vibration issue

[Budd]

This is goin to sound crazy, it's about to get the best of me. I've got one 2 86 Mustang LX convertibles. Both cars are 3.8 C5's. both have vibrations, seems to start at or about 45 to 65-70mph. It feels like it's coming from the right rear,{both cars}. Seem's to start after driven a few miles. I've tried tires and didn't help. I've raised it up and tried shaking and spinning the wheels thinking mabe a wheel bearing. Now here's the crazy part, when the convertible tops are down, no vibration, shaking, shutter no issues. Leaving the tops down isn't an option, we live in Ohio and do enjoy driving them some in the winter months as long as roads are clean. Any helpfull ideas or thoughts would certainly be appreciate.

[93ksstang]

Check to make sure the bolts in the drive shaft isn't coming loose, and also check u joints. My 93 gt did the same thing. I crawled under it and the drive shaft was pretty much being held on with one bolt the other 3 were loose.

[Budd]

The driveshaft and bolts are tight on my white car. However I was told that the u joint itself could be tight but could still be my problem. they said it could only take a needle bearing or 2 being dry could maybe do it. There's no grease fittings on them. I just bought the gray car and have had it on the rack to check it. Sure would be nice if that's all it was. THANK YOU for your reply and input.

[Project86GT]

Did u ever have the driveshafts out? Or they could be out of balance? Also put the car in nuetral at 50 and see if it still vibrates. Or also could be a rear control arm bushing problem.

[Budd]

I'm thinkin the the driveshaft out of balance it do it all the time. Most times I have to drive it a few miles some times longer than others before it start doing it. Your thought on a control bushing makes alot of sense. Like on a down grade and let off the gas it quits. However on an upgrade it get worse. If I get it on the rack with the weight off the rear wheels, I should be check the bushing with a prybar. THANKS for your help

[gt pony]

If you feel the vibration in the seat or floor pan, the cause is in the rear or drivetrain.

[free1986]

I have the EXACT same problem with mine! The only thing I can add is that mine sometimes has a strange vibration at idle in drive, kinda like the lopping of an engine with a big cam, it goes away when I put it in neutral. I think they are separate issues, however. I'd love to know an answer!

[Budd]

I honestly can't say seat or floor, My wife was driving the other day and I was in the passenger seat and it's sure feels as it's coming from the right rear. niether one of my 86's have the quad shocks, and can't see where the other shock on either side would have mounted.

[93ksstang]

When my drive shaft was loose it wouldn't vibrate unless under a load and over 50 mph but being out of balance could also cause it since at lower speeds its not turning as fast but the faster you turn it the more it will vibrate or be a noticible vibration.

[burntorange84]

See this thread & read my posts.

http://vb.foureyedpride.com/showthre...ht=jack+stands

If an auto, slowly increase in drive or use 3 to spin to the problem speeds.

Hopefully this will help.

-j

[86GreenStang]

Maybe a bent wheel. Bad trans mount. Drive shaft or u joints. Check wheel lugs for cracks. Maybe a bent axle. Just some suggestions to look at

[Project86GT]

I'm going through the same thing now, so I brought my driveshaft to get balanced and I explained my problem, my whole rear suspension is new and has urethane bushings in the upper an lowers, he said those bushings don't give much and you feel everything. He told me to go back to rubber ones but I'm not going back to stock arms.
I do wonder if this is the reason maximum motorsports recommends stock hd uppers??

[Budd]

I have the EXACT same problem with mine! The only thing I can add is that mine sometimes has a strange vibration at idle in drive, kinda like the lopping of an engine with a big cam, it goes away when I put it in neutral. I think they are separate issues, however. I'd love to know an answer!

I noticed your's is a convertible also. Both of mine are too, that's the crazy part, both act excatly the same.

[Budd]

I replaced the crosmember the trans mount looked great, I've not tryed prying or lifting on it. We did shake on the driveshaft pretty hard everything seemed tight. I'm thinking of replacing both ujoints in the white car,it can't hurt anything. I've had a few differant sets of wheels and tires on it and the same thing with all. The tires on it now are brand new. I haven't tried putting it in neutral when the vibrating starts. However if I accelerate it seems to ease up, If I deccelerate it quits. Also it doesn't do it all the time. It seems like it takes a few miles for it to start acting up. What's got me, if the tops are down no vibrations no shuttering nothing. I'd think wth the tops down, the air would be pushing down on the rear of the car, maybe not. With the tops down I couldn't ask for any nicer cars to drive.

[Budd]

I replaced the crosmember the trans mount looked great, I've not tryed prying or lifting on it. We did shake on the driveshaft pretty hard everything seemed tight. I'm thinking of replacing both ujoints in the white car,it can't hurt anything. I've had a few differant sets of wheels and tires on it and the same thing with all. The tires on it now are brand new. I haven't tried putting it in neutral when the vibrating starts. However if I accelerate it seems to ease up, If I deccelerate it quits. Also it doesn't do it all the time. It seems like it takes a few miles for it to start acting up. What's got me, if the tops are down no vibrations no shuttering nothing. I'd think wth the tops down, the air would be pushing down on the rear of the car, maybe not. With the tops down I couldn't ask for any nicer cars to drive.

Today I drove our gray car and checked putting in neutral and the vibratetion stops. however I did notice that on an incline it seem to cause it to start the vibratetion. Also I bought the white one last june. we put 9000 miles on it between then and Oct. It never got any worse.

[PaceFever79]

Here's something else to check....it is pretty common for the bearing in the tailshaft to
wear out on C4 type transmissions. With the car on jack stands and in neutral grab the
driveshaft yoke at the rear of the transmission and push up and down. If it has any slop
remove the tailshaft housing and replace the bearing.

[Budd]

Here's something else to check....it is pretty common for the bearing in the tailshaft to
wear out on C4 type transmissions. With the car on jack stands and in neutral grab the
driveshaft yoke at the rear of the transmission and push up and down. If it has any slop
remove the tailshaft housing and replace the bearing.

I've shook both front and the back of the driveshaft on the white one, checking the ujoints. Everything felt tight. I had it on a rack with no weight on the wheels. Tomorrow my buddy is goin let me use the rack, I'm goin check the gray car. I will make sure to check that. Thank you.

[bull-vette]

I had a vibration at over 50mph as well. Replaced tires, driveshaft, etc and it ended up being a bent transmission tailshaft. It took several trips on the rack and several different diagnosis's to get it right. Just a thought of something else to check while it's up in the air.

[82stangracer]

If you're thinking drive train, you might want to make sure the drive shaft isnt warped. My old drive shaft was warped and it ate 2 rear main bearings in the transmission before I found it.

[86GreenStang]

That would be what I checked next is the tail shaft bearing and the pinion bearing if the other things checked out fine.

[Budd]

The quad shocks have been removed from both these cars. Can this possibly be my troubles. I had my wife drive it up the road, it was a 4 lane so I could follow it to see if the tires were running straight and I watched on both sides. The tires didn't seem to be hoppin and from behind they looked to be true. I order a set of quad shocks off ebay I havn't recieved them yet. I can see where the brackets were mounted to the frame behind the rear wheels. I can't see any place at all where they could have been bolted to the differential. I've google imaged them, it's like theres something missing or I'm missing something. Did they even use quad shocks on 2.3 and 3.8 models?

[Ethyl Cat]

If you put it in manual 2 and up the speed to where it vibrates will it still vibrate?

I do not have a lot of experience with a C5, but my thought is that it may be a resonant frequency from the engine exciting the driveshaft. This is shaking the rear end which is attached to the body in the rear which is where you hear/feel it.

Gear ratios in the transmission may prevent it from happening in lower gears. Once you are in third 1:1 and converter lock up(no dampening happening in the converter) This frequency is sent directly through the trans and you notice it.

It seems odd that both of your cars would have the same rear imbalance issue at the same time to me, so I was wondering if this might help pinpoint the problem.

Have you ever heard of a syrometer(briggs and stratton tach)?

These tools are very handy in finding the frequency of the virbartion that is occuring and with a little math pinpointing the source of the problem.

They only cost about $15 at the local lawn and garden shop.


Steve

[Budd]

Steve, Thannks, I'm going to go for a ride up the road in 2nd and see. Yes "odd" is an understatment that both cars are doing it. If I put the tops down on either car, I can not get them to vibrate.

[black1980fiveoh]

My first thought is always universals joints in the drive shaft, then a drive shaft that needs balancing.

Unibody cars are hard to find out where the noize originates from, when I get a loud vibrating noize from my engine compartment, I have a loose tail pipe hanger. I can tell you that drove me crazy and could not believe the exhaust hanger was causing all my grief. So, spend some time under the car looking for loose bolts.

[PaceFever79]

Here's an experiment to try....

Perhaps the weight of the retracted roof is changing something...

Put something that weighs about 100 lbs in the trunk and drive it with the top up.

That won't tell us what's wrong, but it could lead us to further clues.

I'm guessing it could be a drive line misalignment.