JD 4840 hydraulic pressure

Ctbrown · Feb 16, 2023

I have a 4840. Has lost hydraulic pressure. I will move and drive
down the road. Will not steer sitting still. Cleaned the bottom
screen and changed filters with no change. It didnt happen all at
once. It acted like it had air in the system then just quit. It may
have a little pressure but not much.

wore out · Feb 16, 2023

A piece of debris MAY have gotten in the stroke control valve in the hydraulic pump.

If your pump has the optional manual destroker, destroke it, run it for a little while, then back off the destroker.

The destroker, if present, is the little ''T'' handle at the top of the hydraulic pump in the drawing above.

The destroker can be added if not present.

If destroking and operating the pump doesn't clear up the problem a diagnostic procedure needs to be done to verify the transmission pump is supplying adequate oil to the front pump.

If it IS, the problem is in the main pump, and it will likely have to be removed and overhauled or replaced.

the tractor vet · Feb 16, 2023

Now i am by no means and expert on john Deere's but i do know enough to use caution when messing with there Hyd. as bad things can happen when they over pressure . My uncle had a night mare 4630 that was a problem child from day one and one day while deep ripping as he made the turn at the head lands while lifting the 3 point ripper out of the ground turning and steeping on the brake to make the turn something happened and the Whole rock shaft exploded and sending the three point piston across the road and sending it thru the side of the NEW Tater storage building making a hole like and artillery went thru the tin siding . A guy south of me had the left axle housing blowen off when stepping on the left brake . They have run higher pressures on there systems then what i am use to .

matthies · Feb 16, 2023

Is the front driveshaft turning? Have seen the dampner bolt come loose and the front pulley hammered out the keyway and pump stopped. Look more at the shaft itself, more than the coupler shaft.

2SteveWI · Feb 16, 2023

There is a shaft that runs from the engine flywheel to run a hydraulic supply pump under your feet. The front hydraulic pump has to have oil supplied to it. I am assuming that you have a quad range transmission. There is a plug on the back of the tractor behind the bracket for 3 pt. top link. If you have gauges and a manual you can check supply pump pressure. Been a lot of years since I have worked on 30 and 40 series John Deere's but I would make sure there is supply pump pressure before digging into Main Hyd pump.

wore out · Feb 16, 2023

(quoted from post at 21:27:23 02/16/23) There is a shaft that runs from the engine flywheel to run a hydraulic supply pump under your feet. The front hydraulic pump has to have oil supplied to it. I am assuming that you have a quad range transmission. There is a plug on the back of the tractor behind the bracket for 3 pt. top link. If you have gauges and a manual you can check supply pump pressure. Been a lot of years since I have worked on 30 and 40 series John Deere's but I would make sure there is supply pump pressure before digging into Main Hyd pump.

The O.P. stated he is able to drive the tractor, which proves the transmission pump is functioning at least well enough to engage the PermaClutch and the quad range planetary two-speed (IF so equipped). As part of the troubleshooting procedure it will be necessary to determine for SURE that there's enough excess flow to feed the main hydraulic pump.

Also, there's a POSSIBILITY of a huge internal ''leak to sump'' of the output of the main hydraulic pump.

One REALLY needs a copy of the factory service manual and follow the diagnostic tree found there to get to the bottom of what's going on with certainty.

used red MN · Feb 17, 2023

Hello CT welcome to YT! I was going to post mentioning the pump drive shaft. But I, like wore out I figured it would not drive if the shaft was the problem and the pump was not working. Let me clarify what SteveWI posted. The shaft he is talking about it about 6ft long, it is a hex shaft. The plug under the 3 point is actually the back bushing it turns in. By removing the plug you can slide the shaft out to check it. What happens sometimes is the hex portion where it sets in the pump wears round and quits driving the pump. The 1st link shows the Quad range pump, number 21 is the shaft. If the tractor is a Powershift I do not believe it has this shaft and the or pump. I hope this is correct I believe the PS trans pump takes on the duty of charge pump to supply oil up front to the main pump, do not quote me on that last statement.
Quadrange trans pump,

Tx Jim · Feb 17, 2023

IF a JD 40 series tractor with Quad-range trans will move under it's own power then hex shaft that powers transmission pump should be fine IE not rounded off. I agree that a pressure test with a gauge would confirm correct trans pump pressure.

cannonball · Feb 17, 2023

Jim I thought all 4840 were powershifts only..correct me if wrong ..thanks

wore out · Feb 17, 2023

(quoted from post at 05:29:44 02/17/23) Jim I thought all 4840 were powershifts only..correct me if wrong ..thanks

Yep, C.B., you ''caught'' that one!

Powershift, NO hex shaft, NO transmission pump under the seat, but, rather a transmission pump at the front of the transmission.

Still pretty much the same deal, though, as to the problem at hand, tractor ''drives'' so transmission pump is working, but flow forward needs to be checked.

Tx Jim · Feb 17, 2023

(quoted from post at 08:29:44 02/17/23) Jim I thought all 4840 were powershifts only..correct me if wrong ..thanks

OOPS thanks for correcting my mistake!!

I'll regroup ""check frt pump drive coupler"" to be pump shaft is rotating when engine crankshaft rotates.

Ctbrown · Feb 17, 2023

It does not have the manual destroke. 4840's are only powershift so no hex shaft. As far as i can tell the front pump is turning. Man i am lost I've ran out of ideas.

JD 4840 hydraulic pressure

Ctbrown

New User

wore out

Well-known Member

the tractor vet

Well-known Member

matthies

Well-known Member

2SteveWI

Member

wore out

Well-known Member

used red MN

Well-known Member

Tx Jim

Well-known Member

cannonball

Member

wore out

Well-known Member

Tx Jim

Well-known Member

Ctbrown

New User

Similar threads