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Interpreting rear-end noise

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I have zero experience working on rear ends - never had an issue to repair- but I think I’m about to learn, and was hoping you folks might have some advice based on what I’m seeing and hearing, to get me started in the right direction.

I’m getting a relatively loud thrumming out of the rear end at any speed above about 20 mph. It doesn’t sound like the even roar or a wheel bearing, and definitely has a beat.

When I’m accelerating or climbing, it has one tone. When I am decelerating or coming down hill, it has a very different tone. The tempo of the beat (at a given speed) is the same either way, but the pitch or tone is different. When I’m on flat ground and maintaining speed, I can find a spot in the throttle where the sound goes away altogether.

When I started working on it again, after sitting for 10 years, I saw that the pinion seal had puked on the floor. When I topped it up, it only took about 3 oz of gear oil, so it didn’t leak a lot, but there is at least a slow leak at the pinion. Also, I have not greased the u-joints yet either.

I’m thinking it’s probably the pinion gear floating in place, but don’t know rear ends enough to be sure. I’m thinking my first step is to grease the u-joints, drop the rear of the driveshaft, and learn how to replace that pinion gear and reset its tension.

Thought/inputs/cautions?
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There's so many things that could be causing that noise, from a bad axle bearing, to a loose pinion bearing, dry U-joint... start with checking your U-joints, its the easiest. They should have zero play and should be tight in the yoke. If you lost the front pinion seal, you may have loosened up the pinion yoke nut causing the pinion preload to vanish. Those sounds are similar to what you would hear if your pinion preload is too loose.
 

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I don't know how a pinion could get out of adjustment from just sitting. I think I would put the rear end up on jack stands and have a buddy sit in the drivers seat and put the car in drive and start the drivetrain in motion. Take a long screwdriver or wooden dowel and put it to your ear and move it around to the different areas ( axle bearings, pinion area) and listen for loud growling noise. You will be amazed at the clarity and amplification of the noise.
If your problem is as noisy as you say, you should be able to get a good idea of where its coming from. Don't just go and smoke down the pinion nut without knowing what you are doing or you may have bigger issues before you are finished.
 

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Discussion Starter · #6 ·
I don't know how a pinion could get out of adjustment from just sitting. I think I would put the rear end up on jack stands and have a buddy sit in the drivers seat and put the car in drive and start the drivetrain in motion. Take a long screwdriver or wooden dowel and put it to your ear and move it around to the different areas ( axle bearings, pinion area) and listen for loud growling noise. You will be amazed at the clarity and amplification of the noise.
If your problem is as noisy as you say, you should be able to get a good idea of where its coming from. Don't just go and smoke down the pinion nut without knowing what you are doing or you may have bigger issues before you are finished.
I’ll give that running it on stands a try. I assumed that not having much of a load on it would eliminate the sound, but it’s worth a try, and I’m planning to put the rear up on stands tomorrow night to start sorting this out, so I’ll try that.

I get that I don’t want to mess with the pinion’s tension without knowing that it’s off. That said, I can’t say that it wasn’t off before it went into storage. Until recently, I’d only driven it about a mile, and never got it up over 20. My mom didn’t drive it much in the last few years she was alive, and I don’t think she ever drove it fast. Lastly, I’ve been finding enough goofyness with this thing that either my stepdad never fixed, or set up in a really weird way, that I can’t say for sure if it has been right in 30 years.
 

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Discussion Starter · #7 ·
Did the tires set for that length of time?
No. The tires are new. I bought them and the wheels a month ago, and they now have about 90 miles on them.

It does sound a little like that sticky/slappy sound you get with brand new tires, though. I don’t think that’s it, but it’s kind of similar in tone.
 

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At my age, the only rear end noise I need to interpret is whether it's all gas....or not.
At our ages,
Never waste an erection or trust a fart!
 

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Discussion Starter · #9 ·
I don't know how a pinion could get out of adjustment from just sitting. I think I would put the rear end up on jack stands and have a buddy sit in the drivers seat and put the car in drive and start the drivetrain in motion. Take a long screwdriver or wooden dowel and put it to your ear and move it around to the different areas ( axle bearings, pinion area) and listen for loud growling noise. You will be amazed at the clarity and amplification of the noise.
If your problem is as noisy as you say, you should be able to get a good idea of where its coming from. Don't just go and smoke down the pinion nut without knowing what you are doing or you may have bigger issues before you are finished.
I had some things come up last night and didn’t have time to do much more than a visual inspection on the U-joints. The only movement in the driveshaft is rotation. I reefed on both ends of the shaft and I don’t get any play, and didn’t see any damaged/missing seals or leakage. I haven’t greased them yet (both zerks appear to be in good condition) because I wanted a chance to listen to the drivetrain before I changed anything.

I was able to get a video of it up to 50mph tonight. The sound was not nearly as noticeable with the wheels up in the air, but you can definitely still hear it, especially on deceleration.

I tried listening to it both with an oak dowel rod and a shotgun barrel cutoff I had laying around. I tried putting both up to my ear, and against that soft spot between the base of my ear and my jaw. I could definitely hear/feel the sound more clearly with the shotgun barrel, but couldn’t pinpoint its location. I moved it along the entire rear end, and around to the front, as near to the spinning yolk as I was comfortable getting it. It sounded about the same everywhere in contact with the rear end.

Here’s a video (assuming I posted it right, first YT video). Does this sound like anything specific?

 

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Oh wow, I thought you were complaining about a little whine. That’s definitely not a little whine! Not a expert but I’m thinking maybe the pinion bearing or possibly a carrier bearing. What ever is going on I definitely would pull the center section out for a visual inspection no matter what.
Agreed, that thing needs to come out for a rebuild. That's not a good noise in any way. I'd recommend Alan at Ford Rears 8 inch 9 inch Posi Traction Rear Differentials
 

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I’ve got a rebuild kit coming. I figured I was going to learn rear ends eventually, and I guess this is the perfect time.
Good, it’s not magic, you just have to pay attention to what you are doing. You can do it with a minimal investment in special tools.
The added benefit is you will have piece of mind that you saw it done yourself and know you checked everything.
 

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Discussion Starter · #15 ·
Good, it’s not magic, you just have to pay attention to what you are doing. You can do it with a minimal investment in special tools.
The added benefit is you will have piece of mind that you saw it done yourself and know you checked everything.
I think I’m good on tools. I’ve got a couple different dial indicators and bases for my lathe, and most of the hand tools I could ever need. I don’t have a press, and may need to either buy or make one. I figured if I had to do the axle bearings, I’d take them to a shop to get pressed.
 

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Discussion Starter · #16 ·
So, I already need some help.

I pulled the axles and I’m calling those bearings good. The only thing concerning there was that the axles came free easier than I expected. One moderate tug was all either needed to come free. The bearings don’t move in any direction but the one they’re supposed to, and they feel like buttah.

I pulled the driveshaft from the yolk and loosened the 10 nuts about 2 turns each. Then I took to the center section with screw driver and a hammer, and I’m getting no movement.

There’s a square tab, about an inch wide and about 1/16” proud of the housing, right about 8 o’clock, that looked like it was cast in specifically to be a purchase point, so I moved around to the rear, and tried whamming a screwdriver there. It started to mar up the rear surface of that tab, with no movement, so I quit and came here.

Am I heading for a train wreck? Is there something else I’ve got to get loose before cracking that seal? If I pull the fill plug, is there a surface I can safely put a drift against and hit it directly forward?

At some point, I triple checked, and I do have each of the 10 nuts loosened to a gap. Is there a hidden 11th nut I don’t know about?
 

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Did you take the copper sealing washers off the studs?
 

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Discussion Starter · #19 ·
Did you take the copper sealing washers off the studs?
No. I did not. I haven’t remove the nuts all the way, so I didn’t realize there was even a washer there. I just loosened the nuts figuring I could crack it and let it drip drain overnight.

Good to know there’s something else there I need to get off. Thanks for the tip.
 
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