Fordson Super Major Hydraulic Problem

[kiwimajor]

Hello,
We have a persistent and annoying hydraulic problem on our 1963(est) super major. In position control, with some weight on the link arms, it is constantly correcting itself. We have had the lift assembly off the tractor and replaced all of the o-rings (including the unload valve o-ring and main lift seal) and inspected the cylinder for any cracks. We are certain that the overload valve is good and we think that the check valve is OK. The main control valve and the unload valve and their bushings look to be OK. Having reassembled it and found no improvement we used an inspection camera to watch the hydraulics in action by looking through the filler cap and around to the lift ram. The only place that we could see excessive oil flowing was cascading down from above the cylinder. This led us to believe that the problem must lie in the external services/flow control block. Having dismantled the unit and replaced any o-rings that we could find the problem was still not solved. The hydraulics seem as powerful as they should be and don't seem to drop if the engine is switched off. We have set up the quilitrol spring and linkage according to the book but we've still got this damn problem!!
Has anyone got any ideas where we can go from here?
Thanks

[AdrianNPMajor]

Have you checked the unloading valve plug (see photo - as you probably know, it's the plug with the tapped hole lying under the back plate of the control valve assembly)? This may be worn, allowing enough leakage to explain the corrections you are experiencing. I had this problem on mine. The Fordson fitter who replaced mine told me that back in the day they carried colour-coded plugs that stepped up in size. You can see a dab of blue paint on the housing next to the left-hand stud in the photo, which I believe is part of the colour coding system - it indicates the bore size of the unloading and control valves. He said that when wear occurred in service they would fit a new plug the next size up. As the plugs are no longer available I had to get a new one made a few thousands larger. Solved the problem.

The repair manual states that an acceptable maximum number of corrections in a two minute period is 30. Depending on how hot the oil is I get no more than half a dozen corrections within that period now the plug has been replaced.

I am no expert on this subject but other members of this site certainly are.

Best

Adrian

[url][/url]

[kiwimajor]

Hi Adrian,
Thanks for your very interesting information, we had noticed some seepage around that plug but didn't think that it was significant. We may be expecting too much as we hadn't realized that 30 times in 2 minutes (once every 4 seconds) was acceptable. We timed it when the oil was fairly cold and it was around once every 7 seconds with the lift about a third of the way up. With warm oil and in the fully raised position the corrections were almost continuous (less than a second). It may be that we have to either put up with it or re-new everything. Any more ideas?
Thanks
Chris & William

[AdrianNPMajor]

Hi Chris and William

If you haven't replaced the unloading valve plug, I would do so. Do you have a machine shop that could make it for you? It cost me about £30.

Once you've got the plug out, you need to measure it to see which size has been fitted. The chart below tells you the ones fitted in service. Whatever it is, you need to step it up to the next size.

Judging by your symptoms you have got the same problem I had, and this was the solution.

Best

Adrian

Unloading valve plug diameter (mm)

Blue/White 25.400 - 25.405
White 25.405 - 25.410
Blue 25.410 - 25.415
Yellow 25.415 - 25.420
Green 25.420 - 25.425
Orange 25.425 - 25.430
Green/White 25.430 - 25.435
Red/White 25.435 - 25.440

[kiwimajor]

Thanks Adrian,
We will give it a go when we next have a chance to strip it back down. We are hoping to go on a tractor trek this weekend so we may not get a chance to take it apart but we will report what happens when we do. Is it the white bit of paint on your casting that indicates the size of the plug? Does the plug need to be made of high-carbon steel, or will bright mild do the job?
Thanks,
Chris & William

[AdrianNPMajor]

Hi Chris and William

I forget what size the plug was on my tractor, but I think it was the original plug and therefore the blue/white one. I had a plug made halfway between the two parameters of the next size up ie halfway between 25.405 - 25.410mm. You need to micrometer yours to get the exact size and adjust upwards accordingly.

I'm not sure about the paint dabs - I'm hoping another member can add a bit more info here. There are blue and white dabs on my housing, but in different locations so I'm not sure if one bore is one size, and the other bore another, or if both are the same blue/white dimensions.

My new plug was made out of high carbon steel.

Hope you have a great outing on the amazing machine. By the way .........



Best

Adrian

[kiwimajor]

Hi Adrian
Here are some links to the footage from the aforementioned inspection cam that may or may not work.
I am afraid that this is the best that we can do at the moment but it is very interesting. Please note that our Super Major is not the New Performance model so it may be a little different to yours.
Thanks
William
https://docs.google.com/file/d/0BxHGh75 ... sp=sharing
https://docs.google.com/file/d/0BxHGh75 ... sp=sharing
https://docs.google.com/file/d/0BxHGh75 ... sp=sharing

[AdrianNPMajor]

Hi William

Interesting videos though I am not knowledgeable enough to draw any conclusions from them.

The two Super hydraulics differ but not in this area as far as I know.

Best

Adrian