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Discussion Starter #1
1976 model 300. I’ve gone over most of the hydrostatic linkage, replaced roll pins and adjusted tension on the linkage plate. it’s all relatively snug. Very little play. The problem is I have a yard that goes up and down all over the place. No steep hills, but not flat either. When I’m going flat it’s no problem, but if I hit a slight incline or even a little rut The tractor slows down or stops. So I have to push the hydro lever foreword. Then it will maintain that speed till I start going flat or downhill then it will speed up to double the speed I was going uphill. So basically the whole time I’m mowing I’m constantly having to move the hydro lever large amounts to adjust my speed. Any ideas on what this could be? The only slop I can find in the linkage is a very slight amount where the pin for the linkage connects to the swash plate. But it’s not a large amount of play.
 

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Discussion Starter #2
I should add that I only purchased this tractor a few months ago. It’s been doing this the whole time. It has new hygard low vis fluid and new filter. No visible leaks.
 

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Sounds to me like pump and/or hyd. motor is wearing/worn out. Bob
 

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I agree.

I would fix the small amount of slip as that should make it better, but the problem will probably remain.

Where are you located?
 

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Variation in ground speed is almost always a sign of some remaining hysteresis/slop/wear in the linkage, and it may be a very small amount that can be easily overlooked when checking the pins, link end holes, etc unless you actually disassemble the joints. The speeding up when going downhill is a strong clue to me that this is mechanical issue with the linkage and not internal to the pump.

I am less familiar with the closed frame tractors than the later open frame ones, but suspect the sensitivity to very minor angular inputs at the hydro speed control shaft are just as capable of magnifying any wear in the linkages.

It costs very little time and labor to verify the fit of all the linkage joints compared to R&R if the transmission, so if it were my tractor that would be where I would start for sure...

Chuck
 

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Discussion Starter #7
I’m in Reading, Pa. thanks guys for the advice. I have rebuilt most of the linkage. The only slop is where the clevise attaches to the plate on the rear. Small amount of slop in that hole. I will repair that and double check the rest and see what happens. Thank you for the help.
 
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