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Discussion Starter #1
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!
 

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Discussion Starter #3
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!
 

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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?
 

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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
 

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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? :scratchchin
 

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Discussion Starter #7
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? :scratchchin
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!
 

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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
 

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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
 

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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.
 

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Discussion Starter #11
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.
 

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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
 

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Discussion Starter #13
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 ;-)
 

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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
 

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Discussion Starter #15
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.
 

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New transmission, new driveshaft, new u-joints, new ring and pinion, tried other wheels and tires put on it for a test and I still have a vibration. Mine starts around 50 and starts to go away around 60. And it's not a little vibration like you get with an unbalanced tire. It can be teeth chattering.
 

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It sure could be that the rubber insulator of the trans mount is torn away from its metal attachment as was mine on my 69. Cheap fix if that is it. Tell us, when did this start happening? Did you replace a rear end, drive line, transmission, u-joints, or torque converter before this started or has it always done it? I have a 70 with FMX. I had the trans rebuilt, new trans mount, drive line and new joints balanced twice, axle bearing replaced and it still does it. Only thing i havent done is replace the torque converter, check the harmonic balancer, and check the rear end bearings and gear mesh. I bought the car in a basket so i dont know what it did before i got it. I definately feel your pain.
 

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Discussion Starter #18
Okay, update:

After having checked the axle shafts (again) and also checking the play in the differential, we noticed that the shaft splines had some play in the differential, maybe a little less than a millimeter. Though this was a point of concern, I didn't have much choice than to re-assemble everything and come to terms with the fact that the vibration might never be fixed.

That is until we clamped a hose clamp with a small weight to the drive shaft (read in this or some other mustang forum that a guy had done this). We measured the "wobble" in the shaft which was about 1 mm, and then added the weight on the "low", or inside, side (don't know how else to explain it). Took it out for a test drive and the vibration is almost gone, just a slight hum at 60mph instead of the earsplitting, brain melting drone that I had originally. So now I have found a place in town that can balance driveshafts (not too common around here), so hopefully the problem will be permanently solved.

Thanks to everyone for all your tips and help. I really do appreciate these forums :-D
 

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Discussion Starter #19
Just a final update.

Had the driveshaft highspeed balance and made sure that the phase was correct when re-installing it. There is barely a sound from the drive system anymore. Unfortunately, with the drone of the un-balanced driveshaft gone, I could now here the ear piercing whine of the differential. Long story short, we added 770um (micro meter) of shims to set the hackspacing and adjusted the backlash so that median gear had 250um of movement. I call it median because there has either been some wear on the gears or Yukon sent me a crappy gear so there was some variation between the teeth of the gear from 150um to 320um.

Now it's really quiet and I'm just adding STP VibroPlast to get rid of the road noise. Soon it'll be quieter than a Lincoln ;-)
 

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I have a sever vibration in my 65 stang after installing a 9”. The problem is above 50 mph.

Details of swapped parts (It is a combination of used and old parts):
9” housing from 1959 Rachero,
31 spline Yukon axles
Curie disc brake kit, I think its Granada or explorer brakes adapted with special brackets to fit this housing.
New driveshaft with new slip yoke made by Coast drive lines in Ventura. Supposed to be very reputable.
9” with ford posi low mile rebuild. 4.11 factor ford posi unit.
New axles bearings and seals.
Low mileage T5z trans.
Prothane trans and engine mounts, very ridged.

Here are the things I have done:
Fabricated centering rings for the rotors. The Yukon axle centering stub was a lot smaller than the brake rotor hole. The was somehow missed and created a lower speed vibration as the rotors were not moving in a circular pattern.
Added wedges to the rear end, pointing pinion up, since the trans points down (very slightly). The T5 is as high in the tunnel as possible, and the engine is lowered about ½” from factory. The was a result of the Prothane engine mounts.
Run the car in 5th gear on jack stands with the wheels off and vibrations are still present. Did this as well as road test for all changes made on the car thus far.
Checked trans outputshaft runout, .003”-.005” max. Almost no detectable play.
Checked rear end position. This is difficult, and except for a very slight shift to one side (.25” or less), it is very well lined up.
I put a hose clamp on the shaft and located it 180 away from the balance weights to see if the weights were in the wrong location (balanced wrong). This yielded nothing, however I did not mess with this process too much.

Notes: The centering rings helped a little, however the vibration is now a higher frequency than would be caused by a wheel issue.
Running with the wheels off eliminated pretty much anything aft of the rear u-joint.
The pinion yoke looks a little funny. The U joint fits perfectly in the joint, however the yoke could still be damaged.
Although new, the rear axle bearings have some play. This is unfortunate, but I do not believe it to cause a vibration.

Things I am going to try:
Removing the wedges, and even installing them backwards.
Clocking the rear u joint 180 from its current location.
Double checking the driveshaft balance.
Replace pinion yoke
Adjust trans.

Any other suggestions? I have a feeling the problem is realted to all the things I have mentioned, with a closer attention to detail.
 
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