John deere 8430 hyd weak

Lynn s · May 18, 2018

We have a 4wd 8430 that has weak hyd after oil heats. Changed filters but no change then put a gauge on scvs and pegged the gauge but as soon as you use another function steering 3point ect the flow all but quits. Have pressure but not much capacity not sure if the charge pump is supplying enough to the main pump. What direction should i start in. Thanks

Bob · May 18, 2018

If you are gonna troubleshoot and fix this thing yourself, you HAVE to have a factory tech manual.

Change hydraulic filters and check/clean the two sump suction screens, then check clutch pump flow as directed in the shop manual.

Also, with possible oil heating, check to be absolutely sure the airflow side of the hydraulic oil cooler is CLEAN, and the radiator fins, as well, and that the fan pulleys and belts are in good condition and properly adjusted.

In addition to possible charge oilflow and main pump issues, it's possible you have a "high pressure leak to sump" that's losing a lot of your high pressure oil, making the steering priority valve (DEERE calls it a "pressure control valve") cut off flow to hydraulic functions.

From a cool start the component with the high pressure leak will heat up noticeably faster than the rest of the hydraulic system, an infrared temp gun will help you you some sniffing in that area.

4520BW · May 18, 2018

I agree with Bob on getting a tech manual
for it. I have a manual so I can look
things up for ya. My 8430 was looking
pressure and I added some shims on the
relief valve.

Lynn s · May 18, 2018

We have a tech manual we got when we rebuilt the motor but not a flow meter. Sorry should have stated the hyd are not getting overly hot just that when the oil warms they get slow. As for leaks the only one i have is to the draft sensing cylinder. I changed filters but have not checked screens since i have good flow when cold but ill pull them tomorrow. One thing thats not making since to me is that the return oil filter relief valve housing line going to the front pump stays cold but they have it as a low pressure line. Is the pump supposed to pull the oil or what gives it pressure.

Ken Macfarlane · May 18, 2018

They are an old style closed centre hydraulic system, it?s likely
you have compensator valve issues. It will dump fluid back to
sump. Need someone knowledgeable in JD style, they are
similar to White?s system.

Bob · May 18, 2018

The front pump doesn't "draw" oil, it's fed a constant supply of oil by the clutch pump.

The excess flow of oil beyond what is needed to operate the clutch, PTO clutch or brake, and "2-speed" is routed up front to the oil cooler and the main pump along with "function return oil" from SCV's and hitch valve, etc.

If there's little or no demand on the front pump, the oil is cooled and piped back to the rear sump.

You really need to dig into the manual and rent, beg, or borrow a flowmeter, and start by checking the oil flow TO the front pump after it's warmed up.

If there's a leak in the main clutch system, PTO or PTO brake system, or the 2-speed a lot of the oil from the clutch pump that would be sent up front to the main pump is lost to sump as "clutch operating oil flow".

If the flow of oil up to the front pump meets "specs", then it's time to look at the main pump and high pressure hydraulic components.

Note that there's a pump in the rear half of the tractor, behind the transmission, but in this 4WD configuration it's used for lube, NOT for oil supply to the main pump.

Bob · May 18, 2018

(quoted from post at 18:05:13 05/18/18) They are an old style closed centre hydraulic system, it?s likely
you have compensator valve issues. It will dump fluid back to
sump. Need someone knowledgeable in JD style, they are
similar to White?s system.

IMHO, the only similarity to the system White used is that they're both types of "closed center" systems.

DEERE didn't use a "compensator valve" as such, and (unlike White) didn't have a pressure relief valve that "returns to sump" if the pump output pressure exceeds the relief valve setting.

tim s · May 18, 2018

Check your mid sump screen my guess is it?s plugged, there are 3 sump screens on this modle

Lynn s · May 18, 2018

Ok ill start checking screens and see if i can come up with a flow meter to check flow from the charge pump then go from there. Thanks for the responses

Lynn s · May 18, 2018

I knew the charge pump fed the main pump after feeding main functions but the filter relief line going to the
front pump staying cool had me wondering. But i guess if there is no excess oil to return it would stay cool.

Lynn s · May 19, 2018

So i pulled the two screens out today and they were clean but the center screen shown in the book is not as
shown. My main feed line is behind the filter relief housing not behind the hinge. We pulled the return hose off
the draft cylinder and had more of a leak there then first thought. Plugged the fitting and and at least now the
pump is kicking into neutral when not using hyd functions. After putting new seals in the cylinder going to put
it back in the field and see if it helped when we dry out. Thanks to all that replied.

John deere 8430 hyd weak

Lynn s

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Bob

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4520BW

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Lynn s

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Ken Macfarlane

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Bob

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Bob

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tim s

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Lynn s

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Lynn s

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Lynn s

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