Clunking in drivetrain..HELP!!!

[Geologist]

When I am driving above 20 mph, I hear a clunking noise that sounds like it is in the driveline, no vibration, just a clunk sound that repeats.
I have a 20 transfer case with a T-18 transmission, all new u-joints on the cv driveshaft, the driveshaft angles are exactly where they should be, the slip joint on the driveshaft does have some play in it when I push the driveshaft up and down from laying under neath the bronco, but not much. I am not sure if there is suppose to be play or not. I removed the drive shaft to check the u-joints, they are still good, I checked the play in the yoke, It does not have as much backlash/play as the dana 44 up front, not sure if it suppose too.
ANY IDEAS OF WHAT THE CLUNK SOUND IS COMING FROM THE REAR OF THE BRONCO??? HELP!

 

[reamer]

Do ya get it when you lay off the gas, or get it at a constant load/speed?
if ya get it when you lay off the gas, or put a load on it, that's the slop on the slip spline

 

[ND76Bronco]

i would like the answer to this question too. I have a similar problem when i accelerate and it fades off when i get above a certain speed. I had my ujoints replaced a few months ago and it fixed the problem temporarily.

 

[Viperwolf1]

When I am driving above 20 mph, I hear a clunking noise that sounds like it is in the driveline, no vibration, just a clunk sound that repeats.
I have a 20 transfer case with a T-18 transmission, all new u-joints on the cv driveshaft, the driveshaft angles are exactly where they should be, the slip joint on the driveshaft does have some play in it when I push the driveshaft up and down from laying under neath the bronco, but not much. I am not sure if there is suppose to be play or not. I removed the drive shaft to check the u-joints, they are still good, I checked the play in the yoke, It does not have as much backlash/play as the dana 44 up front, not sure if it suppose too.
ANY IDEAS OF WHAT THE CLUNK SOUND IS COMING FROM THE REAR OF THE BRONCO??? HELP!

You can remove the rear driveshaft and drive on the front to see if that cures it. I'd also look at the rear spring bushings and shocks.

 

[ND76Bronco]

excuse me if i sound ignorant but what would most likely be the issue if the problem is solved when driving on the front only?

 

[Viperwolf1]

excuse me if i sound ignorant but what would most likely be the issue if the problem is solved when driving on the front only?

It eliminates the rear driveshaft as the cause.

 

[ND76Bronco]

that makes sense thanks

 

[garberz]

Check the rear axle bearings. Put the rear on jackstands, remove the rear wheels and brake drums. Grab the wheel studs and see if there is any movement up and down. Should be zero play. Also you would probably see some bearing grease on the backing plates.

 

[Geologist]

ok, i hear the noise under a load and when it is not under a load. I can hear it the best when I am coasting in third or fourth, mainly because of how loud the flowmasters are, I have to be off the gas to hear it. I will try removing the driveshaft and driving with the front one, good idea. If that does not fix it, then I will check the axle bearings as stated above.
Thank you to everyone for the help!!!!

 

[jdcone]

Check the rear axle bearings. Put the rear on jackstands, remove the rear wheels and brake drums. Grab the wheel studs and see if there is any movement up and down. Should be zero play. Also you would probably see some bearing grease on the backing plates.

This would be my suggestion too. I just went through this 2 weeks ago. I thought it was the driveshaft, tranny, transfer case, rearend, ect. Guess what? Axle bearings and seals.

 

[techlaf]

"if ya get it when you lay off the gas, or put a load on it, that's the slop on the slip spline"

Not sure what this means? Which scenario of the two, gas on or gas off, is the slop in the slip spline?

I'm trying to figure out a similar problem. I hear a steady but slight clunking sound that decreases in sound and intensity as I let off the gas and slow down. I don't hear the noise at all when accelerating. '75 C4 and Dana 20

 

[Geologist]

When you are on the gas you are putting the vehicle under a load, so there will be a noise, when you let off, the load shifts and will cause a clunk sound then too, but you wont hear it necessarily when you are going lets say 50mph and put it in neutral and just coast. I hope that makes sence.

I will try the rear wheel bearings tomorrow, thanks again everyone for your input and help.