Discovery UJ Replacement

I've had a knocking/ rattling noise coming from underneath the disco for about a week. In the two hundred or so miles I've done since first noticing it, it's gotten loud enough now so that I can hear it over the radio, and if I wind the windows down with the radio and blower off, then it's about as loud as a talking passenger.

I started a thread a week ago, and the help was great but my findings have not really been conclusive.

Got the day off tomorrow, the haynes and rave manuals, and I plan to sort whatever it is out.

My guess, as was my Father's when he drove it, is that it's the Prop UJs finished.

My reasons for thinking this are;
-Same noise as my old disco made before they went
-Knocking that sounds like a length of metal pipe, or a broom handle being rattled inside a scaffolding pole while driving along.
-The noise seems to lessen, even disappear, when turning left of right, but is most prevalent when going straight.
-The noise doesn't change at all when clutch is down, or when out of gear
-The noise only happens when driving, not while static
-The noise has no relation to the revs, or the gear I'm in.
-The knocking gets closer together when faster, and when slowing to a stop it sounds like the 'wheel of fortune' coming to a stop.

Does any of that point to anything in particular?
At the moment, having been underneath and looked at all the bushes, and joints, nothing looks worn, or unstable.

Before I spend my day off tomorrow, replacing the UJ's only to find out that the noise is still there, does anyone have any other ideas as to what it could be?

Cheers.

its fairly obvious if uj is poor normally it will either have play or reddish rust stains around joint

I'll have a good look tomorrow before going ahead with it, but if the UJ's are fine, then I have noooo idea.

The haynes manual say's that on earlier tdi discos there is a UJ at each end of both props, but that on later tdi discos there's one UJ on each prop, and one rubber joint??? What's that about?

the 200tdi has a UJ at both gearbox end and diff end of the prop shaft, the 300tdi does away with the one (from memory at the diff end) and replaces it with a rubber doughnut which the propshaft bolts to with three bolts and the diff flange bolts onto with another three bolts. The 200tdi set up is far better imo.

Okay, so It's outside and on axle stands with the handbrake off, and I've given it an inspection underneath.

The front prop seems to be fine, and both UJs are good, with no rust etc. The only bits up front seem to be very worn bushes on the steering arms etc.

The rear prop has a fair bit of play in it (maybe a 1/4 or a 1/3 of a turn), and when it stops turning, there is a loud clunk (which I believe is the noise I'm hearing when driving), which sounds like it's coming from the diff.

The dohnut, and UJs at the rear all look pretty new, so don't think the problem is with them. The bushes, and rubber mounts for the trailing arms do look very worn, but I can't imagine them making the noise that I'm getting.

Anyway, there are new UJ's (which I won't fit having seen the condition of current ones), A-frame ball joint, and load of bushes for the rear of the disco, on their way to my place now.

My thought's now, are maybe some play in the A-frame ball joint, or if it's not that, then I think the diff is ****ed. (It would make sense perhaps, because there is an oil leak on the diff from the drain plug).

I can't imagine that topping up with oil now, and maybe replacing the seal would go very far, but maybe it's worth a shot?

For now, I'm waiting on parts, and having my finger's crossed I can find the fault before this evening. If not, then it's off to the garage, for a nice expensive bill, and probably a new diff. feck lol.

rotational play in props is expected how much is a different matter ,axle has diff and halfshafts etc all with some .t/box center diff and gears , but diffs should have no endfloat or up down play ,ujs none at all ,to chack a frame and other suspension bits get someone to rock vehicle while sat on its wheels vigorously while you lay under it feeling various parts will show you any that are wrn as you will feel clunk/play before you see it often

Don't I feel stupid...

Went out there again for yet another root around underneath, and after putting my ear against almost every part of the rear axle when wiggling the rear prop, it turns out there is some minor clunking from the diff, but the loud knocking noise is coming from the rear wheel, I get the wheel brace out to make sure the nuts are tight, and about three come off with less than half a turn, and only one on semi tight. Dangerous to say the least, but odd considering, the wheel nuts where about the first thing I checked a week or so ago, and I wobbled the back wheels on a few occasions, to see any play and there was none. It could just be a co-incidence, and the diff or prop might still be fecked, but before I start thanking the heavens that it was an easy fix, is there anything in the hub I can look at, or any reason why the nuts would undo themselves like this?

(About a week ago, on my way to the welsh winter fair, I had to pull over, and the rear wheel was very hot to the touch, and stunk as if the brake was stuck on or something, but I let it cool down, and I've had no problems with smells or overheating since.)

lhs can come loose through direction of rotation but usually the front so id say nuts werent tight enough

Yeh it was the nearside rear wheel, so hopefully that's all it was. What a farking fiasco it has been to find out I had a some loose wheel nuts. But hey ho, it's been a good opportunity for me to have a good inspection of the underside of the disco, and while it's up on axle stands this afternoon, I might see what I can get to, to slop some waxoil on, while it's dry and I've got the time.

well you found issue ,there all simple once you know ,and a good check over is never wasted time

Had a look at the brake pads and they quite thick so were pretty fresh I think, coupled with a rusty old caliper that must be sticking a bit = brakes constantly on and a nasty smell. I sanded a bit off the pads, and tried to push the pistons in as much as poss before refitting them so as to release them if they were stuck, and both pistons moved back by about half a mm so aren't seized up.

Anyway, wheels back on and bolts tightened and all seems well so there was me thinking new diff, when I just had some loose wheel nuts. Ohwell rather it this way round.

On a separate subject, I tried to torque the bolts up to 129NM which is what the manual say's, and could only manage to get one to the correct torque, and that was with all 14 and a half stone of me stood on the torque wrench, forcing it down. It will have to be addressed at some point soon, and will keep an eye on the nuts until they're all torqued up properly.

It shouldn't be that hard to do! Try it with someone elses torque wrench. If you've left your wrench tightened up, you might have knackered it!

tombardier said:

It shouldn't be that hard to do! Try it with someone elses torque wrench. If you've left your wrench tightened up, you might have knackered it!

Click to expand...

I would second that. 129Nm isn't that much. If the spring inside your torque wrench has got rusty it can F*** it up. I learned this the hard way after shearing the head off a bolt.