Vibration @ 70mph+, Bad under decel

[andyshyers]

Curious to see what everyone's suggestions are regarding this:

I have an '86 w/ 200k. It has a vibration that starts at 70mph and is worst when deceleating from speeds over 70mph. Once the speed drops to a lower level the vibration stops.
*The vibration is not due to the wheel/tire assemblies as I have checked both the runout and balance.
*The rear wheel bearings have been replaced along w/ the U-joints.
*The tailshaft bearing is orig. as is are pinion bearings.
*The damper on the rear end housing has been removed (made no difference).
*The driveshaft is stock.
*The vibration is present in netural at speed.
Any thoughts?

Andy

[SVOBart]

Pull the driveshaft and see if there is any unusual wear on the yoke. It might possibly be a worn out transmission tailshaft bushing.

[andyshyers]

Yoke is OK, had it out recently to do the clutch. (I had the vibe before and after the clutch job).

When the tailshaft bearing is on the way out does it kill the yoke, or just get loose until a leak starts?

[andyshyers]

Mike,
Tires are OK, I've checked all 4 and have balanced/rotated them with no change. The problem feels like a bad U-joint, but I've eliminated them by replacement! Are the driveshaft dampers prone to going out of balance w/ age?

Andy

[SVOBart]

It can kill the yoke if its allowed to go on long enough. I had one go bad in an 88 LX and it would vibrate badly when I took my foot off the gas at speed. By the time I finally took the thing apart the yoke was all chewed up.

[andyshyers]

Anything particularly special about replacing the tailshaft bushing/bearing? Can I use a slide hammer or do I need a special puller?

[SVO4PWR2]

where is the vibe/where do you feel it? in the streeringwheel ? brake pedal ? by your feet ? in the back of seat?

at work we have an emmissions dyno where you can run the car about 65 - 80 tops. maybe theres a shop near your that has one.

we also have these "eletric hears" 6 clamps with wires that go on frame/suspension of the car. you listen to each ear separtely.

HTH -RICH-

[andyshyers]

Rich,
I feel the vibe thru the floor/seat. I guess I could try the dyno if I get into balancing the D-shaft.

Andy

[GAboySVO]

I've got two '86 SVOs and my brother has one. All three vibrate at 70 MPH. From what I've read from previous post, the solution was replacing the stock drive shaft w/dampener with the FMS aluminum drive shaft. I would bet money that it is the front drive shaft dampener that is the culprit. After 20 years, rubber gets hard and dry rots.

[silversvo]

vibrations

My roommates old GT did the same thing your car is doing. Come to find out on his car the bearings in tranny were going out. Sounds like you went through all the same things I would have.

[NY eric]

stupid question

Have you tried rotating the drive shaft 90 and 180 degrees from current location to see if it just put back in wrong. I dont know much about stock shafts. but on the aluminum ones it makes a big difference how it is bolted up.

[NavySVO]

Re: stupid question

Originally posted by NY eric
Have you tried rotating the drive shaft 90 and 180 degrees from current location to see if it just put back in wrong. I don't know much about stock shafts. but on the aluminum ones it makes a big difference how it is bolted up.

I personally don't have experience with the SVO shafts, but I have seen the same thing with others by rotating the drive shaft to get rid of vibes. When I remove one, I usually index it before I pull it out just for that reason.

[TheViking]

I had a similar vibration issue after my driveshaft was removed for a clutch replacement. As was mentioned they probably didn't mark its position first.

I bought a FMS aluminum driveshaft and the problem went away.

[andyshyers]

I have noted the driveshaft's position on all of the clutch changes over the years, but it may be worth having the balance checked. Maybe the damper's not quite concentric with the shaft at this point and throwing out the balance.

When the shaft's out maybe I'll replace the tailshaft bushing. Any suggestions on a suitable puller?

Andy

[Rommel]

Vibration

I have an 84 with 279K on it. I have been dealing with the same vibration since I bought the car at 80K. I have balanced and indexed the drive shaft (mine was twisted), replaced U joints, had the transmission completely rebuilt, installed a Centerforce stage 1 clutch, checked the backlash on the ring and pinion, and replaced the outer pinion bearing (it was worn). I am currently in the process of upgrading to an 8.8 rear end from an 88 Turbo Coupe and will let you know if the vibration goes away. I believe my problem is the pinion bearings just being worn out. Mine vibrates starting at about 55MPH and quits at about 80. Recommend you pull the outer pinion bearing for inspection if nothing else fixes your problem. As a side note, replacement parts for the 7.5 rear end are available but hard to find, that is just another reason I am going to the 8.8. Good luck and let us know what you find.