656 Hydro Stalls in Forward

I have a 656 Hydro that works fine in reverse over the full range. In foward it works good from standing still until about half way. If you push the lever any farther than half way, it looses all power for a few seconds and then jerks as it hooks up and works fine after that. Any idea what is wrong? How can it work just fine part way and then hang up?

Hi Neighbor,

All other hydraulic functions work okay? Steering, hitch and remotes operate as they should?

I'd be for checking to see if the retainer clip has come off the far end of the shuttle valve which lives in the center section and is located behind this plug.

Allan

Thanks neighbor for the great diagram. I assume the only way to get at this is to split and take it apart?

Oh heck no; 'bout a 30-minuted job.

That's the beauty of these old hydros. 90% of all repairs can be accessed from the outside of the tractor.

Yank that big plug (it just keeps the darned birds out) and you'll see the valve living back there in the center section. :>)

That jerkin', stoppin', and just plain yankin' ya around in general is the classic symptom of that retainer clip being off the far end of the shuttle valve.

When that happens, the ol' sis doesn't know where "center" is when you're moving that lever around.

Repair will probably cost ya 10 cents for a new retainer clip at any hardware store.

Allan

Your symptoms are such that I have not encountered before. From what you have posted it appears that the problem only affects the hydro motor, not the pump. The hydro pump swash plate changes from vertical in neutral for full angel either way to give reverse and forward in the lower half of the speed range. That parts is operating correctly. The upper half of the forward speed range range is determined by the angle of the motor swash plate. The problem occurs when you start to control the motor servo. One cause I could come up with is that the motor servo is leaking all the oil out of it when it is not being used and then when you start to engage it the pump servo pressure drops off as all the oil flow goes to refill the motor servo. That would allow the pump servo to be forced back to a vertical position until the motor servo fills at which point the pump servo would be forced back to the maximum angle resulting in a jerk. from then on it would work OK until the motor servo was no longer in use and the oil could again drain out. Since the oil level in the hydro section is fill to the top when the tractor is operating the only time the air could get into the motor servo is with the engine off. That would explain why it only happens once each time the tractor is used.

When you start the tractor try putting the range selector lever in neutral and then pushing the speed selector all the way forward for a little bit before trying to move the tractor and see if that eliminates the pause and jerk.

Thanks for your ideas. I had considered the servo to be the problem too, thinking it was either binding or had a mark on the cylinder that allowed pressure to escape.

Let me clarify a couple items. First, occurs both in high and low range (handle to the right of the steering wheel). The problem happens when the SR lever (left of steering wheel is pushed foward beyond midway. Second, I don"t see how air can get in the system when it is all full. Third, the problem doesn"t just happen after the tractor is sitting but does it all the time after being warmed up. I don"t think that much air can enter during such a short period of time???

I will try your idea to see if it does help...Again thanks for taking the time to think about it!

You made my day! I know other components are so easy to access but haven't dug that deep in the center section.

I just want to make sure we are talking the same clip... it is part number 22 in the parts diagram?
right to the rear of the center section on the main output shaft.

Thanks so much for your help!!!

Ok, bear with me as I don't have the tractor here (at my dad's) I was looking in the wrong place. You mean the linkage going to servos. Is it the top clip #96 or the lower one #136?

Thanks again!

What Allan was talking about is the snap ring on the end of the shuttle valve. The shuttle valve is accessed by removing the recessed square plug the arrow is pointing to in Allan's photo. Once the plug is out there is a cap with a slot in it that you unscrew to get to the shuttle valve. The snap ring is on the end of the valve under the cap. In the parts diagram (Power Train > B-10 Power Train, Center Section Body And Related Parts, Tractors With Hydrostatic Drive) the shuttle valve is # 9 and the snap ring # 13.

As far as what I was talking about, I understood that the problem only occurred once when you were operating the tractor. Then after you shut it off the problem again would only occur once the next time the engine was run. As long the tractor was not shut off the problem only occurred one time.

Hopefully you are checking the trans/hydraulic oil level only after the tractor has been run for at least two minutes at 1200 RPM or above. There are no oil seals as such that seal between the hydro section and the rear frame, only shields that restrict the oil flow. With the engine off the oil will quickly drain out of the hydro section until the level equals that of the rear frame. At low idle there may not be enough flow to fill the hydro section so the engine need to run at a faster idle to be sure it fills with oil before checking.

Thanks for the good description of the location and snap ring. I see it now. Yes, I was not initially aware of the unique oil check procedure but fortunately an IH mechanic informed me years ago right after I bought it.

Doesn't sound like a shuttle valve problem to me. If it is already moving forward the shuttle valve has moved to it's proper position. I would suspect the problem may be the SR lever is not moving the control valve fully due to wear on quadrant or lever. It needs to pull control valve spool out enough to allow capsules in control valve to ride down the hump and fully seat the balls. I would just try forcing the SR lever fully to the side when advancing it and see if you skip past the problem area. If so, then you need to do an adjustment on valve linkage or repair worn areas.

Thanks for another good idea to check. I won"t be able to look at tractor for couple weeks but promise to report back what I find.

I understand your suggestion, but it doesn"t exactly match the problem. Going from nuetral to 1/2 speed works fine. The problem is if I go past it (e.g. faster). When I push the lever slowly only part way past 1/2 way or do so rapidly all the way forward, the result is the same..it stalls for a few seconds, jerks and then functions normally. At least this is my recollection. I will test as you suggest if the clip is not missing as suggested in earlier post