My seat violently shaking at fast speeds after 70mph

[BLADDER92FOX]

2 weeks ago i bought 2 used like new rear tires for my car sizes 275-40-17 like the ones i had before but differrent brand. a day after that when i got on the expressway and i was going past 70mph i got this very annoying shaking going on in my car that felt like the rear and my seat were violently shaking. Could it be that they forgot to rebalance them?? Also tires do sometimes vary in size and width from manufacturer,these tires where a little wit wider than the last ones also. Or could this be my drive shaft that needs alignment??? Although my drive shaft is aluminum and i got it new about 3 months ago,could it not have been balanced?? I also have 4.10's in the rear and swap the aod to t-5 but it didn't shake before before i got the tires. Anyone have a clue?This violent vibration makes the car seem like it shaking side to side and my door panels even shake now and my seat vibrates soo much it makes me dizzy.

 

[Darkwriter77]

Ideas:

1. Tire(s) has thrown a wheel balance weight off;
2. Tire(s) may have a radial belt coming loose within the tire;
3. Driveshaft may have thrown a weight off (hard to imagine, though, because I'm pretty sure they weld those puppies on there);
4. U-joint(s) may be failing;
5. If you have one of those weird driveshafts like on some 4-banger models, the rubber vibration damper may have separated from the driveshaft and it's twirling around on there like a donut on a cop's finger ... but I'm pretty sure you'd have a lot of noise coming along with it, if that were the case.
6. Your car is angry that it has not yet received an aluminum driveshaft after you swapped in the 4.10's, so it's going to be fussy until you satisfy its demands. (Seriously, if you're running a stock steel shaft with 4.10's, I'm surprised you never had much for vibration issues before now.)

 

[BLADDER92FOX]

I did get under the car and shake the driveshaft to the side hard and it didn't seem loose nor did the bolts look loose.It is aluminum btw from Ford Motorsports .I wonder if it some got unbalanced. I'll see soon enough when i go to the shop,anyone know how much it cost to rebalance it in case it needs to be balanced?

 

[ShortThrow50]

Hmm. seems like you answered your own question. You said you bought some used tires and the day after you put them on you developed problems. It only costs like 5 bucks to have the tires re balanced at any gas station

 

[Darkwriter77]

Five bucks to balance them? Not 'round here ... more like $40, last time I did it. But then, I guess it'd be cheaper if you just took them off the car, yourself, and rolled them into the shop (no mount/dismount fee)...

 

[jballa]

Darkwriter is right on.... I sold tires for 2 years at a high end tire store and so many times people bought used tires and instantly had problems. The tires wear to the car that they're on and usually have a reason as to why the person who used to own them took them off.

My guess is that either

1. A belt is seperating
2. The tires are feathered from the previous vehicle's poor suspension and will never get better
3. The person who balanced them had no clue what they were doing
4. a weight fell off.
5. You bent a rim around the time the tires were put on and the tech didn't tell you.


In any case, I would try to rebalance first and if that didn't work buy NEW tires. I found that the Falkens 512, Dunlop SP5000, and the Sumitomo HTZ are the best buys for the money. Miles, traction, and appearance with a good ride.

 

[ShortThrow50]

Five bucks to balance them? Not 'round here ... more like $40, last time I did it. But then, I guess it'd be cheaper if you just took them off the car, yourself, and rolled them into the shop (no mount/dismount fee)...

Well here in pa, i took my last 2 tires to sunoco on a sunday and the dude behind the counter took them in the garage and did it free of charge and i didnt even know the guy. I tried to tip him and he wouldnt accept it. 40 bucks is absurd man

 

[91stalker]

Have you noticed any pull since you put the two tires on? When a tire belt seperates, the tire will usually become larger in diameter, causing a pull, but it might be hard to feel if they are on the back. What size are your wheels - factory bullitt wheels? might be too wide of a tire for 8in wide wheel. Did the shop use stick-on weights or hammer on? Sometimes shops wont clean off the inside of a wheel good enough to stick the weight on and they can fall off. All just ideas.

 

[BLADDER92FOX]

I just checked my rims now in the back and it looked as if they had a stick on wieght and it fell off,i see the paper peel of some sort.Plus if i remember corectly,i had hammer weights on there before,and i don't see and weights on either rim,they must have fallen off. My rims are the factory 2002-2004 bullit rims 17x8. I've always had 275/40/17 since i've had the rims on the car,i bought the rims with tires from a friend a year ago. Also the used tires i got have a ton of thread,they look almost brand new too. I hardly been driving the car lately so all this time i hadn't checked the rims for weights. When i go rebalance them i'll make sure they take the tires off and look at them inside also to make sure the belt is good. Good thing its next to my house and i know the guy too.