"Something on the truck goes CLUNK CLUNK CLUNK"
 

Okay, here goes. It is winter, and with colder weather, it seems that new issues just materialize out of nowhere. Well, my latest issue is an irritating and somewhat worrisome 'CLUNK' coming from the rear of my 91 ex cab pickup (4x4, 22RE).

When I start up the truck, no issues. Sitting in neutral and revving the engine, no issues besides some minor noise that I've deduced is just the exhaust system vibrating. When I begin moving, I get up to about 12-15mph before shifting into 2nd gear. Still no issues. But when I get into 2nd and hit about 18-20, I start to hear a rhythmic 'CLUNK' coming from the driver's side rear. I can also barely feel this 'CLUNK' through the floorboard. The noise seems to increase in frequency in direct correlation to how fast the truck is moving. So I get up to 25, the clunking is faster. I slow down to 15, it slows down as well. Once I get up past about 30mph, I no longer hear the noise.

I've run some tests on a long flat parking lot to remove environmental noise like bumps in the pavement, and I can reproduce the clunking when holding about 18mph in 2nd gear and also if I accelerate up to 20mph and then coast in neutral. When I coast in neutral, the clunking interval increases as I decelerate until the clunking eventually stops around 10mph. Another odd factor is that once the vehicle has run for a sufficient amount of time to heat up the exhaust system, the clunking goes away. I was running my test and then took the truck on a short drive, returned to testing, and couldn't reproduce the sound.

I don't think it is directly related to the revolution of the wheels because when coasting from about 20mph to a stop, the clunk sound is sporadic but rhythmic. For example, at 15mph it might go 'CLUNKCLUNKCLUNK' and as I decelerate to 12mph it might go 'CLUNKCLUNK...................CLUNKCLUNK.......... .......CLUNK' until it stops altogether.

I have double checked all lug nuts for tightness, inspected the wheel wells to ensure nothing is rubbing against the wheels, and am pretty lost at this point. Any advice to point me in the right direction would be greatly appreciated! Thank you.

What's the repetition rate of the clunk? If the clunk is wheel related, it will happen about 3-4 times per second at 20 mph. If it is driveshaft related, it will be about 12-15 times per second. Figuring out the timing will give you some insight as to where to look.
If it is wheel related, look for some loose hardware or a fender liner that's dragging on the wheel. A loose piece of plastic could hit the wheel at low speeds, but blow back due to air flow and be out of the way when you get up to speed.

when I had an intermittent clunk i found chunks of my ring gear when I drained the diff fluid. I had sheared 3 teeth.

Like dropzone said, check for metal in your rear diff, other than that there are some things you could try to give us some more info,
is it different in 4X4? does it change if you swerve side to side? does it change if you hit the brakes?
try removing your rear wheels and brake drums, wiggle your axle shafts up and down as well as in and out to see if you have play in the rear wheel bearings.
make sure you don't have something stuck to the rear wheels or driveshaft.

Put rear on jack stands, Put in gear and listen/observe where clunk comes from. Use wooden rod to you ear with one end to suspect area. Rev it up. How to rev up when you're at rear axle? :)

Put it in neutral. Lie under truck. Move driveshaft forcefully up and down. Does it move in any way?
Did you ever have a loud ass BANG, but everything keep working as it should?

More diagnosis from my drive into work this morning:

The clunk definitely seems wheel related and coming from the driver-side rear wheel (about 3 clunks per second at 20mph). It does clunk under acceleration and this morning I could hear it when I was doing 40mph. The sound doesn't seem to care if I'm turning or going straight.

It is currently sub-zero so I haven't spent much time under the truck in the last few days but I plan on getting it on a lift in a few days for an oil change so I will do more diagnostics then.

Look now.

After the clunk, clunk comes a single big clunk.
Then you are looking at junkyards to find a new old third. Or 1700 from marlin.

https://i.ibb.co/z2xx5Yf/yeaniceonme.jpg

I am planning on looking very soon. However, the clunk coincides with every one full rotation of the wheel. If it were a rear diff issue, wouldn't the sound happen about 4 times per rotation? Also the clunk seems to go away when I brake.

A rear diff could have a clunk at wheel speed or at drive shaft speed. Depends on whether the problem is damage to the ring gear or to the pinion.

But, one of the fundamental rules of troubleshooting is that your hypothesized cause must explain all of the symptoms. Otherwise your hypothesis is wrong and you need to think deeper and do more testing to get more clarity. So lets review what we think we know so far.
1) The clunk occurs at wheel speeds, not drive shaft speeds. Eliminates u-joints as a cause.
2) It starts at about 15-20 mph, increases with speed, and goes away above 30 mph. That's either because the noise actually stops, or it's masked by road noise. If the noise actually stops above 30 mph, it's probably not gears.
3) It goes away once the vehicle is warm. This is perhaps the most interesting symptom.

Can you describe the tonal quality of the "clunk" a bit more specifically. Where would you put it on the scale of "thump-clunk-clank-clink-ting" type of sound? Is it a metallic sound, or more muted? Hi pitched, more of a clank than a clunk? Tinny sounding or solid sounding? Like light metal banging together, or heavy pieces?

Does it do it when you are backing up, and/or applying the brakes in either direction?

The suggestion to put it on jack stands is a good one. Just be very careful around spinning wheels and drive shafts if you do this. If your rear tire is 6 inches off the ground and rotating, it will instantly drag you right underneath it if you accidentally contact the tire tread.

Good luck!

Let me be more descriptive with the sound. The sound seems to change depending on my speed, however, as you stated, this could be due to road noise. At lower speeds when the truck has sat for a few hours and is not warm, it sounds more metallic. It sounds like two objects gathering resistance and then relieving suddenly, but it all happens very quickly so it is difficult to say. The sound is like a "tunk..tunk..tunk" at speeds around 15.

I can actually hear the sound at speeds up to 45 (have not gone above this since discovering the sound) but at 45 it sounds like a "bumpbumpbumpbump" and less metallic. Again, my guess is because of road and engine noise.

As you noted, the noise is different when the truck is warm. The sound is still there, but much less detectable at lower speeds. In some cases, I can get up to 25 and hear close to nothing.

Another interesting note is that braking significantly cuts the sound. Going 45 this morning I heard "bumpbumpbump" until I braked, at which point I didn't hear the sound, and when I let off the brakes, the "bumpbumpbump" continued.

Anyways, I am going to put the car on a lift tomorrow when I do an oil change and inspect what I can. I am almost wondering if a component of the drum brake assembly is broken and contacting the wheel as it rotates. I will also conduct the jack stand test and see if I can isolate the sound.

The brakes were one of my top contenders as a source of the problem as well. It's probably worth pulling off the drum to see what things look like in there.

The pawl /ratchet on my friend's Ford was so worn out, the adjusting screw did not extend anymore that it fell inside the drum.

If it goes away when you brake, check the brakes and the bearings.

The ring gear in the diff goes around once per wheel revolution, right? So if it is missing a tooth, and it is, every time it comes around it will make a clunk as the pinion gear tries to move over it.
Keep driving. At some random stoplight, when you let out the clutch and load the system, another one will go klunk. It will then sit between the ring and pinion, lock up your axle and the guy behind you might rear end you, as it is the same thing as pulling the handbrake.
At least if it happens on the highway, you have a slight chance that everything is spinning so fast that you just keep on rolling. It just makes a bang loud enough to make you think the driveshaft just exploded.

Then you remove the rear driveshaft and drive home at 5 mph with people honking at you. Clunk "hey" "yea, I know, " Clunk, clunk, clunk... "hey!!!"

Well I got the truck up on the lift today when I changed my oil. I also drained the third member and found no signs that anything in there is missing teeth. No metal in the gear oil besides the normal shavings that accumulate on the magnetic drain plug. I sifted through the drained oil with a magnet too and came up empty. I also pulled the wheel and drum on the rear driver's side, and the brake assembly looks fine. So that rules out (or at least decreases the likelihood) that brakes or the differential are the issue.

On the flip side, I put the truck in neutral and manually turned the passenger side rear wheel and listened. The driver side and passenger side rear both make an audible sound at the hub when turning the wheels by hand. The driver side is much more noticeable and there is also an intermittent clicking sound...almost like a ball bearing is moving around freely. The sound I hear on both sides could potentially be bad wheel bearings. It almost sounds like the 'Wheel of Fortune' spinning sound...if that paints a picture. Might also describe it as a constant 'dududududud' sound.

I did test the truck by putting it in gear and getting it up to 30mph with the rear end on jack stands. I wasn't able to hear the clunk sound at lower speeds but eventually heard it around 30mph.

Time for more research.

Easy to replace. Alexman Video has it on youtube. I have part number on my post.

And you could not hear/feel where it was coming from?

If you go to the 0:20 mark on this video, the owner records a clunk sound very similar to mine...seeming more and more like the wheel bearings need replaced.

Also, this guy makes a great video on replacing rear wheel bearings without a press. Really great video. You could use this from A-Z on this job as a reference.

It sounded to me like the driver's side rear wheel. Hard to say though with the sound of the truck running in a garage. At the very least, something in there is making a lot of noise that it shouldn't be. It's like the sound of wooden gears turning.

puller if you need one
https://www.ebay.com/itm/Rear-Axle-B...e/192611678638

Nice video and beautiful truck too! ^^^ I'll add to my thread.

Cool. In my case, I had a humming sound that sounded like backup vocals for "Living on a Prayer" - LOL!
I verified that wheel did not turn smoothly and one side was louder than the other here :)
Once I was sure of it, I got MCAX 241 Rear Axle Kit with Koyo bearings from Marlin Crawler:
https://lh3.googleusercontent.com/wX...W=w640-h480-no

https://www.yotatech.com/forums/f116.../#post52399536