Rumble, rumble, toil and trouble?

[DiscoClax]

Hi all,

I've got a vibration that appears to be engine load-dependent and happens mainly around 40-60 km/hr, reasonably clean everywhere else, esp on highway. Hadn't really noticed it at any great level until a couple of days ago when it just suddenly appeared. Seems to be getting worse, too. Feels like UJ rumble, or UJ wind-up due to poor driveline angles, but they're all OK. Nothing specific coming up through the steering wheel, instead the whole vehicle seems to be going off. Happens at same road speeds in low range as high. I can't say for sure if it's any different when cornering to straight.

Tyre pressures, wheel bearings, driveline angles, UJ's and slipjoints all good. Wheel alignment, front suspension bushings/joints/etc all seem to be OK, too. All shock absorbers are new (incl steering).

I do have some play in the Transfer case output flange - front. But that's been there for as long as I can remember and doesn't seem significantly worse than before.

Driveline backlash feels and sounds way worse than before. R-D-R shifts result in a solid thump and a sharp noise every time, whereas it was far more subdued in the past.

One weird thing is that the rubber dust cap on the end of the LH front axle popped off at about the same time as the issue started. I haven't replaced it as yet as I don't have a spare and it went AWOL. Related...?

Driveline is standard apart from a UJ rear shaft fitted. Suspension lift is only effectively about an inch (with the weight of the bar work and gas).

Would welcome forum feedback as to likely cause before I start pulling it to bits. I'm suspecting a front CV is on it's way out, as I seem to recall they're a bit weak and the symptoms match somewhat. However I'm more than open to suggestions, esp as these all-wheel drive off-road thingys are still a bit new to me.

[Les Henson]

Vibration isn't usually associated with a worn CV joint unless it's already partly broken, in which case parts of the cv joint may be causing further damage inside the swivel housing.

Les.

[paintman]

SKF have just done an article in a trade mag on CV joints.

"Wear and partial seizure are the most common causes of failure. Wear in the outer joint is identified as a vibration at certain speeds and is most audible when the vehicle is driven through tight left-hand and right-hand circles at low speed. Worn joints make a rhythmic clicking or cracking sound. Partial seizure is often caused by the joint overheating after the outer joint boot has split, resulting in a loss of grease causing a 'pattering' sensation through the suspension"

Obviously we don't have joint boots, but all the lube can still escape if the seals have failed which will also allow water in.

[DiscoClax]

Both front axle shaft assemblies replaced today with known good (used) units. Doesn't seem much improved after a quick test drive. Issue still there. Bugger The removed parts were in reasonable condition, but with a little bit of float in the CVs. Still serviceable, so I guess I've got a set of spares at least. Thankfully, Les, no broken bits Lube in good condition, with the right stuff in the right places.

Has anyone replaced the front output bearing and seal in the transfer case whilst still in the car? Are there any tricks and/or tips? That's my next step to try and find/sort the rumble out - obviously I'll properly suss out the front shaft at the same time. I know there's some play in that bearing (no leaks though, surprisingly). The transfer case has always been noisy and clunky, so maybe....?

[Orgasmic Farmer]

From your description I would tend to suspect prop UJs but you say there is no play. One thing to bear in mind when checking the UJs is that the car needs to be parked on level ground with the handbrake off to check them, otherwise the weight of the truck against the handbrake will mask any play. There is an article in the technical archives of this forum on changing the rear output bearings on the transfer box with the thing in place. i imagine the front is similar but without the handbrake to get in the way..

PS does your Disco still have the rubber doughnut on the rear prop as these are known to give trouble

[DiscoClax]

Just not sure how tight the bearing is in the housing and whether it will come out without having to strip the 'box down first? Tricky to get in there because the front output shaft will still be sitting there, I assume. Special tools reqd? Not really in the mood to waste an hour or two pulling it apart to find I can't get the bleeder out anyway.

I've got a UJ rear shaft. Got bored with buying the donut's in six-packs...

I've checked the shafts/UJs while on a slope, but with the rear wheels both chocked and the handbrake off, in neutral. Should give the same result. I'll check them again, removed, in case they were just bound in one spot.

[DiscoClax]

Thought I should close this one out.

'Twas the front UJ in the front shaft. Let go Christmas Eve... Kids and ex-wife in car... Nearly 300kms from home... Packed to the gunnels so toolbox left behind... naturally... Every time I got under there to check the bleeder, it felt tight. Even after it really started to rumble it felt OK in the car, but started to feel loose as soon as I started undoing the flange bolts. One of the four cups had shagged out the seal and then bearing - grease replaced by mud & rust & small chunks of metal. Other three like new.

Thanks to all for your sage (and accurate) advice. Next time I'll just pull the bugger out and check it properly...