Replacement fluid for corba hydraulic jack???

I've got the hydraulic ramp jack, not sure of age but several years old, for our cobra trailer that seems to be suffering the common issues of leaking and not raising fully and then slowly lowering... I searched several of the old threads and looked at Cobra's site where they have info on replenishing the fluid. I'm hoping doing so will solve the problem, otherwise on to bigger and more expensive fixes.
Cobra recommends HLP 32 ISO or equivalent fluid. I don't know all the nuances of hydraulic fluids, but I remember seeing a post about a certain type to avoid and I can't find that post again..
I can pick up a bottle of this locally:
http://www.tractorsupply.com/tsc/pro...t?cm_vc=-10005
And here's the data sheet on it:
http://www.smittysinc.net/images/pro...c_Jack_Oil.pdf

Any issues with using this stuff?
Thanks

No problem whatsoever.

Cobra uses about the cheapest Chinese junk jack they can get their hands on, I think. When you drain it, you'll find a silvery particulate sheen to the oil - metal.

Really best to do this after a month or two of use. As if you wait until jack starts failing, you may be stuck looking for new seals. Some are generic metric O-rings, and that way well get it fixed. If it's the seal on the main ram defective (and I've not found that to be the case) then it might be harder to source.

I suggest flushing the jack well with any petroleum solvent, kerosene, diesel fuel, whatever. Drain, refill with any garden variety hydraulic oil, tractor hydraulic oil is just fine.

bumper
MKIV & QV

On Wednesday, April 13, 2016 at 12:57:48 PM UTC-7, bumper wrote:
No problem whatsoever.

Cobra uses about the cheapest Chinese junk jack they can get their hands on, I think. When you drain it, you'll find a silvery particulate sheen to the oil - metal.

Really best to do this after a month or two of use. As if you wait until jack starts failing, you may be stuck looking for new seals. Some are generic metric O-rings, and that way well get it fixed. If it's the seal on the main ram defective (and I've not found that to be the case) then it might be harder to source.

I suggest flushing the jack well with any petroleum solvent, kerosene, diesel fuel, whatever. Drain, refill with any garden variety hydraulic oil, tractor hydraulic oil is just fine.

bumper
MKIV & QV

On a related vein, DO NOT depend upon the jack, alone, to support the fuselage (most likely it will, but hydraulic jacks can fail). This is an issue if you have the fuselage jacked w/o wings and extend the gear. If the jack slips the fuselage will come down on the gear and tip over. Somehow block the ramp to support the load if this happens (this was not an issue with my DG400 which had electric scissor jacks!).

Tom

On Monday, April 18, 2016 at 8:49:55 PM UTC-5, 2G wrote:
On Wednesday, April 13, 2016 at 12:57:48 PM UTC-7, bumper wrote:
No problem whatsoever.

Cobra uses about the cheapest Chinese junk jack they can get their hands on, I think. When you drain it, you'll find a silvery particulate sheen to the oil - metal.

Really best to do this after a month or two of use. As if you wait until jack starts failing, you may be stuck looking for new seals. Some are generic metric O-rings, and that way well get it fixed. If it's the seal on the main ram defective (and I've not found that to be the case) then it might be harder to source.

I suggest flushing the jack well with any petroleum solvent, kerosene, diesel fuel, whatever. Drain, refill with any garden variety hydraulic oil, tractor hydraulic oil is just fine.

bumper
MKIV & QV

On a related vein, DO NOT depend upon the jack, alone, to support the fuselage (most likely it will, but hydraulic jacks can fail). This is an issue if you have the fuselage jacked w/o wings and extend the gear. If the jack slips the fuselage will come down on the gear and tip over. Somehow block the ramp to support the load if this happens (this was not an issue with my DG400 which had electric scissor jacks!).

Tom

You are right, Tom, but there is an easy fix: never, and I mean never leave the fuselage by itself lifted with the wheel down. That is a good way to end up with a hole in your canopy. Always put the wings on before lowering the gear.
Herb

On Monday, April 18, 2016 at 9:49:55 PM UTC-4, 2G wrote:
On Wednesday, April 13, 2016 at 12:57:48 PM UTC-7, bumper wrote:
No problem whatsoever.

Cobra uses about the cheapest Chinese junk jack they can get their hands on, I think. When you drain it, you'll find a silvery particulate sheen to the oil - metal.

Really best to do this after a month or two of use. As if you wait until jack starts failing, you may be stuck looking for new seals. Some are generic metric O-rings, and that way well get it fixed. If it's the seal on the main ram defective (and I've not found that to be the case) then it might be harder to source.

I suggest flushing the jack well with any petroleum solvent, kerosene, diesel fuel, whatever. Drain, refill with any garden variety hydraulic oil, tractor hydraulic oil is just fine.

bumper
MKIV & QV

On a related vein, DO NOT depend upon the jack, alone, to support the fuselage (most likely it will, but hydraulic jacks can fail). This is an issue if you have the fuselage jacked w/o wings and extend the gear. If the jack slips the fuselage will come down on the gear and tip over. Somehow block the ramp to support the load if this happens (this was not an issue with my DG400 which had electric scissor jacks!).

Tom
Good point and advice about not trusting the hydraulics... When looking at old posts for this someone else had mentioned it as well and I know use a triangle piece of wood from an old wheel chock as a block to keep it from dropping fully if it fails under load.
It definitely has a slow fluid leak somewhere and is destined to be replaced at some point. But, how much does temperature play into this?? First use of it this year was when it was still cold out (below freezing temps at night, 30's/low 40's during the day and it wasn't raising more than 2-3 inches and then lowering under it's own weight. Took it home, worked on it the next day, kept it in garage with similar temps, refilled fluid. It would now fully raise, but would noticeably lower at decent rate under it's own weight. Brought out to the airport the next day, set up a system of blocks to keep it at needed height so it's usable in the meantime. Sunny day, temps warmed up to the 70's, and now it works fine.. Maintained pressure and pumped up height without weight on it, with me in the cradle and then with the glider in it; keeping backup blocks in place as well in case of failure...
Destined to be replaced/repaired soon regardless, just curious about if temp fluctuations like that could account for any of this or did the jack magically cure itself by being threated and yelled at for an hour???

The seals are old, they get stiff with cold and leak.
Once warmed up, they seal better.
This explains what you're seeing.

Likely cheap and easy to rebuild, just have to find a seal kit. You can likely find a local shop to do the work if you don't think handle it.

On Wednesday, April 13, 2016 at 3:57:48 PM UTC-4, bumper wrote:
Cobra uses about the cheapest Chinese junk jack they can get their hands on...

To be fair, the Spindelbergers have bemoaned the lack of available
quality jacks; as all jack production has been driven overseas to
the lowest cost with barely acceptable quality. They've told me
they'd be happy to buy better stuff if it could be found.

Spindelberger has always provided great support!
See ya, Dave

Yes, temperature does affect the operation of a hydraulic jack. When the fluid is cold, it is more viscous and does not flow from the reservoir into the pumping ram as easily. It means you are pumping less fluid with each stroke. A short pause between strokes allows more fluid into the ram and more "push" on each stroke. It doesn't help that the jack is mounted sideways either. Other than the reduced efficiency while pumping, there should not be any other effects. If the jack leaks worse and won't hold its height, I suspect that the O-rings were cold and stiff. (At least the disaster wasn't as awful as the "Challenger" in 1986.)

I agree that the jacks are pretty lousy, but I don't know of any that aren't made in the same Chinese factory. At least not in the configuration used on the Cobra ramp. One minor good thing- replacements are about $30 from any auto parts store that sells the tiny little floor jacks designed to lift tiny little cars. You have to disassemble and do a couple of quick modifications to get the pedal lever and valve to work, but it isn't a big deal. I've replaced a few for owners at Moriarty and it all takes about an hour.

But don't trust the thing! Do what they are telling you and leave the gear UP unless the wings are on. And don't let your fingers into the mechanism at any time! Right, Howard?

As a footnote, I have had jacks rebuilt by reputable hydraulic shops, and they used better O-rings but told me that there is just so much you can do with inferior quality. It is doubtful that the rebuild price was worth it. The jack was still pretty crappy.

On 4/19/2016 8:13 AM, Mark628CA wrote:
Yes, temperature does affect the operation of a hydraulic jack.
Snip...
If the jack leaks worse and won't hold its
height, I suspect that the O-rings were cold and stiff. (At least the
disaster wasn't as awful as the "Challenger" in 1986.)
Snip...

But don't trust the thing!...

Heh - to paraphrase Clint Eastwood: "A man's got to know [its] limitations!"

If you like playing with fire, you'll love trusting hydraulic systems to not
leak (slowly or...less slowly!). Even before lawyers became a 'Murican
pestilential ubiquity, every instruction sheet/manual I ever read on hydraulic
systems - and every semi-sensible farm boy - noted to ==N*E*V*E*R== work on
(i.e. "trust") any raised hydraulic system in the absence of "hard
blocks"...tractor bucket or personal car or glider fuselage...even industrial
garage lifts. Yeah, hydraulics can be immensely useful, but they definitely
have their limitations, regardless of operating system pressure or quality of
manufacture.

Bob W.

I lower the wheel, and lower the jack until the wheel just touches the ground, then hold that jack position. There is then no further down pressure on the jack. The fuselage weight is supported by the main wheel, but the fuselage is still snug in the cradle, which keeps the fuselage upright as the wings are attached.