ASV RC30 Charge Pump Pressure Adventure

Markle

LawnSite Member
Wrote up my RC30 Drive Issue Resolution. Love my RC30.. All Fixed!

Your Mileage may vary:

Bought Used W/1200 Hrs. I never had it when new.
I Love my RC-30, but the Drive was Figity (very slight oscillation) when hot, and fully loaded. Wouldn’t skid without rocking the joystick back and forth, or Jerking to get the skid started. Felt like needed more power. I replaced one drive motor due to a shaved key/tapered shaft. I regularly check the drive hub bolt torques to be sure they remain tight, and used the recommended two part Locktite when reinstalling the hubs. Always suspected the other motor had issues but that wasn’t the case. During the motor replacement effort, my RC-30 earned the nick name Puddles for reasons you understand. Theoretically with a proper working drive, you should be able to stall the motor even when skidding. Decided I needed to learn some Hydraulics.. some great video tutorials on Youtube about hydrostatic drives, charge pumps etc. Fascinating stuff. Checked my charge pressure.. Rock Stable all maneuvers/temperatures/Loads/RPM at 300 PSI. The Loader hydraulic functions are not affected by low charge pressure, ONLY the hydrostatic track drive system.

Interesteringly: Early RC30 Serial numbers thru 1056 have a charge pressure specified at 450 – 500 PSI where as later serial numbers (Me) are 340 – 380 PSI. But there is no apparent tandem pump part number difference.

Regardless, I decided to tackle shimming the two charge pump relief valve springs for additional charge pressure. A good time to change AND Flush the hydro fluid, since it will happen by itself when you remove the relief valve caps. 10 gallons of fluid is sufficient with 2 gallon flush. For shims, you need good quality, Flat stainless shim washers. Nothing suitable found at ACE hardware. 16 mm OD, with 10 mm hole. I bought 10 online that were 0.5 mm thick for $15. First try, I put in two 0.5mm washers on each pump, and put in enough new fluid to cover the hydro tank screen plus an inch. Resulting charge pressure was 320 PSI. Not enough. Decided to go for it.. a total of 5 x 0.5mm washers in each side Total is 2.5mm or 0.1 inch. Resulting a pressure of 420 PSI! Perfect for me, no downside. MO POWA! When screwing in the valve caps with all 5 washers definitely took some effort to get the cap threads started, Barely noticeable with only 2 washers each side. There is a slight risk this many washers may cause the internal spring to break, but the results are well worth the risk to me.
Things I noticed to diagnose this issue w/o the pain of getting a gauge with proper quick connect adapter. The charge pressure test port is under the gas tank, but can be accessed by removing the cabin aluminum floor. It’s a special test connector, but apparently fairly standard. The one I got which worked fine was $29 from Amazon, and was the type that fit CATapiller. Suitable pressure gauge sets including this adapter, plus an assortment of standard hydraulic fittings and hoses can be found for maybe $100 on ebay or Amazon.

At Charge pressure of 300 PSI. Suspect LOW Charge Pressure if:
1. Both Joysticks feel very loose, return to center is very soft.
2. Sometimes the drive requires significant joystick movement before things happen.
3. Need to jerk drive to get a skid steer to start when warm and loaded
4. Can feel minor Hydraulic oscillation trying to skid when warm and loaded
5. Increasing RPM above a medium idle didn’t give more drive Torque, but did increase drive speed.
6. Big Chatter when skidding on pavement.. oscillates ON/OFF side to side.. Shakey Puddles!

Theory: Issue actually is insufficient charge pressure for full control of the hydrostatic drive pump warble plate when loaded. More control pressure is required to fully move the warble plate to maximum flow/displacement at HIGH drive motor back pressures. Can’t fully load the engine, doesn’t stall, kinda chatters as it trys to drive the plate to higher displacement running into a pressure limit to go further.

At Charge pressure of 420 PSI
1. Both Joysticks take more hand pressure to move off center, return to center is well defined.. almost snappy.
2. Joystick very fine control, much easier to finely steer a curve without multiple discrete turns.
3. MUCH reduced jerking to skid required when fully loaded and warm.
4. No apparent oscillation.
5. Increased RPM gives more Torque because Engine doesn’t stall as easily.
6. Skidding on pavement MUCH smoother, Much improved skid torque, skids at very low joystick offset..



Night and DAY difference, messy work, similar effort to replacing an auto transmission on a 60’s classic car.



Which Hydraulic OIL to use?

I went thru what kind of oil should I use. I was using the AW42 from Sams Club. Thinking I’d try AW68 before I dug into the charge pressure issue. ASV is apparently very pickey, and specifies uncommon $$ oil. No issues with the AW42.. was nice clear, uncloudy, looked new with the brownish tinge. No apparent dirt at all in the tank, very clean. After reading about pump cavitation, on pump input and thick oil can make that much worse, I bought Triax Agra UTTO XL synthetic blend Tractor Oil.. bright red.. looks more like ATF. Apparently there is Tractor OIL and Hydraulic Oil (AW). Viscosity appears similar to AW42. $76 per bucket shipped from Amazon. Right or wrong. Puddles seems to like it. I like the cool Red Color, brings back the 4R70W Mercon memories, Plus makes reading the Hydro Tank level much easier!
 

Hollowellreid

LawnSite Senior Member
This is great information, and very nicely done. I have a couple PT30's now and a PT60 and know my way around the machines pretty well. I'll save this if I ever need it.

I also have the same test gauge and weird 1/4" flat face port setup, some of the newer machines they moved that port to the engine bay near the hydraulic tank.

They are very selective about what hydraulic fluid works well. The factory asks for some sort of Chevron fluid which is over $100 for 5 gallons but it is also easily cross references to something cheaper.


Well done on the fix!
 
OP
M

Markle

LawnSite Member
Clairification! The Five 0.5 mm shims I added to both sides. were IN ADDITION to the 3 stock shims.. From memory, the stock 3 shims in both sides were 1mm, 0.5mm and 0.3mm, The 5 shims I added were in addition to these 3.
 
OP
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Markle

LawnSite Member
Okay, Markle here, I have like 8 hours on the "Fix". Definite major improvement. I can load the bucket full load of dirt, and climb up a steep hill.. It will climb any hill I have the guts to climb. My yard is full of steep hills.
At the limits of power (Full Load, Climbing HARD), Engine at Medium speed.. chugging somewhat, the drives start to oscillate, and the my new drive hub spacers start rattling. Still pulls Hard, but some instability in the loop. One drive motor is original, and still could be "Weak", but not worth another new motor.

While I was down there, I should of blindly took maybe a turn on the two pump pressure regulator. No further loss of Hydro fluid is required!! Easy, Screw adjustable. Hooking up the pressure guages at motor output is a major PITA, but turning a screw, and seeing if it improves is what us Hydro Hacks do.

Since springs always weaken with time and use, should be reasonably low risk to blindly take a chance, Getting good at removing the Seat+ Fuel Tank.

The oscillation Could be bounding off the drive pressure limit regulators .

Mo Powa.. If it breaks, fix it!

markle
 
OP
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Markle

LawnSite Member
1. Attempted but chickened out adjusting the tandem pump pressure limits.. turns out the screw and locking nut do not adjust the pressure limit, you have to remove the 4 entire valve assemblies (More Fluid!!) and turn some internal spring nut. Wasn't ready to risk it, plus stock limit is specified at 3800 PSI which sounds like another Puddle to me.

2. Status update on increasing charge pressure. No downside, seems more powerful and responsive in All cases. During a recent workout at higher than normal RPM at extended time (Moving several full buckets of dirt at high travel speed), I did notice the drive seemed to get somewhat more Pulsing under steep climbing full bucket load. Would still climb pretty good so didn't think much of it. When I got out, I did notice the hydraulic temp was pretty warm (Hand touch on the tank) maybe 130F? I didn't have the infrared temp sensor this time. usually it's <100F when poking around. Decided I needed more instrumentation.. Hydro Temp, and Engine RPM.

Hydro temp gauges.. bought a 2 channel thermistor digital sensor.. thinking I do tank input and output, BUT will also experiment with the two drive motor case temps. If my other drive motor is marginal, the blowby should make it hotter than the rebuilt side. Thinking this may be a good way to diagnose a weak drive motor.

RPM: On a diesel there is no ignition, so I chose a hall effect tachometer (from china)

markle
 
OP
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Markle

LawnSite Member
errr.. hydro temps at cooler input and tank output.. may also add electric fans to the hydro side of the radiator to help cooling if both motors run at similar temps.
 

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