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I overhauled my hydro pumps after a slow leak for a couple seasons now. After replacing the seals and reinstallation, I followed the procedure to purge the system while the transaxle is released, then reengaged, but still have frothy oil. I can’t find any leaks from the pumps anywhere and the connections are all tight for the hoses. I replaced all of the low pressure hoses and the two drive hoses for the right hand side. I have followed the purge procedures 4-5 times and still seem to have air. Is this normal? Any suggestions from the group? I’ve never worked on hydro systems before, so any advice is appreciated

I have had a couple that I have ran at idle for a few minutes doing the purge with the frothy oil, and I will shut it off and let the air settle from the oil and then purge again. Sometimes it takes a few times. Especially with separate pumps and wheel motors with new hosed. That is a lot of air that has to purge from multiple places.

Hose to wheel motors and wheel motors are the worse because the oil outside of the pump and in the return tank is just make up oil. Think of the drive system as a closed loop and only calls for outside oil when part of it leaks due to internal pump lose.

ILENGINE said:

I have had a couple that I have ran at idle for a few minutes doing the purge with the frothy oil, and I will shut it off and let the air settle from the oil and then purge again. Sometimes it takes a few times. Especially with separate pumps and wheel motors with new hosed. That is a lot of air that has to purge from multiple places.

Hose to wheel motors and wheel motors are the worse because the oil outside of the pump and in the return tank is just make up oil. Think of the drive system as a closed loop and only calls for outside oil when part of it leaks due to internal pump lose.

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After looking further into the purge process I only cracked the bypass valves maybe 1 full turn out instead of 3-4 full turns. I’ll give that a shot and see if it makes any difference given the amount of air introduced as you mentioned.

Still having trouble purging air. Backed bypass valves out 4 turns on each side and purged multiple times with letting it sit and idle for a few minutes then turning off and letting it settle between rounds of purging. Left pump still running anywhere from 150-170 degrees, right pump consistently between 115-125 degrees. When using a mechanics stethoscope the sounds from the right pump are more pronounced when placed on top of the charging port vs the left. I don’t know a lot about hydro systems, but I would assume the sound is more prominent because of the fluid in the pump? Could it be there is an air pocket in the charging port? Any help would be appreciated as I’m ready for this to all be in the rear view and bring it to a shop from here on out.

ILENGINE said:

I have had a couple that I have ran at idle for a few minutes doing the purge with the frothy oil, and I will shut it off and let the air settle from the oil and then purge again. Sometimes it takes a few times. Especially with separate pumps and wheel motors with new hosed. That is a lot of air that has to purge from multiple places.

Hose to wheel motors and wheel motors are the worse because the oil outside of the pump and in the return tank is just make up oil. Think of the drive system as a closed loop and only calls for outside oil when part of it leaks due to internal pump lose.

Click to expand...

Still having trouble purging air. Backed bypass valves out 4 turns on each side and purged multiple times with letting it sit and idle for a few minutes then turning off and letting it settle between rounds of purging. Left pump still running anywhere from 150-170 degrees, right pump consistently between 115-125 degrees. When using a mechanics stethoscope the sounds from the right pump are more pronounced when placed on top of the charging port vs the left. I don’t know a lot about hydro systems, but I would assume the sound is more prominent because of the fluid in the pump? Could it be there is an air pocket in the charging port? Any help would be appreciated as I’m ready for this to all be in the rear view and bring it to a shop from here on out

Just had a thought when I went back and reread your OP. You said that you overhauled your pumps. Did you remove the football shaped cover with the oil pump in it. If so it could be possible that they have been reinstalled 180 degrees from original which will prevent proper purging because they would be trying to pump the oil out of the system instead of pumping into the system.

I have had some mowers that just will not purge no matter what to the point I had to rig a vacuum pump up to suck the air out.
The other big thing is the wheels must be off the ground so they offer no resistance or rather than the oil displacing the air it will just compress it so the wheel moves when off the ground but not under load . The engine needs to be running as slow as possible or the pump will foam to oil before it gets to the wheel motor .
On the Z 345 I did a few weeks ago ( thanks to the help I got here ) I found I needed to spin the wheel by hand to fully purge the motor and it still took about 100 cycles F-N and 100 cycles R - N .
Over the years I have found that doing the F > R > F > R does not work as well as F > N > F > N and then R > N > R > N TO test if it is working I try to stop the wheel spinning with my heel .
And as Illingine has already said don't carry on for hours , If after 30 minutes you are not having any luck, leave it for a day & try again as frothy oil can take forever to settle back down

ILENGINE said:

Just had a thought when I went back and reread your OP. You said that you overhauled your pumps. Did you remove the football shaped cover with the oil pump in it. If so it could be possible that they have been reinstalled 180 degrees from original which will prevent proper purging because they would be trying to pump the oil out of the system instead of pumping into the system.

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I’m assuming you’re talking about this charge port?Yes I removed it. How would I tell if it needs to be rotated 180? I didn’t see any type of marking that would indicate a direction that it needed to face

I am talking about this

Installation is directional

ILENGINE said:

I am talking about this View attachment 68679

Installation is directional

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After looking at pictures taken before/during the disassembly and reinstallation I think that might be part of my problem. It’s bittersweet to see now as I’ve already given up and loaded the mower on a trailer to bring it to the shop on Monday and now my curiosity is peaked enough to pull it back off and see if that fixes it lol

Let us know. Just be aware that if you don't have pictures of the charge pump covers from both pumps they may face opposite directions from each other when installed on the mower.

Before taking the cover off put a mark on the housing on the side of the charge pump cover that has the square end on it and install in this way when putting back together. You are saying oil is foamy. Will it pull at all? Does sound like you have the charge pump cover on wrong. Try turning it 180 degree and try to purge it again. Don't just take the bolts out and turn it if you do you will destroy the spring on the check ball. You will have to lift the cover straight up and reninstall it.

ILENGINE said:

Let us know. Just be aware that if you don't have pictures of the charge pump covers from both pumps they may face opposite directions from each other when installed on the mower.

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Planning to do it tomorrow now (at work today). I’m fairly confident I have the charge pump on backwards on the left pump (which is the problem pump) after reviewing pictures. I’m optimistic right now that this is the reason I’m having trouble with it all.

ILENGINE said:

Let us know. Just be aware that if you don't have pictures of the charge pump covers from both pumps they may face opposite directions from each other when installed on the mower.

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Here is a pic after reinstallation. The indentation on the charge cover is opposite but the ports for each pump are oriented in the same space. To me that would say they’re opposite of what they should be, and the picture I have of the left pump prior to disassembly to replace seals shows that the indentation should be on the opposite side and both pumps would look identical once installed. I mistakenly took my “before” picture before pulling off the metal bar that supports the seat and holds the interlock switch for the seat. First time doing this, learned a lot already lol

I think we are on the correct track. Need to turn the pump cover around on that one pump so both cover indents face the same direction. The indent will face the same direction because the pumps themselves are flow opposites

ILENGINE said:

I think we are on the correct track. Need to turn the pump cover around on that one pump so both cover indents face the same direction. The indent will face the same direction because the pumps themselves are flow opposites

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I haven’t seen any type if diagram that shows the flow path of the hydro fluid? That might help me understand how/why it works the way it does for any future problems. The manuals seem to be lacking some good information from what I’ve seen

definitely lacks information as far as charge pump orientation. Just says to make the pump cover and the pump housing prior to disassembly so you get them reinstalled in the correct direction. Would be nice if they had a graph for the pump units. There is one for the integrated units for which way the cover goes.

Some information on hydrostat systems. The charge pump which is under the football cover pumps oil into the piston pump. That piston pump then pumps that oil to the wheel motor. The oil from the wheel motor gets returned to the piston pump and is then pumped back to the wheel motor. So Think of the hydro to wheel motor as a closed loop system which for the most part is. Now some oil gets lost in the piston pumping phase which flows into the pump housing and is returned to the oil tank. As the oil is lost from the piston pump the charge pump gets oil from the oil tank through the filter to replace what oil the piston pump is loosing. So if the system is lets say 90% efficient then 90% of the oil loops between the piston pump and the wheel motor and is unfiltered, and 10% gets lost and returned to the tank to be filtered.

So in the case of your hydro pumps the charge pump and top plate have the same oil flow pattern for both pumps, but your control lever on the outside of the pumps that controls direction work in opposite directions. Your right hydro when the stick is moved forward tips the piston pump swath plate down in the front, but the left lever moves the swath plate up in the front. Which in turn causes the oil to flow in opposite directions coming out of the pump units.

This is why the SM say to scribe index marks before removing the caps. Also while your are at removing the cap check that the charge spring and ball are in place. Plus these plastic balls do wear and need replacing during rebuilds.

ILENGINE said:

Let us know. Just be aware that if you don't have pictures of the charge pump covers from both pumps they may face opposite directions from each other when installed on the mower.

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Rotating the charge port 180 degrees on the left pump seems to be the fix. Both wheels are turning and the hydraulic oil is no longer frothy like there is entrapped air. I need to adjust the control arm linkage as the “neutral” position pushes the right wheel in reverse and the left arm forward now, but the steering feels much tighter and controlled than before. The pumps sound whinier than I remember. Would it be worth going through the purge process a few times just to make sure there’s not more air in the system somewhere? Both wheels turn even with the bypass valves open as it sits right now.

It wouldn't hurt to do the purge a few more times just to get out any encapsulated air.

ILENGINE said:

It wouldn't hurt to do the purge a few more times just to get out any encapsulated air.

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Good advice ...

ILENGINE said:

Let us know. Just be aware that if you don't have pictures of the charge pump covers from both pumps they may face opposite directions from each other when installed on the mower.

Click to expand...

So after another couple rounds of purging the air from the system I never had a drop in fluid from the reservoir. I mowed (approx 2 acres) and had a little fluid burp out of the reservoir and pumps were running 176-180 degrees which seems hot to me. The fluid was a touch over the recommended level, but only by about 1/16” - 1/8” over full. Anything to be concerned about or just let it ride?

Hydraulics can normally run 100 degrees above air temperature.