Horrible gearbox bearing noise.

[simcoe]

So i recently got the clutch replaced with a npc +30% job so its up to the task after the remap and 3' exhaust.
it always had a slight noise when the clutch was out, clutch in its quiet as a mouse.
After the box was replaced the noise is much worse.

Im assuming its a main shaft bearing or input shaft bearing. Ive done the oil and put some additive in but that didnt make a difference.
It shifts smooth and drives smooth.

2010 fuso 4m50t motor 5 speed manual with 260k on it.

thanks

 

[Ultimark]

I do not know much about Fuso gearboxes, except that with regard to synchromesh gears, having the correct fluid (oil) in a gearbox can sometimes be vital. I'm referring to the ability of the oil to disperse allowing the synchromesh gear to grab and start turning a gear/shaft in milliseconds. As your gearchanges appear to be correct, leave things as they are. However if you start having shifting difficulty the fluid additive may be something to double check.

I was involved with some racing Jaguar cars in another life, one of the mods was to install replacement synchromesh gears over the OEM single units. The grooves in the synchromesh gears were slightly different, which necessitated a very slightly different type of gearbox oil to allow the fast changes that the new synchromesh system was able to do. The grooves in the gears allow the oil to dissipate much like tyre grooves allow water to dissipate when the road is wet. This example I found has noticeable oil grooves, so you can understand better what I'm trying to explain.

https://images-na.ssl-images-amazon.com/images/I/610YovzWJiL._AC_SL1452_.jpg

As for the noise when you are (presumably) idling being louder than before, this sounds a bit like a thrust bearing and/or the thrust bearing arm rattling a bit. Once you put your foot on the clutch and apply pressure, there is no room for rattling around, hence silence. This is a possible explanation for what seems like excess idle rattle noise emanating from the bell housing. A stethoscope can be handy; if you don't have one, then a long screwdriver using your hand to isolate your head/ear from the handle, is another cheap would be if it could be stethoscope; works remarkably well.