How much driveshaft play?

[Anonymous]

Hey everyone long time no post!

Ever since I've had the Mustang, when I drive on the freeway at between 55-70 MPH there is a very loud pulsing HUM. It's a hard sound to describe, but say the word HUM, then pause 3 seconds, then say HUM again, etc. HUM...HUM...HUM... it starts around 55, gets faster to about 70 (where it's HUM.HUM.HUM), then about 75 it goes away.

I assumed there may be some problem in my driveline (duh), and since I'd never checked my driveshaft I pulled it out last night to clean and inspect.

I found it was greasy but otherwise straight with no dents or scrapes. The bearings seemed to be fine, but there was NO grease in them so they were very loose. A couple squirts from the grease gun tightened them right up. Bascially, my inexperienced once-over didn't show any major problems. So, I thought the loose bearings were the problem and I was in good shape.

After a brief freeway drive, I noticed that the sound was even *louder* than before.

Now, while I was under the car there were three things I did notice.

1. The shaft coming out of the rear of the tranny (auto trans), was pretty loose. It probably had 1/8in play in every direction. I don't know if that's normal or not. After putting the shaft back in, I can still move it around. The rear seal seemed fine.

2. At the differential, the yolk (sp?) seems to have some play. That is, when I spun the yolk to spin the wheels, there was a fair amount of slack. Not in-out play, but imagine a steering wheel with 5deg of play in either direction - when I moved the yolk, it was about 5-10deg before the wheels moved.

3. The left rear tire seems to scrape *ever* so slightly on the rear brake. Sometimes, when I would turn the yolk slowly by hand, that wheel would stop turning and the other one would keep turning.

So there you have it. Do any of these things I've described seem alarming? Any other things I should check?

Thanks everyone!

 

[CobraSix]

I'm no expert on drivelines, but that seems like a lot of play. When you pulled your driveshaft, did you notice any wear on the slip yoke? Mine hardly moves at either the tranny or the diffy.

My brakes do that too. I think it is something to do with drum brakes naturally (or am I getting it confused with disc?).

I have several cars that make weird noises at highway speeds. If they go away above 75...go faster .

Seriously though, with a loose driveline it may be causing the driveline to hit the resonance frequency of either the car or something else in the car causing the hum. Also, is your driveshaft balanced properly?

Slade

 

[Anonymous]

I would tend to agree that an eigth inch is a bit much at the slip yolk. Put a mic on both connections and see what the difference is. I just happen to have my Drive shaft out so I will mic mine and see what it is. I would imagine it will be less than a 32. I do remember that there was very little play in mine when I removed it.

Drop me an e-mail
jliegl@haden.com[/i]

 

[rbohm]

8) an 1/8" is way too much play. it is enough to change the u-joint angle, and that will give you humming sound. also the rear yoke will need retorqueing, and a new crush sleeve at a minimum as it has lost its tension. best to pul the old crush sleeve and have a solid spacer made to replace it. also checkk the u-joints themselfs for play. if you find any replace them as well.

 

[Falcon62]

yolk = egg
yoke = driveshaft


If you've got an 1/8" of play in all directions with the slip yoke, you may have a couple things going on. Is the play between the yoke and the tranny output shaft? If so, the slip yoke is probably worn out. There's also a bushing in the tranny extension housing that probably needs to be replaced. These two things combined can cause the problem you described. As rbohm suggested, with that much play you can change the drivline angle and that is not good for ujoints.

At the rear, the way you described the play, sounds like you may have a lot of clearance between the ring and pinion gears. This happens as they get older. I have quite a bit of the play you described in my 72 F-250, and that rear has over 200k on it. Of course, the Dana 60 is substantially stronger than the 7.25.

Did you check the bearing surface on your rear ujoint for wear? Since it was dry, I'd be very suspicious. And what you saw on the rear ujoint goes doubly for the front one, especially with how loose everything is.

When you had the driveshaft out, did you check to see if the balance weights were missing? Even though the driveshaft may look straight, that doesn't mean it is balanced. Think of a tire/wheel assembly, they may be round, but they can still bounce hard.

Lastly, when you pull a driveshaft, you should always mark it and the rear flange so you can reinstall the same way. Driveshaft phasing can cause vibration and noise. If you replace your ujoints, slip yoke, extension housing bushing, and still have a noise, disconnect your driveshaft, rotate it 180 degrees, and reinstall. This may take care it.

 

[Anonymous]

Thanks everyone - couple of points.

1. Yes, the driveshaft has the weigts on them. If yo mean the little 1in rectangles on either end near the u-joints, then they are present.

2. I didn't notice any wear on the u-joints. Again, they were smooth and had some grease in them, but they were really loose. Some of the old grease came out when I re-greased them.

3. The play was at the end of the transmission where the slip-yoke connects. It's not between the slip-yolk and the output shaft - it's the output shaft itself. I could move it around pretty freely. It wouldn't move so much as to touch the rear housing, but it was really loose.

Keeping in mind, I'm no expert on drivelines - so when I say "appears OK' that means there is nothing obvious - everything seems smooth, fits correctly, no pitting, etc.

It seems like that loose tranny part may be the root of the problem, and tightening up the u-joints only made it worse. What would be the cause of the loose tranny?

 

[Anonymous]

UPDATE.

Well, I think I discovered the noise. I jacked up the rear of the car this AM and turned the wheels. Well, remember that slop I was talking about at the rear yoke? Well, I can turn the wheels and the driveshaft will barely move. It's like it gets caught on something or isn't engaging properly. It will move, but not smoothly... It's like... move, clunk, move, clunk, move, clunk., etc.

Bascially, if I speed up this sound in my head, it's exactly what I hear in the car. I always thought that if you move the wheels, the driveshaft should spin smoothly, at some ratio less than the wheels. This is moving, but it's clunky.

Any ideas?

 

[Anonymous]

Hi, 'Vet:

You may have a worn differential. Here's a test to try - but
be sure your car is well-jacked and stop-braced for this one -
get both rear wheels off the ground. Then, engine idling, trans in low gear, let the rear wheels spin. Grab one wheel to stop it. If LOTS of noise comes out of the differential when the power transfers to the other wheel, it's time to pull that differential cover and take a peek at the gears and bearings.

Rebuilding these differentials is not too tough. The only tricky part is in replacing the pinion gear: getting the engagement with the ring gear requires some knowledge and time.

One final note: I'm presuming here that you don't have a posi-track rear axle. I've never seen one behind these sixes in a stock Ford.