656 Hydro Charge Pump Failure - How To Prevent

cgustafs · Oct 11, 2011

I have a 656 hydro that just ate the charge pump. The side of the pump next to the inlet broke off. It looks like a fairly weak casting at that point. I just wonder if there is anything to check to be sure it doesn"t happen again? In particular, I looked to make sure that the throwout bushing in the flywheel was good and surprised there wasn"t even one there! There doesn"t appear to be any support on the front of the input shaft. Could this be placing too much stress on the rotor in the charge pump and break that section of the pump? How to check????

pete 23 · Oct 11, 2011

Since the input shaft on the hydro is supported on two tapered roller bearings it has very little room for any movement and no pilot bearing is used on the end of the shaft in flywheel. What shape were the pump vanes, did it bust them up and wedge in there causing the problem or were the bearings loose. It is quite a procedure to adjust the end play on those bearings. I used to actually do it before I mounted the hydrostatic pump on shaft and then you can tell what you have with out spring pressure against them.

cgustafs · Oct 11, 2011

Thanks for the reply. The pump vanes were chewed up. I assume they got wedged. Is it typical for them to wear out? The rotor and pump wall surface both looked good with no scoring, etc. I don"t recall seeing the procedure to adjust endplay in manual... will have to look at that. The bearings look in good shape, tight and no pitting. How did you adjust play before mounting pump?

pete 23 · Oct 11, 2011

I put the shaft in without all the other stuff on it like hydrostatic pump and swash plate. Get the shimming for correct amount of end play. It requires pulling that front bearing cup to add or subtract shims. Been many years since I did it though so may be forgetting a few things. I just never liked to do it the way the book shows. End result is the same only this way you can actually measure end play. One thing you have to remember about measuring end play on any tapered roller bearing shaft is you turn shaft several times and then you measure by prying shaft or pulling shaft. After you pry or pull it one time you have to rotate it again to get an accurate measurement. I never actually realized that myself until they showed us this procedure when at service training on the CaseIH magnum tractor transmissions. And yes, those charge pumps do tear up.

cgustafs · Oct 11, 2011

Thanks for the description and it makes sense, I have put together many automotive rear ends so understand what you are implying by rotate/measure. So, you say charge pumps do tear up... my bottom line question is, do they just go because the pump eventually wears and implodes or is failure usually related to something else being off? I just don't see anything else worn or out of spec that would cause the pump to fail... but am nervous about just popping a new $4000 part in! Thanks for the helpful comments

656 Hydro Charge Pump Failure - How To Prevent

cgustafs

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pete 23

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cgustafs

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pete 23

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cgustafs

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