Tension Rod question

[2ManyZs]

I've been friends with numerous drivers, crewed for, and driven an ITS car with the aluminum/delrin/or poly, and I've yet to hear of any problems with control arms or T/C rods caused by the bushings. This goes back all the way to the mid-80's.

[ChrisA]

I have used the delrin/metal cup setup on a street driven 73 but the roads here are bad and it was very rough. Since switching to poly I have less steering wheel input but still better than stock rubber. I blasted my rods with walnut shells then cold galvanized them and painted them flat black. I've never seen a rod break but I have seem them bend on my 72 that had been in an accident when I bought it. I'm now wondering if the rods are the same on the 240/260/280. I swapped a 71 onto the 72 and noticed the 72 rod was really pitted and I worried about its structural intergrity besides it being bent slightly. My busings were the G Machine from VB and I didnt have any trouble with hole alignment. Much luck.

Chris

[TomoHawk]

I'm inclined to think about how deep any rust has gotten into the rod to determine how susceptable it will be to breaking.

[ChrisA]

The suspect T/C Rod on my car had deep, eighth inch or more pits on the shank where the bushings where located. Seemed very strange that the rest of the rod was ok. Since it was so close to the threads I didnt risk it. And again, it was bent anyway. In to the garbage bin flyboy!!!

Chris

[RB30-ZED]

Marty is 100% correct about the risk of the compression rods breaking.

My old 510 did just that. With the hard bush in the front and rear it puts more stress on the machined step that locates the front washer coursing them to break at the step.

I now only run one hard bush in the front (compression) and a rubber one in the rear.

Im not saying that it will happen with all hard bushes but it has happened.

Id go for the Delrin cup type or rose joint.

Steven

[Bambikiller240]

Originally posted by RB30-ZED

Marty is 100% correct about the risk of the compression rods breaking.

My old 510 did just that. With the hard bush in the front and rear it puts more stress on the machined step that locates the front washer coursing them to break at the step.

I now only run one hard bush in the front (compression) and a rubber one in the rear.

Im not saying that it will happen with all hard bushes but it has happened.

Id go for the Delrin cup type or rose joint.

Steven

Why does this occur with the Poly bushings, and not the Aluminum/Delrin bushing?

If Poly bushings are "hard", I'd say the Aluminum/Delrin ones are "HARD". When I had Aluminum/Delrinn bushings (through out) they transmitted so much noise and "feel" through the chassis, that iit made me want to swerve to avoid pebbles, let a lone road cracks, divits, and potholes. But it sure handled!

[mdbrandy]

Originally posted by Bambikiller240

Why does this occur with the Poly bushings, and not the Aluminum/Delrin bushing?

If Poly bushings are "hard", I'd say the Aluminum/Delrin ones are "HARD". When I had Aluminum/Delrinn bushings (through out) they transmitted so much noise and "feel" through the chassis, that iit made me want to swerve to avoid pebbles, let a lone road cracks, divits, and potholes. But it sure handled!

Let me take a stab at it:

When the TC rod moves up and down, the threaded end "pivots" at the frame end. When controlled with rubber bushings, the up and down pivot movement just deforms the rubber with little resistance. With PU, the rod has MUCH more resistance at the front bushing to deforming the PU, and thus tends to bend more there, particularly right at the "step" which should act as a stress concentrator. With the AL cup/delrin, you now essentially have a pivot cup there at the front of the frame connection, so there is very little resistance to the rod pivoting up and down.

The idea behind the harder bushings is to keep the rod from moving front-to-back, and the up and down resistance is a side-effect. The PU compresses much less than the rubber, so the front-to-back resistance is much higher at the expense of the up and down resistance increasing as well. The cup/delrin method gives you very little front to back movement with decreased up and down resistance as well, so the rod doesn't bend at all.

So, racing guys, is that a reasonable explanation?

[ChrisA]

Originally posted by Bambikiller240

Why does this occur with the Poly bushings, and not the Aluminum/Delrin bushing?

If Poly bushings are "hard", I'd say the Aluminum/Delrin ones are "HARD". When I had Aluminum/Delrinn bushings (through out) they transmitted so much noise and "feel" through the chassis, that iit made me want to swerve to avoid pebbles, let a lone road cracks, divits, and potholes. But it sure handled!

I wonder what the 510 was used for and what other suspension mods the car had. In 22 years of driving Z's hard I've never experienced a T/C rod failure when running any of the three types of bushings. But I agree with Carl, the delrin/aluminum combo is by far the hardest and most aggresive.

My .02

Chris

[TomoHawk]

That's how I see it.

the PU bushing is so firm, it would be like a solid metal block, so the tension rod HAS TO BEND with the up/down of the wheel. The flexing stresses the weakest part, the stepped/threaded end,and after so many flexes, it breaks.

So you put in the softer rubber bushes to absorb & allow the flexes. Just remember to buy extra sets, so you can replace them after so many years, in case they will be NLA...:disappoin

[ChrisA]

The delrin/aluminum combo was convex/concave to allow for the rod movement as Tomohawk describes but didnt allow much if any lateral movement fore and aft. On a track car its great but like Carl said, one tends to avoid pebbles, cracks, expansion grooves because the shock into the steering wheel was just horrid.

Chris

[TomoHawk]

Originally posted by ChrisA

I've never experienced a T/C rod failure when running any of the three types of bushings.

I guess some people have all the bad luck, huh?

[ChrisA]

What's them Nascar boys always say, "better to have bad luck than no luck at all". LOL

Chris