I have a D8r that quit pulling, I have main pressure 450psi at priority valve but not getting to transmission. I have removed and checked trans valves, no problems found. Took a wild shot and replaced priority valve section, still no psi at trans. Have pressure checked tube inside case its ok. Only getting about 100psi to trans valves. Any suggestions.
Refresh my memory, is this trans a mechanical shift/cables? if so it might have a problem with the plastic screened orifice in the pressure control pack. It controls the modulation time of clutch engagement. If no oil gets through it trans will stay on initial pressure, approximately what you have. Later Bob
Yes cableshift. Our filter collapsed and sent paper into valve. I checked plastic orfice and cleaned it. I thought this only helped with modulation. Could this actually cause main press to never come up?
Yes, the pump pressure must go through it to get behind the load piston of the modulating relief valve and raise the clutch pressure from initial to full. The valve needs more cleaning I think. Later Bob
Thanks for the info, I will replace the orfice today.
Replaced screen orifice and pressure came up. Thanks Bob.
Those screen orifices are finicky things. I recall one in a 988F transmission some years ago that gave us fits.......they are colour-coded to indicate the orifice size and although I can't remember the story too well but we either had to go up or down a size in the orifice to get the transmission clutches to modulate correctly. That transmission went on and off the test bench so many times it was dizzy by the time it finally passed test.
Old post .... Where is this orifice screen?
Buried right in the middle of the control valve. Major disassembly required to access it. What machine are you working on.?
D8R 6YZ00747 Having what appears to be a similar problem. Intermittent loss of drive, appears to be not engaging any clutches. Will likely pull the winch off the back today to do further testing.
In my experience a blocked orifice will cause slow/jerky engagement all the time, not intermittent. Has the proportional solenoid valve for each of the five transmission clutches been calibrated recently.? It'll need a Click Box to do it.
Short answer no. The little history I have for this machine is that the root cause is lack of understanding and maintenance. Couple weeks back I was asked for a transmission filter (just the high pressure) for this cat. After questioning I was just told that the restriction indicator was lit. I found out Friday that it was excessively contaminated with material. Having not seen it I can't say for sure what it was. Build up, failure or partial failure. What did puzzle me is that after a couple hours of basic checks it grabbed third gear and didn't slip at all. Then nothing.
Sounds kind of like you have floaters roaming around in the valves. I don't recall if the diagnostics were good enough in those models to show those deep issues.
In that case would It be a better idea to start from basics.? Drop the oil (is it burned?), remove & inspect the magnetic suction screen(s), cut the filter and see what's inside it, then go from there.
Oil appears reasonable. Not burnt or dirty. Screen is clear. High pressure filter has little or no hours on tho I'm told the old element was excessively contaminated. Low pressure filter is clear. I pulled the winch group and tested clutch pressures. Only clutches 3and 2 here good. Stripped and cleaned 4th clutch spool and alas I have second gear again. Will order oil filters and all spools. Hopefully that will cure it.