Hydro question for Pete 23, detailed challenging question.

A while back I posted about my 1026 hydro tractor surging which I never fixed yet but am looking into further now. I studied an IH service manual on the principles of how this hydro system works. The way I understand it, the hydrostatic drive pump will swash one way or another (up to 18 degrees) depending on whether going forward or reverse. For the forward direction it will increase the output motor speed untill the pump reaches its maximum angle, and then the motor starts to decrease its swashplate angle in order to increase motor speed even more. Now with my tractor it will never surge going in reverse. If I go about the same speed forward as it was the fastest possible speed I was going in reverse, that is about the speed and a little bit faster where the speed will surge...

As a test I was running the tractor in my driveway with the engine at about 1300 RPM I believe. In high range I could increase speed steadily from 0 to 4 mph. At 4 mph it was in the range to where it would possibly surge between 3 and 4 mph. If it was traveling a steady 4mph and if I applied the brakes momentarily to put load on it, the speed would drop to 3 mph and stay there after releasing the brakes. Also in that range there is a gap where the speed control lever is not responsive, you could move the lever up to a quarter of an inch without noticing any change in speed. At high engine RPM's the surging in this range is much more pronounced. So my question to you is, do you think this issue is somehow related to the tradeoff between pump going to maximum angle and motor starting to move? Could there be an issue with play in the motor swash control linkage or something? This issue has me baffled and I dont want to tear into something without knowing for sure, lol. Any input is greatly apprecieated! Thanks!

Hi, first, take the charge, servo and high pressure with a gauge. It act like the servo pressure is low. May be you have a leak on the servo circuit. Bernard le mecano

Being you have read the principles of operation, are you getting a definate increase in fwd when you get to the blue line on the quadrant. That is the point where the motor swash plate should start to decrease angle and pump swash plate will have already reached it's maximum angle. It would indeed be a good idea to check the servo pressures. It has it's own regulating valve and the pin anchoring the servo's has seals on plus the seals and orfices in the servo's. There is also a o-ring on the pipe end that has a snap ring on it and it can move back and forth some and wear o-ring. Just a few ideas.

Now you got me thinking. If I have the engine at high RPM the way it is now the speed is very responsive below the blue range(could lift the front wheels off the ground). Once you get past the blue range it does seem kind of sluggish. At full throttle in high range if I suddenly push the lever from blue range to full forward it will not lug the engine (unless a heavy load). It does get to 20 mph tho. I noticed though that while going up a hill at 20 mph when pulling a load the speed would probably drop to 17 mph before starting to pull the engine down. This hydro does have the capability of stalling the engine.

Do the 2 servos share the same pressure or are they seperate? Pump servo is definitely very responsive but motor servo is definitely in question. Will have to do tests with guages when I get a chance, but I got the PTO out and replacing clutches and seals. Then the tractor has to go back to the field for a while. Thanks for the help guys!