I have scoured most of the Vibration threads here that are relevant, and i thought I fell into the same category (pinon bearing or get an aluminum drive shaft)... until today.

ISSUE/SYMPTOMS:

Vibration begins around 60MPH on the highway 5th gear.

The vibration is a low thumping from the center/aft section of the car (more aft)

The vibration goes away when the clutch is pushed in. (Still in gear)

The vibration "shutters" when the gas pedal is barely pressed (in gear)

With the clutch pushed in (60mph) and the transmission in neutral when i go to engage 4th (or 3rd) the "shutter" vibration begins.

At one point i did engage 4th and let the clutch out and it did not continue to shutter (just the low thumping vibration) but i then shifted to 5th

Vibration tapers off <55mph ; Increases in intensity (not frequency) >65mph.

BACKGROUND:

Car is lowered 1" with the Eibach Kit, tubular control arms (non-adjust), adjustable panhard bar.

The vibration used to be just the thumping at 65mph (not 60) until i "fixed" my torque arm mount.
I was under the car the other week (checking for loose drive shaft bearings) and noticed my bushing was "pushed out" to the front such that barely any rubber bushing was in the clamshell. Well i greased it up and got it back in (this took 3 days lol). The reason for it being pushed out is when i had the transmission out, i did not reinstall the bushing with a zip-tie to hold it in place (like it had on there before)

New Rubber trans mount, new engine mounts (had the engine out last winter), Pinon seal is leaking (not sure if it is related)

THINGS IVE CHECKED/DONE:

Pinon Yoke "seems" tight.

Slip yoke at the tailshaft is loose/sloppy (not sure if this is normal)

new rubber transmission mount/new engine mounts (when the car was apart)

U-joints are tight

rotated drive shaft 180 deg.

New clutch disk and pressure plate when transmission was out (before i knew i had the vib issue)



Any thoughts?

 

In my case the midpipe from the exhaust is swinging against the body when the engine is under load and rpms are quite low.
It's where it goes over the axle.
Give it a try and put something heat resistant between pipe and body, then check for vibration again.

 

Its possible I suppose, it is 3" exhaust all the way back no cat... I had a shop weld it up, so it should be fairly sturdy but who knows...I did look at it quickly while i was under there messing with the bushing, but not enough to check for contact.

thanks for the suggestion. Keep the thoughts flowing

 

Had a vibration occur in my car at around 65+ and increasing in intensity the faster I drove.

Replaced the original driveshaft with an aluminum driveshaft. - No more vibrations.


Chuck

 

I've read about the aluminum drive shaft fix and I think this is where I was headed until today when my vibrations are "shuttering"...I still think this is a good thing to try..

I would probably get a new slip yoke also

 

Drove the car home today and made a few more notes.

1) I was in 4th gear 40mph and experienced the vibration issue. (so its not just 60mph+)

2) The vibration changed to a shuttering as i attempt to shift into 4th gear from 5th gear, but goes away when i accelerate.

3) I pushed the clutch in and was decelerating in traffic and experience the vibration

4) backing up "quickly" in my driveway (letting the clutch out fast) produced an aggressive clattering/shaking from the drive train.

5) Was under my car and "shook" the exhaust, did not notice any interference.

6) The slip yoke has play, how much play should there be?

 

did you check the pilot bushing when you did the clutch? I had a well hogged out bushing once and it caused vibrations.

when you say the U joints are "tight", is this when you have the shaft out and moving the U joints? if they are tight movement wise you need to change joints because you have an issue with how the joint is loaded in the shaft or pinched ears on the shaft. the joints should move freely lock to lock with NO resistance, hangs, or anything in between.

 

This is a good point, what i mean by "tight" is there seems to be no lateral play in the bearings. You are correct that there is a degree of freedom that should be checked out. What i think i am going to do is take the shaft off and get new u-joints while its off...

I cannot tell if the front u-joint has bearing play or its just the movement in the slip yoke.

Either way i dont like the play in the slip yoke... i think it needs a new slip yoke bushing.

Does one normally replace the slip yoke AND the bushing? or just the bushing.

I also just orded a founders performance adjustable torque arm... ive been wanting to do this for a while to eliminate the lowering of the car as the issue.

Another thing i noticed today... i rode around as a PASSENGER for the first time in a while... my feet picked up a slight grinding/binding noise upon take off (1st gear clutch release) from the trans area... wondering what this could be and/or related?

Also to note, i did not replace the pilot bushing i should have but was in a hurry when i was putting the car back together. I looked in there and it "looked" okay and was certainly not the original... but who knows....