Clunk every 3 seconds at 65 MPH...

[unclebilly]

My 95 CH613 gravel truck developed a today. Atleast I noticed it today on the way back from hauling household garbage to the dump...

Everything in the driveline seems tight, the tires are good, rough or blacktop doesn't seem to make a difference. The power diverder lockout maight make it louder but it could be my imagination. I drove with the box part way up and cant see anything weird happening with the driveshafts when it clunks.

Oh, and it isnt the tail gate clunking, this is what I initially thought it might be but this is what it sounds like.

If I roll up the window, I cant hear it.

What say you guys?

Edited November 17, 2012 by unclebilly

[slpwlker]

There any freeplay when you take off or slow down? is it from the driveline area, front? Whats the shifter feel like? Vibrating like crazy or very minimul?

[unclebilly]

There is no freeplay in the driveline (like a cruise control on / off) and there is no vibration in the gear shift. It will do this on a constant climb up a hill.

[slpwlker]

um getting alittle outside my guesses.Could the hood be moving as the cab moves? I get alot of thunks in my Pete. Alot i have written off others I hunt down. Rubber pad on the back of the cab that the hood comes off and the cab moves it will thunk like crazy.

[David]

Does it slow down or go away when the truck slows down?

[rsb502]

as above is the clunk constant with driveline speed meaning gets faster as you speed up slower as you slow down, is it every few seconds at the same interval or does it seem to change pace at a set cruising speed?

[unclebilly]

It is about every 5 seconds at 30 MPH.

[David]

Sounds like something being moved by the wind. I had a loose exhaust stack do this before.

[rsb502]

a clunk at a constant interval with tire rotation leads me to the drivetrain, I dont know what in the driveline is moving slow enough to clunk every 5 seconds at 30mph so that makes me think its the body or frame but it wouldnt be timed with driveline rotation so Im gonna have to go with the only thing I can think of and that is a transmission output or countershaft issue, the gears rotate at a speed consistant with driveline rotation as the gears turn you may have a chipped or broken tooth or pair of teeth that one on a large gear and one on a small gear only come into contact once every two to four revolutions try to keep the truck as quiet as possible on a very smooth road and put your fingertips on the gearshift and put slight pressure to the out of gear side (push ever so lightly like you were pushing it out of gear to put tension on the gears and see if it goes away or you can feel a tick timed to the sound. Another question is this in every gear or just top gear?

[rsb502]

I hope its something i the wind or clunking to a rough road just seems odd to be timed with driveline rotation (faster at one speed slower at another)

[JumperAndSon]

Maybe air pressure related? Bleeding off pressure at regular intervals? Just an outside the box guess.

Tim

[David]

Look for something on top of the tarp or the tarp not retracted tight.

[unclebilly]

I have only noticed this in high range but at 30 MPH, it wouldn't have been in top gear.

Could it be a broken axle?

[unclebilly]

I aired down the bags while i was driving empty and it made no difference.

[rsb502]

well if it only happens in high range that gets into another transmission issue it point to the back box in my mind, it might be an axle but you would hear it all the time under power and it wouldnt be so slow the gears in the carriers are spinning pretty quick.

[slpwlker]

Is it a thunk or a growl?

[Lmackattack]

Might want to have someone follow you in a car and have them pay attention to any sounds from the rear end and transmission. But a clunk every 5 seconds seams like a big interval for a broken tooth on a gear. I would suspect at 30 mph it would be more like every 2 seconds the broken tooth on a gear would come back around.

[57 bcr]

Do you have hub-piloted wheels on the drives? I had a problem a few years back with a slightly loose set binding then shifting and beating the snot out of the hub until the pilots (4) were badly grooved.They would SNAP & POP.Had a couple guys tell me it sounded like a rear end mssing a tooth! Pulled the rear carrier then pulled the truck outside & it still did it!! DOH!! Glad I was the one that found it,rather than a shop$$$$$!!!! Just a thought!

[Superdog]

  On 11/19/2012 at 2:15 AM, 57 bcr said:

Do you have hub-piloted wheels on the drives? I had a problem a few years back with a slightly loose set binding then shifting and beating the snot out of the hub until the pilots (4) were badly grooved.They would SNAP & POP.Had a couple guys tell me it sounded like a rear end mssing a tooth! Pulled the rear carrier then pulled the truck outside & it still did it!! DOH!! Glad I was the one that found it,rather than a shop$$$$$!!!! Just a thought!

I'm with Al,check your wheels,I cracked an inside wheel once,sure sounded like a u joint

[30yearoldjunk]

Over a dozen years ago I drug my dad's '75 R-model out of the weeds. It did exactly what you are describing. Embarassingly, after a few hundred miles I checked the gear lube in the rears, topped everything off, and no more thump every few seconds.

[fjh]

If it has mack diffs It sounds like a power divider issue to me .Are you running un even tires between axles?