Has anyone else had this? I have a 1998.5, 5.9L Diesel Ram that I just started towing a 30' travel trailer with last summer. I noticed that on some hills, but not every one, a thumping sound under the hood kind of like a rubber mallett--- thump thump..... about every second or so. I could make it lessen a bit by downshifting and turning off the AC, this was while the temp was 90+ outside. I'm wondering if it might be a motor mount? This has never happened when I'm not towing, only when towing and only on some hills. Any ideas on how to diagnose this would be much appreciated.

 

if it was a motor mount you would hear it the most when accelerating from a dead stop. the best way to test if it is a motor mount is to pop the hood and have someone watch the engine while you put it in first and slowly let the clutch out or put it in drive and give it some throttle, just make sure you have the parking brake on. if the engine pulls realy far to one side then they would need to be changed out, and that can be done without pulling the engine.

you are saying it is a slow thump, do you have an auto or 5 or 6spd. if it is the 5spd NV4500HD then you might need to have a tranny shop check to make sure the 5th gear sproket isnt trying to walk out or break. if it is the auto 47RH (I think) it could be the torque converter locking and unlocking.

I'm scratching my head on this one

 

Mine has the 5 speed manual, and I'm surely baffled by it too. [sm=confused06.gif] I have not towed since last fall and I have not had the thump since then either. There is no unusual sound when I take off from a dead stop, but I'll sure try the first gear test and see what happens there. If it were the tranny I'd still be a bit puzzled there too as it would do it at times in 4th or 5th going uphill while towing ( even with plenty of speed and power) and would go away or get better if I went down to 4th or 3rd and took the hill at say 35 50 mph depending. I sure appreciate the ideas, and I'll let you know if I can trace it down.

 

Update! I may have found something here, when I was doing some other work this weekend I bumped the ABS brake module with my elbow and discovered that it was missing a shock mount under one of the three nuts that hold it down. Came that way from the factory and it never rattled unless there was enough pressure I guess. All they are is a metal washer with a rubber back, so I put a metal washer and a garden hose washer together and it fit perfect. I wont know for sure til I tow, but I bet that was it, nice that it was something cheap for a change.