Hydraulic pump relief valve - do Ineed to drain the transmission oil?

[Redpla]

Hydraulics on my Dexta have just packed in completely. Control has always been saggy and pretty much "all up" or "all down" on the 3-point, so I've been meaning to do a top-plate service... well, ever since I bought the tractor 14 years ago. So I shall get cracking shortly. Assisted, I hope, by this video which looks reasonably relevant and complete... https://www.youtube.com/watch?v=kBieDlfg4Vo

Most likely, though, this new "won't lift anything" problem is caused by a stuck pump pressure relief valve. I'll service that at the same time. It's quite low on the side of the transmission, so my question is: will I need to drain the oil before I take this out?

And, while you're here, kindly reading my question... anyone know where I can get a draft control pin/dowel which fits (interference fit) in the valve control lever? Only seller I can find is an ebay one with poor feedback. Can't see it at Agriline, Mill Hill, Old20, Vintage Tractor Spares but maybe I'm using the wrong name for it. It's in the video at about 9:35-on.

[Billy26F5]

I'm afraid you will need to drain the oil to do anything on the pump, but I suspect the not lifting is a stuck unloading valve plug, a common cause. The relief valve is generally pretty good, the only problem with the earlier unloading type is that they need delicate handling for operation as when they lift they go from 2500 psi to 300 psi before they'll reseat, the later type reseating only slightly below 2500 psi.
Here's the manual: http://www.smallholderservices.co.uk/si ... hydraulics
The Ford 3000 is not a Dexta, but it's not too different.
Not too sure what dowel you're referring to at the moment. There are plenty of parts that none of the aftermarket companies have.
Sandy

[Jerry Coles]

Hi
Re the darft control pin.
If what you are referring to is the follower pin that does wear, my memory in the distant past on this forum was the recommendation of using an equivalent size twist drill where you fit it and then cut off the excess. A twist drill is usually made of harder steel so won't wear as fast (but then how many more years are you going to use it? If it has worn after the first 50 years of it's life?). IMHO.
Cheers
Jerry

[Redpla]

Thanks everyone.

Had the top off.
There's pump pressure at the outlet on the main casing (when turning-over on the starter). More pressure than my thumb can stop.
Safety valve is free.
Unloading valve is free (and still has a good O-ring on it).
Control valve is free.
Back-pressure valve is free.
Piston seal is good.
O-rings are all in place.
Can't (easily) get to the inlet screen so can't comment on that.
There's evidence that someone's done a rebuild of this before my time - including an Araldited new follower-pin made from the thread and shank of a s/s M8 bolt which was worn-half-through so I've replaced that. They must've done something right because it's been working for the 14 years I've had it - apart from being a long way out of correct adjustment.

Therefore I'm a bit mystyfied why the lifts - front and rear - lost pressure at the end of the last job. The only thing I did to the hydraulics was to top up the oil before the job. Maybe adding those 15 (!) litres dislodged some gunk that got into the valves.

Unless anyone has a better idea, I'll just replace the piston seal and all the O-rings, adjust it properly, and put it all back together.

[Old Hywel]

What oil did you add?

[Redpla]

Same as for the rest of the machine - 15W30 SUTO. It's clearly had a bigger leak from the PTO than I thought, so the level was well down. Pretty sure I checked it only(!) 14 years ago.

[Billy26F5]

All sounds like a good plan, while you're there I would clean the suction and return filters, as then they'll be ready for another 50 years. I wouldn't replace the return filter unless it's damaged. I would also fix the PTO seal and probably replace the oil, but that's just me. The oil is not original spec but probably ok from the easier to find modern types there are.
Sandy

[Redpla]

Well, it's all back together but we're not home yet

Position control works - for the first time ever. That's a big plus. And the rear ram stays up instead of drooping to the floor after 30 seconds. So, when cold, everything is working perfectly.

But after about half-an-hour of work the hydraulics become very weak. Whenever load is applied to a ram, there's a buzzing from one of the valves(?) in the transmission case and the rams go up v-e-r-y s-l-o-w-l-y.

There is the usual loud "click" when the front rams reach their limits - I assume this is the unloading valve doing its thing. If so, the problem is not that.

Anyone got a clue? Oil (much) too thin, perhaps? After all, this problem did begin the very day I majorly topped-up transmission with 15W30 - and before I took the top off and meddled with it.

[Billy26F5]

Does qualitrol work or not? The click is the relief valve (and it does sound like it's the unloading type valve, not the later pressure relief type with a long bolt head). Sounds like a leak but I'm not too sure about that, it shouldn't be the oil but I can't be certain as it's not the kind originally specified.
Sandy

[Redpla]

Unfortunately I can't test Qualitrol easily. It is adjusted (in theory) correctly. However, position control works and is all I need.

Anyway, the original problem is *probably* identified: the "Valve" part of the "Hydraulic Pump Pressure Relief Valve Assembly" (Fig 41 of Section 8 of the March 1958 workshop manual) is broken.

The "valve" and "spring" parts on mine are slightly different to the one in that image: the internal dia of the "spring" on mine is similar to the external dia of the "valve". To overcome this, my "valve" has a large dia seat at its blunt end. This seat is very thin (less than 1mm of metal) and it has partially broken away. The broken-away part has bent up towards the needle-tip of the "valve". This prevents the needle-tip from seating in its hole in the "valve body". So oil is permanently by-passing.

Now got to find a new part. Or maybe fabricate a new seat in the lathe, if I can't source a replacement. Tricky to keep the spring length unchanged, though.

BTW To find the buzzing noise, I used a 3' length of 1.1/4" ABS drainpipe: stuck one end to my ear and waved the other end around the tractor until the buzz was loudest. In this case, it was very clearly localised at the location of the pump and its relief valve. To empty the trans casing of oil I just detached a ram hose, then ran on idle until no more oil came out. Might not completely empty it, but certainly enough to then remove the valve assembly without losing oil. Cleaner than trying to drain it from the bottom and no need for a big tray - which I don't own!

[Redpla]

To wrap this up:

I've fabricated a new piece which seats the spring onto the "valve" part in the diagram. Reassembled (with shim adjustments to keep the spring length the same). Tested. All working OK, no buzzing now, and there's still the usual "click" at the limit of the front ram movement to indicate correct valve operation.

Thanks for all the advice. Fingers crossed this won't recur.

[Billy26F5]

Good work finding the leak. All I meant about testing qualitrol is to attach an implement and see that it lifts and lowers reasonably. Look at the supplement section, there are two unloading type relief valves and it's possible parts might have been mixed up, which is not supposed to happen. If you have a front end loader you're probably better with the later pressure relief type valve anyway (not in this manual, see page 40 in this: http://www.fordson.se/6B_Hydraul_Suplem ... 25-050.pdf).
Sandy

[Redpla]

Thanks Sandy. Mine is definitely "Previous Type" of valve and all the parts as drawn there look like mine - so fortunately no mixing-up. The part which failed is the top-hat-shaped "valve spring seat". I made a fatter one then removed a shim to compensate. Not sure MS is the right material, though - the old part was extremely brittle so perhaps hardened. Think I should fit a new valve ASAP.

Can't find a UK supplier of new valves. A few breakers are "looking in the morning" for me.

The front-loader spends most of its 'working' time doing nothing more than being a counterweight. It's dead useful when you need to lift something, but I try not to over-do it - it's hard on the front axle and the steering. Certainly I've never had the pressure relief valve 'pop' during raising - only when the rams reach their limits.

[Billy26F5]

I'm not sure if I'm right about this but I assume you have the valve used between 957E-49624 and 09C-909585, part no. 957E-638B. There are no new valves around, and I think you'll be fine with your repair, although I might suggest trying to harden it a bit. If you ever use the loader for heavy jobs you might want to fit the later valve, but many were used with the earlier valves and it's only a minor inconvenience as far as the operation goes. I know what you mean about the extra weight, Dexta's were never really intended to be for such generalised use, an important difference with the Major, used for anything imaginable.
Sandy

[Redpla]

Same old problem flared up again yesterday... slow lifting, and a buzzing from the valve in the hydraulic pump and - when lifting the front loader - the same buzzing can be felt in the control valve just after the diverter.

So off with the top and out with the pump. The problem then clear to see: a completely blocked intake screen. The buzzing probably cavitation - the impacts from which won't have done the relief valve any good (nor the pump). Also tons of gritty gunk lying in the bottom of the casing, which I think was rust which had fallen off the inside of the top cover.

I think the inside of the top-cover, including all the levers and springs, were so rusty due to the lack of oil-splash because the oil level was way below the drive-shaft. Adding fresh oil then sluiced this rust off, into the filter, and causing the problem. So it is worth keeping a proper eye on transmission oil level. And if normal driving includes running with a raised front-loader, adding extra fluid to allow for the litres lost into the front rams.

[Billy26F5]

Good plan, cavitation is never good and I would suspect that it was the only thing buzzing. A good clean and you'll be fine.
Sandy