Hey everyone, just picked up a 97 Disco about 3 weeks ago with about 181k on the clock. Love the truck and I got a really good deal on it. The interior has been well taken care of, I would like to say the engine and the drive train has been as well..but I'm not so sure. I will first tell you the problem I am having trouble diagnosing and then tell you what I've done already.

Whenever I am cruising along at about 40-45 mph and I release the gas pedal I hear and feel a slight "clunk" coming from the passenger side and the RPM's of the engine will drop about 1k at the same time you hear the "clunk" and then jump back up. Sometimes, the RPM's will bounce back and forth, dropping about 1k and then back up and dropping again. The truck only does this when it is in drive, when I drive around in 3 I have no problems. This leads me to think it has something to do with the direct drive portion of the transmission.

This only occurs when I let off the gas at around 40-45mph. It does not happen every time and does not seem to be temperature related. Once I am above this speed or below this speed I have no trouble and everything shifts and engages appropriately.


Now, here is a list of everything I have done so far:
Lubed UJoints and drive shafts (no idea on the age of Ujoints or drive shafts, but they have no play in the and no vibrations while driving)
Changed Front/Rear diff fluid
Changed Transfer care fluid
Changed Transmission fluid (Was not able to change the filter as after spending a couple hours laying on the ground attempting to do so, all I ended up with was a unbolted cross member and a broken y-pipe flange.
New plugs/wires
Changed oil
New brake pads on all four corners and new caliper on front drivers.

I am thinking about taking it to a transmission shop, but I want to ask some of the experts on here their thoughts first.

Thanks,
Stephen

 

Does the tach jump around, or is it the actual RPM of the engine? Just the tach and it is an alternator/ battery problem

your tranny has a locking torque converter that the ECU locks at around 52MPH. That could be part of it. Any way to let someone else drive, with the windows down and try to pin point the clunk a little closer?

 

The engine RPM actually jumps around. I also forgot to mention in the first post ever since changing the diff/transfer case fluid I do not hear the clunk. I suppose the best way to visualize this problem is to imagine yourself driving along the road, you release the gas pedal and someone grabs both the drive shafts, holds it for a second and then lets go. You can physically feel the truck slow for a second and then go about its business as usual.

 

Sounds like it could be spider journal on your drive shaft you can check by hand, by twisting the dive shaft. If bad you will have play!

 

Sounds like drive line play to me. I would guess that it will do it at higher speeds, you would have to hit the gas harder to notice it, most likely.

 

Your transmission has no electronics, it is all mechanical so the torque converter locking/unlocking is not going to be quite as smooth as a newer electronic transmission.

Make sure your tire pressure is the same all the way around. I have found that one soft tire will bind up the driveline.

Since you changed the driveline fluids and the noise is basically gone that tells me that the fluid was just plain worn out.

Some driveline slack is normal for a full time 4x4 with 181k miles on it.

 

Guy, I agree 100% with spike - our '97 lockup torque converter locks @52mph on increase, 49mph unlock on decrease. (approx)

Mine's fairly silent, but my drivetrain has very little slop.
as a result, I barely notice it anymore, but my tach jumps accordingly.

I'd double check your driveline, noting any play - some would be expected.(not the u-joints, tho')

luck,greg

 

I also have a 97, mine would clunk when I let off the gas at that speed range, changed the diff fluids to 75w90 Mobil One synthetic and it quited right down. My mileage was only 110K at that time. If you are cruising right around that 50 mph mark then you're locking and unlocking frequently and it will fill like it surging or dragging slightly like you were upshifting/downshifting or something like that.

 

I had a similar problem at around 65-70 mph and at constant speed but it felt like it was coming from the middle of the vehicle. Got under it and noticed my rear flex joint was cracked near almost every bolt. Replaced it and no more problem. My mechanic and I decided the clunking was the flex coupling separating and pulsating at high speeds. Thank God I caught it when I did or it probably would have given out on me at a high speed and dropped the driveline. That would've bit the big one.

 

Awesome, thanks everyone for the information. My daily driver is a 07 Ford Focus with a manual transmission and it has been a while since I've had a 4x4 truck (if you want to call them that, was just two different Ford Explorers). So I am a little out of practice, I don't believe I have ever owned a truck with a purely mechanical transmission.

I have to say, that this is why I love this forum. I have been search on here for a while finding how to's on every little thing that I want to do to the disco. I really appreciate the quick feedback on this!

Thanks,
Stephen