4620 brake valve / hydraulic pump plastic line

M w J · Feb 28, 2020

On my 4620 the front pump seal was leaking so i disconnected the plastic bleed off line and started the tractor. There was no oil coming from the pump side of the line and the pump didn't leak with the line off . Then when I step on the brakes the little line flows oil towards the front pump and does so until I shut the tractor off. When I restart the tractor it flows no oil out the little line until I step on the brakes . So what I need to know is Do I need to overhaul the brake valve ? Thanks Mike

Bob · Feb 28, 2020

As I recall, brake valve has a "T" fitting.

The "weep" line from the front pump and steering "motor" connects to one branch, oil from brake valve enters the second branch, and the third branch attaches to a short line that dumps any oil coming from those sources into the main case.

Either that line to the case is restricted or plugged, or the brake valve is dumping an extreme flow of oil.

Unless the line to the case is clogged it seems odd that there would be enough pressure to push oil past the pump shaft outer seal, unless that is in poor shape, as well.

Check the little "return" line to the case and the fittings and let us know what you find.

M w J · Feb 28, 2020

I will check the line to the case . It just seemed odd to me that with the line off of the T that it flows only drops of oil but if I apply brakes the line flows full even after brakes are released until tractor is shut off . Thanks Mike

JD Seller · Feb 28, 2020

I have run into this before. Your brake valve needs rebuilt. It is leaking pressure oil out that return/leak off line. Is sounds like a seat in the brake valve is lose and leaking. I have seen them that will not leak after starting but once used they will not reseal under pressure.

It is rare for this to show up as a front pump leak. I would still wonder if the front pump is leaking under load when used.

tim s · Feb 29, 2020

Yes this can cause the pump seal to leak...that seal drain line drains the oil that leaks past the main pump shaft seal,,into a small gallery with the secondary pump seal containing it, the leakage then goes through the bore in the pump housing ..through the drain line and on most models to the transmission case,, but on some models it goes through the return port in the brake valve then to the transmission case,,, now with the brake valve every time the brake is applied,,then released a small amount of return oil needs to be released to allow the brake pistons to return a bit to let the pressure on the brake pads relax,,over time the seals in the brake valve let too much oil return,, so when a seal drain return line is shared with the brake return it can flood more oil to return than the small line going to the transmission case to handle, so it flushes to the front looking for a place to go, then it enters that little gallery in the main pump and pushes out the secondary seal,,the seal drain line was re routed to go straight to the trans case to ovoid this.

M w J · Feb 29, 2020

The little return line to the transmission is clear I checked today . I bought a seal kit for the valve today and I am installing it . My JohnDeere service manual explains the valve operation but it does not explain how everything comes apart But I think I can figure it out. I will let you know how it goes . I would just as soon not have to buy a rebuilt valve if the seal kit fixes it The
rebuilt valve is a little over $600. Thanks

4620 brake valve / hydraulic pump plastic line

M w J

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Bob

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M w J

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JD Seller

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tim s

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M w J

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