Tension Rod bushing replacement

[Zedyone_kenobi]

I recently installed the poly tension rod bushings, which proved to be an interesting install. Not hard, once I figured out the trick, but thought I would take 5 minutes to document the steps I took. Keep in mind this is only for the black dragon poly bushing kit.

1) jack up and support car with jackstands

2) remove the front wheels

3) remove the nut holding the tension rod to the chassis (17mm)

4) Remove the two nuts/bolts holding the tension rod to the front control arm (14mm)

5) Slide the tension rod out and clean the nuts, bolts and all threads (I used a wire wheel and dremel)

6) Apply generous amount of grease on the bushings, large washers and inner metal guide provided with the kit

7) Take floor jack and jack up the control arm (keeping the floor jack 90 degrees to the cars body) to near level (IMPORTANT STEP). This allows you to install the tension rod and bushings and still have enough threads sticking through to start the nut. If you do not jack up the control arm starting the 17mm nut on the end of the Tension Rod maybe impossible. Just start the nut, but to not torque it yet

8) Install the two bolts that attach the tension rod to the control arm. This may take some reconfiguring as the floor jack may have pulled the control arm forward or backward a little depending on the angle of the floor jack to the body of the car. You can use a screwdriver in one bolt hole to align the other though.

9) Torque the nuts that connect the tension rod to the control arm to 40 ft-lbs (I forget the exact value but I recall 40 ft-lbs is sufficient for both the tension rod to control arm bolts AND the tension rod to chassis nut)

10) Torque the nut from the tension rod to the chassis to 40 ft-lbs

11) Lower the floor jack, install the tires and lower the car.

[jmortensen]

Did you read any of the stuff about poly bushings snapping the TC rod? The reason you had to take the rod off and not tighten the rear nut is because doing so would flex the bushings. Every time the suspension goes up and down it is now forced to flex those bushings, putting a good amount of side load on the TC rod at the end where that turned shoulder is.

[Zedyone_kenobi]

I read that, and I am not too worried about it. For ever report that they snapped, there were just as many that said they had been running them for years. I think that the extra load probably had something to do with it, but I would wager that a TC rod would have to be already flawed to break. A minimum strength for steel I found was 1018 annealed steel, with a yield strength of 32000 psi (just looking at the first reference I had). If the rod would fail due to tension we can use this number. Figure the rod is 3/4" round along its length, it would take around 24000 lbs. I would need to see where they are failing and what the grain structure at the crack initiation site looks like to see the mode of failure. If it failed at the neck down to the threads or near the bolt holes that hold it to the control arm, that would mean a totally different loading environment and I would need to look at that differently. Also the amount of suspension travel would heavily influence the result as well, as it would indicate the size of the fully reversing load (fatigue perhaps).

It would also be nice to know what it was actually made of, its heat treat specification etc.

I think the failures are real, but I think the super hard bushings aggravated an existing condition that led to these failures, rather than them being the root cause.

Edited September 8, 2009 by Zedyone_kenobi

[jmortensen]

They usually fail right at the step where the rod is machined down for the bushings from what I've seen. It's a square step, a perfect stress riser. The rods are close enough to 5/8" that you can run a 5/8" die down one, and they're failing in bending where the stress riser is, not in tension as the stats you're referencing are given. I agree with you about the suspension travel. The stiffer the better in this situation, as less travel means less movement on the rod.

[MEZZZ]

I dropped my front end yesterday. Started as a brake job and has progressed into Struts, springs and now bushings. I hesitantly orderd a new urethane bushing kit a couple days ago. I ran across this post on another site about the T/C Rods. I read alot about breaking, mostly to racers and the such which I wont be doing. But this post intruiged me and I wnet ahead and ordered the kit to try.

I got the kit from MSA for $26. I decided on going rubber on the backside vs. the poly that come in the kit. Anyone have feedback on this?

http://atlanticz.ca/zclub/techtips/suspension/comprod/ball&socket/index.htm

[jmortensen]

The back side bushing does nothing but allow the front side to move. The front is the part that takes the load when you go over bumps or step on the brakes. Rubber in the back is a good idea. With poly you can also run the rubber in the back and cut down the stress on the rod.

[=Enigma=]

Note that the back would also sustain some compression when braking in reverse, but this insignificant as compared to the compression on the front during braking. Poly in front with rubber in the rear is a good compromise and should eliminate much of the risk of rod breakage while helping to reduce front end squirm under breaking. I think I'll make the swap now too.

[MEZZZ]

Sounds good, thanks for the info. Its nice to know I am on the right page for a change.

While I have the front end out, is there anything else to pay attention to, anything other recommendations? I am cleaning everything, sanding and painting as I go.

[rxsleeper]

FWIW on the ITS car I run the Nylon/aluminum ball and socket on the T/C rod with rubber on the back side. http://www.thezstore.com/page/TZS/PROD/PSDC10/23-4190

I am building a heat shield for the drivers side since the Datsun Comp header puts a lot of heat into that joint which degrades the rubber and nylon quickly.

I have also run the same combo on a street car w/o any problems. YMMV.

Paul

[Zedyone_kenobi]

Mr Mortensen your correct. The neck down is a very high stress riser. When the bolt is torqued, the necked down portion is already preloaded in tension. When the Tension rod moves up and down, it compresses the bushing with the large washer. The washer acts against the hard rubber and I could see how that could produce a cantilever and put the beam in bending. Sounds like a first year machine design problem... now I am getting excited!

Edited September 9, 2009 by Zedyone_kenobi

[MEZZZ]

FWIW on the ITS car I run the Nylon/aluminum ball and socket on the T/C rod with rubber on the back side. http://www.thezstore.com/page/TZS/PROD/PSDC10/23-4190

I am building a heat shield for the drivers side since the Datsun Comp header puts a lot of heat into that joint which degrades the rubber and nylon quickly.

I have also run the same combo on a street car w/o any problems. YMMV.

Paul

Nice to know you are happy with the setup I have opted for. I am awaiting the parts from MSA as well as the poly bushing kit. Hope to have it all by the weekend so I can get it back together.

Stephen, thanks for the great tutorial. When I get it back together, I'll post the pic of it with the new graphite rewinds.