Brown said:

Possibly the gearbox. Layshaft bearings and the 5th gear mechanisms are possible wear points on the r380, which is presumably what you've got. Mine became very noisy just over a year ago, especially on the overrun, plus a sort of rumble or rattle when idling in neutral. One thing you may notice is that it's a bit quieter in 4th, because that effectively locks the input and output shafts together and it's not transmitting any force through the worn and noisy components. If that's the case with yours then it probably is the r380 box. Whilst it's possible to overhaul them at home, you'll want to be very well supplied with presses and pullers, and somewhere indoors clean and dry to work too. For people like me working at the side of the road, it's easier to get a rebuilt exchange unit. I got an Ashcroft one, because they offer a choice of 5th gear ratios and an upgraded 5th gear bearing. But there are cheaper options available. I dunno about fast service. I had to wait a couple of weeks for mine but if you phone round a lot of places somebody might have one ready to put on a pallet and send you.

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