I’m working on a cat 12g 80s model . The pump pressure spec is 300 psi idle . I’m only getting 100 psi. Replaced pump and still have problem / check filters and cleaned screens wasn’t much debris. Tia
@Nige
Please help @Nige
If you want help then it would be a sound idea to try starting with a Serial Number. I know it's hard to believe but it makes finding information far easier........... Got any photos of what you found in the screens.? You did go into both screens, right.? Have you looked at the pressure relief valve (part of the transmission control valve) yet.?
I cannot read the entire serial number / I know it’s a 61m prefix. Yes I’ll post pictures . And I did have the relief valve apart and it looked okay . It’s mounted external with the cooler lines going to it
61M is good enough for a S/N. Have you checked the operation of the inching pedal.? Is the linkage returning correctly.? If that doesn't happen transmission pressure will be getting dumped. Has it got a diff lock valve on it.? If it has, try blanking that off and if that doesn't get pressure back then the next step would be into the transmission control valve.
The complaint was the machine moves for 30 minutes or so then nothing . So I pulled pump pressure, At test port (A) I had 90-110 psi low and high idle . Removed relief valve group to check for debris etc, finally I pulled the transmission and I have the direction clutches out of it . Forward clutch had some plates that were mis shaped kinda concave shaped like a cone ( not completely flats) . Maybe the piston was acting up ? I’ve never seen the plates get that shape they were also miss colored and the friction discs were pretty beat . The screens had a black sludgy substance on them .
Forward direction clutch has been very hot at some time, maybe more than once. The concave and blued separator plates are clear evidence of that. I'd still look at the operation of the modulation valve. Do you know what oil was in it.?
T030 oil - we are in Florida it happened 10 hrs after another shop replaced the shifting cables
Any good way to test the pressure circuit with air ? Where exactly is the modulating valve ? Is it connected to the directional links age at control valve ?
You can test each clutch piston with air, that's about it. The modulating valve is at the other end of the linkage that is connected to the inching pedal in the cab.
I thought so , so I did grab ahold of the modulating valve from the linkage at transmission with cable removed ( transmission out of machine) and it moves very freely . Do you think I need to open the valve body ? Looks like a headache to remove with all the oil pipes . Thanks again nige always a big help
On any power shifts that use oil pipes with ‘o-rings’ on them from the valve body to the planetary housing assembly, always replace them while you’re in there. I’ve seen them either hard(especially if they are the black ones) or deformed from thousands of hours of operation. They can bleed off clutch-apply pressure if they don’t seal. Valve body disassembly and cleaning as well as inspection of all spools and springs is also a good idea
Agreed. To me it makes no sense to go into a transmission to rebuild clutches, re-bearing planetaries, etc, and not to replace every O-Ring, seal, & gasket both in the transmission itself and in the control valve while you are in there. The cost of these items is pennies when compared to the spend on the hard parts.