SO, I have been meaning to post this for a while...

The vehicle here is a 2002 Disco II with 94k miles. It is driven daily to work, but this is only a 5 mile tripover surface streets - not really exceeding 40 mph much. However, we do go out of town in it once or twiceper month - and that is when problems start... After driving on the freeway for at least a few minutes at constant speeds a clunking noise begins to happen when I take my foot off the gas or get back on:

-never happens on a cold engine (you have to be on the freeway for a while for this to start)
-can happen as low as 45mph or as high as 75 - never go faster so don't know
-sometimes barely noticeable sometimes very abrupt - like someone just tapped you on the back bumper
-much, much worse if cruise control is turned on (?!?)
-I have driven many discoverie Is and IIs and this is much more pronounced than typical lash
-no shaking on acceleration or other signs of u-joint problems - just when transitioning from coasting to partial throttle and back...
-engine seems to run worse after prolonged freeway driving - slight hesitation from stoplights after getting off the freeway but goes away in a minute or two...
-this started to happen all of a sudden a couple months ago and hasn't gotten any worse (~3-4k miles).

What I have done so far...
-taken the front drive shaft off to check - double u-joints are original but have no play, no rust etc, regularly lubricated - seems fine...
-slop in the differentials and transfer case is the same as comparing to a '01 D2 that doesn't have the problem

Ok - so this post is getting long - but I just want to describe this in detail because this problem has me stumpped.
Any ideas on what to check at this point??? I am planning on replacing the universals in the front at some point with ones that have the zerks but I really don't think this is the problem...

Other info on the car: sometimesused in deep snow and some dirt roads but no surious"off-road", no towing... synthetic fluids in the axles and t-case, Lucas added to trans, Sea Foam added to gas regularly, all maintance up to date... the vehicle really drives perfectly as long as you don't go on the freeway for too long (few miles).

Thanks for any/all suggestions,
Piotr

 

I'm basing this on my experience with a 1988 Jeep Wrangler I've had for 10+ yrs: When the t-case would get hot, after a few minutes on the highway, I would have a similar experience. Turns out it was low on fluid.

It sounds like you've checked everything else, so I'd check the lash in the t-case.

 

Never try and verify wheter a set of u-joints like yours are good by looking at the. Those 2 u-joints are an accident waiting to happen and I know your local dealer will be glad to drop a new tranny into your truck when they fail.
Have someone replace them, ASAP, with some servicable joints if for no other reason then to keep from blowing $7000 on a tranny that didn't need to be replace.
My first set of u-joints went at just under 36000 miles, the second set at just under 90,000, which was my fault.
Get them replaced then drive your truck and get back to us.
Mike

 

I agree that these are the weakest part of the driveline. However, I didn't just look at the two u-joints. I pulled the drive shaft out, and checked them for play/damagevery closely - they are not about to fail, and theproblems that the truck is having aren't consistent with a damaged/worn double-u. This doesn't mean that I don't plan on replacing them in the very near future - always a good idea to eliminate theweakest link.I just know that this is not causing this problem here... I like the suggestion about the t-case temperature. Does anyone know if there is a temperature sensor in the transfer case (like the one in the transmission)? I doubt it but it never hurts to ask The gear oil level in the t-case is fine, the lash in the t-case is the same as another Disco that drives fine, but it could be a bad bearing or ?? creating excess heat. Any other ideas - please let me know. I really appreciate the help!!

 

Just a quick question about the u joints since people ae recommending those. Where can ou buy them cheapest at? I seen atlantic bristish has them for around $60-$70 but then advance auto parts did not have them for a disco 2 or 1 but they had them fr the range rover classics which on atlantic british it says it is the same part and advance sell itfor uner $15? So any opinions on that and any Rove store sell them cheaper than $60 if advance isn't good.

 

http://www.roverconnection.com/ Is a good place to get good quality u-joints, not cheap ones but good quality joints at a fair price.
Mike

 

My disco1 was doing something similar. Turns out to have been a fuel injector not firing right when on the freeway at speed. This got rid of the rough running portion of it. I still have a bad tick but I can live with that. Hope this helps.

 

Thanks! What steps did you take to find out that it was a bad injector? Seems like pulling out the injectors and testing the spray pattern wouldn't do much good, as the problem only occurs on the freeway

Piotr

 

If you don't mind losing use of the vehicle for a short while, you can have the injectors ultrasonically cleaned and flow tested on a machine that actually simulates a running engine. If you want to go this route, find a local speed shop with an ASNU machine. They can give you a before and after cleaning flow report to weed out a bad injector. If you can't find a local shop, there are plenty of "mail your injector" services as well. It should cost around a hundred bucks for eight injectors.

Another good test might be a cylinder balance test under load to determine which cylinder is causing the issue (I would have to bet thattestbook can do that?). You could also"roll your own" if you got ahold of a junkyard injector wiring harness and at least one old injector, rip the connector off the old injector and wire it up with a switch in series with each injector in turn(with the switch wire and switchin the cab) so you could shut each one down one at a time and observe performance. When you shut the one down that doesn't clunk "worse" you know you found which cylinder has an issue (if that's what is causing your problem).

Might be wise to just get the injectors professionally cleaned and tested to rule them out and then go from there. It would cost about a hundred bucks plus your time and for a truck with 94k on it, itlikely wouldn't hurt even if it turns out not to be the injectors.