1966 Mustang FB-60mph+ vibration... DESPERATE!!

desdain · 06-11-2009

Okay, here is my setup and problem. I have a 1966 Mustang fastback with a 347 stroker, C4 transmission, stock driveshaft, 8 inch rear axle with posi, original leafsprings with slide-o-link traction bars, and Wilwood disc brakes.

When driving at speeds of 60mph or higher, there is a severe cyclical reverberating hum that rattles and vibrates the entire car. It's cycles in and out about once a second, faster at higher speeds. I have put the car in neutral while rolling downhill and the hum is still there, but it seems to become more constant rather than cyclical then. This leads me to believe it's a problem with the drivesystem.

Here is what I have done so far:

- Set the angle between the engine and rear axle by adding wedges between the axle and leafsprings (they were off by 4 degrees, but now they are exactly parallel)
- Replaced the rear bushing in the transmission (the slip yolk had some play in it, but now there is very little play)
- Straightened and milled the axle shafts (when the car was on stands and wheels rolling, there was severe wobbling in the wheels. This wobble is now gone).
- Reduced driveshaft wobble (there was a 1.5mm wobble in the driveshaft caused by bad rear u-joint mounting holes, but this has now been reduced to 50 microns by positioning the u-joint correctly with some tack welds. Yeah, I know this is a no no, but it was our only option. The driveshaft itself is quite straight)
- Balanced the rear wheels

Things I have not done yet:
- Replaced the transmission mounting bracket
- Tried a different driveshaft
- Removed the traction bars
- Two sticks of dynamite up the tailpipes ;-)

I'm getting really frustrated by this as we keep fixing all these different issues, but nothing seems to give any results. Now I'm hoping that someone here can point me in a direction that might give me some results. I have searched the forum for similar posts, but none of the ones I have found have helped so far.

Next I'm gonna put it up on jack stands run it up to 60mph on the speedo and then start removing stuff until it stops vibrating (first wheels, then discs, then drive shaft, etc.). With my luck this is something that only happens when it under load :-(

Thanks a lot!

steve sturgin · 06-11-2009

Hi there DesDain,

I am not sure about the dynamite

Mine had something similar, turned out the steering linkage was rubbing on the sump, the reason i didn't spot this a lot sooner was that when the car is on jack stands the steering is well clear of the sump.

Here is the thread where i worked through mine ..

http://www.allfordmustangs.com/forum...ang-2-2-a.html

Steve

desdain · 06-11-2009

Thanks for the post. I looked through the thread earlier and I'm sure I don't have a rubbing issue. I have rack 'n pinion steering and there is plenty of clearance there.

I'll keep checking and I'll keep posting my findings.

Thanks!

coppah37 · 06-11-2009

How about rear bearings or possibly your driveshaft is out of balance? Where does the sound seem to be coming from? Is it a corner of the car like which wheel? or right down the center like the drivetrain?

v8only · 06-11-2009

drivetrain vibrations are very often the driveshaft.

in the fox world, we upgrade to the aluminum driveshaft, and this nearly always cures it.

try clocking your driveshaft in the different holes..meaning move it over a 1/4 turn and see if that changes the nature of the vibration.

driveshaft shops can check the shaft too and balance it

kiwiboy · 06-12-2009

Had a similar problem and spent heaps of time and money fixing. Although I had balanced all my wheels plenty of times with no luck, I tried another set of wheels and problem went. Not sure why but it worked. Worth a go?

desdain · 06-12-2009

Quote:

Originally Posted by kiwiboy

Had a similar problem and spent heaps of time and money fixing. Although I had balanced all my wheels plenty of times with no luck, I tried another set of wheels and problem went. Not sure why but it worked. Worth a go?

Yeah, I've also thought about trying a different set of wheels, and maybe I need to go ahead and try this. It's hard for me to find someone with wheels that will fit my brake setup here, but I'll ask around.

Thanks!

mwillis · 06-12-2009

If you look through some of my old posts you'll find a thread regarding this same problem. To make a long story short, buy a $12.99 tranny mount and solve the problem. It fixed mine and several others.
Mike

MizzouMike76 · 06-12-2009

Start cheap, and go from there.

I'm not in the US either, so shipping costs will have to be considered. Sometimes eBay sellers have good deals on shipping. I wish I had my Mustang overseas, but no.

Maybe someone in a Mustang club can help with the wheels issue? I bet if you asked, they'd be willing to help, as they will "feel your pain" when it comes to solving problems like this.

Any driveshaft shops around? Maybe even a Mercedes Truck shop can help out, as they're nearly all rear wheel drive, and MBs are built to last, so parts are often repaired instead of replaced.

Michael

Keving · 06-12-2009

The only thing that I can think of that hasn't been mentioned so far is axle bearings, or the rear end unit its self.

desdain · 06-12-2009

There is a diesel shop here that can atleast balance my driveshaft, so I'll probably go and talk to them here in a few days. There is a mustang club here in town, but I don't have any connections there. However, I do know some guys in another ford club, so I'll ask them.

The axle earings felt okay, but they could of course be slightly out of round. However, if they were, I guess the wheels would havea really bad wobble still, but we got that pretty much fixed.

MizzouMike76 · 06-12-2009

I think it would be a good idea to go make friends down at the Mustang club. Not for the wheels, but for the connections you will make, advice the other members can give, and so on. Being in Finland, where there's (I'm guessing) not a lot of English/inch parts lying around.

I was almost your neighbor in a manner of speaking, when I was to work in St. Petersburg before the deal fell through.

Michael

desdain · 06-12-2009

I've got some good connections for parts and the guy can get just about anything within a week. There is a huge american car community in Finland, so the odds of finding the right parts are pretty good.

I also have pretty good connections in the States and I get parts from them all the time.

Next time you're in my neighbourhood, you'll have to stop by ;-)

racin_ryan · 06-12-2009

I feel your pain. I'm in the same boat. I removed my drive shaft to change u-joints and found a drive shaft that had been shortened by a hack. The drive shaft shop told me to pitch it and they built me a new one. New shaft and u-joints reduced vibration by half, but I still have more hunting to do like yourself. Next stop for me is transmission mount and transmission bearing. Good luck and keep us updated. Maybe we can help each other working on the same issue.
Ryan

desdain · 06-13-2009

Quote:

Originally Posted by racin_ryan

I feel your pain. I'm in the same boat. I removed my drive shaft to change u-joints and found a drive shaft that had been shortened by a hack. The drive shaft shop told me to pitch it and they built me a new one. New shaft and u-joints reduced vibration by half, but I still have more hunting to do like yourself. Next stop for me is transmission mount and transmission bearing. Good luck and keep us updated. Maybe we can help each other working on the same issue.
Ryan

Will do :-)

You know, for being such relatively simple machines, the problems sure can be elusive.