656 hydro question

I'm still working on figuring out why my hydro slips in hi-range forward and I talked with a local mechanic today about possible causes. He said he thought it was the check valve by the way I described the symptoms. I haven't had a chance to cap the transmission lines yet like Owen suggested but plan to do that in a day or so. The IH mechanic told me that he had worked on a Hydro 186 a while back that had problems and he replace the check valves but that didn't turn out to be the problem. They eventually figured out a housing was cracked somewhere and fixed it. He gave me the old check valves that he took out of the 186 and told me to try replacing my valves with the ones from the 186 because he was sure those valves were still good. He said he thought the valves in my 656 were the same as the ones in the 186. My question is does anyone here know for sure if they are identical valves? I hate to take my 656 apart and then find out these are not the same as my old ones.

Check the part numbers (caseih.com) for compatibility. JimN

I don't think the check valves are the same, but I would sure do the capping off the lines before I tore inside of it. The possibilities are endless and this will at least tell you if it is inside or outside of trans.

The valves look identical on the parts sheet however the numbers are slightly different: 656=531770R1, 186=531770R2. I'm guessing they are not compatible. On to Plan B.

R2 is a later version of R1. R2 should replace R1 but not necessarily the other way around.

I'm not familiar w/the farm tractor hydro" but Ithink there must be a foot&inch valve off the pedal & a decel or drive control valve that could be causing your slippage in high range. Iknow most of the industiral tractors have these get yourself a good book or mech. these are external valves, good luck RON

The capsules are the same for both tractors, just be carefull not to get the a and b capsules switched.Put a back in a and b back in b.The only difference in part numbers is the R2 is a newer number.DAVE

The 531770R2 number is the high pressure relief valve in center section. The check valves are also in the center section and the A and B capsules refered to are in the drive contol (external) valve. I interpeted your questions as being about the check valve in the center section.

You are right pete, I meant the high pressure relief valves were what the mechanic gave me. What do the check valves do in relation to the pressure relief valves? Which one is more likely to be causing the slippage?

If the problem is in the capsules in the external controls is that something that I can repair myself or does it take special tools or special skills to replace?

Usually the high pressure relief valve is problem rather than check valve, however , I had a couple where check valve was the culprit. One, ahem, the customer had installed the charge filter in backwards and it wore a nice little hole in the end of the filter and that piece lodged in the check valve, other one, check valve seat was all hammered out of shape so it leaked. The check valve seats under high pressure, fwd and rev each have one and when in fwd that check valve is seated and charge pump flow into center section low pressure side is through the rev check valve and vise versa when in reverse.

If the tractor just slips and does not stop moving the high pressure relief valves are most likely OK. A sticking valve will cause the tractor to stop and will not start moving again until the valve resets. Sometimes they will reset themselves but it usually happens when you start to remove them.

These are pilot operated valves and are controlled by the Foot-N-Inch pedal. They are a spool type valve with a tiny hole in the middle. There is light spring to keep them closed. You can open them by hand by pushing on the spool. They need to slide smoothly enough that the spring can push them back closed. The hole in the middle of the valve allows oil to flow through the spool so that the pressure is the same on both side of the spool. Since the pressure is the same, the spring is enough to keep it closed. Pressing down on the Foot-N-Inch pedal allows oil to flow out the end of the relief valve. When the oil flowing out is more than the can flow though the small hole in the spool, the pressure will drop off and the higher pressure on the hydro side of the valve will cause the spool to open dumping oil from the pump side if the hydro circuit. This is what happens each time you use the Foot-N-Inch pedal like a clutch. A sticking valve will cause the tractor not to move again with the Foot-N-Inch pedal released.

With the lines capped off the relief valves can not open unless there is a leak between the valve and the fittings where you have them capped off. Sometimes you will find a crack in one of the jumper lines that go between the valve and the center housing. The line will crack by the flare, under the nut, where it attaches to the fitting on the valve or housing making it hard to find.

The check valves are used to allow oil from the charge pump to enter the closed loop of the hydro system. Each time a relief valve is opened oil is dumped from the loop. Pressure from the charge pump forces the check valve open to allow oil to enter to keep the loop circuit full. There is also some loss of oil between the brass and steel plate on both the pump and motor side.

If the pump or motor plates get scratches or grooves in them they will allow oil to enter between and separate them under load. When this happens you usually have to drop the pressure in the closed loop by either bringing the speed lever to neutral or using the Foot-N-Inch pedal. The tractor will then pull again until you reach the pressure point where the plates lift again. This, or a cracked line, is usually the reason for failure when when the problem only occurs under heavy load.

Thanks for your excellent description Owen. It looks like my problem may just be wear and tear or age and not the hydro itself. It's probably a combination of wear on the plates and on the valves themselves. I still need to cap the lines to be sure it's not in the external controls and I plan to do that ASAP. My next question is, if it should be that the charge pump or motor plates are scratched or worn can they be replaced? What needs to be done to get to them and replace them? Thanks again for all your help. I will print out all the replies I have received and show them to the mechanic I plan to have do the work so that he can review them before tearing into the tractor.

(quoted from post at 06:01:24 07/31/09) Thanks for your excellent description Owen. It looks like my problem may just be wear and tear or age and not the hydro itself. It's probably a combination of wear on the plates and on the valves themselves. I still need to cap the lines to be sure it's not in the external controls and I plan to do that ASAP. My next question is, if it should be that the charge pump or motor plates are scratched or worn can they be replaced? What needs to be done to get to them and replace them? Thanks again for all your help. I will print out all the replies I have received and show them to the mechanic I plan to have do the work so that he can review them before tearing into the tractor.

Click to expand...

When you start having problems with scoring on the plates it gets expensive very quickly. To replace them requires a complete disassembly of the center section of the tractor.

In addition to the plates you would probably also find worn "slippers" on the ends of the pistons in both the motor and pump. The labor is not that difficult with a couple of special tools but you will quickly run up a couple thousand dollars in parts.