My Disco has been having an issue for a while now. We have no idea what it is. I don't even know how to describe it, so I asked my husband to write it up and below is what he wrote. (The "thunk" he describes is pretty loud--sometimes I am surprised nothing is breaking!)

Please help…
My 2003 Disco seems to have a hard knock, not in the engine, and not shifting through the gears in the transmission, but when I release the gas pedal, and then again when pressed.
From starting the engine, everything is normal, put it into gear it and take off it shifts smoothly through the gears, but if I release the gas pedal and coast there is a “thunk”, and then again when I press the pedal.
It is like there is slack somewhere, and wondering if anyone else has had this
problem and have a cure?

 

sounds like take up in the drive line. common to have some slack to be taken up in most cases, but excessive can be sign of other issues. failing driveshaft/failing output bearing/worn/ etc

 

Thanks, dusty1. Hubby says that's kind of what he was thinking as it was coming from back near the transmission. Wasn't certain if it's a chain that could have been stretched. In the differential case, is it chain driven or is it rod driven?

 

no chains
1st thing I would check out is driveshafts....(front has a centering ball that will fail when it becomes dry)
then output bearing

 

Thanks, again. I will pass on that info. BTW, I could swear this noise started (although a lot less loud at first) right after the dealership replaced the rear flex disc. (I have no idea what that is, but that's what the receipt says they did.) I took it back twice right after it was done to have them look into the light clunking that didn't exist prior to their repair and of course they "couldn't find" the clunking or the source thereof. Do you think that could be related?

 

That is the rotoflex coupler.
It mounts the rear driveshaft to the rear differential.
It is a flexible coupling and absorbs vibrations.

 

I agree it sounds like a drivetrain problem, and it has the potential to be very expensive and dangerous if you have catastrophic failure. It needs to go back to the shop ASAP.

 

have the drive shafts and u-joints check they are always need some type of service, but the drive line being a fulltime 4 wheel drive does have a lot of slack

 

Just guessing here, but maybe the rear diff?

You would think the stealership would have identified a driveshaft problem.

I have had 2 diffs fail, but they were both fronts.

If you can get your hubby to drain a small amount of diff fluid into a white cup then look for metal that will tell you something.

 

My truck has done that ever since I've owned it 129k miles ago.

A bit of slop in the driveline is normal.

It all depends on your driving style. The thunk due to lag or slack in the driveline system only is noticeable if you operate the throttle pedal in an abrupt manner.

Using the gas pedal like an "on/off" switch tends to snap the driveline in the manner you describe...

Easing on and off the throttle you don't notice the snap so much.

Learning to feel the vehicle in operation is step one, learning to use it accordingly is step two.