Trying to identify a noise...

Yea - not sure this is going to get anywhere as trying to describe noises on a written forum is difficult. But maybe we can at least identify something - like maybe its not the engine and rather something in the drivetrain, or I can create a process to go through. Wondering if this is something I need to address sooner rather than later.

Getting what I might call a 'knocking' sound - maybe like a bad exhaust leak but coming more from under the engine or transmission area. I don't think its typical engine knock (pre-detonation). For traditional pre-detonation I would expect to hear anytime the engine is running, including when its running in nuetral. I only hear this when in gear and running down the road - not when in gear with clutch pedal pushed in (clutch disengaged). Thus it seems more drivetrain oriented ... am I on the right track? Same for exhaust leak - would expect to hear anytime engine is running.

One major concern that I'd love to rule out (or know for sure) is the crank bearings could be having some issues and causing the knock - and the sound seems to come from the engine area - but again only when in gear and driving down the road. Don't hear it when just running the engine in the garage at any reasonable rpm...so can I safely rule out the crank bearing? I am also starting to get an increase in the the amount of oil dripping out of the rear seal - so that could be connected. Going to do an oil change and see if I am getting any metal flake. Other suggestions?

Drivetrain possibilities...The sound seems to only occur when easing off the gas pedal or just holding constant speed on flat terrain, but not necessarily when coasting in gear or during hard acceleration (of course its tough to hear ANYTHING during hard acceleration so maybe it happens then as well). Maybe some damaged teeth on a gear, either in the T14 or D18 - I get solid gear whine associated with my D18 so wondering if a bearing has worn and gears are clacking? I had a similar but more clacking sound years ago on a T5 in a CJ7 that turned out to be a worn input shaft bearing that then caused the input gear teeth to chip. Starting to think something like that.

Finally, Could something in the clutch cause such a sound? TO bearing would usually make more of a constant whirring sound - not a knock I believe.

Thanks for the help - these kind of things are ridiculous to discuss on forums but appreciate the help.

 

Throwout bearing shouldn't be spinning unless you are depressing the clutch. I don't know that you would hear engine bearings noises when driving.

 

Is it a steady knock, knock, knock, or does it come and go sporadically. Is it light like a tapping or harder than that? Has there been any roar coming from the intermediate gear maybe that has turned into a knock? Of course are all lube levels correct?

 

Thanks guys - yes I checked and topped off any fluids levels. Oil is fine but probably ready for a change (certainly not at 3000k miles but its getting close to a year). The oil does always seem to show some gas thinning - probably due to both some worn rings and the 5-13 thousand foot range I drive it so it can run pretty rich at times. The Transmission/TC was just a bit low but not below the fill mark. I have also checked the u-joint straps, but didn't take them off to see if the u joints themselves might have any issue. Anything to look for? Make sure the caps and needle bearings are all good - will check again to see if their is any slop. No sure about checking slip joints - just remove the driveshaft and check for free play and room/freedom to slip?

The sound is pretty consistent in that its always happening when I am driving down the road - again not so much when coasting, just cruising under easy throttle. The sound has grown from barely audible tapping to more of a clacking/knock - but not a valve train kind of tap or clack - heavier sounding than that.

The sound is tied to engine rpm through each of the gears - thus my initial engine concerns, but just don't hear the sound when in the garage. Kind of wondering about transmission issues, but what would be tied to engine rpm and not to road speed?

Will definitely try running through the gears with TC in neutral - that's the exact kind of 'I shoulda thought of that' idea that this forum is so great for.

The D18 definitely whines/roars - typically more under coasting or neutral throttle. I don't know much about the interior of the D18, but seems plausible that something with the intermediate shaft has grown into a knock. Have been wondering if I am hearing less whine and more knock, but don't really know.

 

Thanks for the input - I need to get another set of ears to help listen, especially when driving!

 

Think I may have identified the issue - well its an issue, whether its the sound issue or not we'll find out. I drove it around the block and definitely determined the knocking is tied to engine speed and not road speed. Then I tried running it through the gears with TC in neutral and no noise what so ever. While fiddling around with the gears, I accidentally found the sound when the engine was idling and the clutch held in. Didn't happen every time, but enough to start the search around the clutch/bellhousing. Crawled around under there with engine running and help to push clutch in and out. Found when the clutch went in, a small gap is opening between the bellhousing and the engine block - only on the upper portion - and I think the knocking is the bellhousing rattling against the block. Looks like a some of the upper bolts are loosening up. One was finger loose (yikes), others have a small gap but are bound from the weight of the transmission.

Need some more time to take the floor hump out and get everything tightened up to spec....will probably have to put a jack under the transmission to take some of the weight off and tighten. Thinking this is the issue...its certainly an issue and seems not to make any noise when jeep is just running in neutral but when the transmission engages it would vibrate the mating surfaces against each other.

May be a day or two (or even after the holiday weekend) but will follow up with the results. thanks

 

I'd say that most likely is the issue. Glad you had help when you needed it. Make sure all the bolts have lock washers, and you might want to consider pulling at least one out to check for possible wear from rubbing and the strain on them.

 

Same here. I would definitely be worried myself.

 

Agreed! - After finding the issue yesterday my wife asked what I was going to do next. Said get cleaned up and eat dinner and think about it...as I was also wondering about pressure plate bolts loosening up (and possibly flywheel as well). No knowledge of who or when the last install was done...some PO at some point I guess, if ever.

At some point in the reasonably near future I think the entire drivetrain needs to come out for some maintenance (new clutch, syncs and seals, bearings, D18 intermediate shaft stuff etc - not sure what else). Was hoping to hold off on that for a bit...as I also want to put terra low gears into the D18. Still debating that as a T18/SM465 would give more a lot more benefit in terms of CR, but like the simplicity of just a gear set inside the same case (nothing else changes). Not really ready to make those final decisions on that topic so I have to decide if I am going to pull everything 'just' to check bolts.

Kinda leaning towards tightening up what I can see. If all is back to normal then I will probably go with it. Wouldn't be surprised if there are still 'sounds' from something loose inside that requires going all in.

 

On the F-head it's all cast iron being held together by bolts and nuts. Is the V-6 the same way, or is there any threaded aluminum involved?