ZD28 Hydraulic Testing

[longta359]

Hello all,
I am new to the forum and am looking for advice on a 2006 ZD28 problem. Machine has 684 hours and has never really been run hard. Left side does not keep up with the right side in forward or reverse. Based on other forums, I drained the fluid (perfectly clear and did not smell burned) and removed the strainer. Other than about 5 metallic particles, it was clean. The magnet on the drain plug was also free of any metal - only a little black came off on a rag during cleanup. I then dissected the hydraulic filter and it was very clean. Like the strainer, it had a few metallic particles, but nothing of significance. (I have pictures, but will only post is someone requests - not really much to see)

My current task is doing pressure testing, but I can't find a hex key wrench that fits the allen plugs on the Transmission. Does anybody know what the size is? I have tried all the english sizes and 8, 9 and 10 mm wrenches. 8 is loose and 9 won't fit.

One post from some years ago mentioned ports on the bottom of the transmission. My machine is on a lift so it would be really easy to access them, if only I knew where they were. Help!!

I removed the Hex bolts that are listed as "forward side" and they are BSPP 04-19 threads. I plan to make a hose to fit this. Do I need to test the ports listed as "Reverse side" or will the "forward side" provide enough detail to troubleshoot?

Thanks in advance for any and all guidance on this project.

 

[Dustyx2]

I don't know how severe your speed problem is but have you tried adjusting per the owners manual procedure? i bought by ZD21 used with about 1200 hrs and before I made the deal for it the dealer adjusted the speed so it would travel a straight line.

 

[longta359]

I found the adjustment in the WSM and will try that. Right now I am in the process of making a pressure test setup to better monitor my machine's health. If that adjustment works, it would be a godsend. Thanks for the suggestion.

 

[longta359]

I finished fabricating the pressure test gauge setup and tried checking the charge pressure. New Super UDT fluid and filter. First tested with a 10,000 psi gauge which was apparently too high to register the charge pressure. Changed to a 160 psi gauge and it reports 85 psi at idle and 130 psi at max speed. According to the WSM, this is way above the 71 - 99 psi specification. The WSM however does not say what to do if pressure is too high, only if it is too low. Does anyone know why this machine would have too much pressure and how to remedy it? I am totally lost here and could really use some help.

Update: Just checked the Lift pump relief valve pressure and it is also way over specification. Spec is 455 - 450 psi. Mine is reading about 700 psi. Pressure readings are on two different gauges and both are high. Would relief valve pressure being high cause charge pressure to be high?

 

[ruger1980]

Is the oil up to operating temp when you are checking pressures?

The lift circuit will not affect the HST unless it is activated continuously long enough to affect charging of the low pressure loop. I doubt you are holding the lift function that long.

Seeing that your problem is speed related it is flow related. Either flow is not sufficient or equal, or you have internal leakage due to worn components. Anything related to charge pump/ pressure settings would affect both right and left HST not only one.

I would focus on linkage related solutions first. This is more likely the cause than a hydraulic fault.
Have you adjusted the max speed correctly for each HST? Is there any excess play in any part of the linkage including the control shaft at the HST?

If it is hydraulic it is most likely due to excessive wear between the rotating group and valve or end plate. You can check this by comparing charge pressure measurements when stroking only the left then the right propel lever under a load or with the parking brake set. Remember oil must be at operating temp.

 

[longta359]

Ruger1980, Thanks for the reply.

I checked pressures at room temperature, so I will have to get the transmission up to temperature and retest. Also, I have not adjusted the linkages, but will do so today.

Since I now have the pressure test setup, I was thinking it would be worthwhile to test pressures as a measure of how bad my HST drives are. Thoughts?

Do I need to test the forward AND reverse pressures (1 and 2 on the WSM)? I only ask because I have not found a tool that fits the socket head screws on the Reverse side. I have tried 8, 9 and 10 mm, 5/16 and 3/8" hex keys. Do you know what fits the Reverse port plug?

The Forward side is a cap screw with BSPP threads and I have removed that for test gauge attachment.

 

[ruger1980]

Pressure is a measurement of resistance to flow or load on the circuit. It is not necessarily an indication of the health of the system.

 

[longta359]

Thanks for responding so quickly.
I was reacting to a statement in the WSM that said as long as the pressure is above 2845 psi, it was considered OK.
One other question that you may or may not know - the WSM says to remove the HST port bolt and install the test gear, and then the motion lever position switches would be temporarily disabled. This makes no sense to me and I can't find anything that says how to disable these position switches. The test protocol says to put on the Brake and then push the motion control lever forward to get a reading. When I do that, the engine shuts off. If I disconnect the brake limit switch, the engine won't start. Suggestions?

 

[ruger1980]

I can only assume they mean to fix the switches so they remain on when moving the motion lever or jumping them temporarily

 

[longta359]

I wish it were that easy. The safety switches on this beast are programmed for two functions. If The brake switch is disconnected, the motor won't start. If the connector is jumpered, the engine will start but when you try to move forward or back, the engine shuts off. Same for the motion levers. The switches that need to be manipulated are only available from underneath, so I would have to make jumper cables with switches to duplicate the two functions.

I think I may have to put the ZD28 in front of a concrete wall, and let the wall be the brakes.

I'm sure there must be a workaround, but it is a well kept secret.

 

[longta359]

I promised an update, so here it is. The threads on the Allen plug is #4BSPT and the wrench is a 7mm allen. I finally got a pressure reading on the left side, which was well above what the WCS suggested as minimum. My pressure was 3600psi (vs 2845 min and 4260 spec). I planned test the right side, but the allen plug stripped and I could not get it out without removing the transmission. The right side was always the stronger side, so I decided not to pursue "purity in testing" at this time.
I also noticed that my Mower lift was really anemic, and disconnected the cylinder (assuming it was the problem). The cylinder was fine. However, the pivot shaft is mounted in two keyed bushings that were totally frozen to the pivot shaft. The design prohibits releasing either key independently, so the rust freeze is a real bear to resolve. Lots of penetrating oil, heat and air chisels later, I got the bushings out and cleaned the pivot shaft up. I added grease fittings to both bushings and reassembled.

This is a cautionary note. I could not find anything anywhere suggesting lubrication on these bushings, while the front pivot mounts each have two grease fittings.

Back to the original problem. I checked the max speed adjustment and it was slightly faster than left side, so I adjusted it. The machine is now working better than it has in years.
Project complete.