John Deere 2840 Hyraulics Problems: 
Tractor came in with multiple hydraulic problems.
Many components of the hydraulic system were contaminated by metal shavings from the braking system.

The information presented here is our findings on this particular tractor and are not necessarily your hydraulic problems.
First what needs explained is that the transmission pump that supplies the main pump with pressure gets it's oil from a screen in the rear end of the tractor. This screen is the only protection for the tranmission charge pump. If this screen becomes plugged, the main charge pump will not supply oil to the main pump, pto brake, pto clutch, three point hitch, steering or remotes.  There also is the main filter to consider. If the hydaulic filter it plugged, the charge pump through a filter relief valve, dumps the oil from the charge pump back into the rear end/transmission cavity. Oil flows from the long screen through the charge pump and onto the outer part of the main filter. It then travels through the outside of the filter to inside the filter and up the tube to the transmission cover where the oil is distributed to the PTO clutch, PTO brake and main hydraulic pump.
A hydraulic priority valve then allows oil to circulate to the power steering and brakes. If the priority valve does not recieve at least 1,800 lbs of pressure, it doesn't allow the control spool inside to provide oil to the three point or the SCV remote valve. As soon as the pressure pasts 1,800 pounds of pressure, it move the spool further into the priority valve housing allowing oil to flow to the three point and SCV remotes.
First of all when diagnosing this system, you must pull the lower screen beside the main filter out and inspect it for debris and damage. Then you must replace the hydraulic filter and make sure the tension spring is in the cast iron filter cover to make sure it pushes the filter up against the rear end housing.
Make sure you remove all plugs under the transmission and rear end housings. On these tractors, you check the charge pressure on the side of the aluminum transmission shift cover. If your tractor has a platform, you will need to remove the steel plate covering the cover to expose a small plug on the right side. This plug is your main charge pump test port. You can increase or decrease the charge pressure by adding or removing washers in the charge pump regulator again on the shift cover. It's a small plug on the back of the shift cover. Also if your PTO is the problem you can easily check the PTO clutch and PTO brake pressure off the main valve on the lower part, right side of the transmission.

You can check your main pump pressure from the remote valve but you have to be careful doing so. Because if someone has adjusted the metering valve in the remote, you may get a false main pump pressure reading. Typically you want pressure around 2,300 psi out the remote. You can also check the main pump pressure in other locations. Main pump pressure, if your charge pressure is good can be increased by the stroke control valve adjustment on the bottom of the main hydraulic pump. Don't get the stroke control adjustment confused with the destroke control. The destroke valve usually has a "T" handle to turn it down when you don't want the pump to work at startup. The stroke control valve is usually an allen screw. When adjusting the stroke control valve, only turn it in (up the pressure) or out (decrease pressure) 1/4 turn at a time. If you get the pump over 2,500 pounds of pressure you could damage "O" rings in components of the hydraulic system.

If you have absolutely no charge pressure at the charge pressure port on the transmission, you could possibly have a split or completely broken steel line in the charge pump system. This also applies if you have no pressure on the PTO ports and your PTO is not working. You must split the tractor between the transmission and rear housing to get the to line locations. 
I know this is not everything that you need to do to diagnose your problem, however it should give you a better understanding on what to look for. This tractor after redoing the brake system because the brake metal from the brake plates went through the entire system, had to be flushed repeatedly.  So far we have changed the filter 7 times and the oil 6 times to remove all the metal in the hydraulic system. We even resealed the main hydraulic pump and replaced the filter screen in the main pump. The metal shavings also destroyed the priority valve and the seals in the SCV valve. The SCV valve seats also had to be reseated. There is no guarantee that this systems problems will not come back effecting one or all of the components again.

Most common problem with metal shavings is the brake lining coming off and now you have metal to metal. Every tractor we have done, it's the right side that destroyed. The left side is alright at the current time, but the brake lining is paper thin so do both brakes on the tractor to save youself a headach down the road. It will give you piece of mind that your brakes are in great shape. Other John Deere utility tractors have the same fate. John Deere 2020, 2240, 2440, 2630, 2640 and others. Some tractors are utility and others row crop with a deck. There are some changes from one tractor to the next concerning serial numbers but the concept and problems are the same.

I sincerly hope this helps some of you who are frustrated by your tractors hydraulic systems.
Owosso Tractor Parts sells the brake disc and brake piston new for these tractors. Order on-line or just give us a call.
 Be sure to have your tractor serial number before calling because early and late brake systems are different.  

This is the right side brake disc. You can see the fiber is completely missing as compared to the photo on right. You can order this disc from Owosso Tractor by clicking the part number AL68095 or the photo.	Brake piston on left ground down. New disc beside it. Part Number L31017 New Brake Disc. AL68095
	New Brake Piston, ring gear Not included. Part Number: L31017
Filter housing with metal shavings. An indication of metal on metal.	New Filter order Part Number AL25554
Both Selective Control Valve pressure spools were damaged by the metal running through the system. Order new Part Number: AR86535