1963-1967 trailing arm shims - Plated or Natural

[Gary J.]

This question is more toward 1967. Are the trailing arm shims a natural or plated finished? The judging manual is not specific.

[Leif A.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Gary,
The factory used steel trailing arm shims were plated to keep rusting prior to installation. Personally, I use the stainless shims to keep them from EVER rusting. Correct shims for '67 had the holes at both ends...no slots.

[Gary J.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Thanks Leif, I kinda figured they were plated but wanted to be sure.

[Joe R.]

Re: 1963-1967 trailing arm shims - Plated or Natural

The trailing arm shims from the factory were not plated. They were natural steel and rusted. Only replacement shims were plated!

JR

[Joe L.]

Re: 1963-1967 trailing arm shims - Plated or Natural

The trailing arm shims from the factory were not plated. They were natural steel and rusted. Only replacement shims were plated!

JR

JR------

That's my recollection, too.

However, I'm also a big fan of stainless steel replacements. That's all I'd ever use.

[Duke W.]

Re: 1963-1967 trailing arm shims - Plated or Natural

The trailing arm shims from the factory were not plated. They were natural steel and rusted. Only replacement shims were plated!

JR

I absolutely agree based on Hector's 16K original miles '67 L-71 that sold on BaT back in February for $250K. When I first drove it, it had a severe instability issue when turning left. I had Hector get measurements on a four-wheel alignment rig, and as I suspected the RR wheel had a little toe out rather than toe-in. These IRS C2/3 Corvettes are EXTRMELY SENSITIVE to rear toe, and if there is toe-out on either rear wheel the car will be a cantankerous beast!

So from the existing shim stack I computed how much had to be swapped from the inside to outside. I recall it was either 2 or 3 32nds worth. After the change the car handled like a C2 should. I drove the "hillclimb video" on BaT, and it was a lot of fun. The installed Kelsey Goodyear 7.75-25 bias ply repro tites at 35 psi are probably the best of that bunch, but like most they can only develop about 0.75g lateral. The front end went where I pointed it, and I could steer the back end very controllably with the throttle. At my age a very controllable 0.75g is a good thrill!

When we removed all the shims for the swap they were clearly plain steel and still shiny on the inside within about a one inch radius of the bolt hole centers. Of the 16K miles I figured very few if any were on wet roads. We just did a little wire wheel cleanup and wiped them down with WD-40.

My guess is that the operator who installed the shims got them backwards... inside on the outside and vice versa.

Maybe one reason why the car had so few miles is that previous owners figured that the car was possessed by the devil!

We exorcised it!

Duke

[Keith M.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Bringing this one back from a few months ago. Curous on additional thoughts of stainless vs. regular steel trailing arm shims. Because I am such a purist am thinking I will get the shims with two holes simply cuz they are original design tho more work to deal with. For same reason was thinking go with original steel and not stainless. Reality is it won't matter one way or the other to me....The car will likely never see rain. Not as cost issue as the shim sets cost the same for stainless or regular steel. Minor appearance issue but who will be looking down there. Is there any NCRS judging considerations for one vs the other. Kind of a splitting hairs decision but would welcome input and reasons for one vs the other.
Keith

[Joe L.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Bringing this one back from a few months ago. Curous on additional thoughts of stainless vs. regular steel trailing arm shims. Because I am such a purist am thinking I will get the shims with two holes simply cuz they are original design tho more work to deal with. For same reason was thinking go with original steel and not stainless. Reality is it won't matter one way or the other to me....The car will likely never see rain. Not as cost issue as the shim sets cost the same for stainless or regular steel. Minor appearance issue but who will be looking down there. Is there any NCRS judging considerations for one vs the other. Kind of a splitting hairs decision but would welcome input and reasons for one vs the other.
Keith

Keith-----

I would NEVER, EVER use the "2 hole" shims. And, it's virtually impossible to discern the difference when installed. It's not necessary to add the cotter pin for shim retention, either. My car has had slotted shims for most of its life and never lost a shim. The trick is to install them properly and torque the bolt to specification.

By the way, my original owner late 1969 has the holes in the frame for the long cotter pins but was never factory fitted with them.

[Keith M.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Keith-----

I would NEVER, EVER use the "2 hole" shims. And, it's virtually impossible to discern the difference when installed. It's not necessary to add the cotter pin for shim retention, either. My car has had slotted shims for most of its life and never lost a shim. The trick is to install them properly and torque the bolt to specification.

By the way, my original owner late 1969 has the holes in the frame for the long cotter pins but was never factory fitted with them.

Good info. Why not use the two hole ones? Not worth the hassle when aligning I presume? I do understand they are indiscernible from slotted when installed. And yeah...if you tuck the rear of the slotted ones..or other ones even... down into the bracket and tighten bolt to torque...they are not going anywhere.

Secondly, I believe you already stated you are a fan of the stainless. Intuitively makes sense. But in practice does it really make any difference?

[Leif A.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Keith,
Good luck finding shims that "tuck down" into the frame...plus, they weren't stock on your '69. Your car came from the factory with the shims that have the holes on both sides. You have to ask yourself "am I looking for correctness and peace of mind" or "am I looking for the easy way out"? Depending on how much you're planning on driving your '69 and what type of roads you drive on, a rear end alignment could be a one and done situation.
Here's my recommendation (and, you can do with it as you please). Take your '69 to a competent alignment shop. Bring two sets of shims with you...slotted and non-slotted. For ease of iniitial alignment, have the tech use the slotted shims to set the alignment. Once the alignment is established, remove and count the number and thickness of shims on either side of the trailing arm. Have the tech pull the trailing arm bolt and insert the same number and thickness shim with the hole in them. Done and correct. I don't care what anyone says about slotted shims not falling out if installed correctly. The factory wouldn't have used the shims with no slots or the later slotted shims ('70 and later C3) with a cotter pin to secure them if they hadn't heard early on from dealers/customers (circa 1963) that the slotted shims fell out on a car that is driven on a regular basis.
Again, your car and certainly your call.
Picture below of the correct installation of shims for your '69.

[Keith M.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Keith,
Good luck finding shims that "tuck down" into the frame...plus, they weren't stock on your '69. Your car came from the factory with the shims that have the holes on both sides. You have to ask yourself "am I looking for correctness and peace of mind" or "am I looking for the easy way out"? Depending on how much you're planning on driving your '69 and what type of roads you drive on, a rear end alignment could be a one and done situation.
Here's my recommendation (and, you can do with it as you please). Take your '69 to a competent alignment shop. Bring two sets of shims with you...slotted and non-slotted. For ease of iniitial alignment, have the tech use the slotted shims to set the alignment. Once the alignment is established, remove and count the number and thickness of shims on either side of the trailing arm. Have the tech pull the trailing arm bolt and insert the same number and thickness shim with the hole in them. Done and correct. I don't care what anyone says about slotted shims not falling out if installed correctly. The factory wouldn't have used the shims with no slots or the later slotted shims ('70 and later C3) with a cotter pin to secure them if they hadn't heard early on from dealers/customers (circa 1963) that the slotted shims fell out on a car that is driven on a regular basis.
Again, your car and certainly your call.
Picture below of the correct installation of shims for your '69.

Hi Leif,
Why do you say good luck finding shims that tuck down into the pocket. Mine are out but I believe they all tucked down into that lip near the rear of the trailing arm pocket thus helping keep them in place. Kind of neither here nor there but curious. See attached pics of shims I took out of my 1969 that I purchased in 1997. You can see that one set is original "two hole" design.

Pretty much everything we do with these cars involves weighing numerous factors, and trade offs, and much of that comes to personal preference and philosophy. I like your approach of two sets of shims at the time of alignment. To me, that would be a good way to go. Personally, I like the two hole set up for no other reason than it was original. I am not building an award car. You articulated some good points. I am 61, anything I do pretty much is going to last beyond my lifespan. In my case there will be one and only alignment needed for life...so two holes keeps it original and ensures they won't go anywhere. The car will essentially never see rain in my lifetime. It is not a an award winner nor show queen but also not a daily driver.

One context for ANY discussion involving ANY technical topic, cars or otherwise, is theory vs practice. As an engineer I understand the endurance of stainless. In practice for trailing arm shims it is a non issue...for me. One can see that the shims on the inner LH side that I just took out are celebrating their 54th birthday this coming October. Sure they are rusted. Did they lose any thickness to any material degree which would thus compromise the ability to do their job? Absolutely not.
Best,
Keith

[Joe L.]

Re: 1963-1967 trailing arm shims - Plated or Natural

Hi Leif,
Why do you say good luck finding shims that tuck down into the pocket. Mine are out but I believe they all tucked down into that lip near the rear of the trailing arm pocket thus helping keep them in place. Kind of neither here nor there but curious. See attached pics of shims I took out of my 1969 that I purchased in 1997. You can see that one set is original "two hole" design.

Pretty much everything we do with these cars involves weighing numerous factors, and trade offs, and much of that comes to personal preference and philosophy. I like your approach of two sets of shims at the time of alignment. To me, that would be a good way to go. Personally, I like the two hole set up for no other reason than it was original. I am not building an award car. You articulated some good points. I am 61, anything I do pretty much is going to last beyond my lifespan. In my case there will be one and only alignment needed for life...so two holes keeps it original and ensures they won't go anywhere. The car will essentially never see rain in my lifetime. It is not a an award winner nor show queen but also not a daily driver.

One context for ANY discussion involving ANY technical topic, cars or otherwise, is theory vs practice. As an engineer I understand the endurance of stainless. In practice for trailing arm shims it is a non issue...for me. One can see that the shims on the inner LH side that I just took out are celebrating their 54th birthday this coming October. Sure they are rusted. Did they lose any thickness to any material degree which would thus compromise the ability to do their job? Absolutely not.
Best,
Keith

Keith-------


The 2 hole shims will not "tuck down" into the frame pocket because the point at which they "articulate" with the bolt is close to the end of the shim (i.e the hole on the inner end).

If one wished to do so, one could create a "short slot" shim by simply "elongating" the inner hole to create a slot. In that manner, one could have the outward appearance and installation location of the "2 hole" shims and still have the advantages offered by a slot. If the shims were installed properly, with the last shim driven into place and the bolt torqued to specification, I'm very confident that the shims will remain in place and never become dislodged.

Would I do the above? Not a chance. I'd use the regular slotted shims and install them tucked down into the frame pocket (as GM did for all 1970+).