Major Diesel Lift Arms Drop

[NCOD92]

I am working on a friend's FMD and he said the arms would drop rather quickly. I didn't test it before taking it apart because I did not have a tester and the bush hog was already hooked up to another tractor. I re-o-ringed the valve body, ram, and pump along with replacing axle seals. He brought universal tran/hydraulic fluid for me to put in and it didn't want to lift the mower but about 1/2 way. Once it snapped cold it would raise and hold the mower for about 5-10 mins.

Next, I tried testing the pressures and it would hit about 2100 psi before the arms hit the stop and would drop to about 400psi. After that, I changed the fluid to 85w 90 and disassembled the cylinder, and lightly cleaned it with a flex hone. Then I took apart the unloading valve and non-return valve and cleaned them with a scotch brite. I used a 5/8 ball bearing and tapped the seat with it as the manual said.

I reassembled it this morning again and it seemed to be holding well. I drove it around a little and now the lift starts to drop again after about 5 mins. I tested the pressures and it's the same as when I checked the first time. The heavier oil seems to have slowed the drop rate some but it still doesn't seem fixed. The tractor has the first style of unloading valve where there is no ball valve.

[SvendH]

On the end of the lift cylinder,next the controlvalve is presses in an hourglass shaped steel bush.about as trick as a thumb the bush has a threadded hole in it for extracktion purpose.
This bush Can get loose in time causing a leak.
Problem is easy to diagnose if liftcylinder is on the workbench,simply apply compressed air to the liftcylinder oilcircuit and air will bubble around the loose Bush.
To cure, extract bush and reseat it with Loctite!
Svend

[Billy26F5]

You might want to change the piston seal at some point too, and the cylinder o-ring as well. Other than that the unloading valve seems good. The non-return valve might need a look at if nothing else works. Once fixed it should hold up for over a month.
Sandy

[NCOD92]

You might want to change the piston seal at some point too, and the cylinder o-ring as well. Other than that the unloading valve seems good. The non-return valve might need a look at if nothing else works. Once fixed it should hold up for over a month.
Sandy

I replaced both seals with one from a kit: https://www.yesterdaystractors.com/Ford ... 34247.html

Do you think I should get one through new holland and try theirs? I cleaned the non-return and the ball-bearing tap on the seat. I looked for a replacement but I don't know where to find one, the Parts manual says obsolete. The only external leak I see is coming from the pin that runs through the lift control lever. I don't see the plug that the above post is referencing.

[Billy26F5]

I would look at the bush, as you've replaced all seals and checked all valves. If none of this works you'll need to check the fit of the control valve, and perhaps find a slightly bigger one, unfortunately not available new (Super Major and Dexta ones are, but they're totally different).
Here's the Ford manual for extra help: http://www.fordson.se/5_Hydraulik_Verks ... 47-166.pdf
Sandy

[SvendH]

The bush I refered to is on the end of the lift cylinder partly covered by a small steel plate,the screw holding the plate plate fits the thread in the bush and is good for pulling the bush out.The Lift will have to come off again to do this Sorry!
Svend

[SvendH]

Update!! Your lift is different to mine which is a super.I see this now thanks to Billy!!
Bit still,if you have the lift off again you could try the compressed air to help find leaks.

[Billy26F5]

Now I understand what bush you're referring to, there isn't one on the Major hydraulics. The air system should be pretty good for finding the leak but do remember you've bought new just about the only parts you can get new nowadays. I think there was a scrapy somewhere that had lots of Major parts, that would be a great place to look for a valve. If you have the largest valve and it leaks you'll need to find another valve chest, but hopefully that won't be the case. Do measure the valve and bore to be sure and if you need a larger valve mark the chest with the new colour code as specified at the end of the manual.
Sandy