black38

iTrader: (1)

I completely agree.

interesting about the driveline and the dyno. For someone who has never dyno'd a car to try and diagnosis a problem. How would you be able to tell?

Resmarted

iTrader: (2)

Well for our cars you don't need to spin the front wheels at all. So putting load on the driveline and taking the vehicle up to speed you'd have the entire driveline loaded up, but not the front end. If you have vibrations you know it has something to do with the driveline, and not the front end. If you don't, well it's likely either the front end, possibly suspension related or maybe even aero.

I honestly can't tell what exactly is this vibration, because the description is a bit vague.

You could probably call around dyno shops and explain what's going on and ask for a discounted price on a dyno run. Or maybe ask if you have them do the dyno for free, you'll pay for labor for them to fix or something. Depends on the shop, but some shops might be sympathetic and be happy to help for peanuts, and some might try to charge. Just make sure you explain the car has no leaks, is stock, and has a minor issue and what you'd like to do.

black38

iTrader: (1)

that sounds like a plan, i appreciate the insight.

scheduled dyno time.

said he'd seen this before and is betting its a rear shock

Resmarted

iTrader: (2)

Right on. Hope it's blatantly obvious and a straightforward fix!

difranchise

My 06 Base with 58k has the same problem. Most shops only balance to 60mph and my guess is the rear tires are not balanced properly. I have not done it yet but I will be paying a shop to balance at a greater speed. Then go from there.....keep us posted.

difranchise

I don't know, the more I read the more I think it may be a driveline issue. UV, or CV joints perhaps. Like someone mentioned before (and I will try this today) we should probably try to get it up to speed and then put it in neutral to see if it still vibrates around 80mph. If it does not than there is a good chance it is driveline.

I will post my results from this test asap...

black38

iTrader: (1)

i've done it and it seems like the shake is still there.

I never tried to take into account the wheels might only be balanced to a certain mph...

i've got a feeling my car is something more than a balancing issue.
I've had 3 shops balance the wheels 5 times...surely someone would've lucked into getting it right once.

difranchise

Black, I agree with your note.

So I tested the vibration on the way home yesterday. The vibration in my car feels in the seat of the pants and throughout, when above 80mph.

I accelerated to 110mph, put it in neutral, and let it coast without touching the brake. It seems the vibration is worse than I thought. It vibrates and stops every other second. All the way down to 70mph.

I am led to believe it is a bent wheel, or misbalanced tire because the vibration is from the rear and only at certain mph. I think based on this test I can rule out the UV joint but not the rear axle. What do you think?

This weekend I will attempt to have the tires rebalanced at a new shop to see if it fixes the problem.

My other thoughts are that the wheel was not seated properly on the hubs, or an axle issue.

black38

iTrader: (1)

sounds like we have very similar issues.

Im taking mine to a shop tomorrow morning and will be dyno'ing it and taking the rear wheels off to have a look.

I went from 285's - 275's on the rear (10.5 rim) but it seems like a lot of guys are running the same size so i cant imagine that being the issue

Resmarted

iTrader: (2)

I have 10.5" wheels with massive 305 tires. Never had a problem. I don't think it's your wheels at all.

black38

iTrader: (1)

So its not the wheels.
Threw it on the dyno and it looks like the right rear is tracking very weird.

So i have a interesting thought. When I got my rotors and pads changed, when getting them mated it took longer for the right rear (the one thats tracking weird) to get full contact. Could something be loose or not right when they change the rotor and pad that is making the tire track weird?
The more i think about this the more I don't see it but thought id throw it out there.

I just can't believe i got two bum tires on a brand new set.
The wheel was turning true. (this was also looked at by the shop owner as well as myself. (I trust him and not me)

Cookiezor

do u mean the wheel was turning true while on the dyno? what if its not aligned good, like toe in or something, when u strapped the car down to move it, u used frame as anchor points not suspension components right?

Resmarted

iTrader: (2)

If the dyno operator is even half competent they didnt use suspension components to strap it down


I dont really understand the rotor question to be honest. Rotor shouldnt be causing the problems you're having. If the tire is out of round call whoever you got it from. Tires do have shelf lives. And if theyre stored improperly they can go out of round.

Cookiezor

You sir, have misunderstood me. He trailered the car cross country. so i'm asking if he strapped it down right that time.

black38

iTrader: (1)

the car wasnt strapped down on the dyno at all.

on the trailer across country it was a uhaul trailer. So they have straps that go around the front wheel only

difranchise

I did not have a chance to get my tires/wheels balanced this weekend. I will put it on my list.

I find it odd (as I pay more attention) that my car does not seem to have these symptoms every time I drive it. The problem is there.....but not always, if that makes sense.

The only thing I will do is balance and or align all four tires/2 axles. As the long as the issue does not worsen I will just wait until I put new rubber on because I hate the tires I have. The A-hole salesman at my old dealership put shitty goodyear eagle 285-40-18 and 245-40-18 on the car. The sidewalls are weak as sh** and cornering is terrible. Never trust a salesperson with tires, why the hell would anyone put an all-season on a Z!?

Resmarted

iTrader: (2)

Lol why don't you tell us, seeing as you paid for them?

Get some R888's. You'll never go back to normal rubber again (until you go broke). JK Take a look around this site. Get a summer only tire, something soft with low tread wear rating. I love r888's but they don't last and are expensive. Sidewall is super stiff though. Tires you really do get what you pay for, unless you get a deal. A good tire will reduce braking distances, help acceleration, and make the car feel sooooo gooood on the road.

difranchise

I would consider a tire like the toyos if I tracked.....but currently I do not.

Currently I am considering the S04 of RE760. If I can pick a max summer with hard sidewalls I will be happy. Also, My Z is used in the summer and stored at least 4-5 months a year. It is Ohio, so we do get rain for a few summer months. Otherwise an 888 would be nice.

bgood

iTrader: (10)

i had this same issue. i changed everything. wheels, tires, suspension control arms. i would up selling the car, but on my race car i has a similar issue. strange vibration that would come and go at sustained speed, and get worse the faster i went. on the race car it wound up being my diff pinion angle was out of line with my trans pinion angle. i shimmed the diff and the vibration is gone. now i get the car up to 150mph and everything is fine. i would check your Diff bushings. on my Z the front diff bushing was warn. it would be something i would check.

Resmarted

iTrader: (2)

Out of defense of the r888; they are actually really good in rain, they're bad with standing water. Some people run them as a rain racing tire actually. R888's don't like cold. But you could probably get 10-15k out of them easily on the street provided no burn outs or hooning. There are a few nittos I'd buy first though for a stock car. Nt05 or most likely an Invo or something like that. Nt05 would probably be overkill. A lot of people like invos.