Hey guy's We have been working on a volvo g940b grader that will throw a break failure lights on the dash at the same time the cooling fan cuts on. When it first came in the light would turn on consistently and after determining one of the four pressure sensors on the break valve was faulty and replacing it, the issue changed. Now after starting the machine and using the breaks as if the grader was in use the light seems to stay out and we maintain 1800-2500psi system pressure. Break pressure is coming from port b2 on the shared cooling fan valve under the engine. The issue now is if you pump the breaks rapidly, once system pressure gets down close the the kickin pressure (1800- 1850 psi) the cooling fan turnes on ( with the fan coil unplugged) and the break failure light will come on at the same time. System presure slowly drops off untill you bring the rpm up or shut the machine down and restart the process. I pulled both the relief and switched it out with a spare as well as the fan spool, it didn't seem to make a differance. It just seems like, when the pressure is quickly bled off by the break valve, it some how backfeeds the cooling fan spool turning it on and dumping our pressure. Last night I did pull off the case drain off the cooling fan and it does not seem to have excessive case drain pressure. I was just woundering if anyone else has run across this issue that may be able to shed some light on how we may be dumping pressure?
Been years since I ran one of those. I wonder if the piston that controls pump volume is getting sticky and not moving the way it’s supposed to?
We ended up sending it back to work as it seemed like we were starting to chase a ghost. We could only get it to fail if you pump the breaks realy fast. The piston getting stickey is very possibly. Thanks!