Vibration when decelerating. - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars

fairmont1998 · 07-21-2004, 05:34

Need some info guys and girls.

My car, an EL Fairmont 5L V8, has developed a very slight vibration in the past few weeks.

I have a theory.

Now, the vibration is only present under deceleration or VERY light throttle. Dropping the auto back into 3 from D will make it more noticable under deceleration. The car has only done 88,000kms. The vibration has only started since I fitted the Superlows. It is not the zorst.

Here is my theory. It's the universal joints. I'm thinking this because now that I've lowered the car the tailshaft is sitting in a different 'home' position, the uni's at different angles. After 88,000 the rollers and races in the uni's would have wear. Now I've changed their 'home' positions they are using different surfaces in the joints, causing the annoying vibration. If the joints were greasable a few pumps with a gun would probable fix it. Also, the vibration appeared suddenly, not gradually.

Any thoughts welcome.
Does my thinking sound plausable?
I'm not ruling out it could be the harmonic balancer or something else entirely unrelated and the timing of it happening when I lowered the beast being a coincidence.

svo347 · 07-21-2004, 05:43

Does sound reasonable... GO change em to be sure !!!

fairmont1998 · 07-21-2004, 06:44

If the general opinion turns out to be uni's what do people recommend? Genuine Ford or something else?

012 · 07-21-2004, 07:10

Could be something as simple as a wheel balance. If a front wheel/s are out of balance, it'll be a bit more noticeable once the car has been lowered.

fairmont1998 · 07-21-2004, 07:16

Thanks AUGZMK, but I definately think it's not wheels.

fairmont1998 · 07-30-2004, 05:15

Any more ideas on this one?
I have ruled out harmonic balancer, I marked it and checked again a week later and the marks still align. The tailshaft hasn't bottomed on anything. Another thought I had is the change of pinion angle may be the cause. The diff housing has multiple mounting holes for the top suspension arms, so may be able to test that theory.

jac · 08-16-2004, 05:29

I would agree that the "shudder" you are experiencing is because of the change in pinion nose angle.
The angle of the pinion nose should be within a couple of degrees of the angle from the transmission slip yoke so that they cancel one another out. The pinion angle changes slighlty as the diff winds, so I reckon your decel vibration is probably because the angles are slightly out. You could try shimming the trans mount or adjust the diff angle to correct.
Let us know how you go....
jac.

fairmont1998 · 08-17-2004, 03:46

I looked at the three mounting holes in the diff for the top arms. Only two are usable, due to the way the captive nuts are held in place, the two outer ones. If I move the arms to the currently unused holes it will drop the nose further. I think this will make the vibration worse, or do you think the nose is too high and has to go down? I'm getting sick of laying under the beast scratchin' my head... there isn't a lot of room under there!