AHC woes

[PADDO]

Did you ever replace the pump? There’s two micro mesh screens in it that will easily be blocked by visible particle contamination. If these screens are blocked then the pump will be starved and have no or reduced output and that will obviously affect height accumulator charging and raise times.
When stopped if you’ve got your foot on the brake for 5+ seconds then the height control system is inhibited.

 

[Das Shtig]

Did not know that last tidbit! I did not replace the pump yet. So—replace pump and clean/flush the system, replace with fresh fluid? Cross fingers?

 

[Das Shtig]

And sorry—should I assume the particles are coming from the accumulator and replace it also? I ask because I don’t want to clog the new pump the same way if that’s what’s happening.

 

[PADDO]

And sorry—should I assume the particles are coming from the accumulator and replace it also? I ask because I don’t want to clog the new pump the same way if that’s what’s happening.

After 30 something years of professional engineering in servo control and hydraulic systems (proper systems, not dinky little car systems) I don’t assume very much - but based on the tsb criteria of known deficiencies in the height accumulator and your description of visible contamination is can’t be ruled out the height accumulator seal is the source. If you do the height accumulator health check (pressure/volume) I described earlier then that might reveal something. The pump is submersed in fluid within its housing, sludge and crud accumulates like a grease in the housing and will block the pump intake so this should be checked and cleaned out. The pump can be easily disassembled (just four cap screws holding it together to the main body) revealing the two micro filter screens and they can be blown out and cleared with squirts of brake cleaner. The little gear pump is very robust with just two moving parts, so as long as its intake isn’t blocked and the motor/coupling is good then you should make good pressure and flow so I’d pull the unit and check/clean before buying more parts. There’s plenty of serviceable takeoffs to be had for cheap too.

 

[parkeyjack]

And sorry—should I assume the particles are coming from the accumulator and replace it also? I ask because I don’t want to clog the new pump the same way if that’s what’s happening.

Did you ever get to the bottom of this? I am having a sloooow raising AHC problem as well. Thanks in advance!