Volvo A35E Serial #: VCEOA35EC00010230 I let the machine run for about an hour; Noticed the bed had lifted about 12" in that period of time with the stick in the locked position. When I started to perform the working pumps test the steering was very jerky in both directions.And a noise seemed to be coming from the little block mounted to the left of the lift dump valve block.When the steering is locked either direction it would still jerk and the steering wheel will rock without your hands on it. If you start the bed to lift, the steering will stop jerking, the noise will go away and it will steer smoothly in both directions. Any ideas? The noise and jerkiness come and go.
It sounds like the pwm valve for the steering pump is sticking, Are the hydraulics overheating?
Yes the steer dump block feels like it gets hot pretty quick. All this started when the brake pump went out. It put a lot of trash in the system.
I'm sure you already know, this is gonna be a cross between hide n seek and whack-a-mole. You'll be chasing these problems as they occur and trying to find the root cause while addressing the symptoms. Gonna be a lot of rummaging through schematics. Let us know, we'll provide assistance where possible
Do you have any good schematics for the steering circuit? Downloaded a manual ,but schematics are limited.
I found the hydraulic schematics.
Can someone tell me what these two codes mean and where can I find a list of codes. SE-4212-14 TECUO2 If one of these codes is for the PWM valve, I started the unit unplugged so that might have caused the code. Thanks
One more code PWM 5901-5.
Did you ever figure out what the issue was? I have an A35E truck with a very similar issue and am getting ready to pull the steering/dump valve out and start investigating
Yeah, that definitely sounds like the steering and bed lift circuits are fighting each other a bit. I’ve seen similar behavior when there’s an issue with the priority valve or something messing with pilot pressure. The fact that the steering smooths out when the bed starts to lift makes me think pressure is being diverted away from steering when it shouldn’t be—or maybe a check valve isn’t sealing properly. That small block making noise near the dump valve could be a compensator or diverter acting up. Had a case once where a worn spool in the steering circuit caused similar jerky movement and random noises. Turned out to be internal leakage causing unstable flow to the orbitrol. This post gives a way: Hydraulic Steering Hope it helps! Would be curious to hear what you find in the end.
No, I have been unable to track it down. But it has been out of the shop for about 4 weeks. We just brought it back in to try and diagnose the issue. Were you able to diagnose and fix your issues? If so I would appreciate your help. If not I will keep you posted. Thanks.
I disassembled the PWM to the left of the dump steer valve. Which is where the noise appears to be coming from. I disassembled the block. Everything worked properly. Replaced the solenoid valve with a known good used one. Made no difference in the performance. However when removing it, the machine had not run for a day. And when I went to remove the two sensors in the bottom of the block, they still had hydraulic pressure on them. To the point they sprayed when losing. I thought this was related to the solenoid valve in the block not allowing the fluid to return to the tank. So I test ran it with a modified valve that would not stop the flow from returning of the tank. This made no difference. I bought a manual, but I can not find the schematic for the PWM. And ideas would help.
UPDATE: After talking to the Volvo Service Dept. he advised me that the dump steer valve has a reputation for getting an internal crack and causing pressure issues. Decided to change the dump steer valve. replaced it with a used one. No issues with initial start up and the noise was gone. About 30 minutes into the test run, while doing the procedure to remove the air from the system, I noticed the bed to begin to raise slowly. The steering started to get jerky if turned fast. After shutting the unit down, went to restart it and it would not turn over freely until I turned the steering wheel while starting. I removed the supply line to raise lower valve in the cab to make sure it was not by passing and causing the bed to raise. It was not. Removed the lines on both ends of the spool to make sure they had no pressure. They did not. I adjusted the spool position manually and the bed was still raising. Sounds like I have another defective dump steer valve that is by passing internally. Any thoughts?
I have figured the issue out with my truck. Initially thought the issue was also the dump steer valve so I removed it from the truck and disassembled it completely. Could not find anything visually wrong with it so I put it back together and re-installed. Same issue was still there. Started hooking pressure gauges back up to this thing and trying to chase down what was going on. What I found was one out of the three main hydraulic pumps was staying stroked up causing it to deadhead the flow at the main steer dump valve. This then caused high pressure at the valve body (was around 3600psi) and I believe due to the internal leakage and design of the valve caused high pressure oil to slightly bypass the dump spool and raise the bed slowly. I ended up narrowing it down to the left rear pump by using a temp gun on the pumps and a pressure gauge on the main valve. I thought it could be the pump controller at first so I took that apart but could not find any issue with that. Removed the pump and disassembled and found a noticeable grove worn in the ball socket joint that the pistons pivot on when the swash plate moves, as well has some wear and groves in the bearings for the swash plate. I believe this was causing the swash plate to stick and not allowing the pump to de-stroke when load sense pressure dropped. We put a reman pump on from Volvo, did a pressure set-up on it and it was fine after that. Hope this helps you.
Thanks for the reply; I ran the machine this morning and the 3 pump's temperature only varied about 15 degrees. However pump 1 pressure side line was about 30 degrees hotter than the other 2. I pulled the pump, disassembled, inspected and found no issues. However when I pulled the solenoid valve the two metal rings were broken, but intact. The control valve had no issues. So I do not know if the broken rings would have had enough leakage to cause this issue. I disassembled the valve, and tested the solenoid and all checked out with no issues. I am trying to find the metal rings to reseal it with. Everyone here wants to sell us the whole solenoid valve assembly. What is your opinion on the broken rings causing this issue? I guess I will be pulling the other pumps down for inspection.