i have a JLG 26mrt that has developed a steering issue. i bought the machine and use it lightly only few times a year. the machine turned and steered perfect and then i parked the machine for 3 months. now the wheels turn right a few inches and then will turn back to center joystick and controls seem operational. seems to be a hydraulic pressure issue or a stick valve in the valve body but im not sure were to start? all other functions work perfect drive and lift. only steering seems to be affected. any ideas would be great! TIA:usa
Welcome to the forum Benbuilt4u. :usa Wait a minute, your steering does exactly what?
thanks! i hope you can help if you push the button on the joystick the wheel will turn right about 6 inches. then if you push the button to turn left it goes back to center but does not go any farther to the left. so i had someone hold the button down and put a digging bar behind the wheel and tried to help it and i got the wheel to move but it did not feel like i was helping it. more like forcing it to move. now the l had similar issue will go 6" left and then back to center. so the wheel does move back and forth with commands obviously just not nearly enough to turn!!
Hmm, that is odd. I haven't thorougly looked through the schematics of your machine, but I'm thinking there's not some wacky component that "centers" the steering. I've never seen anything like that. Can't explain how it centers itself either. Hmm. One thing I have seen so many times on those type PQ controllers is a problem with the microswitches mounted inside the controller handle that controls steering left and right. Have also seen problem with the actuator that pushes against the button on the microswitch not working proper. If it were me, I would take the handle apart on the drive joystick and work the steering microswitches individually, even check voltage outputs of switches with meter, to see how they are operating and if they are operating properly. I will warn you though, taking apart (and reassembling) that joystick handle can be somewhat of task. Patience is required.
ok will do that today. my electrical/ mechanical skills are very good, so it should be a breeze ill let you know what happens.
micro switchs all seem to be working. and im leaning toward a hydraulic issue maybe stuck valve? i also need to clarify that its not going back to perfect center it more or less only has 6 inches of movement back and forth. is there a seal in the front steer cylinder that could have gone to cause it only to have have maybe 3-6inches of movement?
Well, I can't say it's not the cylinder piston seal, but I would think if the seal was bad not allowing cylinder to move, then I would think you could have move the wheels with the pinch bar while trying to steer. Just a thought. It's a fairly simple circuit. Steer switches send voltage to solenoid coils on valve body and the solenoids send oil to the steer cylinder. The steer circuit also sends voltage to the dump valve which delivers oil pressure to the valve body. One thing you could try is locate the solenoid coils for left/right steer, remove the Deutch plug connection to one of the coils, and put a positive and negative jumper wire on the coil terminals to power up the solenoid. Then raise your platform to activate dump valve and see if the steer solenoid turns wheels in either direction. Then try same procedure on opposite steer solenoid. You could also have a problem with the crossover relief valves of the steer circuit. They are cartridge valves mounted on the control valve body. It's just kinda odd for two seperate cartridge valve to have a problem at the same time.
great ideas! going now to do this!
ok jumped power to both solenoid coils and then activated lift and it did not turn so im thinking i have a bad steer cylinder. is it rebuildable?
Yes, in most cases a cylinder can be rebuilt. You can tear into if you like. Even if that's not the problem, at least you have new seals in your cylinder, no real loss there. Another thing I would try is disconnecting a steer output hose at control valve, connect a 5000 psi gauge to that port of valve, operate steer, and see if you get any pressure. Remember, there are two crossover relief valves in that steer circuit, problem could be with them and not cylinder.
ok ill do that tomorrow thanks for your help ill let you know
ok so i pulled the steer hose and pulled the main pressure hose and tied them together basically eliminating the entire solenoid block and it will turn. so its not the cylinder. then i moved some of the soleniods around to see if i had a weak one but still the same. i also manually jumped the pressure soleniod and the steer at the same time and it wont move all the way. seems like whatever bleeds off pressure from the un-used side is not working. basically if i tell it to turn right and loosen the left line so it can bleed off the pressure it will turn. what would cause this i cant see a valve for that. TIA
Now that's interesting. Does it do the same thing if you do this turning left, crack open the right line to bleed pressure and it will turn left?
yes
Well, can't say I can give you a solution to your problem at this point, this is a rather peculiar problem. And I've looked over the hyd diagram, and I'm seeing errors on the diagram. Not the first time I've seen that on JLG diagrams. Also, see errors on component locations of hyd control valve on page 2-14 of service manual. It makes it difficult to troubleshoot something when diagrams are not accurate. :Banghead From what your describing, I think it's time to go into valve components, starting with the 4 way solenoid valve for steering. I have seen stuck spools in 4 way valves on machines before. I have also seen fragments of metal get lodged in spool chamber inside these type valves that prevent spool from shifting properly. Remove the solenoid coils off the actuator spools from both sides of the steer 4 way valve, then remove the actuator spools. Be gentle when removing these spools, I'm not certain what's in there. Sometimes might be a spring and washer, I've even seen steel balls inside these things. Just take it nice and easy when pulling the actuator spools and see what's in there. Once you get the actuator spools off, you now have access to the hyd valve spool from both sides. Using a finger on each side, the spool should move freely in both directions, and it should also freely slide out of the valve body. If you pull spool out, it's gonna dump some oil from the return circuit. If it turns out the spool is free and no obvious problem. You might try switching actuator spools with the ones on deck lift valve. I'm also seeing a restriction orifice in the ports going out of valve to steer cylinder. They could be the fittings that the hose screws on to, they could be inside the valve manifold. According to the diagram, they're inside the manifold, but I wouldn't trust that info after the errors I see. Also have the two crossover reliefs. But there is no logical way that they would be the problem if you are steering right and have to loosen the return on steer left hose to relieve the pressure. That sounds like something is blocking the return circuit on the valve. And the wierd part is it's doing the same thing in both directions. I don't think I've seen anything quite like this one.
i did switch the whole assembly from the lift to the steer and no change and also lift functioned perfectly as it did before. whats the block with one hose out of it right above the steer actuator?
That's part of the system to release the brakes in case machine is dead so you can tow it. Without being there to check this crazy problem myself, I kinda running out of ideas of what to try. :Banghead
i fixed it. left front king pin was seized in the spindle.
Yep, which would pop open crossover relief valves in both directions. Don't see that every day. Glad to hear ya got it sorted out.
thanks for your help!
i have an old trojan with a steering problem i read the thread it may be helpful figuring out my problem