Bad Vibration at high speed

Hi all,

I have been dealing for a while with a bad vibration at around 70 and up mph. The vibration seems cyclic because sometimes it runs smoother than others I even noticed that sometimes when going down hill itstarts vibrating suddenly and intermintently like: Smooth....prrrrt......prrrrt.....prrrrt...prrrrrrrrrrrrrrrrrt!!!!!

I did the press and release clutch test while running and the vibration changes just a little bit and when speed up and put the tranny in neutral still vibrating very bad. Going troubleshooting this problem I did the following: NEW TIRES BALANCED, NEW WHEEL BEARINGS, NEW FORD RACING 3.55 GEARS AND ALL NEW REAR END BEARINGS, STRAIGHT REAR AXLES, NEW U-JOINTS, STOCK BALANCED DRIVE SHAFT, CORRECT PINION ANGLE....WHAT ELSE??????

So from the yoke back is either new or balanced, I notice some in my opinion excessive lateral play on the yoke which coud be a bad yoke or output shaft but they told me at a transmission shop is not that bad....??

I can feel the vibration on my shifter/console area but also on the rear. the flywheel is a new FRPP cast and was balanced bufore I installed it. So basically the only things left to check are the clutch assembly (which is new) and the transmission itself. I noticed that the transmission makes a weird bumping noise when in idle and when the RPM's are on the low side.

What do you guys think? Please post your comments or ideas because I'm getting really frustrated as I have none or very little improvements after all the repairs I've been done.

Nick

Thanks for posting your ideas and following your suggestions I tell you that reving the engine it runs really smooth new motor mounts and poly transmission mount and cross member bushings, and I already turned all four rotors.

It is hard to determinate if the vibration happens at low speeds too but as I increase the speed from ~ 65 is when I start noticing. The transmission don't whine and shifts smooth. The only abnormality on the transmission in my opinion is the weird bumping noise at low idle, it sounds like excessive backlash or something like that but it definitely comes deep from the tranny. I dial indicated the drive shaft and the ends and it is not a lot of run-out. I also run the car while sitting on wide nice stands and there is a lot of noise right inside the bellhousing.

Believe me I'm totally stumped!!! I have poly front control arms bushings, tubular rear LCA and adjustable UCA. I expected road noise but don't think that's causing the vibration. Or it will????

Please bring all your comments and or suggestions because like you may imagine I'm totally burned out!!!

Nick

Ok I'm not too sure which one is the balanced shaft. Are you talking about the input or output shaft?? Or is another shaft?? As far as the tie rod end or any other part on the front is i think out of question, but I certainly appreciate your ideas. The steering is nice and quiet at any speed and the vibration happens even with the car sitting on stands. The vibration has to be on the drivetrain somewhere in between the flywheel and the first u-joint. WTF!!! I'm sooooo pist!!!! Any more ideas?

Thanks, Nick

By the way the clutch is a spec-2 and I might have to replace. Does anyone can guide mo on that? I mean which clutch? I've been thinking on dual friction Centerforce, any issueswith that one? I think I read that they need a special flywheel because it just won't work with the cast iron stock one. But before that I must find and correct the vibration, so please keep bringing some more comments, ideas, and or suggestions. I will really appreciate all your help.

Nick

New motor, tranny bushings. New tranny crossmember bushings and the tranny tailhousing bushing was pressed not that long ago although I noticed a bit too much play at the output shaft but again they said at the shop it is normal so I'm going to have to take the tranny down and have them inspected and maybe relace the clutch assembly pilot bearing and even maybe the rear main seal....DAMN IT, IT IS A LOT OF WORK!!!! But I guess I have no other options.

Nick

Sorry, yes I clocked the drive shaft at the pinion and found that the vibration gets worst so went to the position with the least vibration.

Nick

Thanks 93 5.0 GT!!! I think I'll buy that one, I heard it is a great clutch.

Nick

No I'm sure they pressed the bushing I put the seal myself, but maybe you are right about the bushing being bad an the only explanation for that is that maybe they even pressed the wrong ID bushing. I didn't think about that possibility... Darn it!!!! Thanks again for your ideas.

Nick

Hi all,
I want to share with you some findings and maybe throw a question after.

As a trubleshooting measure I ordered a FRPP aluminum drive shaft from Jegs which blead me 250 bones. A few minutes ago I lifted the ride and let it sit on a set of ramps on the front and a stack of four 2x6 on the rear, I wanted to somehow check the pinion angle and I did it!!! For this I used a digital level and following a few ways posted on the net I decided to give it a shot.

I put the level vertically at the front of the crank pulley and zero the level this way I didn't even have to make any calculations. I then placed the level on a tinny lip of the pinion flange. I say tinny because I didn't remove the drive shaft but I was able to sit the level flat on that little wedge.

My initial reading was between negative 2.3 and 2.5 degrees so I decided to reduce the angle by turning my adjustable upper control arms to approximately minus 1.3 to 1.5 degrees. Locked all the nuts, dropped it and took it for a spin........

SURPRIIIIISE!!!!!!!!!! Most of the vibration is gone!!!!!!!! It rides much, much, much smoother and I'm still going to install the new aluminum shaft.

The new shaft will be here next Wed. but I will double check the pinion angle after I remove the old shaft, this way I will be more certain I have the absolute angle measurement. I'm very happy because I finally see some results after all the troubleshooting as you read at the begining of this thread

Now my question for all of you is: What will be the minimum pinion angle I can run???? I've been reading about pinion angle and it is not recommended to have zero angle, and we all can understand that zero angle means straight line and straight line means NO vibration, but also we understand that the suspension defflects whill which will induce positive pinion angle under acceleration(NOT GOOD!!!).

So what will be the minimum pinion angle??? Details of my rear suspension are these: Tubular lower control arms (Polly bushings at the body and solid bushings at the axle) and Adjustable uppers (Solid bushings at the body and polly bushings pressed in the axle ears). I have no idea how much deflection happens under acceleration with this set up, se please if someone has this or similar rear suspension as mine how much negative pinion angle should I use to have the least drivetrain vibration.

Thanks a lot for the help, Nick