The Fordson Tractor Pages Forum

I have recently had the hydraulics on my NP Super Major overhauled and all seems to be working fine. However, I have noticed that if I select position control and set the quadrant lever about an inch from the very bottom of the quadrant, the lift arms adopt the correct position, but at high revs they continue to creep up, though not under pressure (ie you can push them back down to the position set by the lever). Is this a sign of something being out of adjustment? Is oil leaking past a valve?

I'd be grateful for any info.

Many thanks

Adrian

Thats a strange one because, if oil is leaking into the cylinder, it is doing it at 12 psi (system pressure in neutral) around valves that are closed. It is also going to exhaust when you press down on the lift arms, again without opening a valve. Yet the lift is holding up with a load and working correctly. If the lift was creeping up and holding it would make more sense.

It will not be adjustment, I would suspect a minute leak around the control valve or possibly check valve. Not really worth worrying about at the moment.

Hi Brian. Your namesake at Doe's who refurbished the linkage mechanism and set it up said that he had adjusted the Qualitrol to work precisely but at the cost of a little adjustment on the position control, such that for the first inch at the bottom of the quadrant the arms do not raise when in position control. However, after the first inch of movement on the lever they move in precise steps according to how much you move the lever.

Does this extra info tell you any more?

I'm sure I speak for everyone when I say it's incedibly useful to have such an 'oracle' to refer to!

Many thanks.

Adrian

Not really Adrian, it sounds as if it is spot on and works as it should. To my thinking, if you are leaking enough oil into the cylinder to raise the linkage it should not be possible to push it down again, but I could be missing something.

Have you tried it with a load? If it does not lift a load then there is little to worry about.

The quadrant lever should cause the lift to raise when about 1/2" from the bottom stop and the lift arms should not drop further when in Position Control. You have to select Qualitrol to get the lift arms right down. When you selected Position control with the quadrant lever right down and the arms right down they should raise about 1/2" to 1". You always have to be in Qualitrol when using a PUH for this reason.

Thinking about it I wonder if this is what you are getting. When in Qualitrol lift arms should be right down with the quadrant lever right at the bottom of its travel, when you select Position control, lift arms should raise about 1/2" without moving the quadrant lever from the bottom stop. The quadrant lever starts to control the lift in increments after it has moved the first 1/2" of travel.

Hi Brian

Brian tested the system after completing his repairs and no, this issue didn't show itself with a weight attached. I have got the rear wheels off at the moment to repaint the rims so I can't retest at the moment.

The symptons I describe happen at high revs and the arms can creep up to about half way if allowed to do so.

Adrian

Actually, Brian, I'm talking nonsense!

I have retested it with a weight - myself! If I stand on the arms it doesn't happen, and as mentioned, when the arms begin to creep up I can press them back down with my hands.

Best wishes

Adrian

Perhaps Brian put something in upside down causing the arms to rise instead of sink like they usually do.

Seriously though, I can think of no reason for them to work like that. A small weep past the valves may cause it but even then it does not make sense. Did you change the exhaust filter and check the valve at the bottom?

Ok, Brian, I have just spent the last ten seconds looking for this emoticon!

I thoroughly cleaned the rear axle housing when it was in separated from the tractor and I refilled with new Morris AG90 gear oil. But the blithering idiot tasked with replacing the exhaust filter forgot to do so. I'll give you three guesses who that blithering idiot was!

Forgive my ignorance but which is the valve at the bottom that you refer to?

Best wishes

Adrian

Hi Brian

I've just checked my workshop manual to check what the valve that you refer to might be. I think you may be referring to the 'Back Pressure Valve', which of course I failed to look at as I didn't go near the exhaust filter during the rennovation (what an awful admission to have to make!). If this is the valve you mean, could it be stuck open and, if so, would back pressure explain the upward creep of the arms under high revs?

Kind regards

Adrian

The other thing that might cause these sorts of problem is the oil you have used. Supers never had 90W in the back, the hydraulics will not work correctly due to the viscosity of the oil and the small galleries.

Should be 20/30W or 30W.


Gearbox and Rear Axle Oil Specifications. All Models.

Service letter July 1959 states: Gearbox, Rear Axle and Hydraulics oil specifications have changed. Now all models from 1952 onwards use:

S.A.E 30HD or S.A.E. 20W/30W in all the above at all temperatures.

This is very important in NP Supers. We used to get this problem all the time back in the day when farmers were changing from the 90W to Universal oils and filled Supers and Dextas up with 90W.

Hi Brian

Thanks for putting me right on the oil. I'll change it. Just to be clear, do you think this is the issue with the arms creeping up? I'm going to replace the exhaust filter and check the Back Pressure valve. If it is stuck in the open position, is it possible for back pressure to be a factor?

Best wishes

Adrian

With 90W I would suspect your back pressure is very high as the weather is cold and so is the oil. With a high back pressure the oil is finding it easier to go back into the system than through the filter and back pressure relief valve. After a couple of hours ploughing your problem would disappear only to re-appear next day.

You could use that oil in a Major or Power Major.

Thanks so much Brian. I've learned a lot.

I have a friend with a number of Majors and Power Majors. He'll be glad of the oil, I'm sure.

Best wishes

Adrian

Hi Brian

I have just checked the Morris classic vehicle range of lubricants and they dont make a SAE30HD or SAE20W/30W gear/transmission oil. Is it safe to use a modern spec oil? I must say I didn't spot any, but are there any phospor bronze bushes/components in the rear end that might be damaged by modern additives?

Could you or fellow members recommend a make?

Best wishes

Adrian

Would this be suitable?

http://www.morrislubricants.co.uk/scrip ... roduct=165

You use the same oil as in your engine, many tractors of this and later eras used the same oil right through engine, gearbox and rear axle. HD30W or 20/30W is what should be in the engine.

The idea was that a farmer would buy one barrel of oil to do everything, so eliminating contamination from trailers and other hydraulicly powered implements.

There is nothing in the rear axle to worry about after all, the tractor was designed to work in that way.

That oil will be fine, I am using the Classic 20/50W in my tractors now in both petrol and diesel.

Thanks Brian.