I was ripping some parts off of a wrecked VG S12 today and noticed the tension/compression rod bushings and washers looked very similar to the ones on the 510 and Z cars. A quick call to my brother the Nissan parts guy confirmed that they are, in fact, the same parts as is the steel sleeve inside the bushings. I pulled off the passenger's side mount complete with original T/C rod and bushings and brought it home.
T/C Kit: I have produced a UHMW / aluminum ball & socket assembly to replace the forward rubber bushing in 510s & Zs for at least 15 years. The 'T/C Kit' as it's known is usually the first handling modification done to any of these cars. It's a cheap, easy way to make a major difference in the handling of the car, especially under heavy braking. What it does is eliminate ALL fore-aft movement of the front wheel under braking and cornering loads. This is done by replacing the forward rubber bushing with a mechanical joint. The rear rubber bushing does not need to be replaced unless it is cracked and at risk of falling out. This is because all the rear bushing does is apply pre-load to the T/C Kit's ball & socket to keep it from rattling. The rear bushing is NEVER compressed further except while braking in reverse, and it handles that just fine.
Rubber bushings: With stock rubber bushings when you step on the brakes the forward bushing compresses and the wheel moves rearward. In a panic stop on sticky tires the front wheels can move rearward 3/4 of an inch as each tension-compression rod sees between 1000 and 1200 pounds of force. As the wheels move rearward castor is lost making the car more "darty" and less apt to go straight. The toe also changes significantly so the front tires are no longer pointing the same direction. There is about 500 pounds maximum rearward load on the front T/C bushing while cornering. Again, this moves the wheel rearward reducing the castor and messing up the toe. None of this is good!
Polyurethane: Many people replace all of their stock bushings with polyurethane. Poly bushings are considered a good upgrade as they deflect less but are not as harsh as spherical bearings or other metal-on-metal joints. The car feels 'tighter' and the wheels stay pointing in their proper directions much better with poly than with rubber. Poly bushings still deflect under load, but not nearly as much as rubber due to their higher density. Poly bushings are great in all rotary applications like upper and lower control arms, sway bar pivot bushings, etc. They also work well where they are only loaded in compression and there is very little binding movement. An example of this is sway bar end link bushings. Poly bushings work great here. Tension-Compression rod bushings are NOT a good place for poly bushings and here's why: They increase the loading of the T/C rod itself as it pivots. The stiffer the T/C bushings the worse the binding making the T/C rods flex. The more they flex, the sooner they break.
T/C Rod Breakage: When a T/C rod breaks at speed the front wheel stuffs into the firewall, locks up, and jambs the steering! I once broke a T/C rod on corner entry at serious speed in my 510 and am lucky to be alive. I'd been canyon racing for hours on some twisty mountainside shit with epic drop-offs on one side and boulders on the other. I flicked the car into a left-hander at about 70 in 3rd gear with a serious dose of left-foot-brake and the hammer down. There was a loud 'POP' and it felt like someone hit the steering column with a sledge hammer. My instant thought was broken crankshaft as it was so violent. The RF tire immediately locked against the firewall and the steering wheel would not move. I let up on the brake but the wheel stayed locked and I could not steer. I snapped the throttle shut and thankfully the car pivoted on the locked front tire and turned ninety degrees sideways, passenger's side leading. At this point I was 'along for the ride' so I instinctively pushed in the clutch and drug the brake a bit. I left the tarmac at about 40mph sideways traveling in an arc about double that of the corner. I could not see anything the direction I was going and presumed it to be a drop off. I took my hands off the steering wheel, snicked it into neutral, and pulled my feet back against the front of the seat. One thing you learn growing up in a racing family is to never 'brace for impact'! Pull your extremities in, exhale, and wait for the hurt. It was eerily quiet now. After what seemed like five minutes of near silence except for the rough idle of my L18 my ears exploded with the sound of gravel shoveled into the right side fender wells. The car pivoted hard around the RF tire as it dug in and I spun 270 degrees coming to rest in a cloud of fury. Bap, bap, bap, bap my trusty SSS motor was alive, at least the crank wasn't broken as I'd initially thought four seconds/five minutes ago. I had come to rest in the loose crushed rock driveway of a gravel pit. I could see that there were enough rocks on the hood to fill a gallon bucket. There were rocks on the roof too, but I didn't know that yet. This particular switchback was the only one on the whole road that had any runoff at all and I could not see that as I entered. Good thing I'd stopped to piss about ten minutes before or I'd have needed a change of clothes and a tow truck. As it turned out there was very little damage: One T/C rod and associated hardware, one sway bar end link, one tire, the finish on both right side wheels, and a dozen nasty rock chips in the side of the car. I was beyond lucky. If this had happened on entry to *any* other corner on this road the result could have easily been fatal.
Fitment: It turns out that my existing T/C Kit is a perfect fit for the S12. It drops right in and works perfectly.
Binding load test: I had always wondered how much easier the tension-compression rod moved with a T/C Kit installed but had never bothered to do a 'scientific' comparison. In a 510 or Z this would involve some form of testing under the car as the mounts are welded in. This S12 chassis mount presented an easy opportunity. I set up a quicky comparison with the S12 T/C assembly clamped to my work bench. Here are some pics of what I found:
This is the assembly, as pulled from the car, clamped to the bench:
This shows the hammered stock bushings, with the gauge that's supplied in my T/C Kit as a reference for how far the bushings are compressed. Note that in stock form there is a steel sleeve between the two big washers so the bushings cannot be overly compressed:
I zip tied a tape measure to a piece of flatbar so it could hang off the bench for comparative measurements. Here the stock tension-compression rod assembly is sitting static with nothing touching it and I "zeroed" the tape:
Next I hung the nearest heavy thing I could find lying around, a VG30 starter, from the end hole of the T/C rod with a piece of bailing wire: 
The tape measure shows 7/8" (22.2mm) of movement.
Next I removed the stock nut, forward washers, forward rubber bushing, and steel sleeve from the T/C rod. Then on went the UHMW ball with the flat side against the chassis mount and the centering step in the hole. It is not a tight fit tight as play is required so it can self-align. Then the aluminum cup, washer, and supplied nut went on.
The standard hex nut is used to set the pre-load using the supplied gauge as a guide. When the gauge just slips over the big washer at the rear and the aluminum socket housing at the front the stock locking nut is screwed on and jambed against the first nut so it cannot come loose: 
I slid the tape measure back out and it's still "zeroed":
Adding the weight it's obvious this thing pivots MUCH easier than even stock rubber bushings!
2-15/16" (74.6mm) of movement. Wow, I had no idea a T/C Kit freed up the suspension *that* much! 
More for next time: I wish I had some poly bushings on hand to test against what I did here. Since my broken T/C rod experience I have never run poly T/C bushings and threw away any that I had. I've ordered new rubber T/C bushings from Nissan and will get some of the various Poly bushings that are on the market and do a more scientific binding test as well as an axial loading test using my press so we can see how much each lets the wheel move under a given load.
Price and availability: My T/C Kits are $28 and include all the parts to do one car plus detailed instructions and the pre-load gauge. We have them in stock. For ordering it's best to contact my friend Carter that handles all the sales directly at: [email removed]
Mar 26, 2010, 7:00 am · #1
