C2 Original Trailing Arm Toe Shim Question

[Tim S.]

I am working on a 67 roadster I just bought. I'll give you an overview of the car, as it may contribute to the problem I am trying to solve. Relatively nice driving car with 52k miles. All stock, no mods. Nice clean rust free frame, no accidents, etc. New Goodyear Power Cushions all the way around. The car drove reasonably well, but have driven others that instill much more confidence. The car would be a bit squirrely under hard braking and acceleration. Furthermore, the car had a vibration in it at 60mph that I just could not get out. I am fairly confident no one has been in here before.....it all looks to be factory issue work. In other words, the correct and original toe shims, bolts, hardware, etc.

That all having been said, the right side TA bushing had some slop to it as did the right side spindle bearing. I've been here before, so the best thing to do is to rebuild the arms. I always get a noticeable improvement in rebuilding the arms. No biggie there.

My question is this.....
After disassembly (keeping the original toe shims arranged in their respective locations) the left side is toe'd out. The right side is toe'd in. The steering wheel is off a bit as well. I have not measured anything as of this point. I must say, I have not observed a shim arrangement like this before. Am I leading a sheltered life? Has it been observed where the factory just screwed it up?

I understand the car needs to be aligned after all is reassembled. I'd prefer to use the correct shims after all is said and done. The alignment shop has done, and will do these alignments for me. You can see they are not crazy about it. I live in a remote area so my choices are very limited. As a result, I always try to get as much BS out of the way in order to help the process along.

I could just reinstall the shims the as they were previously arranged and let the alignment shop have at it. I ask the question simply to minimize how much redundant labor this may require. No, I'm not lazy. I figure it's easier to ask a few questions first.

Thanks in advance,
Tim

[Edward J.]

Re: C2 Original Trailering Arm Toe Shim Question

Tim, why not make the rear alignment easier with shims that are slotted on one side. My 72 has shims like that, I believe that 67 has a long cotter pin holding the shims in place. Venders like Blair’s corvette parts sell a complete kit. Adding and subtracting shims is a nightmare and a guessing game, When doing the rear that way. And while your there you want a 4 wheel alignment so check the front steering and ball joints , rubber control arm bushings.

[Leif A.]

Re: C2 Original Trailering Arm Toe Shim Question

The '67 factory arrangement does NOT use a cotter pin. The shims have holes on both ends. What I have done and recommended in the past is buy both the correct shims for the '67 and a set with a slot at one end. When having the rear alignment set, use the slotted shims to attain the correct toe. Once this is accomplished, remove the inner and outer slotted shims, keeping track of the thickness and number of shims used in each of the four locations. Then, remove the trailing arm bolt, insert the correct shims (with holes on each end) referencing the slotted shims removed to attain the same thickness in each location. Once done, you may never have to do this job again. Camber is easy, as I'm sure you're aware.
The steering wheel not being centered can be corrected when the front end is aligned. If the shop, truly, knows what they're doing they will center the steering wheel, lock it in place and then do the front end alignment...tie rods will correct the centering of the steering wheel.
Best of luck.
Picture of correct rear shims for a '67...

[Tim S.]

Re: C2 Original Trailering Arm Toe Shim Question

The '67 factory arrangement does NOT use a cotter pin. The shims have holes on both ends. What I have done and recommended in the past is buy both the correct shims for the '67 and a set with a slot at one end. When having the rear alignment set, use the slotted shims to attain the correct toe. Once this is accomplished, remove the inner and outer slotted shims, keeping track of the thickness and number of shims used in each of the four locations. Then, remove the trailing arm bolt, insert the correct shims (with holes on each end) referencing the slotted shims removed to attain the same thickness in each location. Once done, you may never have to do this job again. Camber is easy, as I'm sure you're aware.
The steering wheel not being centered can be corrected when the front end is aligned. If the shop, truly, knows what they're doing they will center the steering wheel, lock it in place and then do the front end alignment...tie rods will correct the centering of the steering wheel.
Best of luck.
Picture of correct rear shims for a '67...

All of that is well understood and I agree with sending the slotted shims to the alignment shop. I probably should have been clearer in my question. Ever see where the factory just screwed the rear alignment up?

[James W.]

Re: C2 Original Trailering Arm Toe Shim Question

Shims I used when I reassemble my '65 rear suspension after trailing arms and differential rebuild. Much easier to take out and install when doing the alignment. The alignment shop was happy to use them.

James

[Gary R.]

Re: C2 Original Trailering Arm Toe Shim Question

James, those are trick.

One thing to keep in mind with the boxes is most of them are not at the high lash point on true center. Setting up a box without knowing where the high lash is will not get the best performance and most likely it will be off. It will be on center. If all the boxes were textbook, meaning the high lash, arm position, and true center are all in the same position, that would be a perfect world. Reality is they are not, some out 90*.

Some will say the steering was sloppy from new, that is incorrect. These boxes can be setup better than new and certainly have no need for a Jeep box or rack system, but you have to know how to do it.

[Tim S.]

Re: C2 Original Trailering Arm Toe Shim Question

Shims I used when I reassemble my '65 rear suspension after trailing arms and differential rebuild. Much easier to take out and install when doing the alignment. The alignment shop was happy to use them.

James

Did you make those (or had them made)?

[James W.]

Re: C2 Original Trailering Arm Toe Shim Question

I bought them from ZIP and then had a machinist friend of mine machine the notches.

Did you make those (or had them made)?

[Duke W.]

Re: C2 Original Trailering Arm Toe Shim Question

Installing new rear trailing arm bushings usually requires a different shim stack to obtain proper toe settings.

The first thing that everyone needs to understand is that C2/3 Corvette handling is EXTREMELY sensitive to rear toe settings. If in the proper ballpark these cars have excellent handling even with the typical "van tires" that most have installed and with the best currently available performance tires that will fit OE wheels and fenders they will pull lateral g potentially near modern sports cars.

Each rear wheel needs a slight amount of toe-in. Any toe-out on either wheel will make the car handle like it's possessed by the Devil. Look at the following CF thread for a primer on the subject.

https://www.corvetteforum.com/forums/c1-and-c2-corvettes/4261585-need-c2-rear-trailing-arm-center-to-center-distance.html

So the first thing you need to do is get the car on a modern laser alignment rack to get all the current settings, especially the rear wheel toe - not just the total, but EACH WHEEL.

Then if you have a drive-on lift and can get a pole jack to support the spring load you can easily come up with a proper shim stack to dial in the car's handling as explained in the referenced thread.

Radial tire rear toe should be nominally 1/32" toe-in, per wheel. Bias ply tires are okay with this setting, but are also okay up to about 1/16" per wheel. It's important to get each side toe as equal as possible to achieve the lowest possible thrust angle, and zero is nirvana.

With proper alignment set-up these cars handle extremely well - very neutral and you can steer the front end with the steering wheel and the back end with the throttle. The video from this BaT thread shows how great it can be

https://bringatrailer.com/listing/1967-chevrolet-corvette-146/

With bias ply tires lateral g was probably no more than 0.75, but more that that might make and old guy like me gray out. The bottom line is that with a dialed in chassis and prodigious torque this car was an absolute blast to drive up the Palos Verdes hill climb... steer the front end with the steering wheel and the back end with wheel - all very predicable and forgiving, and once you've got it dialed in it will stay that way as long as not accidents to curb impacts that might knock off the alignment settings.

Front toe-in should be the same as rear, per wheel. If the steering wheel is cocked off a few degrees. you have to tweak one or both tie rods, maintaining about 1/16" total toe-in to get the steering wheel straight. It usually takes me one to three adjustments to get it dialed in using a simple carpenter's tape.

Duke

[Mark F.]

Re: C2 Original Trailering Arm Toe Shim Question

All of that is well understood and I agree with sending the slotted shims to the alignment shop. I probably should have been clearer in my question. Ever see where the factory just screwed the rear alignment up?

Anything’s possible, but if it happened, it was probably a rare case indeed. The alignment equipment sensors were automated on the Frame Upside Down (FUD) Line (and somewhat less so at the toe-in pit) to remove individual line worker decision making from achieving correct factory suspension adjustments. Had the rear toe-in shim packs been installed improperly, the guy doing the roll test taking it up to 60 mph would probably have noticed something was out of whack…seems to me if that were the case, the car would want to “walk” across the roll drums one way or the other depending on which side was incorrectly shimmed (also very dangerous BTW).

Per John Hinckley's C2 Assembly Process Presentation (available in the Database of Restoration Documents [DoRD] Sticky Post), here's what he says for the 3^rd and 4^th stations on that line:

FUD-3 Install rear suspension module (subassembly up from basement elevator included the suspension crossmember and cushions, differential and nose bracket, half-shafts, trailing arm assemblies, strut bracket and rods, and rear spring with the ends free). Bolt crossmember and differential nose bracket to frame, install rear jounce bumpers and big-block rear stabilizer bar.

FUD-4 Apply rear hub locating/sensing fixtures (which set rear suspension at normal ride height), adjust cam bolts on strut rods to obtain green camber lights and torque cam bolts. Note trailing arm toe-in shim pack required for green lights, install shim packs and install and torque pivot bolts.

And...here’s the Roll Test and Toe-in Pit sequence:
RT-1 Driver locates car in the roll-test machine and pushes button on pedestal to start machine cycle; front and rear car-width rollers rise up so all four wheels are on the rollers, and driver accelerates. Rear wheels drive the rear roller, which in turn drives the front roller so all four wheels turn at the same speed. The left side of the rollers are smooth, and the right sides have raised sections to simulate a bumpy road.

RT-2 Driver accelerates through the gears to 60 mph, listening for any unusual noises, and compares speedo reading to the machine’s overhead speedo dial to ensure correct speedo gear is installed. Driver slows to 30 mph and exercises lights, wipers and washers, radio, turn signals, horn, hazards, and moves over to the “rough road” side of the rollers to check for vibration, squeaks and rattles.

RT-3 Driver moves back to the smooth-road side of the rollers, accelerates to 60 mph, and applies parking brake several times to “burnish” the shoes prior to final cable adjustment. Driver then slows to a stop on the rollers and pushes the button on the pedestal; the rollers retract and the driver proceeds into the toe-in machine.

TI-1 Car is driven into the Toe-In machine and driver attaches steering wheel lock/level tool to wheel and top of door. Pit operator cycles machine, which moves locating rollers on floating heads against inside and outside of tires and machine spins the front wheels.

TI-2 Watching dials on his control panels, pit operator turns tie rod adjusting sleeves until dials indicate that toe-in is within specifications while steering wheel is held level and straight-ahead; he then positions tie rod clamps correctly and tightens clamp bolts with an air tool and a wrench. Driver removes steering wheel tool, hangs it on pedestal, and proceeds into Final Process Repair for any needed adjustments.

[Tim S.]

Re: C2 Original Trailering Arm Toe Shim Question

I appreciate that post Mark!^^^^^^^

[Tim S.]

Re: C2 Original Trailering Arm Toe Shim Question

Installing new rear trailing arm bushings usually requires a different shim stack to obtain proper toe settings.

The first thing that everyone needs to understand is that C2/3 Corvette handling is EXTREMELY sensitive to rear toe settings. If in the proper ballpark these cars have excellent handling even with the typical "van tires" that most have installed and with the best currently available performance tires that will fit OE wheels and fenders they will pull lateral g potentially near modern sports cars.

Each rear wheel needs a slight amount of toe-in. Any toe-out on either wheel will make the car handle like it's possessed by the Devil. Look at the following CF thread for a primer on the subject.

https://www.corvetteforum.com/forums/c1-and-c2-corvettes/4261585-need-c2-rear-trailing-arm-center-to-center-distance.html

So the first thing you need to do is get the car on a modern laser alignment rack to get all the current settings, especially the rear wheel toe - not just the total, but EACH WHEEL.

Then if you have a drive-on lift and can get a pole jack to support the spring load you can easily come up with a proper shim stack to dial in the car's handling as explained in the referenced thread.

Radial tire rear toe should be nominally 1/32" toe-in, per wheel. Bias ply tires are okay with this setting, but are also okay up to about 1/16" per wheel. It's important to get each side toe as equal as possible to achieve the lowest possible thrust angle, and zero is nirvana.

With proper alignment set-up these cars handle extremely well - very neutral and you can steer the front end with the steering wheel and the back end with the throttle. The video from this BaT thread shows how great it can be

https://bringatrailer.com/listing/1967-chevrolet-corvette-146/

With bias ply tires lateral g was probably no more than 0.75, but more that that might make and old guy like me gray out. The bottom line is that with a dialed in chassis and prodigious torque this car was an absolute blast to drive up the Palos Verdes hill climb... steer the front end with the steering wheel and the back end with wheel - all very predicable and forgiving, and once you've got it dialed in it will stay that way as long as not accidents to curb impacts that might knock off the alignment settings.

Front toe-in should be the same as rear, per wheel. If the steering wheel is cocked off a few degrees. you have to tweak one or both tie rods, maintaining about 1/16" total toe-in to get the steering wheel straight. It usually takes me one to three adjustments to get it dialed in using a simple carpenter's tape.

Duke

Duke,

I had read through the thread(s) prior. Your observations in that 67 were interesting, as it matched my what I saw in my car. It's what triggered my post.

FWIW, I loved the auction of Hector's car. I then was able to put a name with a face. Certainly you drove the car with "spirit" I have the link saved from that auction. I admire the detail of the car, as well as the eye for preservation

[Duke W.]

Re: C2 Original Trailering Arm Toe Shim Question

Had the rear toe-in shim packs been installed improperly, the guy doing the roll test taking it up to 60 mph would probably have noticed something was out of whack…seems to me if that were the case, the car would want to “walk” across the roll drums one way or the other depending on which side was incorrectly shimmed (also very dangerous BTW).

I don't think operator would have necessarily noticed a rear toe problem during the roll test. The right rear toe-out issue (see CF link in post #9) on the 15K mile '67 L-71 did not show itself driving in a straight line. The owner never mentioned any problem, but he drove it very mildly. The first time I drove it and got just a little aggressive - accelerating moderately through a long sweeping left hand curve at about 40-45 MPH - it really spooked me as it wanted to oversteer. Later on a deserted divided 4-lane road quick flicks of the steering wheel left and right revealed a significant instability when flicked to the left. I immediately suspected right rear toe-out and setting it up on a modern alignment rack proved that to be the case. Toe has a significant effect on transient response and any IRS car that has rear toe-out on one or both sides will have spooky transient dynamic response in one or both directions, respectively.

Given the low miles and lack of any evidence that the right rear toe shims had ever been modified from the factory pack I suspected that maybe the operator put the shims meant for the outside on the inside and vice versa, but the 3/32" worth of shims I computed that needed to be moved from inside to outside did not support that theory.

My best guess is the improper shim stack was due to either operator or machine error, but I'll never know for sure.

Maybe one of the reasons this car has such low mileage is that Reggie Jackson, who owned the car (along with dozens of others) for about ten years rarely drove it, and this was likely also the case for Canadian drag racer Dale Armstrong who bought the car from Reggie. Maybe both realized the car was spooky, but neither bothered to find out why, so they just never drove it. The owner at the time of my evaluation bought it from Armstrong's widow and owned it for about 5 years putting no more than about 1000 miles on it.

After correcting the rear toe issue the car handled great - stable, predictable, forgiving, and only limited by the grip of the Kelsey Goodyear repro 7.75-15 tires, which really weren't that bad. A set of Avons would have made the car "super fun."

Duke

[Mark F.]

Re: C2 Original Trailering Arm Toe Shim Question

I don't think operator would have necessarily noticed a rear toe problem during the roll test. The right rear toe-out issue (see CF link in post #9) on the 15K mile '67 L-71 did not show itself driving in a straight line.< OK, and the roll test is obviously a straight line, so it could leave the factory undetected and incorrectly shimmed The owner never mentioned any problem, but he drove it very mildly. The first time I drove it and got just a little aggressive - accelerating moderately through a long sweeping left hand curve at about 40-45 MPH - it really spooked me as it wanted to oversteer. Later on a deserted divided 4-lane road quick flicks of the steering wheel left and right revealed a significant instability when flicked to the left. I immediately suspected right rear toe-out and setting it up on a modern alignment rack proved that to be the case. Toe has a significant effect on transient response and any IRS car that has rear toe-out on one or both sides will have spooky transient dynamic response in one or both directions, respectively.

Given the low miles and lack of any evidence that the right rear toe shims had ever been modified from the factory pack I suspected that maybe the operator put the shims meant for the outside on the inside and vice versa, but the 3/32" worth of shims I computed that needed to be moved from inside to outside did not support that theory.< OK, and even though your theory was not supported, it makes me wonder if the green light sensor mechanisms on the alignment fixture would be able to detect a reversed (inside-outside flipped) shim pack ?

My best guess is the improper shim stack was due to either operator or machine error, but I'll never know for sure.< yep - if machine error was the culprit, I wonder how often calibration was checked on that fixture...

Maybe one of the reasons this car has such low mileage is that Reggie Jackson, who owned the car (along with dozens of others) for about ten years rarely drove it, and this was likely also the case for Canadian drag racer Dale Armstrong who bought the car from Reggie. Maybe both realized the car was spooky, but neither bothered to find out why, so they just never drove it. The owner at the time of my evaluation bought it from Armstrong's widow and owned it for about 5 years putting no more than about 1000 miles on it.

After correcting the rear toe issue the car handled great - stable, predictable, forgiving, and only limited by the grip of the Kelsey Goodyear repro 7.75-15 tires, which really weren't that bad. A set of Avons would have made the car "super fun." Duke

As for the other end, I spent many hours in assembly plant toe-in pits and other than potential machine error, the operator would have to be unconscious not to get those alignments right...the dial indicators were huge - maybe 15" or so in diameter...All you had to do is keep turning the wrench one way or the other until the point of the indicator swung up to the 12 o'clock position. and, yes it gets VERY cramped with two guys in there while i was evaluating potential carbon monoxide exposures...

[Duke W.]

Re: C2 Original Trailering Arm Toe Shim Question

Can you provide more detail on the plant front toe adjustment at the end of the assembly line.

Was someone in the driver's seat holding the steering wheel straight?

I assume you set each side separately, so that, assuming someone was holding the steering wheel straight, the steering wheel would be straight driving down a straight road with no camber.

Also, can you describe what equipment was used to make the actual toe measurements. Mirrors? Light beams? Lasers? Was anything attached to the wheels?

The reason I ask is I have been doing my own alignments for over 40 years because even though modern field alignment equipment is excellent, the operators rarely understood the involved geometry and always wanted to set everything at their "book" recommendations, not my requirements, which were for more aggressive driving, like maximum negative camber and positive caster, equal on both sides, within the range of adjustment.

Even though front toe should be the easiest thing to do it was always a pain. Since I could only measure total front toe I had to keep the steering wheel straight, but it always cocked off center as I adjusted the tie rods. Having a helper hold the wheel straight helped, but it was usually still slightly cocked off center on the test drive, so I had to go back down under and tweak (maybe 1/8 turn) one or both tie rods to straighten the wheel while keeping total toe and my required range, and sometimes it took two or even three tries to get it right because I am fanatic about having the steering wheel straight when driving in a straight line.

At some point I realized that at least on my cars if the tie rod length the same on both tie rods as close as I could measure, the steering wheel would be almost straight, but it still usually took at least one tweak for me to be satisfied.

Duke