speed related vibration

[50tbrd88]

Hoping one of you experts might be able to point me in the right direction here...

I am fighting a vibration and would appreciate any ideas you guys could throw at me. Its not very noticable at speeds under 60 (where I do most of my driving) but rears its head the faster you go. At 70-80 mph its really bad. It is not RPM related at all, all speed related. It definately seems to come from the rear of the car.

The vibration started after I swapped to a junkyard Thunderbird Turbo Coupe 8.8 rearend (went from stock 2.73 gears to 3.73), changed springs (lowered the car quite a bit), and added CHE lower control arms. It has the brake rotors that came with the axle but I had them "turned" at my local NAPA.

I have done the following since the vibration started (some to try and cure the vibration, others just mods):

1.) rearend completely rebuilt, every bearing, etc
2.) I recently changed to T5 manual trans from AOD (including crossmember, trans mount, etc)
3.) new motor mounts
4.) tires rebalanced twice
5.) exhaust changed
6.) added CHE adjustable upper control arms and set pinion angle (I have had two shops go through the rear axle, one guy specializes in drag car/race car rearends and could find nothing wrong with the axle)
7.) changed u-joints
8.) cussed, stomped feet, turned red, hit things, etc
9.) took driveshaft to driveline specialty shop and had them check balance...balanced out 100% perfect
10.) put stock rear springs in, still had vibration

So I am at a loss...I've read that the two most common speed-related vibration problems are 1.) tires or 2.) warped/bad brake rotors. As mentioned earlier, I have had the tires rebalanced twice and the original TC brake rotors were "turned" when I swapped in the axle. Could the rotors be warped, bent, or somehow messed up enough to cause a vibration as described??

Any ideas? I don't want this thing to shake apart on HRPT...

HELP ME!!! lol.

[Barry Donovan]

how is tension of driveshaft, tranny to diff..
maybe too tight?

[50tbrd88]

how is tension of driveshaft, tranny to diff..
maybe too tight?

I just had the driveshaft out in last week or two to install the T5. Went back in easy, not tight or hard to fit in there at all. Good thought though.

[Huskinhano]

Was the T5 swapped before or after the rear?. I'm wondering if the rear trans bushing is worn? Recently I was reading a post about driveshafts on another forum. One of the guys was from Modern driveline. More specifically the post was about length of driveshafts and how far or close the yoke should be to the trans seal. The guy said if the yoke is too far out, it won't engage enough and cause vibrations. Maybe this could be the issue. Not sure how the length of the AOD compares to the T5. Maybe the T5 is a little shorter?

[brandontinley]

are the brake rotors seated all the way on the axles we had a guy bring in a mustang that had put on new rotors and then had a vibration. the rotor wasnt pushed on all the way it was hitting on the lip of the axle and therefor the wheel wouldnt go on all the way. its just a thought probably not it but hey worth a try

[50tbrd88]

Was the T5 swapped before or after the rear?. I'm wondering if the rear trans bushing is worn? Recently I was reading a post about driveshafts on another forum. One of the guys was from Modern driveline. More specifically the post was about length of driveshafts and how far or close the yoke should be to the trans seal. The guy said if the yoke is too far out, it won't engage enough and cause vibrations. Maybe this could be the issue. Not sure how the length of the AOD compares to the T5. Maybe the T5 is a little shorter?

The T5 is a brand new addition and was just swapped in a week or two ago. The vibration has been present for a loooong time before that ;) AOD and T5 shafts are supposed to be the same. I do know that when I re-installed the driveshaft, it fit almost identically as it did with the AOD.

are the brake rotors seated all the way on the axles we had a guy bring in a mustang that had put on new rotors and then had a vibration. the rotor wasnt pushed on all the way it was hitting on the lip of the axle and therefor the wheel wouldnt go on all the way. its just a thought probably not it but hey worth a try

I would hope they were seated correctly, but nothing would surprise me at this point. I plan to rotate tires/look everything over this weekend so I will check into that!

Thanks for the ideas guys, keep 'em coming. It has to be something simple.

[Scott Liggett]

Are you running big, fat rear tires? If so, how much weight did they have to add to balance them? If you have more than 3.5 oz in one area to balance them, they will vibrate at speed. Break the bead on the wheel, spin the tire 180* on the wheel, refill with air, rebalance.

Also, check your wheels to make sure they are not bent. One of my factory rallys on the Caprice is bent. Balanced fine, but wobbles enough at freeway speeds to get sent to the spare in the trunk.

[SuperBuickGuy]

check your drive shaft angles - I'd bet the angle at the rear end is 0 degrees..... normal problem in lifted 4x4s the solution is to put some angle into the rear yoke. Ideally the angles will be complimentary and more then 1.5 degrees

Also, check your motor mounts. I had a drive shaft problem that was solved with new motor mounts.

[Bamfster]

check tires for separated belts, if you move rears to front and back to front,does it change? Does any one wheel/tire have a lot more weight on it than the others?

[TC]

The vibration started after I swapped to a junkyard Thunderbird Turbo Coupe 8.8 rearend (went from stock 2.73 gears to 3.73),

This alone would be what I'd be looking at. IMO you have a bent axle........Not the housing, but the axleshaft itself.

IF rotating the tires doesn't move the vibration to the front of the car that is probably what it is......

[88pony]

This alone would be what I'd be looking at. IMO you have a bent axle........Not the housing, but the axleshaft itself.

IF rotating the tires doesn't move the vibration to the front of the car that is probably what it is......

I tend to agree. When I did my junkyard 5-lug swap, I went back twice to get a good axle shaft. I ended up buying new. The shaft itself were straight but the flange at the end wasnt square. Maybe it was just Fords '80s tolerances? I wasnt a terrible vibration but the tire and wheel wobbled. The most annoying part was the drum and shoes were not square to each other and at low speeds I would always hear a squeek.
When I changed my mustang from aod to t-5, I got another driveshaft with the swap. The manual shaft was only about 1/2 inch shorter but the front yoke doesn't have the damper on it.
Is the vibration a slow one or fast one? Does it stay constant at a set speed or does it come and go withen a few seconds? Do you feel it in your seat, the steering wheel or even the gas pedal?
Also check your trans mount along with the motor mounts.

[SuperBuickGuy]

Hoping one of you experts might be able to point me in the right direction here...


The vibration started after I swapped to a junkyard Thunderbird Turbo Coupe 8.8 rearend (went from stock 2.73 gears to 3.73), changed springs (lowered the car quite a bit), and added CHE lower control arms. It has the brake rotors that came with the axle but I had them "turned" at my local NAPA.


HELP ME!!! lol.

Here's why I think it's just an angle problem with the driveshaft - when you lowered the car you made the driveshaft either this perfectly flat, or put both u-joints angled the same direction (would look kind of like an n)..... really easyish to fix - get adjustable upper control arms or redrill the holes in the upper control arm to rotate the axle where the front U joint is at a +1.5 degree angle, and the rear U joint is at a -1.5 degree angle.

[50tbrd88]

Thanks for all the replies, fellas.

check your drive shaft angles - I'd bet the angle at the rear end is 0 degrees..... normal problem in lifted 4x4s the solution is to put some angle into the rear yoke. Ideally the angles will be complimentary and more then 1.5 degrees

Also, check your motor mounts. I had a drive shaft problem that was solved with new motor mounts.

Here's why I think it's just an angle problem with the driveshaft - when you lowered the car you made the driveshaft either this perfectly flat, or put both u-joints angled the same direction (would look kind of like an n)..... really easyish to fix - get adjustable upper control arms or redrill the holes in the upper control arm to rotate the axle where the front U joint is at a +1.5 degree angle, and the rear U joint is at a -1.5 degree angle.

That was my thought at one point, but I did install adustable upper control arms and set my pinion angle just like you mentioned. Very little change in the vibration after doing this.

I put new motor mounts in last year with no change at all (I even had TWO broken motor mounts).

This alone would be what I'd be looking at. IMO you have a bent axle........Not the housing, but the axleshaft itself.

IF rotating the tires doesn't move the vibration to the front of the car that is probably what it is......

You might be right. I am going to get the wheels off this weekend and try to look for any problems with the axle shafts. I still have the original 7.5" rearend and I believe the axle shafts are the same, so I may be able to just swap axles if that is the problem.

[50tbrd88]

I tend to agree. When I did my junkyard 5-lug swap, I went back twice to get a good axle shaft. I ended up buying new. The shaft itself were straight but the flange at the end wasnt square. Maybe it was just Fords '80s tolerances? I wasnt a terrible vibration but the tire and wheel wobbled. The most annoying part was the drum and shoes were not square to each other and at low speeds I would always hear a squeek.
When I changed my mustang from aod to t-5, I got another driveshaft with the swap. The manual shaft was only about 1/2 inch shorter but the front yoke doesn't have the damper on it.
Is the vibration a slow one or fast one? Does it stay constant at a set speed or does it come and go withen a few seconds? Do you feel it in your seat, the steering wheel or even the gas pedal?
Also check your trans mount along with the motor mounts.

This vibration is what I would call fast. It gets worse as you increase speed...really gets noticable between 65 and 70 mph and gets a little scary from there on up. Crusing around on the 2 lane roads we have where I live at 55-60 mph its not that noticable. You definately feel it in your seat, not in the steering wheel at all, and maybe some in the gas pedal.

[50tbrd88]

Are you running big, fat rear tires? If so, how much weight did they have to add to balance them? If you have more than 3.5 oz in one area to balance them, they will vibrate at speed. Break the bead on the wheel, spin the tire 180* on the wheel, refill with air, rebalance.

Also, check your wheels to make sure they are not bent. One of my factory rallys on the Caprice is bent. Balanced fine, but wobbles enough at freeway speeds to get sent to the spare in the trunk.

Tires are not fat by most folks standards, lol. 245/45/17's, but they are waaay fatter than what was stock (215/70/14). I have not been happy with these wheels since I've had them. They are Cobra R replica's and are very cheaply made (and heavy). I have had them rebalanced twice by two different shops...but I really doubt if they took the time to break the bead and move the tire on the rim.

I'm going to rotate the tires...I think I tried that very early on and the vibration stayed to the rear of the car. They are due to be rotated so its worth a shot anyway.

I wish I had another set of wheels/tires to try out and see if anything would change. My original 14" wheels will not fit over the brake calipers since I converted to disk on the rear and swapped Mustang front brakes on.