The twisting is only a problem with poly bushings, on the smart struts the rod ends should take care of that....or do they have poly bushings at the ends? If so, then yes poly ends + a threaded rod will break loose. Guldstranf uses rod ends.

 

Here is VBP reply:
In reply to your E-Mail

The problem referred to occurs on very few corvettes and is usually caused by drive line vibration.
The vibration may come from bad U joints, Bent or out of balance Drive shafts, where the most common is a loose slip yoke bushing. Reversing a problem rod will cause the rod to tighten rather than loosen which is a short term fix for a larger problem. Lock tight also may help but in most cases the harmonic vibration is stronger causing the locktite to fail.


Thank You for your inquiry
Robin Wilkie
Technical Advisor
Vette Brakes & Products, Inc.
robin@vbandp.com
Phone (727) 345-5292


I am kind of disappointed with this explanation and might be taking them off and going back to stock unless I come up with a solution. I am not crawling under my car every time I drive it to see if these things have loosened up. This is total if you ask me.

 

I guess I'm still thinking in terms of race geometry. Technically, in a broad sense, there is no toe change in a C-3 rear suspension in an avarage range of motion such as we would see in street use. Certainly nothing like the front, steerable wheels with their short, badly angled tie rods. However with any IRS that uses uneven links (as in the C-3), under significantly higher loads (on a racetrack, for instance) there is definite toe change. Granted, it is relatively small amount, but if I can reduce it, I will. It was even worse on my Corvair (very similar setup), but it is being solved with a 6-link setup and custom trailing arms.

Hans

 

A 6 link does nothing for toe change in the rear, nor do custom trailing arms. The toe change is a result of the suspension motion that the virtual triangle, consisting of 1/2 shaft and trailing arm w/ both 1/2 shaft u joints and trailing arm bushing as the corners, goes through. There is no way to eliminate this toe change by sticking with a stock like suspension, the trailing arm will remain the same as will the 1/2 shaft. Toe change is directly related to the amount of suspension travel, with the change getting worse with the suspension travelling forther from the center pos (1/2 shaft horizontal), stiff springs & shocks will minimize suspension travel and mask the toe change problem but it's still there to rear it's ugly head under hard cornering, giving a rear oversteering situation. The only way to stick with a somewhat stock like system and attributing the toe change is doing what gm did, use a rear toe control rod and a sectioned trailing arm that is not a fixed member, eliminating it from the "triangle. Now, although slightly warped that triangle consists of the /2 shaft and the toe control rod, where the rod is perpendicular and in line w/ the 1/2 shaft. Another way to eliminate it is to use the trailing arm bushing as a fore/aft locator only and allowing it to slide on the through bolt, a sliding spherical end would be nice. This will eliminate the trailing arm as the member that dictates the toe setting, you'd have to use a toe control rod also. Only problem would be any wear issues on the slider pin (through bolt) and the pocket in the frame rail would have to be wide enough to allow the sliding motion to not touch the sides at the extremes of suspension travel.

 

I really like the idea of the adjustable struts. I mentioned before that lockwire could be used to secure the nuts. Someone mentioned that when the lockwire broke you would have the same problem. I have seen studs hanging in jet engines by lockwire. The studs had broken but I have never seen lockwire fail. You don't even have to drill the nuts; just wrap lockwire around the strut behind the nut, bring the wire across a flat section of the nut to the opposite end and do the same thing at that end. To adjust the strut cut the wire make your adjustments and rewire. This is what I will do when I make this change. It is a cheap mod to make, it is so much easier to set camber and you can install beefier units for greater strength and less flex.

Bernie

 

This has been my concern ever since I've seen threaded rod ends tear out from rods on airplanes. I think heim joint ends are very strong in certain applications - like a smooth race track or on an aircraft. For day to day use on a street car, I don't think they will last over time. I would think the strongest arrangement for a driver is the stock 1-piece rods with the poly inserts. I think Mid America has them.

 

Stock ones are adjustable

 

That is fine for securing the nuts, but as I posted, the nuts were still loc-tited in their original position, it was the SLEEVE that started to unwind.

 

As a pilot and a motorcycle racer 0.032 stainless saftey wire is the way to go here. Done right it wont ever come undone until you want it to. 0.040 is heavier for the more paranoid among us.

I saftey wire anything that I dont want coming undone at speed.

 

I have a set of Smart-Struts waiting to be installed. You guys are making me paranoid.

I guess I'll drill a hole through the rod and cotter pin the whole mess.

 

if these new points provide much better geometry, why didn't GM put there in the first place?

 

Although mine are tight I'll install some NordLock washers - probably on the weekend.... here's the link:
www.nordlock.com

 

My guess: they built the cars as cheap as possible, just like they still do

 

This guy told me the same exact thing about my dual spring mounts coming loose all the freaking time. I wonder if this is the excuse they
give everyone now. This really make me wonder.

 

I think Chev needed to factor in body roll. Keeping the lever arm effect minimized at the diff avoids excessive camber changes when the body leans on a hard turn.

 

My thoughts...

I’m not sure if a jam nut is the correct solution here. People just think it looks right.

The problem is fundamental: not enough bolt stretch to withstand the alternating tension and compression loads applied to the members. And with left and right hand threads, it does not take much external force to ‘release’ the assembly. Vibrations accelerate the problem. Loctite is ok, but just a band-aid solution.

Ideally, the internal threads in the shaft should be recessed a bit. To simulate this, add some flat washers between the nut and the shaft. This will increase bolt stretch and therefore allowed for a tighter connection.

Use two nuts per end: shaft, add flat washers, then tighten a jam nut, then a normal hex nut. It sounds weird, but I think the triple thread thing is required because the system is has left and right threads.

 

Correct, but the VB&P strut adds the adjustable length strut for camber adjustment, freeing up the stock eccentric for vertical inner rod end height adjustment if you choose to use it that way. By the way, TwinTurbos geometry explanation is excellent. Wish I could explain the thing as concisely as that!

I guess what I'm trying to get across is that I'm trying to improve the stock setup as much as possible without replacing the whole mess with a C-5 cradle and solving the problem that way. I just can't afford to go that way and it would ruin the value of my car.

Hans

 

Isn't the eccentric for camber adjustment? I don't see how a "height" adjustment would be significant from the cam. I agree about Twin Turbos reply. Time to get a wrecked C-4

 

I''ve been very interested in all of this conversation since I installed some "smart rods" two weekends ago and have yet to tighten them down. What I've missed in all of the message traffic is a suggestion (statement) as to the torque that the nuts should be tightened to. They're relatively large in diameter (an inch?), and perhaps they could be tightened down to 100 ft lbs or more. I've looked at some torque sheets, and for hardened nuts, it looks like you could go to 200 + foot pounds. To really torque these things up, I'll buy the correct crow's foot sockets and use my really long handled high torque torque wrench. What torque are people recommending? The Nord lockwashers look interesting. I think I'll give them a call. Has anyone just tried normal lock washers? For the brute force high torque solution, how about grade 8 nuts?



The VBP comment about driveshaft vibration needs a little more explanation I think.

 

Whoa Nellie...some later thoughts.

As the trailing arm move up and down, it makes an arc at the attachment point of the strut rods. The natural up and down motion will therefore create a slight twisting motion that will tend to unscrew the strut rods. Of course, the strut rod bushing should take out a little of this twisting motion, but with the polyurethane inserts of the strut rods, they don't rally flex very much.

It really looks like the nuts/rods have to be pinned, or you have to use heim joints. The heim joints will rotate clockwise and counterclockwise as the trailing arms make their slight arcing motion.

What do you think about the idea that the natural up and down motion of the trailing arm is going to twist the strut rod/nut junction loose? Actually, this is not really my own idea, It appears that others (such as Zwede, for one I believe) have suggested this in other threads.