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Banging noise from transmission?


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Hi all,

Thought I'd try and see what the combined wisdom of the forum thinks.

Loaded up my Td5 90 CSW (converted to forward facing rear seats) with a bull bar, roll cage, winch and have been running like this for years. It's occasionally been used to carry heavy loads (LOTS of paving slabs) and tow.

Now I've loaded it up for our holiday in Wales: newly fitted Mantec rear wheel carrier & Simbar 4-bike rack, four bikes (two adult and two childrens - none of them expensive bikes, so heavy). Also two kids (9 & 6), some luggage, although not a huge amount - say 50kg.

We set off for holiday and at slow speeds I noticed a clunking from what I think is the transmission, and it seems to be coming from the rear - logical since that's where all the extra weight is. It is road speed related, not engine speed (and is there at high speeds, but just drowned out by the engine and tire noise :mellow:). We carried on anyway, and I assumed I would soon need to visit a garage, but having unloaded it, it has stopped making the noise. Evidently overloaded, but I am struggling to understand what I see as a medium-heavy load is responsible for this, but if I acknowledge the springs are 15 years old, maybe they're worn and need replacing. There did still seem to be plenty of "bounce" in the springs though, when loaded.

So the question is what was the clunking? Is the propshaft compressed and able to push a bearing into the diff or the back of the gearbox to cause the clunking? UJs not turning in their "happy" plane?

Thanks all

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I suspect the prop shaft, but check your wheel nuts are secure and check the tyres for damage. Check the rear diff pinion bearings for play.

I did have a problem with the rear diff on a 90 that sounded like the rear door rattling and was road speed dependent, and it transpired to be the diff cross pin's roll pin having sheared, allowing the cross pin to slide out. It can't go far as it gets held in by the ring gear, but the end of the cross pin was contacting the head of the pinion at higher road speeds, leaving witness marks on both. You would e able to see the pattern on the pinion with a torch through the filler plug hole.

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Thanks Snagger. Wheel nuts are good, and the tyres aren't fouling / damaged. There's no play in the props haft, but I haven't removed it, or even put a strong screwdriver in the UJs yet. I suspect it was happening once per wheel revolution, because in a quiet corner of a car park, once we'd heard the noise half way there (after being caught

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(continued after the cliff hanger / missed key) ... in the inevitable crawling traffic jam, I rolled it with the engine off, and it seemed to happen every couple of metres, so about a tyre circumference I guess. I think the difference or a wheel bearing sounds like the main culprit, but since it's stopped doing it now I've unloaded it, I'm not looking at the wheel bearing anymore.

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Chock the wheels, pop it in neutral with the handbrake off and have a crawl underneath. Give the props a good wiggle up/down and fwd and back to see if there is any play in the U/J's and bearings. If it all looks okay, give the UJ's and sliders a squirt of grease.

Then still securely chocked and in neutral etc, jack ups each corner in turn and give the wheels a fwd/back push and pull to check the bearings, then a spin to see how the diffs sound.

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Haven't had a chance to look yet, but appreciate all the tips. So, given that the front end of the different (and the back end of the gear box) hold output /input shafts that are held in place by beatings, how does excess weight from an overloaded vehicle cause them to move? I would assume they can rotate but not move backwards or forwards. Is this what "pinning a diff" is all about?

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