I have a 420e that when first started has no hydraulic pressure and gives a low brake pressure alarm. after a few minutes the pressure will gradually increase untill full pressure comes back. this will happen intermittently and after the machine is shut down and restarted. Ideas?
Assuming you're not real low on Hydr oil, I would suspect he Hydr filter is restricted/plugged. The brakes on 420E's are hydraulically boosted from the pilot hydr system, so it will be impacted by low hydr system pressure as well. With your hydr pressure returning after a little while, it does sound like a restriction and not a failure.
M hydr oil level is fine and suspected the filter issue and changed it. Problem is still the same.
Hmmm. Again assuming that you have a ST machine - When you start the machine, does the loader work right away - and before the backhoe pilot hydraulics return ?
You don't say what S/N prefix your machine is but my first thought would be that the hydraulic accumulator has partially or totally lost pre-charge pressure. Although the accumulator is located in the implement pilot hydraulic system it also serves to boost oil pressure at the brake master cylinders.
when th machine starts there are no hydraulics period thinking I prob. have a pilot pump issue. time to check some pressures.
It takes about 15 seconds for the pilot hydraulic accumulator to recharge if it has been drained by leak down or if the charge has been depleted as Nige is suggesting. Is that about what you are seeing for a delay ?
No it takes a couple minutes then gradually builds up it is getting worse
Can you verify the pilot lockout switch on the right instrument panel is working and not corroded ? Might want to pull it out of the panel and check the plug to the switch. Guessing here, but that solenoid may be sticking. But if you do have a ST front end with a mechanical loader valve, it should work as soon as you start it. But if you have an IT it will also rely on the pilot hydraulic pressure. PM your email if you want the hydr schematic.
Yes I verified the switch and also replaced the selinoid. My next step is to check the compensator.
Before going any further, check the accumulator .................