2005 RTV 900 charge pump with low pressure

i doubt it is the servo. not sure what is going on but once it drops it stays there. i still think something is obstructing the suction. rev it up and it sucks the obstruction into place and it stays there until shut off. then repeats the process. if it was a leak it would be constant. i think. back to that hose again??? in some cases the hose separates internally and a flap on the inside causes the problem. did you say that you replaced that hose? with an oem???
 
The problem with a degrading suction hose has happened before to a member or 2 if I remember correctly. I also remember a coolant hose doing the same thing. Rubber doesn't last like it used to- especially fuel lines and tires from China if parked in the sun for just 2 years in my case.
 
I didn't state what is happening with the pressure correctly. When idling, it's at 55#. When I rev it up it jumps to about 80-85# and immediately falls to about 20# and stays there as long as the engine is revved up. When I let it go back to idol, it goes back to 55# pressure.
Sorry for the confusion.
Yes I replaced the hose that had a split in it from the housing to the filter with oem.
 
well this is an enigma. the pump builds and maintains pressure just fine until rpm and flow increase then something in the system lets go and pressure drops and stays there. if it is a spring controlled bypass valve the spring would return the valve under low idle. or at least it should. i think there is a floating obstruction that blocks the suction flow during high flow and then stays there as long as there is suction. then when the machine is shut off the backflush moves it out of the way again. i would inspect the whole suction side including the filter. next would be to start inspecting the bypass valves. are you doing this with the HST speed control lever unhooked?
 
I just discovered something new, at least to me. I've been moving the lever that controls both the regulator valve and engine in order to rev it up. I just started it and it is still idling at 55# pressure. I revved the engine directly at the throttle control on the engine, not activating the regulator valve, and the pressure went to 75-80# and stayed there as long as I held the throttle open.
Also, I've used my air hose and blown back into the inlet and outlet on both filters and also thru the port to check the charge pump pressure. All of them seemed clear and each time I would blow the plastic cap off of the filler cap to the transmission.
 
AHHH that makes a big difference. you have a leak inside the hydrostat. could be valve plates or a HP bypass valve. the problem isn't in the low pressure side.
 
When I first got it, there was some damage to the top of some of the pistons and in some of the cylinders in the HST pump. I cleaned the damage up in both and they were compressing with no drag. Do you think that might be where the problem is?
I also had to replace the valve plate for the HST because of damage and it looked like it had heated up and was canning.
I had already pulled both of the HP bypass valves and they don't look like there is any problem with them. Thanks for you help.
 
damage to the cylinders??? they have to be darned near perfect to work ok. if you can see scratches or wear marks you have to replace the whole assembly. good to always replace the valve plates. if they are scratched or warped then you will loose pressure. check the swash plate for damage also. if it has wear then replace it. use plenty of white assembly grease when you reassemble
 
I'll order a new HST pump. Like I said, I already replaced the valve plate for it with a new one so at least that's taken care of. Eventually something has to work.
 
Looks like I'll be back on here in about a week. Got the pump ordered but they said it wouldn't arrive until next Thursday/Friday.
 
Ok I'm back. I finally got the HST pump in. Just to recap what I've replaced, HST pump, HST pump valve plate, charge pump and the charge pump relieve spring.
Still have the exact same problem. Idles at about 50#, revs to about 80# and stays there as long as the throttle is held open rev it directly at the engine. When using the regulator control lever it jumps to about 80# and then drops immediately to about 20#.
Any suggestions would be appreciated because I'm at my wits end.
 
Nomansland said:
Ok I'm back. I finally got the HST pump in. Just to recap what I've replaced, HST pump, HST pump valve plate, charge pump and the charge pump relieve spring.
Still have the exact same problem. Idles at about 50#, revs to about 80# and stays there as long as the throttle is held open rev it directly at the engine. When using the regulator control lever it jumps to about 80# and then drops immediately to about 20#.
Any suggestions would be appreciated because I'm at my wits end.
Click to expand...
I know this is a old thread, did you ever get this resolved?
 
You must log in or register to reply here.
Top