Just rebuilt my 88 D100 engine and all was weell for a bit; then I bagen to hear a knock or clunk once in awhile. There is no steady ryhtem to it and on smooth roads, I rareely ever hear it. But let me drive on a paved road with a few dips or low spots and that knock will come back. Now I will say that I have stripped by cab of all of its sound proofing as I am rebuilding her; however the noise sounds like its coming towards the back on the cab like someone with a hammeer hitting the bottom of the truck. My first suspicion was the drive shaft so I put it up on a hydraulic life and took my rubber mallet trying to reproduce the sound...couldn't do it. I tapped all along the drive shaft and took both hands to tried to shake it at the U-joints but there was no play whatsoever in them. Lucky me I have sealed u-Joints so I couldn't grease them if I wanted to. The closest sound replication I had was knocking on the belly of the Cat Converter. I then knockeed around on and shook the exhaust pipe nesr the hangers a u-bolts......the sound was almost duplicated there also. I inspected all the bolts holding it all together and nothing was loose nor slipping. I thought that if it was the drive shaft, it would make a noise regardless of whetheer I was driving on a smooth road or not...it would make a constant noise I thought.

Does any of this ring a bell to anyone??

Thanks for your help

 

Check all your suspension mounts as well. I bushing going south is a real possibility there.

 

Thank you...I definitely will. Just so happens Im replacinmg my rear springs anyway: still have originals on

 

you can always replace the universal joints with greasable ones if you think they are bad. usually they are most noticeable when shifting from park into reverse or reverse to drive. have you changed the rear diff fluid? wouldn't hurt to pop the cover and check things out while changing the fluid. may also be worth checking the motor mounts. they can clunk even if just 1 is bad and would likely not be as consistent. it would likely be more noticeable off the line or when you are hard on the throttle but not as noticeable with light driving.

 

Thank you sir,,,and yep Im definitely replacing those U-joints with greasable Moogs. Great ideea for checking the diff!! Motor mounts are brand new and I have inspoected them a few times since we rebuilt the 318.

Going to replace originalk leaf springs next bushings etc, but Im wondering what muffle to go with when I replace the exhaust pipe...and reccomendations for the muffler and the CAT?

Appreciate it

 

unless the bushing are completetey gone which would be visible they are likely not clunking. as far as muffler goes really depends on your preference. the muffler won't really change the sound too much. i would personally just try to find a muffler that is made of quality material and not going to rust out on you. they will sound about the same if all the pipe is factory size. i also like dumping them out the passenger side in front of the wheel.