sykikchimp

Hello,

Got a strange problem, did a search and couldnt find anything. I'm hoping someone here may have heard of this before.

My rear end has developed some pretty severe slop when shifting left to right at speed. For example if I do a small lane change at 65+mph the rear end seems to almost shift and then catch as the car changes direction. At 70mph, a slight bend in the road causes the rend end to almost "bounce" on the suspension.. not up and down but horizontally as if something is loading up and shifting my toe around. When driving straight at high speed the steering feels extremely vague. the direction of the car seems to change by itself with almost no input other than road irregularities. These changes in directions seem to originate from the rear end.

It feels very much like I have a blown bushing in a toe arm or something. Its much worse when going right than left which leads me to believe it would be a bushing on the left side of the car since that is the side that loads up on a right hand shift.

Now I looked under the car and my rear diff mount bushing is definitely blown. I poked around through searches here and no one indicated this kind of symptom from that so I'm thinking it is not related. Correct me if I'm wrong.

I also looked at the bushings in the suspension arms in my rear left suspension and did not notice any blown bushings.

Are there some hidden bushings I'm missing or maybe some other component that tends to fail that could cause this type of symptom?

TLDR: Weird rear end sway, blown diff mount bushing but no other bushings clearly blown. What could be the culprit?

Thanks!
Sykikchimp

terrasmak

iTrader: (8)

Sounds like a toe out feeling on the front end. Check your front control arms and compression arm bushings.

idrive_MD

iTrader: (8)

I've actually been having this EXACT issue for a looooong time now. I'm assuming you have stock camber arms and stock toe-bolts since you didnt mention it...I have the SPC camber arms and toe bolts and the only thing I ever noticed was that it looks like the urethane bushing has seperated from its metal liner, so now it rests at angle to the bolt axis.

I also have the rear diff failure, but it seems like only excessive wheel hopping and vibration stem from that issue.

I have new arms waiting to go in, but yeah, they've been waiting lol...Best bet, new rear camber arm(s) or have the toe bolt looked into.

Voboy

iTrader: (58)

get it on an alignment rack

sykikchimp

I do in fact have the rear SPC camber arms and toe bolts. I will definitely check them out and the front camber and toe arms.

Thanks for the advice guys! I'll report back with my findings.

2000atlanticgt

iTrader: (5)

I have also been experiencing this very same issue, rear end sway after some road input mostly at highway speeds but mine seems more prevalent on slight left hand turns. This issue is definitely originating in the rear end as it feels like the rear end is steering.

I have checked the alignment on my car myself twice, confirmed all of the rear alignment specs are in stock specs. My front specs are out as I have my front camber set to around ~1.9 on each side and toe set slightly out (0.04 per side - will post my alignment print out later when I get home).

This weekend I put a lot of miles on the car and can really induce this easily now to try and show other people that are trying to help me look at the car. With no other cars around at highway speeds I can make a slight left hand input to the wheel and experience what feels like a shift in the rear suspension cradle then when I straighten the wheel back out can feel it return front this shifted position (very hard to explain but hopefully you get the point).

On a lift I have checked every bushing in the rear end that I can, used a pry bar to put pressure on the bushings to check for excessive play, checked for any loose control arms, toe links, anything but can not find anything wrong. This mysterious left to right sway in the rear end feels worse when the tires/car are cold but it is still there even after it warms up if you know what you are looking for.

I do have Kinetix rear camber arms with the SPC lock out bolts, stock toe bolts, and stock ride height (running 2008 350Z Nismo shocks/springs - not the S-tune). My rear differential bushing is NOT blown or leaking any fluid.

My next plan is to put the stock rear camber arms back in, set the alignment again and see if anything changes. If that doesn’t work I might try taking the front toe back to a toe in setting but I am very confident that has nothing to do with what I am feeling. After that, I guess I will just have to drop the entire rear suspension out and inspect the rear suspension cradle bushings better or just replace them.

terrasmak

iTrader: (8)

Its the toe out, the car does this when you toe it out. Trust me , my car is aligned for the track right now (toe out) completely changes the way it handles.

2000atlanticgt

iTrader: (5)

I'll take your word for it and adjust the front toe first as that is really easy to do. I'll let you know what I find, thanks for the advice.

2000atlanticgt

iTrader: (5)

Here is my alignment sheet from a few weeks ago. Had the issue before this so just checked it to see if there was something out causing the problem. Issue was the same before and after checking the alignment, no change at all. As suggested later this week I'll go back and change the front toe to see if that resolves my issue or not.

2000atlanticgt

iTrader: (5)

Well, I was skeptacle but it was worth a shot. However no change to the issue of rear end sway I am having by setting front toe from slightly out to slightly toe in.

I'm going back to my original plan now and will take the Kinetix rear camber arms off and install the OEM arms as my next step as it really feels like a bad bushing in the rear end, just going to have to find it.

Latest alignment sheet:

terrasmak

iTrader: (8)

Tire info now, front, rear, sizes and brand.

kacz07

iTrader: (15)

Yeah. I would think it's your tires. What's your PSI? Could be sidewall flex or something.

Lawn Dart

iTrader: (4)

Your rear toe alignment needs adjustment, without a doubt.

2000atlanticgt

iTrader: (5)

I bought the car in May 2010 and bought these same tires. I am now on my second set of the exact same tire but the issue just started about 2 months ago.

Direzza Sport Z1 Star Spec

Front: 245/40R18
Rear: 245/45R18

As for pressures I have tried raising them starting with cold pressures anywhere from 30 to 35 making sure all 4 tires are exactly the same with no changes. Right now they are 32 cold, and around 35-36 after my 20 mile commute.

2000atlanticgt

iTrader: (5)

Why do you say that, it is with in factory settings?

Let me clarify, before and after of all of the above alignment measurements there was no change in the way the car handled or felt with regards to this odd rear sway feeling.

terrasmak

iTrader: (8)

I'm mind bottled right now, the alignment tech would have/ should have noticed most bad bushings. The front compression arm bushings are hard to tell if they are bad, front LCA is simple to tell. Most problems usually don't happen to the rear suspension, its the front.

Do you have a true coilover? If not, remove the shock and check it, 3 bolts a side to check.

2000atlanticgt

iTrader: (5)

I'm doing the alignments myself and on a couple different times now have checked for damaged bushings both front and rear.

I have had a few others mention shocks might cause this issue so as you suggested I am planning on unbolting them and checking them. I am running low mileage (~5k miles) take off 2008 350Z Nismo shocks/springs. The donor car for these shocks/springs did sit for ~1 year and I have done 7 track days on them as well.

I am still not convinced the aftermarket rear camber arms might be the issue though. All 3 of us with this problem in this thread mentioned aftermarket rear camber arms. When I went back to check the factory rear camber arms there is not much of a bushing there, more solid metal than rubber on the chassis side. I really think there might be more give in the Kinetix urethane bushing at this location than the stock arm. Easy enough to swap them back out and check after another alignment so planning on trying that as well.

2000atlanticgt

iTrader: (5)

Problem solved!

Checked the rear shocks and they both seemed ok with about the same force required to compress them and they released the same on both sides as well.

I removed the Kinetix rear camber arms and confirmed the urethane bushings were not cracked but they did have (especially on the passenger side) free play in them. I could easily move the urethane bushing about 1/16" or 1/8" in the axial direction of the arm. This is with no load so I am sure with the load of the car there was much more movement which is what I was feeling all along, not to mention the change in rear toe as the camber arm bushing was moving. Compare this to the stock arms that do not move at all and the difference is very easy to see.

Reinstalled the stock rear camber arms, set the alignment again, and after road testing last night and again this morning no more rear end sway!