I went on a couple of bumpy trails yesterday, using 4 Low in 1-2. After getting back on the road, I noticed a noise that slowed as the vehicle slowed. It sounded like something was stuck in the tire but I couldn't find anything.

Rolling in neutral didn't change it. Brake application didn't change it. Engine speed while rolling in neutral didn't change it. Only vehicle speed. It would slow with the speed of the vehicle and stop when the vehicle stopped. Revving when stopped didn't make the noise. It seemed to be occurring at all speeds.

After ten minutes of driving, I went over a bump and heard a single loud clanking/banging sound from underneath the Jeep. The Check Engine Light came on. Then the noise was gone. Nothing fell off. My wife said this has happened to her once before in this vehicle, over a month ago.
The code is P0740, Torque Converter Clutch Circuit Open. I've been getting this code periodically without this noise issue as well. I tested shift solenoid resistance and they are within spec.

Any idea where to start? I wish I had a simple diagnostic flow chart to follow.

99 XJ 4WD 4.0L AW4 231

Thanks

 

Just a thought. Is it possible you got something caught around the driveshaft that was banging on the floor and finally fell off, like a stick or vine or even a piece of rope? I ran over a sleeping bag in the woods once that wrapped up around the driveshaft of my big Chevy 4x4.

 

It's possible, I guess. It was a pretty loud clank when I hit a bump and the noise stopped though. I don't see any fresh scrapes on the driveshaft.
I'm picturing something in the transfer case, differential, or transmission going bad but I have no idea how to diagnose it.

 

Pull the rear diff cover and inspect the planetary cross shaft that holds the little spur gears in place. When you said "differential" a chill went up my spine! My rear axle blew up because that cross shaft had broken where the bolt held it in and once in a while it would bang and I couldn't figure it out. Then one night there was a REALLY LOUD bang and the jeep slid to a stop! It had locked up and the T/case jumped out of 2wd. I finally got it to roll, stuck it in part time 4wd, and limped it home. Next morning I opened up the rear diff to find bits and pieces. Maybe we can save yours before that happens.

 

Differential gears seem to be fine. Fluid was fine. No chunks of metal or any particulate that I could find. I had never opened this before so I guess I'm happy to see it in good shape.

What else could it be?

 

Was the front wheel drive still stuck in gear?

 

It didn't seem to be. I didn't really check though. If it happens again, I will check. What is the easiest way to check? I guess just in case, I should avoid using 4wd until I figure this out.

 

Well, my first guess was you had something stuck in a tire tread and it finally flew out and hit the inside of the fender, but I waited until now to see what the smarter people had to say.

 

Sometimes torsional stress will prevent the 4WD from completely disengaging. If this is the case backing up while applying a little pressure to the lever will usually free it up.

Allowed to do it at speed by itself usually results in a pretty loud clunk.

 

Hmmm. This could have been the case. I've driven several road miles in 4wd then. I'm trying to remember if it felt like it shifted smoothly out of 4wd. Would this potentially cause the P0740 Torque Converter error code? It could be unrelated but there was the loud clank and immediately after, the error code.

 

Yeah, I don't know. It seems 740 is triggered by a pile of different things including easy stuff like poor connections or low fluid.

Meanwhile, you may want to take a look at the transfer case linkage to make sure it's not sticky or sloppy to make sure that isn't causing incomplete disengagement of the 4WD.

 

Yes. Take a look at the bushings on both ends of the reaction shaft. If the frame end has popped out it gets really sloppy.

 

I figured it out. The front, passenger side U joint caps were coming out, scraping against a hub mounting bolt. When we went over the bump, we probably loosened a u joint cap enough to move further out, banging hard against the hub bolt head.
I determined this by putting the front end on jack stands and spinning each tire by hand. The passenger side made a scraping noise at the same point every rotation. At very slow speed, it even stopped the tire. Then I looked at the u joint. I had previously only looked at the driveshaft u joints. Caps clearly coming out and contacting the hub bolt head.
It felt satisfying to temporarily fix it by hitting the caps back in with a BFH.

Terrible picture but you can see the hub bolt head in the middle with the u joint cap touching it.

 

GOOD CATCH! Lucky you caught it before to came completely out. I'd say the snap-ring either wasn't seated or it broke. Sometimes the joint ears get bent removing the old joint and the distance between them gets too close to get the snap rings to seat properly. They are forged and can be straightened easily in a vise with a BFH or wedges.

 

Now THAT'S impressive!