car vibrating bad

[olblu66]

Have a unique 427 WITH 400 MILES ON IT. IT HAS A 428 ENGINE.I dont feel safe in it over 60 miles per hour.Tring to keep up in atlanta traffic it vibrating pretty bad at interstate speeds. Around town its ok..0 to 55. As people pass me on interstate 85 , i probably look like im scared to death at 70 or higher,so i have to drop back down between 55 and 6o.Any one else have these problems. It was a turnkey car. THANKS .

[Aggressor]

I had a similar problem develop on route 81 about half way from Pennsylvania to Alabama. I was driving to the 2002 Homecoming and a severe vibration developed that started at about 45 MPH and limited my speed to about 55 MPH. A tire weight must have loosened and came off at speed. A precision rebalance in Gadsden saved the trip and allowed me to race the car at Talledega.
- Geary

[pgermond]

What wheels/tires do you have? At 100+ mine is like it is on rails.... at 70+ I hardly have to keep my hand on the wheel

Phil

427 Roadster, #4279436
Southern Automotive FE
3:31 and Toploader

Roseville (N.Cal)

[clayfoushee]

All Cobras are very sensitive to wheel and tire balance issues. All you have to do is visit CC and do a search to see how common the complaint is on all types. One problem is the cheap, crappy tires that are available in 15" sizes that we need. They are almost always out-of-round and hard to balance.

The only semi-good solution is to find a shop that has a Hunter 9700 machine that balances for "road force variation." It's not a perfect solution, but the best we have in the absence of decent 15" tires. Some people get lucky and get a good set of tires, but with the $80/tire POS stuff available, it's tough to get 4 good ones.

Clay

'98 Unique #9299, 427FE side oiler (452.1-stroker), top-loader (close), 3.31 rear

Annapolis, MD

[K.Wilson]

I would have to ask a few questions before I offered any advice.
Is it car speed related or RPM related? Does it vibrate the same in third gear as in forth at the same speed? Does it stop if you take your foot off the gas and push in the clutch? If it vibrates with the clutch in it should not be engine related and may point to wheel/tire.
Do you feel it in your fingers thru the steering wheel (front wheels) or do you feel it in the seat of your pants (rear wheels/driveline)?
The most common resonante frequency for tires/wheel vibration is the 55 to 65 MPH zone depending on wheel/tire size.
The most common engine balance related frequency is usually in the 1200 to 1600 RPM (or in frequency bands ie. 600 to 800, then 1200 to 1600 and 2400 to 3200) depending on the engine type. The most common brive shaft out-of-balance condition is usually in the 25 to 35 MPH range depending on rear end ratio.
Given your 55 MPH car speed it sure sounds like tire/wheel......
Keith

[olblu66]

Well i have Compomotive HB 15IN. WHEELS. Fronts are P245/60. Rears are 275/60. It is car speed related. Fine below 60.IT;S not the steering wheel and seat vibrating, it feels like the whole car is shacking.Do the wheels have weights on them?

[KrAzEcJ]

Weights? You had them balanced and theres no weights?

Unique 4279459

[casaleenie]

Probably put all the weights on the inside...
They have to be put on both sides of the wheel.. no way around it for a good balancing job...

AL
2899386

[dmiller]

my two cents.

drive at the speed, or a little faster, that the vibration is bad, depress the clutch, let the engine go to idle, if the vibration continues it is the wheel balance, or rolling stock.

if vibration stops, it is the engine or tranny. if engine/tranny, you should be able to duplicate the vibration at different road speeds by being in a different gear and maintaining the rpm that the vibration occurs.

doug

[clayfoushee]

All I know is that I've had 17" very expensive Y-rated tires and wheels on my car, which I sold to CJ. On those tires and wheels the car was glassy smooth. I now have 15" period-correct BFG TA POS tires (same sizes as you Blu) on the car, and it's not.

Before having them done on the Hunter 9700, they were terrible.........now they're tolerable. What the machine does is find the high and low spots on both tire and wheel and match them up as best as possible. Most balance machines don't do that.

Clay

'98 Unique #9299, 427FE side oiler (452.1-stroker), top-loader (close), 3.31 rear

Annapolis, MD

[eliminator]

quote:Originally posted by olblu66
Do the wheels have weights on them?

Yep, if they are balanced they would[:O][:O]

Rick
#4279405

[Brent]

In my many tire experiments over the last 6 months I have mounted and balanced (on the Hunter 9700) 7 sets of front tires.
2 pair BFG TAs
1 set Eagle GTII
3 pair American Racer
1 pair of Yoko Avid

I have seen road force variation as little as 3 lbs and as much as 93 lbs!!!

I must say at this point the Avids were almost scary as close as they were. The right front was 3 lbs and the left was 9 lbs both at 800lbs force applied.

You can actually zero balance a tire with 93 lbs road force variation and it will beat you out of the seat and try to wiggle the wheel out of your hand. I have seen tires that only took 2 ounces to balance to zero and would shake you to death. The Lexus dealer that allows me to use his machine told me that Lexus refuses to use any tire with a road force variation over 15 lbs. They throw it away!

Have fun


Brent
427 SC Chassis #4279401
Candy Apple Red/White
402 FE/Toploader/3.54

[gasman]

Brent, When is Tireguy ready with his tires?

Steve Foushee
Unique #4279389

[Brent]

??????????????????????????


Brent
427 SC Chassis #4279401
Candy Apple Red/White
402 FE/Toploader/3.54

[gasman]

Brent, The testing of the last set with the not as soft compound sounded like he was close based on your comments. Do you think tires will be available in the next 6 weeks?

Steve Foushee
Unique #4279389

[Brent]

I do not know.
He posted on CC that they finished speed testing and they will now carry a V rating (-:. He has finished the tread and sidewall hybrid compounds so that part is ready to go. He has purchased a Tire Uniformity machine to shave the tires perfectly round proir to shipping. He is also zero balancing the tires in sets. I know this does not answer your time question but it is all I have right now.



Brent
427 SC Chassis #4279401
Candy Apple Red/White
402 FE/Toploader/3.54

[souzape]

Brent - do you what sizes are going to be offered?

Phil Souza

[Brent]

295-50-15 and 245-60-15 for sure. Others I do not know.



Brent
427 SC Chassis #4279401
Candy Apple Red/White
402 FE/Toploader/3.54

[souzape]

Those are pretty big for those of use with 289 cars....hope he might consider 235/60/15 and 255/60/15s too.

Phil Souza