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4020 Sudden Loss of All Hydraulics

S

Scmarkyp

New User
Hello All,

I have a 1968 Deere 4020 - Syncro. The other day, it suddenly lost all hydraulics. It has no brakes, steering, 3-point, SCV....nothing.

I immediately suspected the transmission pump, as I just recently replaced the main hyd pump. I removed the rockshaft housing, and re-sealed all the connections between the tubes and the transmission pump. The gears in the trans pump looked good. I cleaned the lower screen, which had barely any material in it - nothing that would restrict flow. I also re-sealed the bypass valve, on the left of the transmission near the filter. Naturally - I replaced the filter at this time, too.

I installed a manual de-stroke valve for the stroke control valve on the hyd pump.

I fired it up last night after doing all this and still no hydraulics. I tried de-stroking the pump with the manual de-stroke valve and still nothing. I have a gauge plugged into a rear SCV and I have no sign of any pressure at all.

I'm kind of at a loss of where to go next and I'm hoping for some advice from all you experts here. Thanks so much!

Mark P.
 
I should also add - I have verified that the pump is turning and is not making any abnormal noises.

Thanks in advance.
Mark P.
 
If the hyd pump shaft is turning when the engine crankshaft turns then I'd guess the hyd pump has a faulty stroke control valve. If tractor has aa de-stroking screw then turn DS screw down then out to see if that helps free any foreign debris from SC valve seat. Another possibility is broken trans pump gear or gears.
 
Is there oil coming to the front pump? I am also curious as to why the front pump was replaced. Tx. Jims idea is simple enough to try.
 
Thanks for the reply guys. I bet the hydraulic pump doesn't have 20 hours on it. I did take the stroke control valve out of the pump and verify that it was clean - there did not appear to be any visual issues with it.

It does have a manual destroke screw on it - and I have tried turning it down and it has not helped.

Transmission pump is functioning just fine and the gears are intact.

Any other ideas of a culprit?

Thanks guys.
Mark P.
 
I am slowly (but surely) restoring this tractor. I replaced the pump because of age and because I had the front end all torn apart to replace the radiator, oil cooler and fuel tank - there was no previous failure.

Mark
 
If trans pump is pumping oil to frt pump and stroke control valve is functioning properly then there should be some stand-by pressure.

Are you ""100% positive"" that frt pump shaft is turning with engine crankshaft?

Have you tried checking stand-by pressure in front of pressure control valve that's under the hood??
 
Have you checked the rockshaft access cover on the bottom of the rockshaft housing i have found a fue that were broke and all oil that the trans pump moved went right out there take the plug out where you auj the 3 point and look in with the engine running if oil is comeing down in there it my be broke
 
I had a chance to work on the tractor this weekend. I have done the following:

Verified that the pump is turning with the crankshaft
Removed rockshaft housing and inspected rockshaft bottom cover.
Replaced the stroke control valve in the pump - which appeared to be new - no grooves or junk in the valve.
I tested the output of the transmission pump, per the service manual and a 5 gallon bucket. It performed just as the JD service manual said it should.

If you all have anymore suggestions, I'd be very interested to hear about them. TX Jim - Where is the port to test under the hood?

Thanks guys.
Mark P.
 
(quoted from post at 21:43:01 04/12/15) TX Jim - Where is the port to test under the hood?
Mark P.
Click to expand...

I can't remember if pressure control valve sits far enough away from firewall to access the plug(parts key 1) for removal. Plug thread size is .375 ORB.

You could also check pressure on top of hyd pump on the head at the plug(parts key 7) thread size .562 ORB

I also think there may be a plug on SCV control valve that one can check SB pressure but it been a long time(30 yrs) since I looked under the hood of a 4020

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