Vibration Issues between 75-90mph

FLA370Z

So I have searched around the forums and couldn't find anything similar to my situation. From around 75 to 90 mph I get this shake/vibration starting from the rear and like a wave moving towards the front....the weird part is that it will vibrate for 10 seconds then go away then come back for another 10 seconds at the above mentioned mph range continuously cycling. I was looking to see if anyone has gone through a similar experience and what their solution was. I will list potential problem areas that I have eliminated below do to recent service and checking:

1) I have aftermarket wheels and Michelin PSS tires (75%), all wheels were just high speed balanced and have the proper hubcentric rings on hubcentric spacers.

2) I have after market Stillen Sway Bars front and rear and all new SPL endlinks.

3) Checked the driveshaft U Bolt and seems to be fine

4) I don't know if this matters but I just changed the transmission fluid and diff fluid with the recommended Red Line products.

5) I'm on HR springs with adjustable camber arms, vehicle is fully aligned.

6) I have taken the lugs on and off a handful of times, properly torquing them down each time.

This issue started about 2 weeks ago and nothing has changed from a aftermarket part standpoint. My setup above has been like that with no issues running those tires and wheels and spacers etc.

The only thing that has been recently changed is the diff (75W90...2 Qts) and transmission (MT-85...3 Qts) fluid change but that went smoothly and I believe is unrelated but figured I would put all information down.

Any help/suggestions would be greatly appreciated, thank you.

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Stillen Gen 3 Intakes | Berk Test Pipes | FI 12''| Eibach Front & Rear Sway Bars | HR Springs | SPL Front/Rear Arms | ECUtek | Akebono BBK

elhombre

Did you remove the driveshaft and not mark its original place when you took it off?
Re-installing the driveshaft is its non native position will cause the shaft to be off balance and if it is off balance you will definitely get a vibration.

I had a similar issue with my cosmis MR-2's they would vibrate (from the rear) at around the same mph range as you. I switched back to my stock wheels and the issue disappeared.

I would definitely re-check the balance of the tires/wheels. The only way to really get a vibration that is speed sensitive is to have a rotating part hit its natural frequency and resonate.

It only took a few pot holes to throw my freshly balanced wheels out of balance.

FLA370Z

Thanks elhombre, I actually never took the drive shaft down I just looked to see if all of the bolts were still in place and after reading some posts on the forum looking for any leaks around that particular area. I haven't hit any potholes and this setup before was running very smooth, I will however have the tire shop re-balance all 4 wheels and see where that gets me, thanks for the suggestions.

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Stillen Gen 3 Intakes | Berk Test Pipes | FI 12''| Eibach Front & Rear Sway Bars | HR Springs | SPL Front/Rear Arms | ECUtek | Akebono BBK

rovert

Could possibly be wheel run-out relating to the spacers.
All the balancing in the world wont fix it if it is.
Jack each corner up & check each wheel at some point on the rim for run-out.
You will need a dial indicator attached to either the car or something that won't move.
Similar process to indexing a brake rotor.
You may be able to fix it with cleaning all the mating surfaces inc the wheels & indexing the spacers, or maybe not.
P.S. your spacers are trying to Kill you.

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08 Skyline 370GT SP Coupe 5AT: Diy TT

DOOMMONKEY777

Few things, cause that, incorrectly installed spacers or spacers inner bolts do not let the rim sit completely there's like a 2mm distance btw them. Tiers you have are old and dry and they are summer tiers they will bounce at high speed in below 55F.

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Kids don't do Drugs, Drugs are bad, so let the professional druggies do Drugs for you. 537whp/496lb/tq@8-9PSI 93 octane

crazy4oldcars

Possibilities:
Out of balance wheel, though that is usually noticable at any speed.
Out of alignment. This one gets my vote, if the wheels and spacers check out.
Busted belt on a tire. Like balancing, it's usually noticeable regardless of speed.
Fix-a-flat in a tire. Never ever use this crap. You can't repair the tire afterwards, and it leaves a chunk of crap in the tire that has to be removed.(Don't ask. I don't want to talk about it.)
Worn shocks or struts. #2 on my list of possibilities.
Good luck.


Kirk B.

jchammond

does it duplicate the problem in 5th gear?

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FLA370Z

Thanks for everyone's inputs, I actually cleaned all contact surfaces and traded out the rear spacers for another set (I had qty 4 but only use spacers on the rear). I also didn't use spacers and went for a highway run and still had the issue. This leads me to believe that the front tires may have some cupping, I ordered a new set of front tires and will keep everyone updated as to if it was the issue or not.

crazy4oldcars good point about the struts, i am on springs with stock struts. Worth looking into, plus it will give me a legitimate excuse to convince the fiance for me to buy more car parts (coils) lol

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Stillen Gen 3 Intakes | Berk Test Pipes | FI 12''| Eibach Front & Rear Sway Bars | HR Springs | SPL Front/Rear Arms | ECUtek | Akebono BBK

SpacemanF1

Did you try getting your tires balanced yet? You might have lost a wheel weight.

DOOMMONKEY777

Yes, this car is a Lemon we need to throw more parts at it.

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Kids don't do Drugs, Drugs are bad, so let the professional druggies do Drugs for you. 537whp/496lb/tq@8-9PSI 93 octane

JC-Nismo

Tires could be out of round amongst a host of other issues, but one sure way to find out is to put your stock wheels back on and see if the problem still exists. What size wheels and tires are you running?

FLA370Z

Front tires were the culprit due to an uneven/chopped wear pattern. Replaced them and got an alignment, now the car rides amazing. Thanks for everyone's help it was much appreciated!!!

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Stillen Gen 3 Intakes | Berk Test Pipes | FI 12''| Eibach Front & Rear Sway Bars | HR Springs | SPL Front/Rear Arms | ECUtek | Akebono BBK

FLA370Z

I'm 20x10.5 all around with 295/30 in the rear and 275/30 in the front

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Stillen Gen 3 Intakes | Berk Test Pipes | FI 12''| Eibach Front & Rear Sway Bars | HR Springs | SPL Front/Rear Arms | ECUtek | Akebono BBK