Heard a clunk and then

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.

Or maybe just inspect the torque converter bolts.

Of course, why you are running a 904 behind a 340 is beyond me.

Do you have a mechanics stethacoat (SP?) Like a Drs. uses to listen to your lungs? If not a 18 inch long round piece of wood can work also, try it
I have used one many times to help narrow down where some engine noise is coming from

My Cuda had the 904 in it when I bought it, and doesn't it free up a good amount of horsepower? With everything I have found so far, I'm thinking the snout on the torque convertor broke. It's happened to me before but with different symptoms. I have been using a /6 convertor and if this one is broke I think it's time to upgrade the convertor to something stronger. With the driveshaft out and on a lift, it's no job to drop it.

Stock 904's don't live long behind something with power.

When you're drag racing and a few HP might actually be relevant they run a 904 based unit, but you can bet it is no where near stock.

Chrysler never put a 904 type trans behind the 340 for a reason. They fail.

Yep, I've run the 904 behind a few modified 318s. One was in a light street rod, I changed out 3 of then before I installed a 727 and solved the problem. All 3 904 had converter failures.
The one 904 I ran behind a 340 was fun for a while, but after about the 1st summer I switched to a 727, the 904 killed the torque converter. Nearly every V8 904 I've ever pulled had cracks at the corners of of the pump sloes on the converter drive. I didn't hear any noise from any of my 904 failures though nearly all had aluminum and brass coating on everything inside of the pan. The plugged up filters stopped movement.

I had a near stock 904 in my Duster and in my Scamp. Duster weighed 3000 and the Scamp weighed 2700. Went from a 340 to a 360 and then to a 408. Et's from 10.40 to 9.60 off a trans brake. The only problem I ever had was cracking the converter hub. Switched to the A500/42RH style hub with the flat drive hub and never had another problem. Not sure why you guys think they won't hold up.

Non stock 904

I believe I said stock ones fail. Had a mild 360 tear the ears off the front band of a A998 twice before I went A833 instead.

Can a 904 style trans be built to handle it? Yes. Cheaper to swap in a stock 727 and not worry about it ever again,

Very near stock. With the exception of the upgraded converter hub and a transbrake valvebody the rest of the trans was all factory stock parts.

I had four 904 failures in a span of about 8 years, every time the fix was a 727. If I was to venture in that direction again, why on earth would I take another chance of a 904 failure when the fix is pretty easy, especially on a street driven car? Swapping out automatic transmissions because of too light design failures is never fun. Installing a 727 into an A body is a bit more work, but usually once its done, its done. That extra effort up front is easier then a 2nd or 3rd 904 swap.

Were those used transmissions like that 46RE you were trying to use that had water in it or were they fresh transmissions? Like I said, I don't understand. I ran that trans for over 20 years. I pulled it down after the first year and it was still like new inside. You could still read the ink on the clutch plates. Never went through it again. I'm sure it's still in the car.

The 1st trans was probably the one that came with the motor, after that, they were all rebuilt. I discovered how cheap it was to rebuild a 904 or a 727.
The torque converters were also either new or remans. I'm sure the clutches and plates were OK, but everything inside the transmissions was covered with the insides of the torque converters. It was more time consuming to clean up the mess then it was to throw a rebuild kit into a clean trans. I could buy rebuilder 904s for $25 or 727s for $40 each, and the replacement torque converters were $25 each then. Good used trans were $150-$175.
I suppose, rather then blame the 904, the blame probably lies in the torque converter hubs or the front pump. When you install them both new, and less that a year later pull it out to find another cracked hub its pretty hard to figure out which caused the problem.

You also need to know I was pretty hard on everything I drove back in those days. I didn't need the hot rod to run in order to get to work, and it showed. I have matured in my driving style since then, some.

The 46RE being installed as a used trans was against my better judgment at the time, my track record with used auto transmissions isn't very good, never has been. But the cost of rebuilding a 46RE (a $600 kit was the cheapest I found) is much higher then rebuilding a 904 or a 727 ($125 kit). I'd gotten to where I was rebuilding those myself, but its been several years since I've rebuilt a trans. The 46 RE has me a bit nervous ripping one of those apart, and inside a welding shop (or at a body shop) wasn't good environments to rebuilt any trans, which were the only options at the 46RE's time. Gene

Creeping up on 100 trans brake low 9 sec passes with an incredibly stock component 904. Only real “jewel-ray” in the build is the A&A front drum spring pack . Also went the A500 pump gear