Terex (asv) PT 80 Sluggish drive controls

[Knucklehead11]

I have recently purchased a Terex PT 80 with about 1800 hours. The machine works well, but the forward / reverse control is sluggish in operation. This gets worse as the temperature drops to the point where it seems like a time-delay from control input to movement starting (or direction changing) this is not only annoying, but downright dangerous if working in close quarters. The main hydraulics are strong,and once the tracks are engaged there is plenty of power... it is just that the actuation is slow. I suspect an issue with the charge circuit and have ordered the correct quick-coupler to do pressure test. All other hydraulic circuits work fine, the issue is limited to the drive system. Any ideas? Similar problems?

 

[oldnslo]

Is the delay the same for both tracks in both directions or more pronounced on one track and or one direction

By temperature drops do you mean cold oil Vs hot oil?

 

[Knucklehead11]

Is the delay the same for both tracks in both directions or more pronounced on one track and or one direction

By temperature drops do you mean cold oil Vs hot oil?

The delay is the same for both tracks, and in both directions.
As far as the temp goes, it is pretty cold here in Northern Michigan right now. I have been keeping the machine in a shop at about 50 degrees, and using it only to move snow. So far I have not been able to get the Hydraulic oil temp off the peg on the gauge, and I don't know if this is a gauge problem or if the oil is not warming up because of the low (15 degree) temps and light use. When I left the machine out one night in the cold temps the problem was noticeably worse, making it almost unusable. after it warmed back up to shop temp it went back to usable but aggravating....

 

[oldnslo]

being worse on cold weather points towards the possibility of the charge pump(s) not operating at the correct pressure or an orifice in the pump control circuit being partially plugged. I do NOT know what type of control is used on the HST drives on your machine. Do you have a hydraulic schematic for this machine?

 

[Knucklehead11]

being worse on cold weather points towards the possibility of the charge pump(s) not operating at the correct pressure or an orifice in the pump control circuit being partially plugged. I do NOT know what type of control is used on the HST drives on your machine. Do you have a hydraulic schematic for this machine?

Thanks for your interest and help!
I also suspect a charge pressure issue. I have ordered a coupler for the test port and hope to have it before the end of the week to test the pressure in the charge circuit. The manual states that low charge pressure can be the cause of sluggish operation. here is a link to the manual, hydraulic schematics are page 15-20. http://manuals.gogenielift.com/Parts%20And%20Service%20Manuals/data/Service/Terex/IO/2046-310.pdf

 

[oldnslo]

Knucklehead,
In looking at the service manual is shows a pilot generation block which looks like it feeds the charge pressure to the travel joy stick. I believe this block also supplies the pilot pressure to the loader control joystick. Not sure if there is a test point on this block to measure the pilot pressure being supplied to the joy sticks. Low pilot pressure to the joystick would also cause the sluggish movement since this is common to both drives.

I also noticed there is a suction strainer on this model. Does the pumps sound real noisy when cold Vs warmed up? If yes this could point to an inlet strainer being partially plugged but I would suspect you lift pump for the loader would also show signs of low fluid flow.

 

[Knucklehead11]

Knucklehead,
In looking at the service manual is shows a pilot generation block which looks like it feeds the charge pressure to the travel joy stick. I believe this block also supplies the pilot pressure to the loader control joystick. Not sure if there is a test point on this block to measure the pilot pressure being supplied to the joy sticks. Low pilot pressure to the joystick would also cause the sluggish movement since this is common to both drives.

I also noticed there is a suction strainer on this model. Does the pumps sound real noisy when cold Vs warmed up? If yes this could point to an inlet strainer being partially plugged but I would suspect you lift pump for the loader would also show signs of low fluid flow.

Thanks Oldnslo, those are all good lines of thinking. I have received the quick-coupler for the test port and this weekend I plan to change the hydro oil and filters and will then do a pressure check on the charge system. I'll post results.

 

[oldnslo]

For reference I suspect the pilot pressure to the joystick needs to be a minimum of 300 PSI to provide full travel speed

The joystick will provide a variable pressure from 50 to 300 PSI to control the travel speed.

 

[jayburmister]

Did you ever fix your sluggish response? I have a SR-80. I have had sluggish response in the past. Drop the lines off the drive joy stick into a bucket and flush the oil out until it appears clean. The joystick hydraulic lines have no flow through them, they are only used to divert pressure. I am interested in any feedback.

 

[Knucklehead11]

UPDATE: A pressure test on the charge circuit indicated that it was within the specified range although on the low end. I cranked up the relief valve until the pressure was at the top end at operating RPM. This made a slight improvement in the sluggish operation. As warm weather arrived, the problem became less of an annoyance and as the machine gets very little use in the summer, the issue was put on the back burner... Now that the temps are once again dipping into the 20's the problem is again becoming more if an issue. The drive controls are very sluggish and become much more so as the temperature falls. Running the machine at a higher RPM produces an improvement but this is relative to the temperature. The loader controls work as they should, but it seems like the spools for the motor valves are not actuating properly (perhaps because the loader spools are much smaller?). Another thing that i have noticed is that the cylinders for the attachment lock (which also run off the Charge Pump via the pilot block) operate very slowly during cold temps as well. I am beginning to suspect the charge pump. Is it possible that the pump could be developing pressure in the normal range but is not pushing enough volume to properly operate the drive spools?