CAT D8N STEERING TROUBLE

[naheed]

hi guys having a problem with my d8 its completely lost steering in both directions!
serial 5tj-01036
went out to work last week, was perfect no problems,10 mins into work and boom no steer.
did some pressure testing on the circuit and got only 400 psi on the steer motor(which im guessing is charge pump/lubracating pressure),so got the hydraulic pump out and changed the barrel,pistons etc. put the pump back in but zero difference,also opened and checked the motor but it looks like its in great shape so put it back and still no steer.
tiller and pilot pressure also checked im getting 300 psi there,pilot pressure is actually reaching the hydraulic pump but the pump is not stroking.trying to find out the problem i also took the actuator neutral adjustment about 2 turns out to see if the machine would steer in that direction and yes it worked.
would really appreciate if anyone could help me figure out why the actuator is not making the pump to stroke.

 

[Mark250]

if the machine will turn by using the neutral adjustment .it sounds like lack of pilot oil to the actuator
have you checked the mechanical side of the control pilot valve and the steering pilot pressures

 

[naheed]

hi mark,
yes got the pilot valve out cleaned it and found nothing wrong in there.
im getting about 300 psi on the on both taps with lever full turn right or left..

 

[Mark250]

hi both these taps should have approximately charge pressure in neutral
and when you operate the tiller one of the pressures will drop off
if that is not happening you have low pressure from the tiller pilot valve or the control valve that operates the control piston has a problem

 

[naheed]

hi mark,
yup you were right both taps should have continuous pilot pressure,which mine didnt have!
so after another back breaking experience i got the pump out again,inspected all the charge pressure lines and found the culprit.
an o ring had come into the line and was blocking the pressure.dont know how it was able to get there?
put the pump back in and steering was back!
thanks for the help and advice mark

 

[Mark250]

Good to hear