Jackjack Posted November 15, 2021 Share Posted November 15, 2021 (edited) Hi I have a series 3 88 with a 200tdi engine in. the gearbox is noisy on light overrun I changed the diff but as it is worse in 4th im guessing it is a layshaft bearing or something along those lines. the question is am i better off repairing rhe gearbox (i dont have a heavy right foot) or is there a short bell housing gearbox that i can swap over without having to get the welder our moving engine, new props etc. Dont mind cutting the gearbox tunnel just not into fabricating (only just stopped the vibration from the props) will a R230 LT85 v8 /lt77 / LT77 v8? with short bell housing work? thank you for your advice Edited November 15, 2021 by Jackjack Quote Link to comment Share on other sites More sharing options...
Snagger Posted November 16, 2021 Share Posted November 16, 2021 The only time I had problems in 4th was also on the overrun just after fitting a Tdi, too. It transpired to be the spigot bush in the engine crank shaft, but I only worked it out after several gear box rebuilds and numerous attempts at adjusting the selector forks and rods. So, check that first! 1 Quote Link to comment Share on other sites More sharing options...
missingsid Posted November 16, 2021 Share Posted November 16, 2021 11 hours ago, Jackjack said: the gearbox is noisy on light overrun I changed the diff but as it is worse in 4th im guessing it is a layshaft bearing or something along those lines. Fourth gear in most gearboxes is a 1 to 1 drive as it is the one gear that does not use the layshaft so it is not turning at all. That is why when the layshaft breaks you can often drive on in 4th at a cautious speed. Quote Link to comment Share on other sites More sharing options...
Jackjack Posted November 16, 2021 Author Share Posted November 16, 2021 12 hours ago, Snagger said: The only time I had problems in 4th was also on the overrun just after fitting a Tdi, too. It transpired to be the spigot bush in the engine crank shaft, but I only worked it out after several gear box rebuilds and numerous attempts at adjusting the selector forks and rods. So, check that first! how weird, surely the spigot bush isnt doing anything with the clutch engaged its just kind of sitting there? Quote Link to comment Share on other sites More sharing options...
Jackjack Posted November 16, 2021 Author Share Posted November 16, 2021 12 hours ago, missingsid said: Fourth gear in most gearboxes is a 1 to 1 drive as it is the one gear that does not use the layshaft so it is not turning at all. That is why when the layshaft breaks you can often drive on in 4th at a cautious speed. its got to be a bearing somewhere in there. its quite violent just like when the berings fail in a angle grinder. its the only bit of the thing i havent fixed or replaced so it must be that, everything else needed sorting. also previous owner didnt think it needed oil... Quote Link to comment Share on other sites More sharing options...
Snagger Posted November 19, 2021 Share Posted November 19, 2021 On 11/16/2021 at 10:43 PM, Jackjack said: how weird, surely the spigot bush isnt doing anything with the clutch engaged its just kind of sitting there? It keeps the primary pinion and main shaft aligned. If the spigot bush is worn, the pinion can skew, also skewing the main shaft. This was causing the synchro hub to be pushed aft on the overrun in 4th, amusing the box to jump into neutral. Multiple box rebuilds made no difference, but replacing the bush fixed it permanently, with not a single reoccurrence since. If a worn spigot bush can cause that, it can cause misalignment that creates noise. If you are not having issues in any other gear, that’s where I’d look first. It’s a cheap part and easier to replace than rebuilding the gear box anyway. Quote Link to comment Share on other sites More sharing options...
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