68/C3 Strut rod question.

[Terry F.]

Hi again. Can someone tell me the original color of the strut rod on 68. I am assuming they were natural???

Also, The outside diameter of the ends on my strut rods is roughly 1 13/16 inch diameter. I believe the originals were about 1 9/16 inch diameter?

Thanks in advance, Terry

[Gene M.]

Re: 68/C3 Strut rod question.

Should be smaller diameter same as 67 and finish is natural. Sometimes the coloring was darker than what cast metal typical looks.

[Wayne M.]

C2 and Early C3 Strut Rod Ends OD 1.54" to 1.59"

measured with a caliper; varies because of seam flashing irregularities.

[Mark #28455]

Re: 68/C3 Strut rod question.

Discussion at Orlando regional was that the strut rods are an as forged finish so they shouldn't have a silver color, but a color similar to the forged finish on an unpainted sway bar or unpainted coil spring (ie hot rolled steel).

What has everyone else seen?
Thanks,
Mark

[Terry F.]

Re: C2 and Early C3 Strut Rod Ends OD 1.54" to 1.5

Looks like I have a nice set of replacements on there. Thanks for your help. Terry

[Joe L.]

Re: 68/C3 Strut rod question.

Terry-----

As has been mentioned, the OD of the 63-74 strut rod ends was about 1-1/2". However, the KEY dimension is the inner diameter. For the 63-74 strut rods this is 1.25". The 75-79 strut rods, also catalogued by GM as the SERVICE replacement strut rods for 63-74 models, have an ID of 1.375. The OD of these rod ends is about 1-13/16", as you have measured.

All of the rods, either the 63-74 or the 75-79 are FORGED pieces. Their finish varies but is usually a "darkish gray" or "black" with "bluish" scaling. It's virtually impossible to duplicate and if the rods are "treated" to any sort of surface cleaning, especially of the abrasive variety, the original appearance will be "forever lost". Unfortunately, these things usually require some sort of surface cleaning since they RUST. Remove the rust by virtually any method and the original surface finish is lost with it. Another case of "the wheat being thrown out with the chaff".

One thing to keep in mind, here, though, regarding the "easily detectable" and "gauche" SERVICE rods (when used on 63-74 models):

For the 1975 model year, GM changed the configuration of the rods, enlarging the ends and using larger diameter bushings. They commensurately revised the lower ends of the spindle supports, enlarging the "ears" to work in "harmony" with the revised strut rods. Now, you don't suppose that GM went to all this trouble AND EXPENSE because the 63-74 style worked just as well, do you? I don't.

My STRONG suspicion is that the 63-74 style rod was found to be weak. While I've never heard of one of these things failing, I'll bet that GM did. I can see no other reason for the change. If you look closely at the 63-74 rods, you will note that the cross section of the ends is quite thin. Forged or not, it's almost scary when you realize just how thin this is. By increasing the OD of the ends, they were able to significantly increase the cross section of the ends and, undoubtedly, beef up and strengthen the rods considerably.

I fully expect that this is also why GM discontinued the earlier rods and replaced them with the later for SERVICE of 63-74 models. That's because the 75-79 part is an IMPROVED part which owners of 1963-74 model Corvettes can take advantage of (the issue of "correctness" doesn't enter the equation, at all, when GM does this sort of thing; for their purposes, FUNCTIONALITY is everything and "correctness"= "0").

By the way, the 75-79 rods can be used with the 63-74 style spindle supports with the smaller "ears". Sometimes, it may be necessary to do a small amount of grinding on the "webbing" of the supports to use the later rods. However, when I originally installed these on my car many years ago, I didn't have to do any grinding, at all (I converted back to the original style recently but I really believe that it was a mistake to do so and I may "re-convert" at some point). You gain about 95% of the benefit by replacing the rods, alone, so there is no real need to replace the spindle supports, also.

My philosophy as far as changing the rods? No surprises here; it's the same as I've stated MANY times before: FUNCTIONALITY and the things that flow from it (like SAFETY, RELIABILITY, durability, performance, etc.) are PARAMOUNT. "Correctness" is nice and is ALWAYS to be strived for, but is SECONDARY to FUNCTIONALITY. Absolutely. Positively.

[Terry F.]

Re: 68/C3 Strut rod question.

Yep, there must be a lot of force on those struts. I think I will try to round up a set of originals for the sake of it. Before I knew there was a difference I replaced mine with the later versions.

Thanks for all the feedback, Terry

[Terry F.]

Re: 68/C3 Strut rod question.

I think that original coloration of the new part is part of the manufacturing process. I helped out in a foundery for a short time and did sand castings of small parts. I suspect these struts were sand casted with steel. The coloration is a result of high temperature and contant with the air (my opinion).

If you wanted to acheive the same coloration you could probably clean them (glass bead, etc.) and bake them in your oven at 500 degrees untill coloration fits your personal taste. Splash a little oil in a few places to give it that fresh out of the sand cast burnt look.

I would take the bushings out first though.

Thanks for you insights, Terry

[Terry F.]

Re: 68/C3 Strut rod question.

I was looking at some pictures of early and late strut rods. I might add this as an observation. It appears that when they went to the larger end strut rod they also increased the diameter of the steel bushing that has the teeth on it. Then, inside that bushing they installed a sleeve to reduce the inside diameter to its original size.

To make a long story short, just looking at the difference you can tell it would greatly improve the grip strength (surface contact) on the bushing when bolted in place. As noted on the board, these strut rods like to slip out of place over time or when not tightened or serviced properly (as I recall/I don't always trust my recollection).

I suspect that as years went by the earlier C2's started to have more maintainance and received complaints about not holding the rear alignment due to slipage. Increasing the diameter of the bushing greatly increases its mechanical leverage and holding power. They also kept it that nice thick wall design.

Now, I also looked at pictures of the new repro's. The one's I saw in my opinion are JUNK! They are a step backwards and are a poor design compared to even the first design original strut rods. Couple of problems....the center steel bushing is the "small" diameter, slightly thinner wall, the teeth appear to be slightly rounded, the steel bushing is SPLIT, appears to be made from mild steel. So....as you go zipping around corners, that small, weak bushing will want to spread, flex, and slip ever so slightly. Eventually, it will give out completely. I think they might even be dangerous. Being able to spread apart, it will really be able to work itself loose. Sorry if I offend anyone that purchased a repro set. If you note Paragon offers a bushing replacement that is not split.

I would like to know the properties of the original steel insert. It looks like it is made from rigid wall steel tubing instead of roled mild steel. I wonder if it was slightly harder steel.

I hope I have not restated something that has already been said or I just wasted a lot of time.

Best regards, Terry

[John H.]

Re: 68/C3 Strut rod question.

Terry -

The strut rods were steel forgings, not iron castings; they were made at Chevrolet - Detroit Forge (same plant that made the stabilizer bars, connecting rods, spindles, etc.).

[Terry F.]

Re: 68/C3 Strut rod question.

They look like they were casted out of steel, rough tecture. Then had the ends machined.

I am not familiar with forging process.

Terry

[John H.]

Re: 68/C3 Strut rod question.

Terry -

Forging starts with a steel billet "blank" slightly larger than the finished part; it's heated to cherry red, then transferred through a series of matched-metal progressive dies (usually in three or four steps) in a press ("forging hammer") which shapes the part fairly close to its finished shape. After it cools, it's machined to its finished form. Forgings are STEEL, and are FAR stronger (and, more importantly, more ductile) than castings, which are very brittle.

[Terry F.]

Re: 68/C3 Strut rod question.

Thanks for the info. I once had a person describe the process of making a "drop forged steel crank shaft." The process you descibed sounds real similar.

When I looked at the strut rods, they seem to have very similar casting appearance to the parts we made out of aluminum as a kid (I used to follow a cousin of mine to work in the summer). I think we poured cast iron also. Very small operation, about the size of a basketball court. Dark and dirty, every day had a task assigned to it. Big work up untill we poured. Place would get pretty hot. The sand casts would explode as they released gases that would ignite. Fun to do as a kid.

Any ways, the length of the strut rod shaft looks sand casted. That is why I thought it was casted. I wonder if they can sand cast steel? It might not have the right character to be poured in a sand cast.

Thanks again, Terry

[Joe L.]

Re: 68/C3 Strut rod question.

Terry-----

Steel can be cast. Actually, the only difference between steel and cast iron is the carbon content. Steel is less than 0.6% carbon and cast iron is equal to or greater than 0.6% carbon. Of course, there are all sorts of steel alloys as there are all sorts of cast iron alloys. But, the 0.6% is the "dividing line".

Generally speaking, cast parts will exhibit a narrow parting line. This is the "seam" in the mold into which the cast iron is poured to form the part. Forged parts will have a wider parting line. If you look closely at these rods you may be able to see the wider parting line. It's not so pronounced on these parts as it is on other forged parts and, sometimes, the parting line is removed by grinding. If present, you can only see it on the ends; you usually can't see it, at all, on the shaft portion.

[Terry F.]

Interesting. Thanks, Terry *NM*