Howdy guys, as the title states, I've got a Case 1155E Highlift that has low modulation pressure.
The problem that warranted the check-up was that when you have all the gear levers engaged, it doesn't go into gear until around 1800 RPM (it varies) and does so with a bit of a jolt and then you're off to the races with full power. It's like having a automatic transmission vehicle, rev it up to about 1500 then shift it into 'D'. Before it "jolts" into gear, the transmission input shaft spins freely. If you rev it up to ~1500 RPM and play with the levers, it does jolt slightly as you put it in various gears, and the input shaft does slow down some, but it has basically no power to the ground, modulation pressure at that point is ~50psi. Once you rev it up enough, modulation pressure jumps up to 170psi and it slams into gear.
Hopefully "modulation pressure" is the correct term, it's the pressure that the stock transmission pressure gauge would normally get, I temporarily installed my own gauge.
I also installed a pressure gauge on the outlet of the transmission filter. In neutral I get 150psi @ idle, 250psi @ ~1200RPM, and WOT yeilds ~310psi. If you put the transmission in gear, take off ~10psi from those readings.
I've replaced all the filters, and changed the oil. I bought this dozer with a "slipping transmission". After troubleshooting I tracked it down to the engine which I fixed, it's got great power now, once it goes into gear.
After reading through the service manual, I inspected the pressure regulator in the transmission control valve unit. I pulled it apart and first off the washer was in backwards, not a huge issue but it shows that someone was likely in there before me. But the spring only measures 5.07" long when the specification in the service manual says it should be 5.66" long. I tried shimming it ~ 3/16", but that completely prevented the modulation pressure from going over 50 psi, basically it never jolted into gear regardless of RPM. Judging from the service manuals diagrams, when the pressure regulator spool is in the relaxed position, the spool covers the output port preventing any oil from flowing until enough oil pressure enters the input of the spool to compress the spring. My current novice opinion is that something is preventing the pressure regulator from opening when it should resulting in the low pressure until it finally opens and everything slams into gear.
I shot this video to help describe the issue I'm having, this is with the shim removed again.
https://www.youtube.com/watch?v=lZwZvD2OWjc
I would appreciate any advice on this issue.
Thanks!
The problem that warranted the check-up was that when you have all the gear levers engaged, it doesn't go into gear until around 1800 RPM (it varies) and does so with a bit of a jolt and then you're off to the races with full power. It's like having a automatic transmission vehicle, rev it up to about 1500 then shift it into 'D'. Before it "jolts" into gear, the transmission input shaft spins freely. If you rev it up to ~1500 RPM and play with the levers, it does jolt slightly as you put it in various gears, and the input shaft does slow down some, but it has basically no power to the ground, modulation pressure at that point is ~50psi. Once you rev it up enough, modulation pressure jumps up to 170psi and it slams into gear.
Hopefully "modulation pressure" is the correct term, it's the pressure that the stock transmission pressure gauge would normally get, I temporarily installed my own gauge.
I also installed a pressure gauge on the outlet of the transmission filter. In neutral I get 150psi @ idle, 250psi @ ~1200RPM, and WOT yeilds ~310psi. If you put the transmission in gear, take off ~10psi from those readings.
I've replaced all the filters, and changed the oil. I bought this dozer with a "slipping transmission". After troubleshooting I tracked it down to the engine which I fixed, it's got great power now, once it goes into gear.
After reading through the service manual, I inspected the pressure regulator in the transmission control valve unit. I pulled it apart and first off the washer was in backwards, not a huge issue but it shows that someone was likely in there before me. But the spring only measures 5.07" long when the specification in the service manual says it should be 5.66" long. I tried shimming it ~ 3/16", but that completely prevented the modulation pressure from going over 50 psi, basically it never jolted into gear regardless of RPM. Judging from the service manuals diagrams, when the pressure regulator spool is in the relaxed position, the spool covers the output port preventing any oil from flowing until enough oil pressure enters the input of the spool to compress the spring. My current novice opinion is that something is preventing the pressure regulator from opening when it should resulting in the low pressure until it finally opens and everything slams into gear.
I shot this video to help describe the issue I'm having, this is with the shim removed again.
https://www.youtube.com/watch?v=lZwZvD2OWjc
I would appreciate any advice on this issue.
Thanks!
CASE 1155E Low Modulation Pressure
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