Vibration at 90+ MPH

merc123

merc123

Active Member
Jan 27, 2003
420
2
39
North GA
#1
When I was at the track there was a strong vibration that came in at about 90 and stayed with it up until 100 or so. Once it got below 90 it stopped.

It felt like it was shaking the whole rear end of the car but nothing in the steering and couldn't hear much driveline noise. Reading posts on here I'm assuming with the new 4.10's I'll need an aluminum driveshaft or stay below 90?
 

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#2
That seems to be a common culprit. I haven't had my car over 85 since I got 4.10's, so far I have no excessive vibration. The cheap thing to check first would be the balance of your tires, before going out and blowing money on an Alum. driveshaft.
 
#3
Wheel weight fell off? Bent rim? Who knows. Mine vibrates in the front past 50+. It's slight but aggravating. I think my rim is bent a bit. I already had the tires rebalanced, etc etc etc.
 
#4
The driveshaft may need to be balanced for the new rear end. It was probably fine with the stock rear setup. I'd take it to a shop that can do that and go from there. It will surely be cheaper than buying an aluminum driveshaft.
 
#5
I need new tires all the way around so that could be it too. Since I don't regularly hit 90 MPH I can't really see it as a big problem...especially with the new super speeder laws that add $200 to any ticket if you are over 85...

I was thinking they were only about $200 for the aluminums...not so much. I can't believe the $700 price tag for the 05+ ones!
 
#7
It's possible it's the driveshaft nearing "critical speed" and if it is you definitely want to stay away from the vibration as it can damage the output shaft bushing of the transmission.

If it's focused at the back of the car you might have a wheel weight off or the driveshaft was damaged when it was removed for the gears. Might want to get under the car and check the D/S for dents, missing weights etc.

Also check to see if there's marks (like grease pencil) on the differential yoke that the installer would have used to install the shaft in the same position it was removed. If not, you might consider taking the shaft out and rotating it 180-degrees and re-installing it.

Do you still have the vibration damper weight on the rear axle housing?
 
#8
bhuff30 said:
You said that you went to the track and didn't even bother to tell us what you ran? :notnice: :(
Click to expand...

There wasn't anyone around to give me my time :D

trinity_gt said:
It's possible it's the driveshaft nearing "critical speed" and if it is you definitely want to stay away from the vibration as it can damage the output shaft bushing of the transmission.

If it's focused at the back of the car you might have a wheel weight off or the driveshaft was damaged when it was removed for the gears. Might want to get under the car and check the D/S for dents, missing weights etc.

Also check to see if there's marks (like grease pencil) on the differential yoke that the installer would have used to install the shaft in the same position it was removed. If not, you might consider taking the shaft out and rotating it 180-degrees and re-installing it.

Do you still have the vibration damper weight on the rear axle housing?
Click to expand...

When I reinstalled I didn't mark the drive shaft (rookie mistake) but it had a yellow mark already on it assumingly from the Ford tech that did it the first time. I just lined the yellow mark back up. I do still have the damper weight on the rear axle. Going to check yokes and stuff this weekend just to be on the safe side.

Starting to wonder if it's leaking somewhere too because it looked like there were some stains in the parking lot of the apartment...just can't tell if it's from mine. Had some residue on the outside of the cover, especially around the bearing cap bolts (aftermarket cover).
 
#13
I would suggest the aluminum driveshaft and a driveshaft loop even if that doesn't solve your problem. I'm guessing at the speed you are running around 5000-6000 rpm's. I never noticed the problem and I had the driveshaft running at over 5000 rpm's at speeds from 130-160. However, I for safety reasons, I changed over to a balanced aluminum driveshaft with the loop.

It's possible you just hit resonant frequency on the driveshaft which means faster failure if you stay there plus possible increased wear on the bearings and u-joint. Change it.
 
#14
It was about 3500 to 4000 RPM. I can't feel the vibration at that RPM in any other gear. I think it had to do with the speed. I've got some new tires coming so I'm going to get them balanced and see if they make a difference.
 
#15
It's likely the driveshaft being over-spun and becoming unbalanced due to the gears.

I didn't notice it last time I went to the track (trapping 109mph), but at one point I was at 120-125mph and all of a sudden it felt like the car was about to come apart. I let off real quick and never approached those speeds again, at least until I replace or re-balance the shaft, check the u-joints, etc.
 
#16
Question? Did you remove the "dog bone"?

How about excessive play/slop in the U-joints?

However, I agree with the other replies that the drive shaft could be out of balance. Possibily due to it not being installed in the same way it was removed.

There is a procedure in the Ford service manual to find the "sweet" spot for the drive shaft. I won't lie. It's a PIA. I involves using a pair of screw clamps and rotating around the drive shaft. By trial and error, the best point to add weight can be determined.
 
#17
wmburns said:
Question? Did you remove the "dog bone"?

How about excessive play/slop in the U-joints?

However, I agree with the other replies that the drive shaft could be out of balance. Possibily due to it not being installed in the same way it was removed.

There is a procedure in the Ford service manual to find the "sweet" spot for the drive shaft. I won't lie. It's a PIA. I involves using a pair of screw clamps and rotating around the drive shaft. By trial and error, the best point to add weight can be determined.
Click to expand...

If you're asking me in response to my post:

Yes, the dog-bone is gone from the differential. It actually removed itself partially at 55mph, I helped it the rest of the way before it became a projectile.

I haven't checked the u-joints for play, but then again I haven't driven the car in over a month unfortunately. It's dead for at least another week or two.
 
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