I purchased a Yale GLP050 propane forklift for use around my hobby farm a couple of months ago. Havent used it a lot yet being winter here in the north but I find that after it has sat for a few days when I first start it up, the transmission clutches or the torque converter dont seem to engage when I first start it up - almost like all the oil has drained out and not pumping. If I move the shift lever between forward and reverse and rev the engine the transmission gradually starts to engage and the machine will move but does not have much drive power to move over any rough spots in the ground. After 5 or 10 minutes it seems to shift more normal and will climb a fairly steep hill in my driveway. When operating normally I do notice that when I shift into reverse the transmission engages fairly quickly and you feel it engage crisply. When shifting to forward it take and extra few seconds to engage and the engagement is softer than in reverse. Transmission oil level is normal. My first thought was that the forward and reverse clutch packs must need rebuilding but I had to do that on my Case 580D backhoe which is a similar setup with a torque converter driving a hydraulic shuttle transmission. With the backhoe it would work fine when first started and the oil was cold and more viscous but as it heated up the clutches would start to slip when pushing hard - this is the opposite - no drive when cold and works OK when hot. Could it be the torque converter ? although I thought it would behave the same - work better when oil is cold rather than better when oil heats up. Is there some problem that could cause the oil to drain out of the transmission pump circuit and lose its prime ? I see in the hydraulic schematic from the manual (see attached) there is a cold relief valve that dumps oil back to the transmission sump when open - was wondering if possibly that valve is opening too much when oil is cold so that not enough pressure gets to the transmission control valve ? I am planning to change the transmission oil soon - any thoughts on staying with regular oil or switching to full synthetic ? Some pictures of the transmission for this class of machine show an oil filter on top of the transmission and there is an oil filter listed for this model but I don't see one anywhere on mine - I have attached 3 pictures of my transmission. If no filter I guess the only thing to do would be to clean the strainer in the sump at the bottom of the transmission. Any feedback or suggestions on troubleshooting this problem will be greatly appreciated.
I think that the problem is going to be in the inching valve. If you look at the shift solenoid you can see a button on the side. Take a couple of 2x4's and tilt the mast fully back. place the 2x4's under the mast and tilt forward until the wheels come off the ground. Push the button on the solenoid and see if you get the clutch to engage. If it doesn't then I would suspect the inching valve. Also hook up a gauge and see what your pressures are doing. Its been a while since I messed with one of these but it usually is the inching valve.
Also make sure the inching pedal is returning all the way. I had a Yale G60DP that would move then it wouldn’t. Even had a forklift specialist look at it. One day I decided to clean it up real good and find the issue. I noticed the spring on the inching pedal wasn’t connected on one end. I hooked it back up and it ran perfect.
thanks for the suggestions guys. I will check the inching valve - it certainly works once the machine is warmed up and driving OK - pushing the brake pedal in a little disengages clutch and when your foot is lifted off pedal it goes into gear no problem but maybe when it is cold it behaves differently.
I had a look at the transmission valve today - the inching valve is actuated by brake hydraulic pressure from a line steel tubing teed off of the brake line to the front axle. The brake pedal is returns freely and there is a small amount of pedal travel before the rod from the brake pedal pushes on the master cylinder so I dont think there is any residual pressure pushing on the inching valve from the brake line. Of course the inching valve still might not be fully releasing if the valve is sticking. I was going to try southerman13 suggestion to raise the drive wheels and push the button on the side of the solenoid valve - got the wheels off the ground but couldn't get the button to move. I first just tried with my finger but that didnt work so I tried pushing by hand with the end of a steel rod and still couln't get any movement - I didnt try prying with something to get more leverage in case I might break something. I have attached a picture of the solenoid valve on top of the transmission showing the button I was pushing - if I dont have the right button let me know.
sorry I referred to the wrong person in my last reply - southernman13 did provide feedback on the inching valve but it was Paul Council that suggested pushing the button on the solenoid valve.
follow up to my earlier message re pushing the button on the transmission solenoid valve - I started the forklift up this morning - tried forward and reverse immediately after starting and had no drive. Button on solenoid valve would not push in. I let it sit and idle for about 15 minutes till everything was warm - pushed button again and the button was still fairly stiff but I was able to push it in - it did not engage drive and the button stayed in about halfway after pushing it. After that I tired engaging forward and reverse with shift lever and reverse engaged OK but I had no forward drive at all. Even at full throttle it did not try to move at all in forward. I was able to grab the button with a pair of pliers and pull it the rest of the way out - after that I had both forward and reverse drive. I used the lift to move a few pallets around and it ran fine in forward and reverse for about 20 minutes and then the transmission started to slip - engine would rev up OK but limited drive - I was working outside and didnt have enough drive to get it back into my shop. I shut if off for about 15 minutes and when I restarted I was able to move normally in forward and reverse - parked it back in my shop till I could investigate further. I am going to check the transmission pressures but I am having trouble finding the 3 test ports referred to in the manual I have. The picture that shows where they are supposed to be is real poor quality cant really see their location. Are they on the top or side of the transmission case ? If anyone has a better picture or diagram of their location and could post it or send to me that would be great.
It should be up top on the valve body. they will look like bolts that are securing the valve body to the transmission,but they are 1/8" npt pipe thread plugs. It sounds like your solenoid valve is sticking. I don't remember it is possible to open it up. But I would remove it and try to open it up and clean up the spool. It sounds like you are on the right track your gauges should tell the rest of the story.
Thanks foe thanks for the reply Paul, I came to the same conclusion this afternoon that the solenoid is probably sticking. I raised wheels off the ground again and when the button was pushed in it went into reverse but when I switched back to forward the button only came out part way. I shifted back and forth between reverse and forward a few more times and each time I went into forward the button would come out a little more until after the 3rd shift it was all the way out. I figured if the spool is not shifting all the way sometimes so it is still partly in neutral that would reduce the flow to the clutches and could be the cause of the loss of drive. If the spool is not moving freely that probably explains why it isnt shifting into gear when cold and is better when it warms up - the spool is probably freer when everything is warm. I cleaned the outside of the button and sprayed some WD40 on it and in the small gap between the button and the end housing of the valve. I pushed the button in while in neutral and then shifted to forward a dozen times spraying a little more WD40 ever 3rd or 4th time. When I finished the button pushed in easier and when I shifted to forward it popped back out all the way each time much so the spool must be moving a little easier. I was surprised to find that even when the forward gear is engaged and I can still push the button all the way in so it shifts to forward - harder to push because the solenoid is energize but still possible to do with one finger now that the button is freer. I was wondering if this is normal or maybe the valve coil is weak and part of the problem. Will see how this works before I get brave go inside the valve.
Now the weather is warmer I am going to try and sort out the transmission problem on my Yale forklift. To recap to date - when I first start the engine there is no response from the transmission when put in forward or reverse. After 10 minutes or so of running I start to get some movement when either gear is engaged and engine revved up. If I keep shifting back and forth and moving a bit eventually the transmission seems to engage normally. Up till now I had only used it for a short time to do a few small lifts inside my shop on concrete floor. Now that the snow is gone i did use it outside yesterday to move a few things - worked Ok for about 20 minutes and then I found the transmission started to slip quite a bit so I put it away. I dont have much experience with transmissions but it seemed to me like the transmission pump might not be pumping properly when the machine is first started. I want to check the transmission pressures but I have been unable to find the pressure test connections on the transmission valve yet - going to give it a good pressure wash this weekend and see if I can find them. In the meantime decided to pull the two hoses off the transmission oil cooler connections on the radiator and see if there was any flow in these lines when the engine is started. I started it and let it run for a couple of minutes and there was no flow out of either of the two hoses. Attached is the transmission oil flow chart from my service manual - It would be great if anyone that is more familiar with transmissions could have a look at the diagram and let me know if there should be oil flow in the transmission cooler lines when the engine is running.
Followup to last post - I ran the forklift again - little longer than last time - after a few minutes of running and shifting between forward and reverse I started to feel a little jerk as the clutches engaged - still no oil coming out of lines - the end of the line was about the level of the top of the transmission case. I revved the engine up a little and I started to get a small dribble of oil out of the one hose when it was in forward or reverse - when I shifted to neutral the oil level in the hose dropped down out of sight right away. Does that seem normal ??