I was driving along about 30 MPH, just a steady speed and all of a sudden a big clunk and shake like I ran over something or like something hard broke. I looked in rear view mirror, nothing. I then started easily to get back up to speed and clunk, clunk, clunk. I let off the gas and it goes away. I'm only about a mile from home so I ease it slowly all the time under slight acceleration I get a clunk, clunk, clunk. I stop at stop sign and then proceed and still get the clunk. I go down hill coasting and no noise unless I give it just a little gas. Pop it into neutral and rev engine, everything seems ok. I get it home, put it on lift and everything looks ok, u joints, drivshaft etc. What do you think? Cuda 340,904, 741 differential with 3:55.
TIA

I'd guess it is in the differential.

Check your pinion nut or any up and down movement with the pinion yoke.

[censored]. To me it sounds like a disaster. Have it hauled to the nearest toxic waste site. My bets are pull the shaft you lost a cap.

Well the noise has to be coming from some section of the vehicle, front, center, rear, left, right, center. Should tell you where you need to look.

My guess, spider gears and mebbe axles. DAMHIK

8 3/4 w/o sure grip? Or a cone style sure grip? If so my bet is the spider gear shaft has wobbled out the hole in the case.
Doug

Non Sure Grip.

Hmmmmmmm to me it seems when your coasting in neutral the only thing that is not function is the 904 or am I wrong?? Doesn't the drive shaft keep turning when coasting.....but then again it's not under load. Hope it is just the drive shaft / universal and not the trans or third member, axle.

FWIW from personal experience:
A light clunking - more like a rotational rattle - was a u-joint breaking up.
Heavy clunking - again rotational - was a ring & pinion, specifically teeth broken off on the ring gear.
In both cases, made it home, but the ring gear event sounded bad, I could feel it as much as hear it.
Oh, there was another, again rotational, when a shop under-torqued the pinion nut on my Dana 60; that was more of a lighter clunking, all the time.
That one I caught quickly, with no resulting damage.

I've had this happen to me twice.

First time with a big block Corvette - pull over, can't "see" any visible signs but its persistent decide to get the car towed to a local shop. Diagnosis ... crank is broken in half diagonally across the center main which allowed the engine to run but clunk.

Second time with an '88 Dakota. It "appears" a cap let go in the diff.

If you can drive the car then I'd discount the rear end. Just because the clunk wasn't there in neutral doesn't mean its not the engine!

You said it looks ok on the hoist. Did you run it ? If not.

Put it on the hoist and have someone place in gear and let the wheels spin while feeling the rear axle housing.

Drag the brakes and do this in drive and reverse.

I've heard that dreaded clunk, clunk, clunk, a few times.

Once I heard in in my car with a built up 318. I pulled over to the side of the road and opened the hood. I saw the fan belt was off, so I grabbed it to try to roll it back on and noticed the crank pulley moving up and down. I was a bit relieved for about a second, it took about that long to notice the harmonic balancer was moving along with the lower pulley. OOPS! Broken crankshaft through the front main bearing. Yea, I broke a crankshaft on a 318. The next motor was a 340.

Another time was with my 3/4 ton pickup. It was loaded up to go to a swap meet when it developed a clunk, clunk, clunk, as I was leaving my buddies shop. I turned around and went back, he was a transmission guy. We took it up the road about 200 feet and the trans grenaded. We managed to coast to the side of the road and drug the truck back to his place where we replaced the transmission, before we went to the swap meet. OOPS!

One other time I got the clunk, clunk, clunk, coming from the rear end on my Road Runner. That one was under acceleration for the first few miles, then by the time I got home it became persistent all the time. On that one, the spider gears had a problem and caused the cross shaft to start spinning. As it spun, it started elongated the hole in the 8 3/4 case and it started to wear a grove in the case. The noise started when the cross shaft finally started bouncing off the outer housing. I felt pretty lucky to make it home on that one. the next center section was a 3:23 Sure Grip.

One other time I was driving down the road and got the dreaded clunk, clunk, clunk, and discovered the needle bearings in the front u joint on the driveshaft were gone. That one wasn't too bad.

Usually clunk, clunk, clunks, are pretty expensive to fix. Gene

Poorboy- i had a similar experience in my charger. Driving the Taconic Beltway, it felt like I hit a Boulder. The clunking followed. It was somewhat drivable, but only a few feet at a time. Initially thought we broke a flex plate. It broke that crank right in the middle and scattered bits everywhere in the pan. Pickup completely packed full. Also- lots and LOTS of blue smoke. Vehicle was religiously and meticulously maintained.

Some friend could have put a big zip tie on your driveshaft

3406E Caterpillar crank. Broke at #1 rod journal. Barely made a sound but had a vibration, much like a u-joint except when I stopped, the vibration didn't... Other than that, if you didn't know what a healthy one sounded like, it sounded fine, diesels being clattery and all.

I knew it was bad news when I saw the damper running in and out an inch or two.

Kevin

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Driveshaft, U joints and differential look great, no broken or missing anything. Only thing left to do is pull the transmission.