Hi I have a Cat D5G and the lift cylinders drop both together at the same. They both drop Under load pushing and also when not under load. No external seals are leaking. Would the internal seals be gone and cause this if they both drop at same time? If not what else could I look for
I like to start at the cylinder and work back towards the valve. You can take the lines off the cylinder and use compressed air to check and see if the seals are good. Could be a seal in the cylinder blown or the piston could have came off the rod.
If you lift the front of the machine with the blade does it (also) creep down fairly quickly? If so is usually cylinder seals. Only needs 1 of the cylinders to leak but should do seals in both cylinders at the same time. How many hours on the machine?
Does the blade control valve have a quick drop position ?
I assume that you mean a "float" position.? I'm assuming that the OP is complaining about the blade cylinders coming down with the blade control in the HOLD position. FLOAT is different to a quick drop valve which (if so equipped) is usually located in, or bolted to, the head of each lift cylinder.
I didn't mean float, Nige I never ran a D5G but I have run Caterpillar dozers that have a quick drop feature for the blade. The control lever can be pushed forward past the float position and the blade will drop amazingly fast. I was running a D8N that had that feature. It developed the same symptom that Nathan described in his question. The mechanic that repaired said there is some kind of valves in the blade cylinders that has something to do with the quick drop. I don't know what he did to that valve but the blade worked normally after he was done with it.
Tink our D5G does not have that feature. Never experienced what OP is talking about on our D5G. Resealed the cylinders a couple of years ago but that was due to leaking seals.
Can't say I've ever seen anything like that. I looked at a D8N and the 4 positions shown for the blade control lever are raise, hold, lower, & float. On the bigger dozers the quick-drop valve is mounted on the head of each lift cylinder and basically bypasses oil from the rod end to the head end of the cylinder under certain conditions. This allows the blade to drop faster than the speed at which it would drop if it was simply being supplied with oil from the implement pump while at the same time avoiding pump cavitation. From what I can see the D5G lift cylinders do not have a quick-drop valve as CM pointed out above.
That should read from the head end to the rod end. Sorry about that.
I must have been running an odd ball dozer because the valves that were worked on were at the top of the blade cylinders.