Hey Guys,

I really need your help on this one. I have been having an issue with my G35 Coupe, that is really taking a toll on my love for the G :

I have removed my Vortech a while ago, to prepare to drop an LS6 (C5 Z06) in there (already have the engine, 6sp transmission, fuel system, fast 102 intake mani, etc). In order to make sure that all aspects of the car's performance are up to par with the serious bump in low rpm torque that the car will be getting, I have been taking the car to the limit at the track.

I am getting a really weird issue in my handling. During long right turns to get into intersections for example (those that you almost do a full circle to get on), my front tires start to hesitate and my VDC kicks in. During the track, I get that same thing, and if I turn off the VDC, then I don't get the front wheel cut off but then I get a crazy rear wobble, like my rear wheel bearings are messed up.

Quick feedback on the car:
Pertaining to handling, the car has Stillen sway bars, BC coilovers + rear camber arms, brembo brakes (centric rotors, pMu pads, SS lines), new front and rear wheel bearings. front lower arm bushings have also been replaced as well as the rear ones. Lightweight aftermarket seats, no spare.

Another weird thing is that there is a light grinding noise coming from the driver's side, just like the noise of a worn wheel bearing, eventhough I just replaced them (I know that the work done was top north, I took it to Slammered Inc (Danny Greengobblin's shop for reference to the OGs here))

It's so disappointing because I went once to track the car, and I was very excited and could really tell that I am gonna get into it hardcore, but then the wobble came, then we went for a couple more laps and it seemed to get worse, so we decided to spare the car before something serious happen.

(sorry for the long thread)
What do the experts think it could be? All other performance parts of the car are working so well, and if this continues to be an issue I feel like I'm gonna say f. it and end up trading the car for a C7 vette, and it would suck to be so close to a really clean LS swap and end up giving up after 8 years of modding the car because I can't get to the bottom of this!!!!

BTW I know that 275/35/19 fronts would be a better match for the rear setup, but it doesn't seem that it's what is causing this, the wobbling really is coming from the rear.

Pics as a thank you for helping

 

Try unplugging the VDC controller, it's under the center console in the 350z (little box, behind shifter). It's the only way to truly shut it off. I would take your wheels and tires in to make sure they're balanced correctly/well. After that, it's pretty much just inspecting the car to be sure nothing is loose or broken.

 

^Thanks Dave, I'll def look into that.

Any other track guys knowledgeable of the performance mechanical aspects of our platform wanna chime in? (82 views, 1 comment :/ )

 

Bump for a very good guy and in for good feedback. Let's get him back on the track!

 

If you are dropped real low in the back..the suspension will bottom out and hit the bump stops and make the car jump sideways...common problem with G & Zs

 

A few questions. Did you feel the wobble in your hands or in your butt? What is your ride hieght, distance from the bump stops, and spring rates. What tires are you using? We will probably ask more as we dive into this.

 

Hey MHoward, thank you for the input

I am running the reg spring rates from BC Racing, and shock settings as such: typically 6 from softest at the track. I usually run 6 from hardest, but was told that at the track 6 from softest would be best. Regardless, the wobbling happens either way.

The wobbling is not vibration from the steering wheel, it's affecting the car so I guess to your question, I feel it on my butt (lol wtf)

The car is certainly not slammed, the rear setup is at its highest although that is still pretty low, but I have prolly a two finger gap there.
The tires are Hankook V12s, so fairly grippy.

I have dropped the car off yesterday at a specialized aliment shop who works on most of the lowered cars, and drift cars around (shop is called Autoglitz for reference for the locals, who prolly know it by name). They said they will check all of the suspension parts, do an alignment, look at the rear axle bushing, and check the steering sensor setup since the car is lowered and that could be causing the ABS to kick in.

Will keep you guys posted

 

Did you check for rubbing?

 

So, when you turn VDC off you get no problems at the front, right? At that point the only problem is the rear wobble, correct? Is this the case 100% of the time?

Does this happen ONLY in long right hand sweepers (ex turn 5 and 10 at PBIR)?

The grind is coming from driver side REAR?

Did you recently change tires? Sizes?

Did this problem just show up out of the blue or did you make changes to the car, go to PBIR and then notice the problem?

Is the 'wobble' a short frequency or more of a long frequency wallowing type wobble?

 

Sooooo I think I found out the issue.

The rear driver's SPC camber arm is defective and has play on it. I have reached out to SPC and conference the head tech in, and they are going to call me back. SPC mentioned only sending me the part that is defective, but I requested to have the whole arm replaced (both sides), as I'm now pretty skeptic of the item, and would like to do a full replacement so nothing bad happens at the track. Don't know if they will.

Autoglitz also recommended me to get a solid axle bushing pressed in, and that I should replace my front tires as I have camber wear on them.
I am considering stepping up to 275/35/19s on my 9.5 fronts, to go with my 305/30/19 on my 10.5 rears. Thoughts?


Will keep you guys posted on the SPC thing once I hear back from them. Thanks again for the inputs

 

I had a similar issue when getting of exit ramps my VDC would kick on driving me crazy, Didnt loose control but VDC kicking in while making a turn makes the car completely unstable. Believe it or not it went away after replacing tires. I believe my front tires had some bad wear that would cause this...

 

275/30-19 or 285/30-19 would be a better match.

 

Thanks Terramask, I will go with the Hankook Ventus V12 EVO K110 275/30R19 96Z ($214 per), as per your suggestion.

SPC is sending me a new set and I will ship them my old one (they are holding a security deposit in the meantime)

I am also going to replace the OEM rear axle bushing with a solid aluminum one that is getting machined this week. Since I'm doing that I will also replace the ears. I'm also adding front spc camber kit to minimize camber wear since I DD the car about 50 miles a day back and front from work. I'm also getting a diff. cover with the vents to help keep it cool

Once thats' all done I'm rebuilding my brembos, adding new pads (prolly P MUs street again, really liked the balance of track and street with min. fade), and having the centric rotors turned.

I'm hoping that the car will be perfect at the track once I'm done with this major overall, otherwise I will burn this car down in the middle of I-95.

 

Hey Guitman, sorry I didn't reply before, just saw your post.
I will respond even though I think we found the culprit, as people in the future may be able to use this thread to diagnose a similar issue

So, when you turn VDC off you get no problems at the front, right? At that point the only problem is the rear wobble, correct? Is this the case 100% of the time?
Yes, it is, I'm guessing the VDC problem was the front camber wear, which I underestimated.

Does this happen ONLY in long right hand sweepers (ex turn 5 and 10 at PBIR)?
Correct, great knowledge of the track

The grind is coming from driver side REAR?
Yep

Did you recently change tires? Sizes?
Currently 305/30/19 on 10.5 rear, 245/35/19 front (changing to 275/30/19 front).

Did this problem just show up out of the blue or did you make changes to the car, go to PBIR and then notice the problem?
No long curves at the limit to be able to notice it, just mostly your usual hard corner exits to make your daily commute less boring

Is the 'wobble' a short frequency or more of a long frequency wallowing type wobble? I guess I would say it's more of a wallowing type wobble.

 

Awesome, good luck.

How bad was your front camber? How bad are your front tires?

Did they tell you what specifically was wrong with the arm? Excessive bushing play?

They are machining one-off rear diff bushings?!?

 

camber was bad not horrible but enough to lose some tracting during stress

The camber arm i havent gotten a chance to see, but the shop told me they had never seen a defective arm before so i guess i just had bad luck

The diff bushing is a product that Danny (Greengobbling) developed in Cad around 06 and he gets them done 5 or 6 at a time but he ran out of his last batch so it should be done in afew days

 

I have brought this issue of rear camber arms up a couple other times after finding this issue on my car. I think any of the rear camber arms that have rubber or urethane bushings are hurting handling not helping it. The stock OEM bushing is almost completely solid aluminum. Anything other than a solid bushing is making this softer allowing more movement resulting in camber as well as toe changes in the rear alignment when under load. Put the stock arms back on, that is what I did and I have not had an issue since. There is plenty of adjustment in the rear for camber changes and after checking my alignment many times before and after track days the rear alignment does not change due to the eccentric washers like so many people claim.

Check out post #17 and #18 of this thread including the picture of the OEM bushing I am referring to. The Kinetix rear camber arms that I had were complete garbage, still sitting in my garage collecting dust, I would not sell them the quality is so bad.

https://my350z.com/forum/brakes-and-...uspension.html

 

Point taken, but the camber arm bushings work as part of the bigger system along with all of the other bushings, so if you replace the rest of the bushings by aftermarket urethane bushings (as recommended by most if not all of the platform experts), I am assuming that the camber arm urethane bushings won't be the bottleneck of the suspension setup as a whole, since they will all have a similar failure threshold.

 

Not sure what you are traying to say. Replacing a near solid bushing with a softer bushing is going to allow more movement, period. I had a rear end sway that was directly related to the rear camber arm bushings having too much play and being softer than OEM. These are the bushings on the camber arms themselves, not on the chassis. I do not have any issue with replacing factory rubber bushings with something more solid as long as you maintain your articulation.

 

Funny I was at Autoglitz today getting rear tires and was talking about you and your car

They have nothing but good things to say about Danny as well.