Loud chattering in Super np gearbox

[Evos3960]

When I take one of my Super np's on the road and running in top gear on relatively low rev's ( up to about 1400revs ). there is a very pronouced chattering which seems to come from the gear box, so I changed the oil and put 90 gear oil in instead which did seem to improve matters somewhat. However there is still considerable room for improvement, dare I drain the oil again and put 140 in instead. Any advise would be appreciated.
.
Peter

[henk]

I suspect a bearing is making the noise. If so it needs to be replaced by a new one.
Not a plessant thing to have on your to do list.

[AdrianNPMajor]

From what you describe, this is perfectly normal. It's gear backlash. I hear this when I'm whizzing along in 6th then cut the revs. I had a broken gearbox, so had to take it apart, and I checked everything, so I knew there was nothing amiss when I first heard this.
Re gear oil, there are various discussions here. I favour a thicker oil. I use Morris AG90 for the gearbox and rear axle, but I'm tempted to put AG140 in both. This is not what Ford recommends. On a winter's day on start-up AG90 in the rear axle pulls the engine down when the PTO is engaged, but half an hour into ploughing the same oil is as thin as hydraulic oil.
With this type of gearbox with its designed-in backlash I think a high viscosity oil is desirable, even if it does cause drag on start-up and shortly afterwards.
Best, Adrian.

[AdrianNPMajor]

So sorry, Henk. I was writing whilst you posted your reply.
Yes, the clattering could indeed be a failed bearing.
I found my problem by putting the tractor on stands and running it through the gears. In my case, the clattering was present with both high and low revs, so I knew it wasn't gear backlash. It had to be a failed bearing, and it was.
Best, Adrian.

[shepp]

Hi Peter

If your tractor has a belt pulley the noise could be coming from the drive gear and dog clutch if it has some wear in it. Try removing any pulley and put the blanking plate on and see how it is.
If it does not have a pulley or you remove the pulley and it is still noisy, then as everyone has said the noise will be coming from a bearing or bearings. If it annoys you the solution will be to remove the box and fit new bearings.

The original initially recommended oil in the early 1950's from Ford for the Major gearboxes and final drives was for a 90 gear oil - note NOT a 90EP gear oil. For temperatures above 90 Fahrenheit it was for a 140 grade, and for temperatures below 10 Fahrenheit it was an 80 grade. However soon after the multigrade universal tractor oils became available in the later 1950's Ford changed the recommendation from 90 gear oil to a 20/30 multigrade for the gearbox and final drive.

You could put 90 or 140 grade oil in your gearbox, it may quieten it for a while, but if you have bearing issues then as soon as the oil has warmed up and gone thinner...… back to square one!

[Evos3960]

Hello Henk, Adrian np Major and Shepp,

Thank you for your reply boys.
This tractor does not have a belt pulley on so the problem will be either a faulty bearing or backlash. I tend to think that as the problem manifests itself on relatively low revs and not while the tractor is pulling it will be backlash. As this is a show tractor and it doesn't do any work I will leave it for now and see if it gets worse, which I would have thought it would if it were to be a bearing.

Anyway thank you all once again,

Peter

[fenhayman]

Are the wheel nuts and those holding the rim to the centre tight?
Is the diff lock pedal fully up?

[shepp]

I agree with the other views posted that some of the chatter will be from backlash in the gearbox - you always get some backlash with straight cut gears and once they have some wear on them there will be a bit more noise. Consider the noise from a David Brown gearbox which also has straight cut gears, whereas the MF gearbox with some gears that are bevel cut is quieter.