Power Steering Pump Fits John Deere 790 Compact Tractor

One New Aftermarket Replacement 

Power Steering Pump Assembly

 that fits JD 790 Compact Tractor  

JD Tractor part # AM876753

White Horse Distribution

Specializing in parts for engines, hydraulics, driveline and electrical since 1995.

No warranty against cracking or twisted off shafts!!!

There are really only 2 things that cause a pump housing to crack.

1)- A defective pump casting.
This is very uncommon. In fact we have only seen this one or two times in the last decade. The pumps we sell and the Yanmar original pumps are a very high quality product. A defective casting is very easy to see. The walls will be much thinner in the spot where it broke or there will be a sandy material or air bubbles in the casting.

2)- The pump was "dead headed".
This is MUCH more common. This style hydraulic pump will pump as long as the engine is turning. That oil MUST have somewhere to go (liquid does not compress). If the oil flow from the pump gets restricted then it starts to (very quickly) build up pressure. The pressure can almost instantly hit 6,000psi or more before something gives. Usually it is the pump shaft or the pump housing... sometimes it is the key on the pump shaft. 

What causes the restriction?

If you have a loader then it was caused because either 
a)- your loader valve is defective causing too much pressure to build up. Could be a stuck or broken relief valve or a plugged port or other things.
b)- your quick disconnect couplers are not completely opening. This happens when the valve mechanism inside the coupler (usually a ball) gets wore down over the years. If the couplers do not completely open when you hook them up then the oil will have nowhere to go.... cracking the pump housing or twisting off the shaft.
c)- your loader or power steering is just not hooked up correctly.

No Loader...
Then there is likely a problem with your three point valve causing too much back-pressure

Question )- If this was caused by "dead heading" then why didn't my original pump do that? 

Answer )- Well... something must have happened to the original pump or you would not be buying a replacement pump in the first place. It is VERY unlikely that you wore out your original pump unless the hydraulic system was seriously neglected. I have customers with 10,000+ hours on their tractor and the original pump is still going strong. You are replacing your pump because SOMETHING went wrong and that SOMETHING was not fixed the first time. Also, the new pumps will be much more efficient and are capable of building much more pressure than your 30+ year old pump was.  Your original pump may have enough wear on it that it could tolerate a restriction in the system and "bleed" enough pressure back through the pump that it did not hurt it. The new pumps are very efficient and are tight enough that they can not "bleed" that pressure back through the pump and something has to give.