NAN777

guys,

i need some idea where to start looking for... i have vibration starting at the rear of my car.... it starts vibrating at around 180km/h but the moment i approach 210 km/h the vibration is really kinda make the whole car vibrate....

i've check my wheel balancing... but the vibration still there....i need some ideas where to start... drive shaft or what ?

cp1

i was thinking driveshaft too but on the other hand why are you driving that fast? id be more amazed if you told me everything seemed fine going 200!

RX7Crazy_84

iTrader: (1)

umm start from drive shaft then work your way to rotors(brake)! tell me this when you press your brakes does the car shake and vibrate at all??

DaveW

Could be a damaged or out-of-round tire... That would not be corrected by balancing.

advantagedent

wheels are not balanced at that speed ther set for 55mph at most.
find a race shop for real race cars ie. nascar champ thay can help you that might be it.

DaveW

When the tire dealer a the racetrack balances the tires for my and other racecars, which often see over 140 mph, they balance them at only a few RPM, equivalent to maybe 30 mph. If this is done correctly, it will not cause a problem. A tire properly balanced at a low speed is still balanced at higher speed. However, a small error in balance will definitely show up more at higher speed as the centrifugal force increases.

That's why I mentioned an out of round or damaged tire as a possibility, since he said he had the tires balanced. Whether they were done correctly, is another story.

EFS.O

Check the rear brake rotors for warping.

NAN777

tyres are new, it's balanced on the car itself.. not off wheel balancing...

yeah.. it sounds pretty dangerous... everything goes well until i hit 200 km/h

my brake doesn't vibrate when i'm braking down from high speed.. but when it's hot.. yes.... it's the front...the rear seems to be fine.... but yet i think i'll check on the brake rotors in detail....

i don't ignore the possibility of my gear box as well due to it's pretty worn out... difficult to engage some gears... free play became very tight sometimes etc...

checked with mechanics, they say if the long shaft / drive shaft bearing is worn, it'll be leaking oil everywhere... it's very less likely bent as well as they say it'll be very vissible even at low speed...

EFS.O

Check the rear brake rotors and dont forget to report back.

SLOASFK

iTrader: (5)

RX-7 gear boxes don't typically wear out. Other than the 5th gear synchro breaking, the gear box is very stout.

If you're having difficulty hitting gears, I'd suggest flushing the tranny fluid.

Like others said, check your rear brake rotors for warping. If that's not the problem, start checking suspension components.

DaveW

If this is done correctly, it's a great thing - all off-balance rotating components are compensated for.

However, there are a few drawbacks to this:
1. If tires are used in different positions on the car other than the corner of the car where the balance was done, any off-balance non-tire/wheel components will cause errors in the balance.
2. If the tire/wheel is removed, and then replaced, but not in the same rotational position ("clocking") on the hub, a situation similar to #1 will occur.
3. If the tire slips on the rim, balance will be off for any type of balance technique.
4. In my experience, the "on-car" balancers have never been capable of the same accuracy as the normal tire and wheel-only balancers, allowing small balance errors which will show up at higher speeds, as centrifugal acceleration increases.

rash_rvg

iTrader: (1)

why is that? the 7 is very stable at high speeds... Everything is fine when i'm at 300kms/h (no typo, 300!)

DaveW

Another thought:
Is there any chance one of the new tires has a manufacturing defect, causing force variations? The balance could be correct, but it would still vibrate at speed. While unusual, it does happen.

Dave

SLOASFK

iTrader: (5)

This makes me think...

What kind of tires do you have on the car and are they rated for this kind of speed?

LAXitives288

iTrader: (1)

200 kmh is only 124 mph. I don't think the rating is the issue.

SLOASFK

iTrader: (5)

M 81 mph 130 km/h
N 87 mph 140km/h
P 93 mph 150 km/h
Q 99 mph 160 km/h
R 106 mph 170 km/h
S 112 mph 180 km/h
T 118 mph 190 km/h
U 124 mph 200 km/h
H 130 mph 210 km/h
V 149 mph 240 km/h
W 168 mph 270 km/h
Y 186 mph 300 km/h


There are a lot of tires that shouldn't go fast. I wouldn't be so quick to dismiss, let the OP answer the question.

LAXitives288

iTrader: (1)

I didn't notice he was in Malaysia, you've got a good point there.

NAN777

okay...
tyres i'm using Toyo Proxes T1R, they are new... i think they are Y rated or Z rated...245/45 R17
even with my older tyre which is a smaller size... 225/45 R17 i also have the problem....

probably the tyre defect, rim problem or even absorber can be excluded...shocks are newly rebuilt.

i haven't check my rear rotors yet...i have an extra set that i can machine and put it in...stay tuned....

but i got my mechanic to check the bushings of my rears... just by shaking them... he found 2 piece is loose... if take out everything it might be more...
replacing them cost hell alot of money.... almost USD 80 per PIECE....

NAN777

the interesting part is that i fixed the issue....

the fix is.... replace my tranny.... got a JDM year 2000 tranny... no difference on the gear ratio except missing one sensor which the 16 bit ECU doesn't need....
and it's newer than anything outside which was made between 1993 to 1996...

i can go more than 200km/h without any vibration.... but around 230 km/h my rear wing vibrates... i'm using the 99 spec adjustable rear wing...probably i'm adjusting it to be giving too much down force that the wing itself vibrates at 230 km/h.

* don't try this at home... 200km/h is very dangerous