David brown 780 live drive hydraulic issue s.

[Autotech]

I have a strange fault on a david brown 780 live drive the hydraulics lift in the down position but won’t stay up with engine off and won’t lift full weight,, a strange one ..? the type hydraulics it has a four way lever for application / service s. and a speed lift / action regulator dial, on a box nor handbrake . I’ve cleaned out the two valves under the 2 bolt plate on axle noting 1 has an external plunger on top of valve I suppose this is to relieve pressure . I’ve not done an oil change yet although I have filters but no 40 weight oil which I’m struggling to acquire thi I’ll is a tadge milky mmmmm any ideas folks .? Any help would be appreciated ..

 

[Selectamatic]

If your arms raise in the down position, the Selectamatic Pointer may be in TCU. Move the hydraulic lever right back against the spring and turn the dial to the Centre Position (this is height, depth control is fully to the left, pointing toward the seat) Do not use excessive force to turn it, it should just click across when the lever is right back against the spring in its quadrant. If it does not, stop and come back!

They wont stay up with the engine off means there is a leak somewhere.

The external plunger is a dump valve, give it half a turn to lift, designed to lower emty trailers or hydraulic arms quickly.

Change of oil and filter will do good, dirt and water ingress is the main enemy of these systems.

 

[Exfarmer]

The oil in the gearbox / hydraulics should be a SUTO oil for engine and and gearbox.

 

[Autotech]

Thank you for the info about the dump valve I wasn’t to sure on that as I hadn’t seen any pics if one .. yes it is in Tcu as this is the only mode it will lift in , although in a downward lever opp manner manner . The service lever has 4 positions I take it these can be in any order can you help. It has 4 positions there is a pipe off the base of this unit with wot seem to be a service valve although not quick release I was intending on fitting one to this pipe it locates a the seat base with two bolts .. but yea no power on height and lever moves easy with main lever against spring

 

[Autotech]

SUTO sorry I’m not sure wot that means I’m a tech with new restoration and learning all the time .? I believe as you say same for engine and hydraulics

 

[Autotech]

Googled it super universal tractor oil. Thanks

 

[Selectamatic]

Thank you for the info about the dump valve I wasn’t to sure on that as I hadn’t seen any pics if one .. yes it is in Tcu as this is the only mode it will lift in , although in a downward lever opp manner manner . The service lever has 4 positions I take it these can be in any order can you help. It has 4 positions there is a pipe off the base of this unit with wot seem to be a service valve although not quick release I was intending on fitting one to this pipe it locates a the seat base with two bolts .. but yea no power on height and lever moves easy with main lever against spring

The Service lever, as you call it is actually a three way valve...

It has four positions...

1/L - For using linkage and auxiliary hydraulics simultaneously
L - For using the linkage
1 - To supply hydraulic oil to port 1
2 - To supply oil to port 2, usually the trailer tipper pipe.

You lever should be in the L position, move the lever to the extreme right, toward the seat, then back one.

 

[Autotech]

Thanks for that . as the manual only shows turn type valves x 3. On this unit . Which left me not sure and-decals on lever guide missing the oils under SUTO are mainly 10/ 30 the manual advises 20/40 wot would you advise ? Where would you advise connect a pressure gauge to check the pump pressure is there a common fault of pressure loss on these hydraulic systems

 

[Exfarmer]

Thanks for that . as the manual only shows turn type valves x 3. On this unit . Which left me not sure and-decals on lever guide missing the oils under SUTO are mainly 10/ 30 the manual advises 20/40 wot would you advise ? Where would you advise connect a pressure gauge to check the pump pressure is there a common fault of pressure loss on these hydraulic systems

Suspect you have an early manual which had the 3 hand wheels under the lefthand side, later tractors had a 4 way hand lever running left / right in the same Place. Some tractors had none and no trailer pipe
whether you use 10/ 30 or 20/ 40 much depends in the average air temperature

 

[Selectamatic]

Taps were on early tractors, lever much more common.

Leaks could be anywhere!

you should be getting 2500 ish psi at the trailer pipe.

Lift the linkage, close off the three way valve, does the linkage still drop?

 

[Autotech]

Sorry must have misunderstood it has 4 position Lever not a valve . Wheel type valve was on my manual appologys so Lever to position 2 from seat and tcu Lever to hight ie centre . And no lift . Operation. Just can't understand if Lever to tcu and main up /down Lever to lower and arms raise but with no strength / power . I think possibly leak from pump o ring or hopefully not split pipe . Will check pressure to tip pipe to see if faulty divert spool valve but still anyone any methodical test method I would be greatful to use!

 

[Exfarmer]

Sorry must have misunderstood it has 4 position Lever not a valve . Wheel type valve was on my manual appologys so Lever to position 2 from seat and tcu Lever to hight ie centre . And no lift . Operation. Just can't understand if Lever to tcu and main up /down Lever to lower and arms raise but with no strength / power . I think possibly leak from pump o ring or hopefully not split pipe . Will check pressure to tip pipe to see if faulty divert spool valve but still anyone any methodical test method I would be greatful to use!

Ihave seen a split in the pipe below the camels hump also failed or ring there

 

[Exfarmer]

On the Tcu position right down I think there should only be about 700 pounds in the system

 

[fandm]

Hi got the same problem myself to make the arms raise and drop i have to use the 4 position lever.
1st position from the gearbox will drop the arms 2nd position will lift the arms 3third position used for aux will keep the arms at a set position,
The quadrant control for setting height and depth does not work, no matter what position you have the tlc,
So have to use 4 position valve its a bit of a ball ache but gets things done.
cleaned the 2 valves at top of the box, that is another ball ache.
Watched a video on how to get the out otherwise they would still be stuck there, solution use a 3/8" 24ft or fine thread bolt not feet and a expansion bolt.
does anyone have a solution to the control quadrant not working. Thanks in advance.

 

[Autotech]

I’ve just had some history before the loss of rear arm action it had a 6 ft topper attached ,, would this be too heavy for the hydraulics for a 780 ? Many thanks starting to strip as I have low pressure and will only lock arms up mechanically from n/s swivvel lock

 

[fandm]

i would think if you cannot use a 6ft topper because it was to heavy you need to throw the tractor away.
It is one of the lightest things you can use

 

[Exfarmer]

Try asking on the DBTC forum, there is not much they dont know about these tractors. The hydraulics were very advanced for their day

 

[Bald n Grumpy]

If your arms lift with the lever in the lowering position and you have all other settings correct it could be a stuck valve in the control unit have had this happen myself

 

[fandm]

Hi thanks for your reply. is the spool valve under the bypass valve when the bypass valve is removed.
there is a cross slotted screw head that can be seen that looks like a diagram of the spool, as it is the only one like that in the diagrams, is it possible to tap this to free it,
Thanks

 

[Bald n Grumpy]

The valve I mentioned is called the latching valve and is in the front of the control valve unit at right angles to the bypass valve and is not easily accessible without removing the whole unit