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MG MG Y Type - Jackall Fluid

Chaps,

I'm sorry to bang on again about my Jackall system, but I have another query.

I've got it all working, there are no leaks and I can get all four wheels off the ground. 'Great' you say. 'Go away then and stop bothering us Saul'. However in order to get it off the ground I have to pump like a nutter.
I mean I have to pump the handle really really fast - like 'pulling muscles in your arm' fast. If I pump at a "normal" rate then all the jacks extend and the car lifts up onto its toes but that's as far as it goes.

The pressure relief valves are fine and if I get the car off the ground it'll stay there forever without sinking. The only explanation I can give is that in the pump the pistons themselves can't be as good a fit as they might be and when confronted with the high pressure needed to make the old girl leave the deck there must be a tendency for the hydraulic oil to "leak" back around the pistons and not be pumped. After all, the pistons don't run through any kind of seal and just rely on there being a very good fit within the casting, and this will obviously wear with use over time.

So no big surprises? However I have to come clean and explain that I am running the system with (Halfords) Hydraulic Jack Oil (for trolley and bottle jacks) and one thought that did spring to mind was that perhaps if I use another recommended fluid (like motorcycle fork oil or penrite shock-oil?) then matters may improve. Obviously if the oil was thicker then I probably wouldn't have to pump so fast.

Therefore please can anybody tell me whether they think any of the suitable fluids would indeed be "thicker" than the hydraulic oil I'm currently using and in fact which would be the thickest (and therefore possibly the most suitable for my worn pump).

Thanks in advance as always.

Cheers,
Saul.
Saul

You will kick yourself Saul as the answer is to use motor cycle fork oil. This has been covered before but for you, I have added it to the Technical Advice Page.

Paul
Paul Barrow

The 'thickness' of the oil is not really relevant, but the thinner it is the sooner it shows up poorly seated ball-valves. You need to ensure everything is really clean inside the pump, pipes and reserviour. Any dirt or hairs will ruin the seating of the valves, and you will just be shoving oil back and forth, a bit might go to the jacks hence your arm weary efforts.

Motorcycle oil is perfectly OK, but any SAE 20 mineral oil is OK. Do NOT, repeat NOT, use brake or clutch fluid and this is vegtable based and will rot all the seals.

Once the pump ball valves seat OK, you will find the pump handle is quite hard to move, as you will lift the car in a very few strokes.

Did you refit the little spring-plate correctly over the ball valve? Did you check its seating was in good condition?

Neil.
Neil Cairns

Thanks for the info Neil.

I did indeed clean the pump thoroughly and check all the valve seats.
The fact that once the car is completely off the ground I can leave it over-night without it dropping one jot surely means that all the valves are sound, even when under high pressure, doesn't it? Or am I missing something???

I correctly put the leaf springs back over the relief valve balls and even added a washer to the outside of the spring so that I could guarantee it wasn't giving-way at too low a pressure.

The lack of ommph in the pump is purely on pumping (just when the car starts rising) which is why I suspected that the pistons themselves weren't doing as good a job as they should and that a "thicker" fluid might help.

I bought some SAE15 fork oil yesterday and will give it a go this weekend, however it seems even thinner than the hydraulic oil I have been using so I'll not be holding my breath for a dramatic change in how much my arm aches by Monday.

Cheers,
Saul.
Saul

Would silicone brake fluid work? I can find out what the viscosity is.
Scott Barrow

The valves that hold the fluid into the system is screwed down by that little black plastic knob. The valve that permits the fluid to be pumped into the system is controlled by a little 'plate-spring'. They are two separate items. The second is basically a non-return-valves that lets the pump push oil into the jacks. The first is one that lets the oil out back into the reserviour.

The non-return-valve has a small screw holding down the spring onto a tiny ball bearing. If the slightest bit of dirt gets onto its seat, or the seat has a crack, or is in any way faulty, it will not pass fluid properly. It lives under the little alloy side panel, ( to the front of the pump.) To re-seat it, first check the ball bearing is perfect, ( they rust and also get a groove on them caused by the seating,) tap the ball with a hammer. The seating is only alloy, so not too hard!!

The only other problem may be badly worn pistons in their bores, this is not repairable. Find another pump if this is so.

Neil.
Neil Cairns

This thread was discussed between 09/05/2005 and 16/05/2005

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