weird vibration??? can't figure out-

[bradass31]

Hey guys, I've had my 93 cobra for about 3 years now and love it- when i first bought it i opened it up a few times to around 140 or so out on the highway and it was always really smooth. last year i put new tires on it (bfg's) and as soon as i left it was vibrating really bad around 75mph. I took it right back and they balanced the tires again and then it started doing the same thing around 100mph, but i didn't have time to go back right then. I ignored it for a while and now im trying to figure it out. I had the tires balanced several times at several different shops. I thought the tires might have a slight wabble to them because nothing changed. So I replaced the tires AGAIN- and it's still doing it, the vibration is not in the steering wheel its more in the shifter like its something to do with the drivetrain. I pulled my drivline, put in new U joints and had it balanced and nothing changed??? I'm stumped... I was almost positive that it had somthing to do with the tires or my drivline but after changing them again and having the drivline balanced I don't think that any of that is the problem. Has anyone had any similiar problems?

Also I just bought another fox '88 hatch that basically has the same vibration in the shifter.. only it's around 80??? does anyone know if fox bodies have a notorious drivtrain vibration of any kind??

any thoughts or advice would be great! thanks guys-:shrug:

 

[Kevins89notch]

have you checked the driveshaft yet?

 

[#1pony]

I still have the same problem in my Cobra. I have had the tires balanced, drive shaft balanced, u-joints checked, and it still happens around 75-85 mph. The only thing I can think of is maybe the input shaft on my transmission is bent, or something related to the transmission???? My vibration is coming up through the shifter as well.

 

[blownfox]

I had the same problem and when I did a tranny swap with a new driveshaft it went away. I guessing it was the driveshaft.

 

[bradass31]

yeah- its gotta be somthing with the tranny or driveshaft- but i don't think its the driveshaft... I need to find a shop that can balance the driveshaft at high rpm- I belive the machines normally used don't go spin very high so a slight wabble would be undetected. someone else thought i might have a bent axle but i don't think thats it either- its just really weird that it "all of a sudden" started doing this-

 

[cobra186]

Check your driveshaft for dents... maybe the shop damaged it while swapping out the tires.

The output shaft in the transmission has a bearing/brass bushing in the tailhousing that wears out over time and will cause a vibration. Check to make sure your driveshft has no play when its slid into the tranny. If the yoke moves up and down any then that bushing is worn too much.

If the input shaft bearing is worn it will cause too much free play in the shim stack and could cause a vibration.... usually you will have a whine coming from the trans also if this occurs.

Worn bearings in the rearend, especially the pinion bearing, could cause a vibration... but you will usually have a whine if they are worn badly.

Lastly... most tire shop these days don't balance tires correctly either. The machine is only as good as the operator controlling it. A roadforce balancer would be your best choice if anyone in your area has one.

 

[bradass31]

thanks man- so to replace the bearing/bushing in my tranny will i need to totally gut the tranny or can i get to it all from the rear? basically is it somthing i can do myself or will i need to have it done? Ill need to get under there and check for play but i don't think there is much- driveshaft looks good though- no dents. ill try to call around and ask about the roadforce balancing too-

 

[cobra186]

The bushing in the tailhousing can be taken out 1 of 2 ways.

1) They make a special tool that can reach up inside the tailhousing to pull out the bushing.... but from what my transmission guy says they often do not work.

2) Remove tailhousing from the transmission and then you can drive the old bushing out & install a new one. This requires you to pull the tranny out of the car so that you can remove the housing.

 

[red95gts]

And if you're going to pull the tranny out, it would be the perfect time for a rebuild. Or, at the very least, re-shim the input bearing to compensate for bearing wear over the last 16 years.

 

[kcp203]

I know that many people with Fox mustangs have had similar problems over the years, and most times it was fixed by swapping for the FMS aluminum driveshaft. I don't know why the stock units are so hard to balance right.

 

[bradass31]

thanks guys- ill probably pull the tranny and replace that bushing and see what happens- it doesn't feel like theres very much play but i think its a good place to start untill i can get it figured out.

 

[Blaine@PSI]

I know that many people with Fox mustangs have had similar problems over the years, and most times it was fixed by swapping for the FMS aluminum driveshaft. I don't know why the stock units are so hard to balance right.

same here. i had the vibration and switched to aluminum driveshaft, all vibration is gone and i can drive the car at 90mph cruising with no problems.

one other thing you might check is the balancer on the front of the motor. if you speed shift the car it can cause the rubber to squeeze out and become unbalanced and you will feel it thru the drive line.

 

[sled]

I know that many people with Fox mustangs have had similar problems over the years, and most times it was fixed by swapping for the FMS aluminum driveshaft. I don't know why the stock units are so hard to balance right.

yeah, this is true. I don't know why they start to do this, but I've had 3 fox bodies with this problem and the FMS aluminum drive shaft has solved the problem everytime. I believe it actually has to do with the rear. The aluminum shaft dampens the virbration from the rear.

 

[93Cobra#2771]

I'll wager 1/2 of the 5.0 fox bodies all had the same problem as you describe. Some were born with it and had entire drivetrain swapped out and STILL had the problem. I'm convinced it wasn't a single thing causing the event, it was a bunch of little things that add up and cause the event.

The FMS alum. DS usually cures the issue, but not always.

 

[drkhrse]

Mine had this problem~75mph after I changed the rear control arms (mac). After a long battle trying to figure it out it ended up my pinion angle was wrong. I replaced the upper arms with adjustable ones, set the pinion angle and it now performs great.

 

[bradass31]

yeah its really weird- you guys have all given me some good places to look- thank you all very much. I had another guy tell me that it could be my bearings and/or my 5th gear going out but i don't think so-

 

[psycholx]

Any luck on this?