Gearbox or Diff... Where is the problem?

[Mean Green]

So, I have been looking forward for weeks to my 1st offroad run in months and the 1st trip for the "new" Discovery 1.

Spent the day yesterday giving it the once over, gave it a service and checked all the levels. Got up nice and early this morning, filled the flask, made a lunch and headed off.

20mins into the 90min journey, I am cruising happily at 70mph on the motorway and thinking how well the Disco drives, considering it is 20 years old and almost 200k miles. I am getting ready to stop for my planned fuel stop and as I lift off the throttle there is a little bit of a shudder through the car and a rattly grating sound - kinda like a wheel bearing but more metal on metal.

So I pull into an empty supermarket car park and have a look round - nothing to be seen and no hot wheel from wheel bearings etc. I drive around the car park making tight circles to check diffs but there is nothing to feel or hear. I decide not to risk heading further away from home and nurse it home on quieter roads.

The car drives fine in all gears and pulls well - but the terrible grinding comes back as soon as you lift off and on the over run. I head back and try all scenarios that I can think of to determine when the noise is present. And in general is seems to be coming off load.

I stop at a mates on the way back and we jack it up, but all wheels spin normally and there are no noises or excessive play - there is a tiny little play on the front pass side wheel bearing but I do not think it is enough to be the problem. We both go for a spin round the block and the noise comes back as expected on the overrun. We have a good listen but cant really decide if it is front or rear. No noticable play in the props etc etc

So ... any ideas?

I should say there is already a question mark over the gearbox as I think the synchromesh between 1st and 2nd is badly worn as you need to be careful and deliberate with the changes to avoid a crunch. And I have a replacement gearbox ready to swap, but I want to know if this is something else.

[Simon Smith]

1. Heard a similar noise on many occasions on many different vehicles. Every time it has been a UJ. Just because there's no play in it doesn't mean it's good, in fact sometimes they have been almost solid once removed.

[Aragorn]

Removing the propshafts in turn would also let you rule out each diff as well as check the UJ's as above.

[Clint]

When I had this on my 300tdi it was the rear diff kicking the bucket.

Hope this helps.

[Thon]

Had exactly this issue on my 90 many years ago - turned out the front diff drive flange locknut had eaten its split pin and was gradually unwinding itself, allowing the pinion shaft to loosen-off its bearings and make 'orrible noises.

[Mean Green]

Thanks for the suggestions - gives me a few other things to check that I hadnt thought of.

I might as well start with the props as they are the easiest and take it from there. Thanks.

[mahon257]

You could try removing the front prop... go for a drive... if that doesn't cure it, it will at least isolate rear/centre diff?

[mikeyb13]

I agree with Thon, sounds like pinion shaft bearing

[Mean Green]

Had exactly this issue on my 90 many years ago - turned out the front diff drive flange locknut had eaten its split pin and was gradually unwinding itself, allowing the pinion shaft to loosen-off its bearings and make 'orrible noises.

I have not had a chance to look at it yet - but if it is the pinion shaft does that mean a new diff?

Also can someone just confirm that my method of checking everything is correct ...

1. Jack up, remove wheels and put on axle stands

2. remove props (Diff end only or completely? )

3. spin diffs - there should be little or no movement other than spinning and no noise

4. Anything else?

5. Put back together

Thanks

[Thon]

In my situation, I could have kept the old diff in place as it appeared undamaged but chose to put in a known good one instead as it was all apart. I think if you find the same problem on yours then removing the diff and inspecting is the way to go. In my case it was very obvious that the pinion shaft nut was properly loose so didn't take much diagnosing.

I would not remove wheels if you are just doing these checks - put on axle stands high enough to lift wheels off the ground but no need to remove wheels at this stage. I always leave wheels on if at all possible. I would do one axle at a time and make sure to chock whichever wheels are still on the ground, as you'll need to have the transmission in neutral and handbrake off. I would start by just undoing diff end of the props.

[Mean Green]

Thanks Thon.

Will have a looksee and report back... just need the time to do it

[Snagger]

1. Heard a similar noise on many occasions on many different vehicles. Every time it has been a UJ. Just because there's no play in it doesn't mean it's good, in fact sometimes they have been almost solid once removed.

Too true. So many people think you can check a UJ with the prop fitted, but you can't.

[Mean Green]

Ok.. finally had a chance to have a look at the Discovery.

I have removed the front prop and both UJ are in good conditon and are moving freely. There is no lateral movement on the diff that I can feel - how can I tell if it is anything to do with the pinion shaft / bearing? Does that involve a strip down of the diff?

[Snagger]

Free moving UJs aren't necessarily good. If they're loose enough to flop about under their own weight, they're worn out, and a UJ might have corrugations of wear on the spider that bind under load but are free unloaded.

[Mean Green]

I will take it for a drive tomorrow without the prop and see what happens. But to add to the issues, it looks like the rear diff pan has rusted through - I topped it up and there is now a puddle of EP90 under the diff and it appears to be coming from the diff pan rather than the filler or drain. I think when I jacked it up to spin the wheel bearings the first time the trolley jack on the underside of the diff has been enough to burst through the weak metal.

The joys of Land Rovers

[Thon]

I presume you checked the diff drive flange and the locknut for movement?

On mine, the split pin was "eaten" and the nut proper loose, so spotting the issue was easy. You need to check for up and down & in and out movement on this drive flange and there should be no play at all, and the nut and split pin should be tight.

I would also lift one wheel and slowly turn it whilst feeling for roughness and excessive play on the drive flange/pinion shaft - on mine it was fine whilst under load but as soon as you lifted off the power the noise appeared.