vast majority have not got 100% fresh components in the suspension department, not to mention the possibility of corrosion on the frame and suspension. What this combines to is the likelyhood that the car itself cannot repeat a precise setting despite the best efforts of the garage. Combine this once again with the real world possibility that the first good bump or pothole will probably knock a wheel away from the garage setting, and you could end up convincing yourself that you have a serious problem with the car.

I'm not trying to suggest turning a blind eye to cronic misalignment problems, just wondering if we could end up holding ourselves to unrealistic expectations.

Mike


Quebec NCRS Chapter

[Jack H.]

Re: UJ- some thoughts

Mike, my car was fresh out of the shop from 3-year frame off. The alignments I had pulled at previous shops were big ticket items that weren't cutting the muster.

My Texaco fella was happy to take the time to 'prove' himself to me and let me watch/learn. It was he who volunteered the 'acid' test and the car was simply backed off the ramp of the alignment pit, out 10 feet or so into the drive then, returned onto the ramp. The alignment mechanic volunteered the 'acid' test as a means to sort wheat from chaff at alignment shops. He felt confident going into the proposal he and his machine would pass with flying colors which happened.

Since, I've heard fellow club members groan about this/that shop and their experience. Virtually NOBODY else would accept the bet/challenge to do the test and I've had maybe six fellow chapter members that drove out of their way to use this Texaco station where all reported complete satisfaction....

On driver cars, there's an unwritten rule of the road. Alignment tech should inspect and advise customer if suspension components are too far worn to expect good/accurate adjustment. But, on factory fresh restoration done by qualified shop, folks should expect "on-the-money" results and I was amazed by how far off other high end shops in my area with quality reputations turned out jobs!

I wasn't suggesting that everybody try the 'acid' test with each/every alignment shop. I WAS suggesting that alignment technicians who have confidence in their abilities and their equipment might take the 'bet' and for those with chronic problems this might be a means of sorting good guy from bad guy (if the shop believes in its work and customer is willing to pay for extra setup labor)....

[Terry M.]

Re: High Tech alignment tools

UJ,

I agree acid test - with fresh suspension components - should be no big deal. We used to do it on the mirrors and light machine. How else does the teacher know that the student is performing the task properly. Roll it out - drive it some - and come back and check the work. Of course in the business world it is reasonable to expect to pay for the tech and machine time involved.

I also suspected high tech wiz bang show I saw had capability to program individual settings - I just didn't see that part and circumstances were such that it was not good politics for me to ask at the time. I'll get to play with and learn that machine - and the old Coors hauler will get more than its fair share of time on it. I'll have to get those gator backs off, but oh well....and the thought of going after the rear toe shims just causes me to want to reach for a cold one... oh well move it to the todo list.

On the way to playing with alignment of my fleet I have noticed that beginning in 1976 (I skip from 1970 to 1976 models, so I don’t know exact change point) the factory alignment specifications contain additional listings. In 1970 we see a speck of 3/8 + or - 1/32 (or some such numbers - these are made up). In the 1976 FSM I see a new car setting, a warrantee setting and a third column the name of which I have forgotten. Each column has + and - figures as a tolerance range for that column, but each column has larger and larger tolerances.

Almost gives one the impression accuracy of alignment is no big deal??? It doesn't say that, just leads one to wonder how accurate you have to be. Maybe techs see this and begin to get cavalier about their job??? Na I guess too many just don’t give a &^@%.

I did notice that the tolerances programed into the machine I saw demonstrated were at the large end of the specs. I am sure, if one can program the specs, one can also program the tolerance as well - just takes more skill. One thing I was told is that the machine measurements can exceed tolerances of the equipment itself, and the factory demonstrator emphasized the need for periodic re-calibration of the entire system - which, or course, they were willing to do for a fee. I remember learning to calibrate the light and mirrors style machine - seems to me the electronic equivalent ought to be capable of being calibrated by the operator occasionally. Again, just another skill level.

Is the tech just pushing out jobs to enhance his/her paycheck or does he/she care about the quality of their work? One can have all the fancy wiz bang tools in the world - none of that guarantees a satisfactory job.

Terry