770 hydraulic pump

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weths
Posts: 40
Joined: Mon Jul 16, 2007 6:28 pm
Location: Gilberdyke

770 hydraulic pump

Post by weths » Sun Apr 14, 2013 7:06 pm

Hi all ,wanting any information on changing hydraulic pump ,difficulty ,location ,price ,etc thanks

Guest

RE: 770 hydraulic pump

Post by Guest » Sun Apr 14, 2013 8:07 pm

Pump situated inside the PTO unit housing at the bottom front, removal of the unit needed to access the pump. Difficulty on a scale of 10, I would say 4. Price will probably vary but expect to pay around £380 plus VAT. It does not include the drive gear, you have to use the one from your existing pump. More info on your problem may throw more light on things as it might not be your pump that's the trouble.

weths
Posts: 40
Joined: Mon Jul 16, 2007 6:28 pm
Location: Gilberdyke

RE: 770 hydraulic pump

Post by weths » Sun Apr 14, 2013 8:54 pm

when moving the lever there is no pumping noise or arm movement so looing at the worst cenario

Guest

RE: 770 hydraulic pump

Post by Guest » Sun Apr 14, 2013 9:02 pm

It could be something in the valve chest such as a sticking valve. Very often you won't hear the pump when you pull the hydraulic lever back into 'select' if there is something awry in the chest.

weths
Posts: 40
Joined: Mon Jul 16, 2007 6:28 pm
Location: Gilberdyke

RE: 770 hydraulic pump

Post by weths » Sun Apr 14, 2013 9:13 pm

are they located under the small cover near the lever

Guest

RE: 770 hydraulic pump

Post by Guest » Sun Apr 14, 2013 10:22 pm

Yes. Behind the lever on top of the axle there's a plate with 2 1/2 inch bolts holding it down, the valve chest is under there. On the other models there is a tall 'plunger' which is the dump valve but on the 770 this unit was not fitted as standard so it may not be on yours, if there is a dump valve fitted let us know before going in there but if not then remove the cover and look in the hole, there you will see the top of the valve chest. Here you will see 2 large slot screw heads, you need to remove the one on the right nearest the mudguard. You may have to initially loosen it with a hammer and appropriate chisel as they are often quite tight. After loosening it unscrew very carefully as there is a compression spring under it under pressure and on top of the spring there may be a very small aluminium disc and minute steel ball, don't loose anything. Then remove the spring. Now, in the hole the spring came from in there is the lift valve, get a tapered clean stick the same size as the hole in the valve, push it in the valve tight enough so that when you pull it out the valve comes out with the stick. Now look in the top of the valve, in it you will find a little brass slot-head setscrew, take it out. Under this set-screw is a very small nylon gauze, if it won't come out by tapping the top of the valve down on a bit of wood then don't poke at it, leave it where it is. Wash out the valve and filter gauze with either a thinner or petrol to remove any dirt and then put the filter gauze back in if you removed it and the setscrew. Push the tapered stick back in it and put the valve back in the chest but 'feel' it in, if it feels a bit tight you will need to 'polish' the outside of it with some very fine steel wool, the valve should more or less fall in its place under its own weight but if you do need to polish it make sure you wash it again, it has to be perfectly clean. Re-assemble it all and try the hydraulics, come back and tell us if there's anything happening.

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mistermcgregor
Posts: 157
Joined: Sat Sep 08, 2012 10:09 pm
Location: Southampton

RE: 770 hydraulic pump

Post by mistermcgregor » Sun Apr 14, 2013 11:24 pm

Points to observe. Absolute cleanliness at all times.
Wash parts in clean liquid,do not wipe with cloths as fibre may be left.
DO NOT use any abrasives and certainly not steel wool.
Clean the valves in the same way as cleaning glasses.
Hammer and chisel!!!!!On David Brown hydraulics?????

John_Allen
Posts: 1894
Joined: Sat Dec 31, 2005 3:59 pm
Location: Cumbria UK

Re: RE: 770 hydraulic pump

Post by John_Allen » Mon Apr 15, 2013 12:08 am

mistermcgregor wrote:.
Hammer and chisel!!!!!On David Brown hydraulics?????
Yes, I know it sounds like sacrilege, but sometimes a previous owner has mashed the head of the "screw" and a screwdriver won't stay in the slot.

If you haven't got a wide enough screwdriver, it is better to try to use a bit of flat steel (cut and shaped to fit) and an adjustable spanner rather than ruin the head with a badly-fitting screwdriver. However, in the heat of battle, speed and convenience tempt people into ill-advised short-cuts!

I agree about avoiding abrasives, but sometimes the parts are already damaged and a gentle abrasive is needed (1500 wet&dry with plenty of lubrication may be better). I like to keep a can of brake cleaner to wash parts down - carburettor cleaner will do a similar job, but I only have two carburettors - the lawn mower and garden rotovator - so don't buy the stuff!

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erkki
Posts: 2032
Joined: Sun Apr 09, 2006 12:02 pm
Location: North Finland

RE: Re: RE: 770 hydraulic pump

Post by erkki » Mon Apr 15, 2013 10:00 am

One more thing,

There should be a restrictor orfice plate between the brass screw and nylon gauze. There is a pin hole in the middle. The pin hole must be clean. The nylon gauze is there to prevent particles to achieve the pin hole, that is why its important not to punch holes to the gauze.

In the shop books the importance of clean is emphasized which is ok. But actually the system is not more sensitive to dirt than any modern hydraulic component. Cleaning the by-pass valve is simple operation, which I have made a few times on the field by the simple tools in the toolbox. Just do not drop parts or dirt to the rear axle housing.

RGDS erkki

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DB780
Posts: 1623
Joined: Fri Dec 30, 2005 4:06 pm
Location: Lincolnshire

Post by DB780 » Mon Apr 15, 2013 10:24 am

As John notes it's sometimes necessary to use fine wet&dry (I use 1000 or 1200 grade) soaked in diesel or paraffin to clean up valves that are damaged so long as you are not too aggressive and clean the valve well afterwards you are doing fine.

Guest

Post by Guest » Mon Apr 15, 2013 1:08 pm

I know others have their preferred methods but I always use a micro fine steel wool to polish the chest valves as its softer metal than the valves and does not scratch or abrade the surface in any way whereas any caborundum based material will, may be ok to remove rust and corrosion spots on the surface of the valve but if it has rust or other corrosion on it then it and the chest may be beyond redemption, water in the oil being the cause.

Talking of fine grade steel wool, another good use for it is in cleaning the brown film that builds up inside of the glass lift pump bowl.

Eric_T
Posts: 1408
Joined: Sat Dec 31, 2005 11:57 am
Location: North Wales

Post by Eric_T » Mon Apr 15, 2013 3:43 pm

If wirewool is softer metal than the valves, and it does not abrade the valve, there is little point in using it at all.

I agree with Mister McGregor, keep wirewool away from sensitive hydraulic parts.

Guest

Post by Guest » Mon Apr 15, 2013 4:02 pm

Perhaps you ought to try it Emyr, then you'd see. It's the deposits that builds up on the surface of the valves that make them stick, that's what you want to remove from the original surface. How many times have people been told not to use anything abrasive on these valves as they are manufactured and originally machined to an exact size. :roll:

John_Allen
Posts: 1894
Joined: Sat Dec 31, 2005 3:59 pm
Location: Cumbria UK

Post by John_Allen » Mon Apr 15, 2013 7:48 pm

It would be interesting to do a comparison of the abrasion produced by wire wool and 1200 wet&dry. I was using some fine wire wool this morning and, while I couldn't see scratching, it certainly moved a lot of crud, where wet&dry with lubrication seems to take forever to clean anything off (it soon blocks with crud). I have, on occasion, used 1200 or 1500 grade wet&dry to flatten defects in paint and, if used properly, you can't see any abrasion marks on the paint.

The thing that bugs me with WW is that the "dust" gets everywhere, but one of its big advantages is that it is better at moulding itself to the more complex contours (eg spheres) so there's less risk of producing flat spots.

weths
Posts: 40
Joined: Mon Jul 16, 2007 6:28 pm
Location: Gilberdyke

Post by weths » Mon Apr 15, 2013 8:31 pm

thanks for the info ,will try having a go soon ,will let you know how I get on ,Cheers

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