Strange driveline clunk

[Ginja]

Wondered if any of you have experienced this. In crawling traffic my car (69 Coronet 383/727) has a clunk that sounds something like a wheel weight hitting as it goes round. Its either not as audible or doesn't happen (I think it does but my car is loud) while rolling, but I think its much reduced in volume under load. I know its not the front end, and its not the trans (2nd trans with same noise). I think its the rear axle somewhere. My sure grip isnt working too well - wondered if it could be related to that. My 8 3/4 axle has green bearings and is one part of the car that I've yet to tear apart. Any ideas - if I rotate the wheels on the lift there is a slight bump noise but it could be coming from anywhere - so hard to locate.

 

[Red63440]

I would check your universal joints, a bad universal would be more noticeable at low speed. Do you notice any vibration?

 

[747mopar]

Make certain that it isn't a U joint then pull it apart, takes 15-20 minutes. We can spitball but until you investigate that's all it is.

 

[Cranky]

With the rear wheels off the ground, do you have an axle end play? With the Green bearings, there should not be any....at all.

 

[Ginja]

Thanks for your replies and bear with me I'm learning as I go here - lots of 'firsts' on this car - axles being one of them.

Red - U-Joints have slight play, as in I can microscopically move the opposing parts with my hands - I presume that's bad?

747 - do you mean pull the differential out? Slide out the axles, undo the bolts in the axle and plop (well, crash I presume if its not well supported). What will I be looking for in there?

Cranky - There is ever so slight end play in both axles.

The engine has a cam, and funky rockers, hooker headers, flowmaster 40's and edelbrock performer and a big holley carb - with all that its kinda hard to hear noises but I don't feel any undue vibration, just a wheel speed and very audible internally 'clonk'.

 

[Cranky]

Years ago I could hear a bump bump bump that sped up with the speed of the car. The slower I went, the better I could hear it and could hear it better while through an alley way doing about 20. After checking the u-joints (pulled the drive shaft out to check for looseness) and pulling the drums off the rear, I went to the front and pulled the drums off....and found a cracked inner bearing race. Yeah, I knocked the bearing out figuring they were original since the car was bought new by my sister and figured may as well replace them while there. That was a first and never seen it again since. Someone else on here was having a clunk sound and it turned out to be a rear brake drum that was touching the backing plate but not all the time iirc. Some times you got to start taking things apart to find what's going on.....

 

[Ginja]

Years ago I could hear a bump bump bump that sped up with the speed of the car. The slower I went, the better I could hear it and could hear it better while through an alley way doing about 20. After checking the u-joints (pulled the drive shaft out to check for looseness) and pulling the drums off the rear, I went to the front and pulled the drums off....and found a cracked inner bearing race. Yeah, I knocked the bearing out figuring they were original since the car was bought new by my sister and figured may as well replace them while there. That was a first and never seen it again since. Someone else on here was having a clunk sound and it turned out to be a rear brake drum that was touching the backing plate but not all the time iirc. Some times you got to start taking things apart to find what's going on.....

Oh, I'm with you there, its been apart - most of it, just not the axle. As a relative beginner in 3 years I've had an engine out for the first time, replaced the trans, rebuilt the whole front steering system (inc cutting the column to add a Borgeson box), replaced drums for discs (spindles, bearings and all), added a servo, renovated the fuel system, rebuilt the carb, added a fan/clutch and shroud combo, replaced the radiator... and it goes on. But the axle - not touched that yet. So I don't think its the bearings at the front, or the rear. And its neither a bump nor a click but somewhere in between. The drum/backing plate idea i'm going to look into more closely as it seems worse when the car is hot or has load in the back - just did 600 miles over 4 days in it and slowing into traffic on the motorway (freeway - I'm in the UK) was when I heard it the most, with a trunk full of camping gear. I think its wheel speed as opposed to driveshaft speed as well.

 

[oldbee]

Years ago I could hear a bump bump bump that sped up with the speed of the car. The slower I went, the better I could hear it and could hear it better while through an alley way doing about 20. After checking the u-joints (pulled the drive shaft out to check for looseness) and pulling the drums off the rear, I went to the front and pulled the drums off....and found a cracked inner bearing race. Yeah, I knocked the bearing out figuring they were original since the car was bought new by my sister and figured may as well replace them while there. That was a first and never seen it again since. Someone else on here was having a clunk sound and it turned out to be a rear brake drum that was touching the backing plate but not all the time iirc. Some times you got to start taking things apart to find what's going on.....

There ya go. Alley between buildings or thru a bank ATM with a wall right there, the sound bounces right back at you. Ujoints going bad will show up right away.

 

[Macdon221]

I just went through this...one of the ujoints had a "stiff spot" in the rotation. I just replaced both and it was gone. I used spicer ujoints. Replace both and it is quick and easy and fairly cheap and it would rule it out.

Something to think about...you had said that your suregrip is not working well...but you did not explain further. Maybe it is related to something in the differential. Maybe the backlash of the differential would cause a clunking if way off.

As a side note...when I had the drive shaft off I got ambitious...I replaced the rear axle bearings and seals, front hub inner and outer bearings and seals, as well as tore open the diff and replaced all four bearings in there as well and clutches. Reset it all to factory settings. What a huge difference now in the both the smoothness and sound. The little bit of gear noise I has around 30-40mph is now totally gone.

 

[Sam69sat]

Probably not your issue but check the springs for a possible broken leaf. Had that happen before and it made a clunking noise. And also when i replaced the springs, the new ones had plastic leaf spring inserts between the leafs. Those plastic pieces of crap make clicking noises that sound like a u joint going bad.