The retarder control is very simple so it might be worth checking out the foot control as this could be your issue, the mag valve needs to have electrical power to energize the air spool going to the retarder valve on the gear case, this would be a rare fault to have on a dumper, no doubt when you had the 2 front pumps off the drive case you looked at the screen filter behind the plug on the drive case? the retarder warning light on the display should have helped you spot the fault showing retarder on, I would always go through all the controls, warning lights and fuses on a service/repair job, the mag coils (solenoid) when faulty just don't work? did this dumper get the big engine rebuild due to a "Tarder Fault" in the very start, the G/Box usually lasts around the 16'000 18'000 hours on A25C's, they are 1 of the easy ones to remove/replace compared to the later series dumpers but they are still pigs to tackle, I do have the trolley frame for gearbox removal on Volvo Dumpers, the last time I used it was on an A30 about 4 years ago.
tctractors