Welcome, glad you came in for a post!!!!

A member, Case Nut, carefully researched and ended up with an exact match:

http://casecoltingersoll.com/showth...read.php/21817-I-replaced-the-hydraulic-pump-in-my-646?highlight=hydraulic+pump

Please see this thread too: http://casecoltingersoll.com/showth...ead.php/21631-1974-Case-646-replacement-hydraulic-pump?highlight=hydraulic+pump

I would carefully review this info, make sure you have the same pump. I understand different pumps were sometimes used on the same tractors.The dealers may have a match for you too. Rich

 

I would go with 0.66. The 0.84 to much for system to flow, engine be loaded all time just pushing oil, return line pressure be higher blown ed off return hoses are busted. And tiller turn so fast bed up soil traveling to fast do same.
The Cessna Pump you choosing good choice set back ports on side of back pump keep pump pressure line out steering gear. 0.61 to 0.73 pump work find, but any with tiller in summer going to build a lot hydraulic heat.
Any time replace pump with new are used back off pressure reliefs before crank engine up the proper way brake in pump run at 0 pressure few minutes then 500 psi few minutes then 1000 psi then 1500 psi then 2000 psi and on up to PTO pressure 2450. Your working with 2 main relief one in travel valve other in PTO valve. A gear pump needs brake in don't go straight to 2450 this make deep streaks in path gear teeth shorter pump life. Couple minutes at each pressure all need. In this process moving pressure up you may find pressure stops going up that be broke spring in relief if doing with drive motor lines cap off and PTO lines plugged the quick coupling do this no need plugs are caps on PTO. While gauge line still on travel valve un cap ports hook lines back up in high range bucket up to tree read pressure should be same as was with caps are drive motor bad, if linkage set right on TCV, always adjust linkage on 646 (600 series) in reverse this when spool goes into valve, on 200 or 400 series do linkage adjust in forward the banana plate changes to reverse spool in. All wear in linkage lessen spool travel into valve 600.

 

I strongly support that bigger is not better, here.

You don't need a FAST loader, you need one with control and reliable strength.

Using the 4436-B pump you reference, Case Nut yielded 7mph ground speed. You really don't want 9 mph unless you are always working on smooth pavement ... and that start up acceleration would likely challenge the Onan CCK every time you push the pedal in high range.

I don't have any specific recommendations on non-OEM pumps, and unfortunately with the pricing in place I can't really recommend the OEM pumps at this point. The article referenced and other similar ones lead to a host of information that will let you know just what you are getting in to with various set ups.

Best of luck.

Brian

 

droak,

You mentioned lurking here for awhile. Before coming to the conclusion that you have a tired and worn pump, have you eliminated the engine, hydraulic system oil, relief pressures, drive motor, banana plate and travel control linkage/components as contributing causes?

If so, the Hydraulic System Specifications and Test Procedures Service Manual (9-00787, revision 7-97-RP-500-117) shows a 646 to produce 8.5-9.5 GPM (3600 RPM, 0 PSI). That should put you somewhere between .55 and.65 CI. BTW, as a point of reference, the Ingersoll 6018 uses a .603 CI (9 GPM, 0 PSI) pump for the travel/PTO/lift circuit.

Where did you get the information that the original pump was .73 CI? The only CCI tractors that came close to that displacement were the All Hydraulic (AH) models with .745 CI (11.25 GPM, 0 PSI) and the 3000/4000 PS (power steering) models that diverted a couple gallons to the the steering circuit.

As has been mentioned, adding a larger pump results in more stress on the engine, higher heat generation in the hydraulic system, and unwanted results. If your pump is the cause of your problems, then a properly sized replacement pump will restore performance.

Dan