Two steps forward,one step back. T/C rod length quandy

[zKars]

Again, I'm proof of the old saying, 'no good deed goes unpunished".

I'm on a bent to improve the overall enjoyment of my Z, and a couple of days ago I decide to scrap my front adjustable control arm setup in favor of some actual suspension that knows how to soak up bumps, ie stock rubber bushings rather than bone crushing vibration passing heim joints.

The installation was straight forward, stock control arms, stock T/C rods with fresh rubber bushings. Job took me till fairly late in the afternoon, and I wanted to be done in time to make it over the usual Wednesday evening show and shine at a local venue to meet up with other Z club buddies. Finished up, through on the tires, fired it up, and headed out to the show.

Then the fun began. As I backed it out of the garage in to the lane, I turned the wheel and what should I hear but the lovely sound of front tire rubbing furiously on the front valance! Crap! oh well, off I go to the show. No rubbing on the way, UNTIL I get there and have to crank the wheel to get into a parking spot. Gruncccchhhh... yikes!

I get out and look (finally) and sure as h-e-double l, the wheels are way forward in the wheel well. Both side nice and even, but way wrong. Great caster setting, but incompatible with my 205-50-16 tires and my stock valence.

Now what the heck is going on? how can stock T/C rods cause this lovely surprise????? Pretty hard to get this wrong. Yes the control arms are on the right side (short side forward), T/C ends tightened all the way to spec. Any ideas gang?

I'm going to have to go through my T/C collection and see if there is any difference in lengths, but I think they are all the same through all S30 aren't they?

with one turn right, contact!

Good news though, (two forward, one back remember), the ride on Calgary's rough streets is fabulous! No more bone jarring whacks. And it handles just fine

Edited August 21, 2015 by zKars

[Zed Head]

You know the wheels aren't centered in the well right?  Compare the gap to the back wheels with the wheels straight.  They look fairly normal in your pictures.

 

I run a 205-70-14 which should be 25.3", with stock parts, and no rubbing, although there's barely a finger's width available when the wheels are turned.  But, your 205-50-16 should be 24.1".  So, there is something odd going on.  Are you sure you're not running a 60 series tire?  25.7".

 

Maybe you left a part in the bushing cup in the frame and it's pushing the rod forward.  Pretty sure all of the TC rods are the same.

[Zed Head]

Another thought - since you may not have looked at the stock assemblage of parts for a while, is it possible that you left the big washer off of the back?  This would allow the small washer and nut to pull through the rubber bushing, letting the wheel move forward.

 

When I broke a TC rod, the inner control arm bushing was flexible enough to allow the wheel to move all the way forward inside the wheel well and rub on the inside of the well.  That's what it did after the bump in to the curb when parking broke the rod.

 

http://www.carpartsmanual.com/datsuns30/DatsunZIndex/Axle/FrontSuspension/tabid/1729/Default.aspx

[zKars]

Thanks for the input Zed. There is quite a difference front to rear to the fender, pictures may not convey well. I see it in the pictures, but then I know what I'm looking at! Barely 2 fingers in front, fully 4 behind. The wheels are not turned slightly, both sides are identical. Hadn't really considered that the normal position may not be visually centered though. Oh, and a correction, I actually have 205-55 16 yoko S-drive tires, 24.8" diameter.

Pretty sure I got the assembly correct at the frame pocket end, one small washer, then a big cup washer, then a bush, then the frame, then last bush, then the last big cup, then the nut. I'm sure I have the nut torqued down so I'm touching and squeezing the central trapped sleeve. No extra there.

I also just measured the wheelbase, stock should be 2300mm, I have 2320mm +/- a couple both sides, so that tells me the wheels are somewhat forward. Any more ideas?

While I'm at it, let me mention another observation about this process. I considered putting a poly bush on the back side of the T/C frame pocket as has been often mentioned by others doing this, leaving the rubber in front to keep bump compliance. But when I torqued the thing down, the rubber front bush was nearly crushed flat before you get to the lock down point at inner sleeve contact, as the poly bush doesn't even start to squeeze, so that didn't feel right. Went back to two rubber bushings. Can't imagine trying to get the nut on with TWO poly bushings! Remind me never to attempt that foolishness.

Edited August 21, 2015 by zKars

[240260280z]

Hi Jim,

 

Weird problem.

 

The stock rubber on my 280z had ~ 7 to 8 threads showing when tensioned. I will guess it was factory at the point I swapped in poly then the ball and socket

 

 

http://atlanticz.ca/zclub/techtips/suspension/comprod/index.html

[Zed Head]

How about rim offset?  Your wheel seems to extend outside the fender well.

 

Also, on the poly/rubber bushing combination, poly goes in front and rubber in back.  But that would probably make your problem worse since the rubber would compress and the poly wouldn't, effectively making the TC rod longer, in-use.  Something I've never really considered before.  But that's the way people do it, it stiffens up the suspension under braking when the arm is pushing the rod back in to the frame and the poly bushing.  But leaves soft rubber on the back of the rod end, removing the bending load, which I think is why they break when poly is used front and back (which I had when mine broke).

 

Here's some pictures I took a while ago.  Are your washers set up like these?  Rim offset, plus wide tires, plus a backward washer might push your wheel edge turning radius in to the fender.

 

Edit - in the picture, the nut at the end of the rod is a second, locking Nylock nut.  When I had poly on both sides the extra stress would loosen the single nut.  I've been paranoid ever since.

Edited August 22, 2015 by Zed Head

[zKars]

Thanks for the confirmation pictures, I'm now sure I have it assembled correctly.

I'm running 16x8 rims, +5mm offset, tires fit perfectly inside the top of the wheel well. Not like they're sticking out or anything that would make this tire rub situation worse.

This poly on one side thing is bugging me. I can see reasons why you might want it one either side, depending on whether you are trying to dampen compression loads, like when dropping a wheel in a hole or rut, or when you are trying to reduce caster changes due to steering and damping loads where you might convince yourself to put it in front or the back, or both. My objective is the former, hence my choice of rubber in front.

Now when I look at your pics of the bushings with the second locknut, I see rubber bush in the back is not very compressed. This is very different from experience when I put my rubber in front/poly in back. The rubber went damn near flat before I reached lockup length.

I'm wondering if you don't have the unit compressed enough to lock the big washers against the center tube (lockup length, like the rear wheel bearings against the distance piece). That would contribute to the nut backoff problem you're having. Also don't re-use an old nylock or crimp nut.

I can also see an issue with using one poly one rubber in terms of the relative centering of the bushings and the resulting effective length of the T/C rod. Poly in front biases the rod too long, poly in back makes it effectively too short. It's only "right" when you have the same bushing on both sides. You can use this to your advantage, or you can cause caster problems.

I might just be putting that poly bushing back in the back and pull that wheel back. Now back to work.

Edited August 22, 2015 by zKars

[240260280z]

Jim the typical install is poly in front and rubber in back to prevent breaking the t/c rod.

 

The front poly is the rocking point and the back is compliant.  It is more for up/down control arm movement than front back t/c rod movement.

[Captain Obvious]

Weird. I wish I had some silver bullet solution, but I don't. As far as I can tell, the T/Cs were never changed throughout the whole run. Same part number from inception to end of model. If you've got the rear nut torqued down until you've compressed the bushings to the point where you're clamping on the inner sleeve, then I don't know what else to look for. What are the chances that your wheel/tire combo is just too large and you've been masking a potential rubbing issue all along with your adjustable setup?

 

And I know it's ridiculous to even ask, but I got nothing else... When you attached the T/C rods to the control arms, you got both bolts installed, right? You didn't do something ridiculous like use one bolt through the front hole on the rod and the rear hole in the arm and get the whole arm pushed forward? I know, but I gotta ask.

[240260280z]

You could pull the control arm  (and wheels) back by reversing the bushings in the control arm where it connects to the cross member but it may reduce the caster and make the car squirely.

 

[zKars]

Thanks for the input guys, as always, and even CO's desparate and appreciated attempt to point out even the most unlikely assembly option. I've been known to do sillier things. I did in fact use both bolt holes in the control arm. hmmm to fix this, I could put only the back T/C rod hole in the front control arm hole ... ;0

Blue I'm not sure putting the control arms on the wrong side to put the bushing offset to the rear will not help move the wheel back. The T/C rod length determines the wheel fore/aft position so I think you'd only put the control bushing in a nasty out-of-square cramped position and skew the control arm.

I realize we are mostly concerned with the bushing joints rotation (up down) stiffness, not the back/front motion, which only happens (and is small) during changes in rod compression or tension, which are transient and only happen when going over bumps or hard braking etc, but its the static position (parked) and resulting length difference that is definitely affected depending on which bushing pair you use. P|R, P|P, R|P or R|R. Same on both will self center the bushings on the frame pocket hole, (stock length), poly front make the effective rod length longer (frame pocket to front hole of T/C rod), poly in back makes it shorter.

Well, I'm not putting poly in front, its going to make the rod static length even longer and make my issue worse. Time to trim the valance maybe. I'm not changing tires again!

Edited August 22, 2015 by zKars

[zKars]

Progress. Well, some.

After re-reading and staring at your pictures above, I realized I put the big washers on backwards.Convex toward the bushing faces, not away from. Duh!

I tore the T/C rods off and switched them. I also put poly bushing on the back (I know I know) to try to get a little less length due to the offset compression of the bushings.

Couple observations. The manor in which the bushings squish is quite different with the washers in the convex to bushing orientation. With the poly on the back, when tightened fully to inner tube contact, the front rubber bushing has squished less (more remaining thickness) then when its washer was concave toward it. Hadn't expected that, but it's true. Other than the rumors of pending T/C failure now, there is clearly ample rubber bushing in front to allow all the TC rod movement I'd ever want or need in any direction without binding or fear or causing undu stress on the rod if the suspension droops or compresses to maximum.

My wheel now sits about a 1/2 further back in the wheel well. Turning now does not rub. I also rolled the valence edge a bit further and trimmed the end of the BRE spoiler to give just a bit more room. One could also loosen the valence mounting bolts and slide it forward a bit to gain a wee bit more room. This idea came from some 'guy' in a PM on the topic, excellent advice I might add...

Edited August 22, 2015 by zKars