HMG37

iTrader: (1)

I have had my G37 for 8 years and 100,000 miles, and I lowered it on Swift Springs and Vossen CV5s (20 inch staggered) at 18k miles. I started noticing ride quality issues around 60K and replaced my OEM struts with KYBs for the X sedan. I didn't notice a vast improvement, but owed it up to the stiffer struts.

Since 90K, my ride quality has deteriorated vastly. I am afraid to hit any bumps as it jars the whole car. With even 1 passenger in the backseat, there is no wheel gap left in the back and the wheels are almost tucked.

My question to everyone is: Is this the work of the Swift Springs needed replacement after 6 years and 82K miles? I wanted to confirm before I go down the path of replacement.

Hugh Jorgens

Springs and bushings control the height of the car (assuming nothing else is bent or broken).

The lower the car goes, the less travel the shock will have. So ride will deteriorate as ride height drops for any reason.

Conventional twin tube shocks cannot affect ride height by wearing out. But they sure can affect ride quality as they wear out.

Your shocks may be worn out also. But the premature wear is a result of the sinking ride height.

To get your ride height issue sorted...check the condition of the bushings and springs. If you never re-clocked all the bushings when you did the springs, then...they're all dead by now for sure. They've probably been dead a long time though, in that case. If your car's ride height "settled" a few weeks after you did the springs...then that's when they died. RIP.

Maybe your rear suspension rubber spring isolator is worn out?

Springs should never sag appreciably through their entire lifespan unless they're very low quality or something else is wrong. But...everything does have a life span. 80K miles is a pretty short lifespan for a good spring...but...its possible.

HMG37

iTrader: (1)

Thanks Hugh! I am going to make an appointment to get the bushings checked out including the SPC arms I am running. Any kits you recommend that could be used for replacement?

Hugh Jorgens

for sure.

Have them pay special attention to the rear spring bucket arm bushes and spring isolator. They may be sagging with the car's weight on them. It wont be visible if the wheels are off the ground.

Genuine OEM (Infinti) parts would be the only ones I could recommend fully. But I have had good luck on other cars with Hardrace. Not sure what aftermarket choices are out there. Just remember to tighten the bushings once the car is resting at ride height (don't tighten them with the wheels in the air).

mummy2

Sounds like you blew your shocks. Those KYB's are meant to be used with factory springs only. Springs and shocks have to work together and if they aren't in sync you'll have either a bumpy or bouncy ride. And shocks that are worn will definitely effect ride height when they wear. The other guy missed the part were you said the car sags with a passenger in the back seat.

Hugh Jorgens

His shocks are likely worn, yes. And that would be a result of the much stiffer springs and the ride height being lowered (the bumpstops will be over active and wear the shock even faster).

I may have misunderstood his ride height issue also. The car's bum isn't sagging? It just seems like loads up too much with a passenger in the back? If that's the case, maybe you just didn't notice this until now. Putting a passenger in the back will lower the ride height.

The only issue in that case may be a rough ride due to worn shocks.

But...how can a twin tube shock affect ride height as it wears? It can't...unless you're talking about shock bushing sag? The AWD shocks themselves don't have lower bushings, right?

HMG37

iTrader: (1)

To reiterate, I put the Swift springs in at 18k, changed the OEM to KYB at 65K, and currently the car sits at 98k. Without anyone in the car, the car's stance looks normal, but with even with me in the car, every pothole or bump is jarring, and with even a single passenger in the backseat, the car starts tucking the rear wheels (eliminated wheel gap).

With people in the backseat, sometime it feels the back part of the car is not connected to the front when's its going over bumps. (not sure how to describe it).

Hugh Jorgens

Ok. Mybad. I thought the ride height was sagging.

Forget my comments about bushings sagging then.

Your shocks may be worn out. This has nothing to do with the ride height reduction when you load up the car. Your shocks can't control static ride height as they wear out. But they definitely do control how much the car bounces around while hitting bumps.

Obviously, you realise that the car is going to ride worse-than-stock with springs. But you're just trying to get back to the "acceptable" ride you had between 18-60K miles.


Start here:
How is the alignment? An alignment with toe being way out will cause a bad ride AND instability. Have them check the bushings for wear also.

Then look at the shocks. They're 33K miles old and they're being over worked by your springs. They're also easy and cheap to replace (compared to bushings).

Ultimately...your bushings are likely worn out. I'm betting this is a majority factor since they are the only constant for the last 100K miles. And if they were never clocked when the car was lowered...well...they're dead asf. Bad bushings also would explain your instability. But bushings are expensive and difficult to replace. If the alignment and shocks doesn't fix your issue....this is what you're stuck with.

Mikey997

Do you stilll have your wheels for sale in Allentown? That thread ended and could not respond on it