Has anyone ever shimmed your hydrostatic relief valve?

[gsdavis1]

I have a Mitsubishi MT180HD. It is hydrostatic drive. This is the first winter I have owned it and when it is really cold I can feel the hydrostatic relief valve kicking in every so often. Once the oil is good and warm it is OK.

When it happens it feels like the tractor loosed drive for a second or two then it is back. Only does it when it is cold. After the tractor warms up for about 15 minutes of working it, it goes away.

Does cold fluid act this way?

 

[beenthere]

I can only say that my Deere 4300 doesn't. Maybe just give it that extra few minutes to warm up.

Are you thinking of changing the relief valve? and how will you do that?

 

[kennyd]

Does cold fluid act this way?

Yes. Try sucking syrup through a straw...

 

[jinman]

gsdavis, I think you just might be seeing charge pump cavitation instead of relief valve lifting. If your problem is relief valve lifting, changing the relief valve will mean very little. If you shim the relief valve and raise pressure, you may end up with an exploded transmission. The only reason the relief valve would open is if the HST pump is supplying high pressure to the HST motor, but the motor is not turning. If it is charge pump cavitation, it's a case of the charge pump not being able to pull/suck enough fluid through the filter to supply positive pressure at the HST pump inlet. In cold weather, I think the charge pump cavitation is the more likely scenario.

 

[AKKAMAAN]

Does cold fluid act this way?

It takes more pressure from pump to push high viscous (cold) than low viscous (varm)...You might benefit from a lower viscocity fluid at wintertime, or just take cup of coffee while warming up...warming up a closed loop hydrostatic 4wd, I think you have just have do a light duty travel session for 15min....to the coffee shop??:laughing:

Do not change pressure setting to solve this problem...:thumbdown:

 

[wdchyd]

Me thinks "Cold weather " Hyd Fluid would be much better solution than messing with anything on hydrostat......(and warm up time).....

As others have already said....:thumbsup:

 

[gsdavis1]

Can anyone fill me in on what charge pump cavitation is?

 

[wdchyd]

Yes. Try sucking syrup through a straw...

Same idea....Oil too thick, clogged strainer, restriction......

 

[J_J]

Can anyone fill me in on what charge pump cavitation is?

Cavitation is caused when the vapor threshold of the fluid is exceeded, and bubbles are formed. It is the explosive force/collapse of the bubbles that can erode metal.

You can visually see this on propellers as they rotate through the water, generating bubbles. Cavitation is something you don't want, and should always try to avoid it when possible.

http://en.wikipedia.org/wiki/Cavitation

 

[Ford tractor]

Yes. Try sucking syrup through a straw...

Or more like frozen molasses in January!

Switch to a multiweight hydraulic fluid. Kubota Super UDT is a 5w30 equivalent, there are also generic fluids with similar specs. JD also makes a winter fluid.