Tue Nov 22, 2005 8:17 am
Along the lines of my previous "hydro creep" question, I have concerns about my release valves:
My valves were frozen when I got the tractor, and it took lots of work to un-freeze them so they would move at all. Basically, I had to put them in a vise and use a drill shank to pound thru the hole on the bottom against the ball to move the protruding pin back out, carefully emery-cloth the exposed shank to remove corrosion, then repeat the cycle may times until they worked somewhat freely.
Now, the tractor will immediately slowly roll backward on a slight incline when shut off. Along with the "freewheeling" symptom I described earlier (which I and others attributed to my trunnion lingage being worn), my co-worker and fellow Cub afficionado insists that my release valves are contributing to the freewheeling.
Can leaky release valves cause the freewheeling effect when going downhill?
Tue Nov 22, 2005 10:54 am
The valves could contribute to your problem. Any time a hydro is parked on a grade, the brake should be set (the brakes need to be in good working condition). When shut off, the hydro pressure will slowly equalize, whether you dump it with the lever or not, and the tractor will roll away - the steeper the hill the sooner/quicker it may roll. If the valves are worn, it may allow this to happen quicker. But if they are worn badly, they should also be leaking.
The freewheeling, as you call it, or picking up speed going down hill, is all from the worn trunnion and the two springs in the trunnion slot. The springs basically keep the trunnion centered to maintain the speed you selected, and to soften speed changes. If the spring and trunnion slot are worn, the tractor will pick up speed going down hill, and lose speed going up hill. If it were not for the springs, it would be hard for you to stay on the tractor when making any speed changes because they would be instant. If I were you, I would go on and make the trunion repair and replace the the two springs (inner and outer) and the two buttons. If the release valves are not leaking, I would try them for awhile before replacing them, as they are pricey (about $100 each) unless you can find good used ones.
Tue Nov 22, 2005 11:07 am
Are the springs and buttons available as replacement parts?
I was wondering about the function of this trunnion set-up. Bear in mind, this is my first Cub, and I have never driven a hydro in proper working order. If the springs/brackets are worn, and allow the hydro swashplate actuation lever on the outside of the hydro to move within that slop, then if the parts are all NEW (and there is no slop), is the spring pressure alone sufficient to prevent movement of the lever when the lever WANTS to move, due to a hill or load?
It seems like if the springs are soft enough to provide GIVE when you move the speed control, then they wouldn't be stiff enough to PREVENT the swashplate lever to move if it WANTED to going downhill or under load.
I know, I know, just do the trunnion fix. I thoink it will have to wait until early spring downtime.
BTW, by "leaking" valves, do you mean visibly leaking? Mine are not.
Tue Nov 22, 2005 11:50 am
Yes, the springs and buttons are available from Cub Cadet dealers. The damoer spring plate assembly, cam control assembly, and trunnion shaft assembly (requires hydro disasembly to install) are also available, but pricey, thats why you repair them. The part numbers for the springs and buttons are:
Spring, damper light (inner) 394 039 R1 need 1
Spring, damper heavy (outer)394 826 R1 need 1
Pin, damper spring guide (button) 394 041 R1 need 2
You can go to these sites for some repair help
If all the slop/wear is removed and
the linkage to the speed control lever is properly adjusted, including the friction adjustment for the control lever, then yes, the new springs will keep the speed in check when going up or down hill - there may be a very slight increase going down hill just because of the law of gravity, just as there is in your car or truck when going down a hill, but nothing like what you appear to have now.
Tue Nov 22, 2005 1:12 pm
Thanks a MILLION for the links and all the advice. I understand it all now, it's pretty simple.
Tue Nov 22, 2005 1:48 pm
Paul: Even I understand it now. Good explanation. Thanks from a gearhead.
Tue Nov 22, 2005 2:59 pm
I'm not sure I understand it all, and what I told is about all I know about them (remember I'm a gear head too, I just happen to have a couple of hydros). It's a good thing that the Sunstrand 15 (I think thats the model number) is just about bullet proof, cause once you get inside of it, all the swash plates, and pistons, and magic, and stuff, get in my way of figuring it all out.
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