John Deere 3350A front loader hydraulics problem

[ROAMER]

Hi everyone!!!

Greetings from Croatia. My first post!!!
I usually do hydraulics for excavators, but rarely I do work on tractros as well, if I can't wiggle my way out of it
Friend has 3350A with front loader and wants to upgrade the distributor as original one is leaking and he wants to change the position of it. I've never worked on Deere 3350A.
I had a look at the existing system and I can't figure out few things. Existing distributor is located on the right hand site of the seat, and apart from hoses going from 2 valves to the cylinders, it has 2 hard pipes and one flexible hose coming to the block. Flexible hose is coming from the either a small pump or regulator mounted at the bottom right hand side of the trancmission housing, so that must be supply. One hard pipe is going to the hydraulic filter, and another is going in the housing under the seat. Both hard pipes have rubber piece of hose that is tightened just with screw type clamps, so they have to be return or very low pressure. The one going back to filter is return obviously, but I don't know what the one going under the seat is for?
Can anyone please help me with this?

Many thanks!!!!

 

[ROAMER]

 

[ROAMER]

Getting desperate here

 

[Sharpy]

I think your 3 pipes are
Flexible line is high pressure feed from priority valve
Pipe to filter is return pipe to low pressure lube and main hyd pump feed circuit
Pipe to top cover is low pressure return (only used when the pressure is too high in the low pressure circuit.
Also please remember this is a closed centre system so you must fit a closed centre spool block .

 

[ROAMER]

Thanks Sharpy!!!
So what I taught is some kind of regulator bolted to the transmission housing (picture attached above) is actually a priority valve?
Wen you say pressure too high in low pressure circuit, what are we talking about? 2 bar, 5 bar, 15 bar?
Also, is there by any chance a schematic diagram for this tractor that shows the connections? I bought some documents, but none of them show this front loader configuration.

Thanks again!!!!

 

[Sharpy]

If I remember correctly the pressure relief valve works at around 100 to 150 psi but that is very approximate. Most aftermarket loaders would not bother with 2 return lines, most would only return to the low pressure circuit.
Basically plumb feed from priority valve to closed centre spool block, return to low pressure circuit.

 

[ROAMER]

OK, thanks for the advice, I will try it like that. So basically pipe that goes under the seat I just block off and that's it?

 

[ROAMER]

Just to mention, this looks like factory or dealer installation for the loader. Not second hand. Levers and pipes are all JD green with their part numbers.

 

[Sharpy]

Yes, it looks like a standard jd spool block for tipping trailers etc, you could just T your feed and return into the existing system and leave the original setup assuming that this suits your new setup.

 

[ROAMER]

What is on the picture is the spool block for front loader, I am looking at removing existing one and replacing it with aftermarket one with 4 spools. 2 for existing loader that will replace existing block, and 2 for additional quick coupling ports at the back.

 

[Tractortech]

Now Then..
I assume this is a 'no cab' tractor, perhaps a roll frame??
Your loader must be connected to the existing SCV,s (spool valves to us, distributors to many others). Rather than disturb the current set up, why not add a 2 function valve with joystick control for the front loader??
The SCV's you currently have are modular. The base of which is supplied from oil after the priority valve. The return flow Is directed to the return filter of the spin on type, filtered oil is then sent into the low pressure line which supplies the main pump at the front of the tractor. The excess return oil is sent by a valve in the SCV base to the rockshaft housing at the port near the seat..

 

[Tractortech]

This gives an idea of the loader valve set up...

 

[ROAMER]

Thanks for the info Tractortech!!!!
Tractor is with a cab.
New valve block has already been purchased as per my friend's liking. Original one is leaking and he doesn't like the position of it.
From what I have found out in the meantime, line that goes back direcly under the seat can be left out, and all of the return to go via the spin on filter, but loader will be slower because of this. True? Also do we know at what pressure system sends excess oil back under the seat direcly? Maybe I can install low pressure regulator to acomplish this for me.

 

[Tractortech]

Well, here's the dilemma...
Retuning all the oil through the spin on filter may cause it to burst, that's why the bypass valve is in the SCV base. However, in reality the bypass valve arrangement could cause a restriction, which used to prevent tipping trailers coming back down in a timely manner, so we used to remove the ball and spring which allowed the oil to return to the rockshaft housing.
The 40 series tractor which is basically the same tractor used to return all the oil to the rockshaft housing as they never had the spin on return oil filter.
When a loader was fitted to either a 40 or 50 series tractor, the loader used to return into the filter bowl. That's the one bolted vertically under the transmission case with a ½" UNC bolt, (a ¾" AF spanner fits) unfortunately, your filter bowl has no return port so you'd need to change it..
Oil returning to either the spin on filter or the actual filter bowl has to overcome the 10.5 bar low pressure Oil which supplies the main hydraulic pump.
The main hydraulic pump is 'closed centre' not CCLS or PFC type so has no sensing line. I hope the valve you have is correct. An 'open centre' valve won't work either..
I hope you can understand all this ok. I know no Croatian, but your English looks good..

 

[ROAMER]

Ok, so if I was to return all the oil to the rockshaft (under the seat) housing and plug up the other return, what would be the bad side of that?
No problem with closed centre. When new valve was bought, I requested both closed centre plug and power beyond fitting, because I didn't know at the time what I will need.
English no problem. Lived in Australia for 20 years

 

[Tractortech]

The downside of oil to the rockshaft housing is that the transmission pump has to source oil for its own functions and also to supply the main pump. When the loader oil is returned into the filter bowl, it effectively feeds the main pump, saving the transmission oil pump a job and gives faster cycle times. Single acting cylinders cannot return to the filter bowl as they can't overcome the 10.5 bar pressure

 

[Tractortech]

John Deere Parts Catalog

Find parts & diagrams for your John Deere equipment. Search our parts catalog, order parts online or contact your John Deere dealer.

partscatalog.deere.com

This might be of some use to you..

 

[ROAMER]

Ok, I did not know that part, tranny pump supplying main pump etc. Hence all the confusion on my side. So at what pressure does return oil stop feeding into spin on filter and starts going to rockshaft housing? As I mentioned before, maybe I can install low pressure regulator, or use existing block where returns are connected originally. I just need to remove spool valves and install blanking plate. Plug up supply fitting, and existing block will keep doing it's job like it did so far. I have to do this install rather quickly so only other option for me is to make a port on that filter cover.

 

[Tractortech]

It won't stop returning via the spin on filter, when it can't cope, the valve opens and allows the excess to go to the rockshaft housing..
We used to remove items 20 to 23 as I recall..
This allowed a trailer to come back down. A loader was always returned to the filter bowl as it had it's own spool valve mounted on the loader frame..

 

[ROAMER]

Bad expression on my side. It starts sharing the flow so to speak.
Well in my case, return is as you saw. No bowl filter return. I think I will remove the valves and leave the block to keep the return function