C6 makes clanking noise when it is put into D and R

[Geiri]

My C6 makes a loud Clanking Noise when it's Put into D or R or moved between them.
Driving is fine. What Part might be making the noise

 

[Broncobowsher]

C6 or C4? C4 is common in early Broncos, it was the factory option. C6 is pretty rare swap because it is so large and doesn't fit very well.
I first read this as a sustained noise when in gear, but I think I read that wrong. Is it a single clank? If so I am pretty sure you have a U-joint about a breath away from falling on the ground. Fix the driveshaft. If it is really that loud, you probably should not be driving it.

 

[DirtDonk]

That or your idle speed is too high. Or both.
Does it lurch pretty good when going into D or R?

Paul

 

[tirewater]

As mentioned likely a U-joint issue, especially if you've got one of those "kah-chunk" noises when shifting. You could try switching to 4wd w/ hubs locked to see if it makes the same sort of noise. My D-20 rear output shaft has more wear on the 2wd position than the 4 position, so there's more noise for me when shifting R,D while in 2wd.

A quick visual inspection under the truck would give you some clues. Just grab the rear driveshaft and twist with your hands and you can feel/see the play.

 

[Broncobowsher]

For the driveshaft check, it can't be loaded. That includes the park pawl. Chock the tires, set the park brake, engine off and take it out of park. That will unload the driveshaft and now you can check for play/wear.

 

[Rustytruck]

I take the drive shaft off to check it especially the center bearing in the cardan joint. it can look complete but the needle bearings are gone inside.

 

[TX-ZACH]

What is the rpm at idle?

 

[Geiri]

Sorry for not responding. I had to make an important trip.
To explain better the Driveline is still in a Ford Econoline I will move the complete driveline over to a 1976 Bronco in coming months.
I have uploaded a video that might help. Front wheel drive is not engaged. It might be the 9" pinion but even beneath the car it's hard to pin point. My old ears are not helping

RPM is about 1000 engine is not warm.
I can feel no play in the drive shaft. The car drives very nicely, no shaking or other indications. Inspected fully not long. Nothing found.

 

[Broncobowsher]

That is a huge amount of backlash in the rear axle. Really low gears and a detroit locker maybe?

 

[bax]

chain slap in the transfer case

 

[TX-ZACH]

Check your why the rpm needs to be this high. Mine did the same thing coming back from my motor build. Timing was off, carb was set to high as a result forcing a hard shift point. Check time, Check vac lines are in correct position or leaks then go back to carb adj. There are some threads posted.

Once I corrected the clunk vanished. My rpm at warm idle is 500-600.