Sounds like something is off balance

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carfreak6970

carfreak6970

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Hello,

So I would like to say this issue only started this year. But the car is a 68 Dart with the slant six, A904 and the 7 1/4 rear end. the rear end is out of some early 70's abody from a junk yard that I put about 25000 miles on. The outer axle bearings were replaced by me before the car hit the road initially.

What I am experiencing is a noise that sounds like something is off balance. The frequency of the noise changes with speed, but the volume stays consistent. When driving it seems like it was coming from the right rear, so I switch the rear wheels but the noise did not change location. I also greased the U-joints when I did this. I thought that greasing them did quiet the noise but I could have been mistaken. It has about 20 miles on since that tire swap and U-joint grease, and the noise is still present.

Could this be a U-joint issue? I disconnected the drive shaft and inspected the U-joint caps to make sure they spun freely in the drive shaft and they did.

My concern is the 7 1/4 is about to have a catastrophic failure. In a couple weeks I plan on taking the car down to OBX from Pittsburgh (approx. 1000 mile round trip) and would really not want to have this rear end blow 100s of miles from home. What am I dealing with here?

Thank you
 
Could be? I am not sure. I am not to well versed in rear ends like I probably should be.


another thing
The tires were bought new from tire rack 2-3 years ago, and maybe have 3,000-6,000 miles on them. if that.
 
Does it make the sound when you are sitting still, at the same rpm, in park? If so, it's probably in the engine, trans. If not, try swapping the tires front to back. if the sound changes, it's probably the wheels/tires. or, try putting up the rear on jackstands, if the sound is there, it's not the front suspension, and you should try listening to each side to see where the sound is coming from. Rotate the driveshaft 180*, and re install. If the sound changes, it's probably there. Remember, you are looking for changes in sound, or vibration, it doesn't have to be better, just different. A cheap auto parts store automotive stethoscope will help narrow it down.
 
The sound is not made when sitting still.

I did not change the tires front to back, but from right rear to left rear and no change in sound.

I could try the running on jack stands to see if there is any changing from side to side, or from rotating the drive shaft 180 degs
 
Having a stethoscope to listen to the axle housing could be a quick way to find the issue. Listen near the axle bearings, and the housing. Could be bad bearings in there. I know you said you replaced the axle bearings, but sometimes, new parts are ****. I had 2 new power valves fail on my car. you can also remove the rear wheels, and drums, and see how it sounds. Drums are balanced like every rotating part. Just don't step on the brakes, you'll blow out the wheel cylinders. Check for missing weights on the driveshaft.
 
Had a chevy 1/2 ton that made a rubbing noise. Nothing in the brakes and never really got any worse. Decided to pull diff carrier and check it.
A carrier bearing was pitted. It made the noise for years.
It would be a good idea to pull drums and have a good look,making sure e-brake isnt partially on or a sticky wheel cylinder.
Hot drum is a good indicator too.
 
Years ago had similar issue with 7 1/4" rear. Sounded like right rear.
I balanced drive shaft, not it. re balanced all wheels, not it. Replaced rear wheel bearings, not it.
Switched axles one side to other. Sound moved to drivers side.
Went to junkyard picked up another axle......Noise gone.
Ever so slight bend in axle. I couldn't see it.

People give those rearends away nowadays. Id swap it out with another.
Cheapest thing to do instead of replacing bearings in carrier etc.
 
In the beginning of the season I took the drums off and inspected the brakes, and nothing looked out of the ordinary.

so potentially a bent rear axle? What would be the issue with driving on something like that? I could easily get another 7 1/4, but I picked up a 8 3/4 housing for it last summer, and have access to a 3.23 center chunk and suregrip that need to be rebuilt. I would rather swap that in, but don't have enough time to get it rebuilt. Plus I would also need to update the front brakes since they are currently the 9 in drums.

thank you all for the help
 
carfreak6970 said:
In the beginning of the season I took the drums off and inspected the brakes, and nothing looked out of the ordinary.

so potentially a bent rear axle? What would be the issue with driving on something like that? I could easily get another 7 1/4, but I picked up a 8 3/4 housing for it last summer, and have access to a 3.23 center chunk and suregrip that need to be rebuilt. I would rather swap that in, but don't have enough time to get it rebuilt. Plus I would also need to update the front brakes since they are currently the 9 in drums.

thank you all for the help
Click to expand...

I wouldnt worry about driving as is, driving normally, no excessive speeds, no lengthy trips, etc.
And yes, get the 8 3/4 swapped into car and not have to worry about dinky rearend problems, especially with additional horsepower.
 
Tooljunkie said:
Hot drum is a good indicator too.
Click to expand...

This...check temperatures of rear axle, brakes too. Id run it on jackstands and let it come to a stop by itself (if it ever does in neutral) then check heat of rims/drums
 
mycuda said:
I wouldnt worry about driving as is, driving normally, no excessive speeds, no lengthy trips, etc.
And yes, get the 8 3/4 swapped into car and not have to worry about dinky rearend problems, especially with additional horsepower.
Click to expand...

Would a lengthy trip be a 1000 mile round trip?
 
I think you need to make a decision to either throw money into the 7.25 or the 8.75
It will be less to fix up the 7.25 than to get the 8.75 completed,
But what you spend on the 7.25 will be gone, as you said folks give them away.
If staying with the 7.25, I would change out the front and rear drive shaft universal joints. Some wear there can be the source of lots of strange noises. I would also pull the cover off the diff, take a look see at the gears, look for wear, excessive play,,,refill with a quality diff lube.
If that is all good, probably a rear wheel bearing, but when they go there is almost always a leak at the wheel seal.
 
Yea Ill just switch out to the 8.75 at some point. Need to work out some funds for that. Just picked up the 10in drum brake set up for the front. So I have everything I need, just needs rebuilt. Thank you all
 
I would
drive it up to the noise/vibration zone, put it in neutral and shut off the engine.
If the noise remains it has to be;a bent driveshaft, in the rearend, axle bearings, or tires. Easy tests

If noise is gone, I guess that means the problem ain't in the rear,lol.

So then repeat the test but do not shut the engine off, just let it idle in neutral, as you cost down. If vibration/noise persists, it ain't in the engine.

So if it ain't in the back, and ain't in the front... I guess it pertains to the trans, but that is highly unlikely
 
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I have done similar tests to those (with the exception of turning the engine off) and the noise still persists. but thank you for that
 
neither a bent driveshaft, nor out of balance tires, nor tires with blown cords or out of round... make noise, they just shake.
Axle bearings and rear ends make noise..... but usually don't shake.
But when the bearing gets to a certain point, be it a tapered bearing out of adjustment, or a green-bearing type worn, then the brake-drum and shoes get involved. This is an easy find, just jack up the the rear end and test for vertical play at the wheel. and of course rotate it; noisy wheel bearings are obvious.
A bad pinion bearing will make noise as the pinion moves back and rubs on the case and the pattern goes away.It also allows the spinning driveshaft to vibrate.
Bad side bearings are just noisy, but in my experience this doesn't happen very often. If they went bad I suppose it could be accompanied by vibration.
A bad pinion angle will cause a subtle hard to find vibration, but not usually accompanied by noise.
Two different diameter rear tires will cause the side-gears to rotate at different speeds. This heats the oil and soon the crosspin wants to seize to the spiders. In the meantime this does make noise, AND vibration as time goes by.
Good luck in your search
 
If it is a bent axle (or wheel), I'd think you'd see so running on a lift.
 
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