Ford 555e Low Transmission Pressure

[dtcohen]

Hi All,

I recently purchased a 555E backhoe with the power shuttle transmission. The "low transmission oil pressure" light was on when I bought it, but overall the backhoe was in good shape with less than 2000hrs showing on the tach. The backhoe moves forward and backward fine and the engagement is pretty firm. My hope was that this was just a faulty pressure switch. I was able to start troubleshooting this weekend. I unplugged the switch and the light went out. When put a jumper across the two wires the light came back on. This tells me that the circuit is working properly. I then removed the pressure switch and took it to the work bench. With no pressure on the switch I am getting continuity between the terminals (makes sense, low pressure causes switch to close and light to come on). I screwed the switch into my oil gun that I use for oiling rollers and idlers on older track machines and put some pressure on the switch. When I applied pressure, the switch opened. I didn't have any way to measure the pressure, I just know that it was opening. I have screwed a test port into the port that the switch came out of and plan on borrowing a gauge from work to measure the actual pressure.

My questions are:
1) What should the operating pressure of the transmission be?
2) Is there anything that could be causing the low pressure that could be checked before pulling the transmission out?


I have ordered a service manual for the machine. It should be here in a few days.

 

[TVA]

See if short passage to the sensor have some packed dirt/gunk in it, these being dead end and not a flow through can accumulate debris in them, since transmission seems to work OK. If you have plugging problem the mechanical gauge will show low pressure too, and miss lead you in to unnecessary work. Make sure you have unobstructed passage from main gallery to pressure sensor.

 

[dtcohen]

See if short passage to the sensor have some packed dirt/gunk in it, these being dead end and not a flow through can accumulate debris in them, since transmission seems to work OK. If you have plugging problem the mechanical gauge will show low pressure too, and miss lead you in to unnecessary work. Make sure you have unobstructed passage from main gallery to pressure sensor.

I hadn't thought of that. I will try to get the fitting out and make sure it is clean.

 

[NH575E]

Good suggestion to make sure the port is clear TVA.

Assuming you have the Power Shuttle this is the page I found on pressures.

 

[NH575E]

This page says trans pressure switch should be 145 psi @ 2000 RPM.

 

[TVA]

Good suggestion to make sure the port is clear TVA.

Assuming you have the Power Shuttle this is the page I found on pressures.

View attachment 187427

Got to remember KISS!

 

[dtcohen]

Just an update on this. Over the weekend I had some time to do some more investigation. I put a gauge on the port where the pressure switch goes and was reading ~196psi at 2000 rpm. That is assuming that the tach on the machine is reading correctly. I think it may be reading a little low due to a worn out/slipping alternator belt. I got a new belt yesterday and will put it on this afternoon. So it is just below the spec, but shouldn't be low enough to cause the light to come on. I believe the trans pressure switch is my problem.

I was reading through the service manual and in the electrical section I found a troubleshooting procedure for the switch. It didn't really make sense though. It said that if the pressure drops below 145psi that the light will blink. My light was staying on solid and the buzzer was on. It also said something along the lines of "no trans pressure = 0.03 ohms, transmission pressure read continuity". That didn't really make sense to me because it seems like it should just be open or closed. Open when pressure >145psi and closed when pressure < 145psi. My manual says it is from 99 and I believe my machine is a 97 model. Would that make any difference?

 

[NH575E]

Do the light and buzzer quit when you unplug the switch? If so and the pressure is in spec it's the switch. If not then the wires are probably grounded somewhere.

 

[dtcohen]

The light and buzzer to quit when I unplugged the switch. I put a T fitting in my oil gun line so I could measure the pressure while bench testing the switch. The first time I tried it the switch didn't open until I was up to ~300psi. Obviously this was way to high. I kept releasing the pressure and retrying the test and each time the pressure where the switch opened was a little lower. It finally settled to opening at right around 145psi. Maybe the switch was just a little frozen up from sitting for several years? I reinstalled the switch in the tractor and now the light and buzzer turn off when I start the tractor.

I tried doing a stall test on the tractor using the procedure in the service manual. The stall speed on the engine was high and it didn't sound like there was much load on the engine. I checked the forward and reverse clutch pack pressures (ports 3 and 4) and they were at 191psi at 2000rpm with the shuttle shift in neutral. So just below spec. Revving the engine past 2000rpm caused the pressures to go up over 200psi. I am a little skeptical of the tach on this machine. It is showing ~1000rpm at idle, which seems high based on the sound of the engine. I am going to put a piece of reflective tape on the crank pulley and check engine speed with a photo tach to verify what the engine speeds actually are.

 

[dtcohen]

Alright folks,

I think I have finally convinced myself that my transmission is ok. I measured the engine speed using a photo tach on the crank pulley. It turns out that my tachometer is indeed reading incorrectly. When my tach shows 2,000rpm the engine is actually only turning about 1,400rpm. At high idle the engine is turning ~2,250rpm and the tach is showing 3,000+ rpm. So when I measured the pressure with the engine actually turning 2,000rpm they were within spec.

I didn't have anybody to help me with a stall test (I needed somebody to hold the photo tach while I worked the controls), so I set the engine speed to high idle, put the transmission in 4th gear, held the brakes, and shifted the shuttle lever into forward, then into reverse. The engine lugged back to what I am guessing was about 18-1900rpm.

Not sure why the Tach is reading so far off, but that doesn't worry me too much. Thanks for the help and documentation to help me go through the troubleshooting process.

Daniel

 

[Jayroget]

Is anyone following this thread still? Wondering where is the location of the transmission pressure sensor. I think mine is plugged or bad.

 

[Jayroget]

Is anyone following this thread still? Wondering where is the location of the transmission pressure sensor. I think mine is plugged or bad.

I found the switch. Unhooked wires, light/buzzer went out. Think dirty or faulty switch.