I've got an early 99 7.3 with the 4R100 which was rebuilt a few years ago (before I bought the truck) by a local shop. Recently, after a long western adventure towing the small 5th wheel (good times, tranny was never too hot) we started getting a banging noise when the truck idles. When you rev the motor up, it seems to go away or at least diminished so much that I'm not sure if I hear it in the truck. There is still a subtle throbbing noise but possibly this is the usual number 8 cylinder doing its thing? This is true in Park, Neutral, and Reverse and Drive (with brake held). In any event, on the advice of a local mechanic I put in a new torque converter (actually rebuilt, but from White Bear Lake Ford (Tousley)). After it finally came, I spent all day Saturday putting things back together and in victory started her back up at 11pm and basically covered in trans fluid ... to the exact same noise. Alas.

Since then I have run the motor with the inspection cover off. The converter and flywheel don't seem to be hitting the trans case, and the starter gear is not touching. You can hear the noise from the top of the engine but it is deafening underneath the truck. I can't tell if it is coming from the transmission side or the engine side. It's not a whirring, so I don't think that it is the trans pump. It's a bang bang bang bang, quite loud. The flywheel is not cracked. When I looked it over with the tranny off I thought that maybe the weld beads for the gear to the wheel itself had cracks around the edges ... that is, they didn't look welded together, but more like the weld was sitting on top, but then I decided that I was just being paranoid, and bolted her all back up.

So, does anyone have any ideas what I should do now? I'm willing to replace the flywheel if that's the next step, but if there is more diagnostics to do first, or it is something else, well, I've already sunk quite a bit in in parts! I'm confused why revving the engine makes things go away, but this symptom must be known by those in the know!

Thanks for advance for any help.

 

When you had the trans out did you remove the flex plate (what you called the flywheel) to see if it was cracked? If you didn't remove it you wouldn't be able to see the crack that usually makes this kind of noise.

 

No I didn't remove it, but just looked at what I could see when the tranny was dropped. Now I know for next time! This was my first transmission out, an adventure to be sure. So can I take it that redropping the transmission (it will go much fast this time ... all the stuck stuff has already been jostled loose and I know how to get at that top bolt and not to take the t-case off) and inspecting or possibly just replacing the flex plate is the next step? From your remark it sounds like this is a known noise. I was terrified that somehow it could be the crankshaft!

Thanks.

Ben

 

They can crack around the bolts to the crankshaft.
If there is a stiffener plate the cracks may not be visible to an untrained eye.

 

I'll pull it off and have a look.

 

Yup, that was it. It was so cracked it would have soon fallen off. Thanks for the advice.