johnc Posted November 11, 2003 Share Posted November 11, 2003 Lowering the car is not really the issue, the original design with the rubber bushings works through the entire range of front suspension travel. The culprit appears to be the additional defelction force required by poly bushings. It adds more stress into the TC rod and causes a failure IF there is a stress riser somewhere on the rod that concentrates force. One preventative may be to shot peen and polish the TC rod removing all sharp edges. Quote Link to comment Share on other sites More sharing options...
Afshin Posted November 11, 2003 Author Share Posted November 11, 2003 Well this is my first picture post, Iguess I need to downsize a little more. As you can see the rod snapped at the end of the metal sleeve that fit over the rod, so that was the pressure point. It's hard to see in the picture, but the angle that the rod is pointing to is a little off from the center of the mount. That placed a steady pressure/deflection stress on the rod which greatly increased the rate at which the rod developed fatigue and hence failure. In other words the hard poly bushing was always placing torque on the rod, not just during suspension compression. Also the amount of torque will only be that much higher during suspension compression than if it were starting from the factory non-lowered angle. If the bushing was softer it would have not applied enough pressure to snap the rod. [/img] Quote Link to comment Share on other sites More sharing options...
Afshin Posted November 11, 2003 Author Share Posted November 11, 2003 I just added two more pictures. If you look carefully at the bushing washer you can see that it is angled, there is space at the bottom between the washer and the bushing, and it is compressed at the top. Again this shows that with the lowered suspension on the ZX and poly bushings there is continuous load on the side/wrong axis of the TC rod. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted November 11, 2003 Share Posted November 11, 2003 This picture brings up another factor which has not yet been discussed. When the nut at the end of the T/C is tightened, it tightens the bushings until the inner sleeve makes contact with both outside steel flanges. When this happens, the bushings no longer compress, and any over-torque applied to the nut then only pulls against a "step" in the rod. In the above photo, it appears this is where the rod snapped. I am curious as to how much of an effect this would have on accelerating the failure by over-torquing this nut. If I remember correctly, this is a self-locking nut. Quote Link to comment Share on other sites More sharing options...
TomoHawk Posted November 12, 2003 Share Posted November 12, 2003 What I'm trying to figure out now is how to fully fix this' date=' while maintaining a "tight suspension".[/quote'] How about using a rod with ball joints (heim joints?) at both ends? It guarantees full travel range with a constant length and no stress. Quote Link to comment Share on other sites More sharing options...
Afshin Posted November 12, 2003 Author Share Posted November 12, 2003 Well I took my control arms and TC rods off today and took a nice look at everything. As you can see in the new picture the TC rod does not align with the chassis mount. However, a bump steer spacer by going below the strut housing and on top of the control arm not only corrects the tie rod/steering rack angle but does corrects the TC rod angle. So that problem will be taken care of. I then checked the range of movement for the rod with the poly bushings. It is absolutely terrible. No wonder it broke. I have been thinking about making custom rod ends vs trying the MSA/G machine kit. Considering that the kit works on the 510 and that the Z and ZX use the same bushings, I think the kit should work on the ZX (easier that making my own adjustable rod end bar). Replacing a stiff bushing for a pivot point will greatly improve things, I can then use a stock bushing on the non-load bearing side. I guess everyone should consider using bump steer spacers on lowered Z and ZX’s for both bump steer and correcting TC rod angle. After looking at the ZX set up closer, I strongly recommend against using two poly bushings without further customization/precautions, at least on any 280zx. [/img] Quote Link to comment Share on other sites More sharing options...
Guest BigWhyteDude Posted November 12, 2003 Share Posted November 12, 2003 thanks afshin, now i can see what you have been talking about. im a visual learner, i have to see something to know what is going on. Quote Link to comment Share on other sites More sharing options...
icice9 Posted November 12, 2003 Share Posted November 12, 2003 DAYMN!! i just changed my TC rod bushings this weekend to the eurathane ones from energy suspension... looks like ill be changing it back to stock now after seeing your pics... Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 12, 2003 Share Posted November 12, 2003 You could put a rubber bushing on the rear and use the poly on the front (for us Z guys we would want poly in the front and rubber in the rear too, even though the TC rod is the other way around), and move the TC rod up and down to test how stiff it is, and let the rest of us know how that works. If you prefer you can get the G Machine setup from VB, or get a custom rod end style and have adjustable caster. Jon Quote Link to comment Share on other sites More sharing options...
TomoHawk Posted November 12, 2003 Share Posted November 12, 2003 Doesn't the G-machine setup take care of flex with the cupped aluminum thing and the plastic piece with the rounded end? All that stuff should pivot/swivel easily and the rod should only experience minimal stresses, according to how tight the nut is on. Of course, a pair of new RUBBER bushings would only help minimize what flex is left. Why use Polyurethane bushings on something that flexes and breaks? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 12, 2003 Share Posted November 12, 2003 The G Machine stuff wears out a lot faster than a poly bushing. I used mine for 3 years or so and probably had 30K on it and it was still fine, but you won't be able to use it for 10 years without any maintenance, like a poly bushing. The poly bushing works great on the side that takes the braking load, but it is too stiff for both sides. If you use the poly on both sides, as Afshin stated previously, the TC rod is very hard to move through its range of motion. I think that problem would be lessened by putting the rubber on the backside, because it is still flexible enough to allow the rod to move freely and the backside of the TC mount doesn't take the load under braking. Icice9 could test that theory very easily, unless he threw the rubber bushings away when he swapped. Jon Quote Link to comment Share on other sites More sharing options...
tickwon Posted November 12, 2003 Share Posted November 12, 2003 Afshin, I have too broken a T/C rod. But I didn't know it broke until I hit the brake. I heard something that sounded like a rock hit the underneath of my car, but I didn't think anything of it. Just prior to that I hit this pot hole, not too large, but large enough to jolt the car. I have 205/50ZR15, so you can feel ever thing on the road. I was cruising at about 80 mph and I'm coming up on the exit ramp I need to get onto. So, I let of the gas and at about 40 mph I hit the brake, my right wheel got shoved into the back end of my wheel well, sending me turning in that direction off the road. The car was okay, I was freaking out. I was forcing the wheel in the other direction the whole time of the slide. It was the T/C rod that snapped. Now I have that performance rod kit with the ball/socket...hasn't broken since. I'd just thought I'd add my story...still have yet to read every one else's insight. Good luck...not a fun experience. Chris Quote Link to comment Share on other sites More sharing options...
tickwon Posted November 12, 2003 Share Posted November 12, 2003 Afshin, I just saw your pictures of your rod, yup, mine snapped in the same place. Chris Quote Link to comment Share on other sites More sharing options...
Forrest Posted November 12, 2003 Share Posted November 12, 2003 Where can you get the adjustable TC rods? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 12, 2003 Share Posted November 12, 2003 I had mine built by a machinist, and mine are 3/4" rod ends with aluminum turnbuckles. Used to be you could order 5/8" units from Mike Kelly. Not sure if anyone is actively selling them right now. It would be a good seller I'm sure if someone made them. Jon Quote Link to comment Share on other sites More sharing options...
Mikelly Posted November 13, 2003 Share Posted November 13, 2003 I had a guy on here (Sorry, but I forgot who!) sent me one from a 280ZX and it was snapped as well... I still have it in the shop somewhere... I couldn't come up with an economical way of fixing it, but I could provide a step by step on what it would take and what tools to buy... I personally want nothing else to do with making parts for people, as I simply don't have the time, but I'd be happy to provide a parts list and list of tools required... Mike 8) Quote Link to comment Share on other sites More sharing options...
Pop N Wood Posted November 13, 2003 Share Posted November 13, 2003 What about the MSA TC rod kit? They allow things to pivot They also have adjustable http://www.zcarparts.com/store/merchant.mvc? Quote Link to comment Share on other sites More sharing options...
Mikelly Posted November 13, 2003 Share Posted November 13, 2003 The 280ZX TC rod doesn't look like the TC rod you show... That appears to be from a 300ZX... Mike Quote Link to comment Share on other sites More sharing options...
ZR8ED Posted November 13, 2003 Share Posted November 13, 2003 I had my drivers side snap where the rod becomes threaded. I had just done some drag runs with some friends...I was on my way home and hit the brakes for a red light, when "thunk!" the car veared left sharply and I had to becareful stoping the car. It was ok when driving...but when stopping..it was scary.. I replaced mine and replaced my worn bushings with poly bushings..no probs since...this was more than 8 years ago... (mine looked rusty in the area where it met the frame mount.) but the metal was clean where it broke... Lucky it didn't break while racing! Quote Link to comment Share on other sites More sharing options...
JMortensen Posted November 13, 2003 Share Posted November 13, 2003 What about the MSA TC rod kit? They allow things to pivot That is the G Machine setup. I don't think MSA actually makes anything (could be wrong) I think they just resell everything. The one on the bottom looks like what I have on my car, but as Mike said it is for a 300ZX, so it doesn't have the bent end like Z's and 280ZX's. EDIT - Scratch that. The one on the bottom doesn't have a turnbuckle, so to adjust it you would have to unbolt the rod end, turn it out a thread or two, then bolt it back up. Mine has a turnbuckle like a tie rod end, and like the ones Mike used to make. Jon Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.