Hi all I’m having problems with my D6t blade slowly creeping down when the joystick is in the neutral position blade drops from fully raised to ground in around 2 minutes also the rippers slowly drop down probably 2 inches and hour. The machine is a pilot control valve setup s/n WFH00351. Any advice would be greatly appreciated thanks
How many total hours on the tractor.? Do you have an infra-red heat gun available.?
It’s got 19,000 hours machine was rebuilt 5000hrs ago. Yeah I do have a infa-red temp gun
You need the hydraulic system cold to do this. Try raising the blade (or ripper it makes no difference) until the cylinders stop moving. Continue to hold the control in the raise position while an assistant points the IR temp gun first at the area of the cylinder where the piston is (top end of the barrel), then moves downwards away from the piston. Can you detect an increase in temperature of the cylinder barrel between the piston location and further down.?
@Nige I gotta ask but is that a way of determining cylinder bypass? I assume you're looking for hotspots from oil squirting around seals?
Ok thanks nige I’ll give that a try and report back thank you.
It is, but it only really works (or at lesst the temp difference shows up better) when the hydraulic oil is relatively cold.
Update on the cylinder drift. The blade cylinders on your 6T have piston bypass valves, so the test will not work on them because when the piston gets to the end of its stroke the oil will bypass as soon as the valve opens. Has the blade cylinder drift slowly got worse over time or did it appear literally overnight.? The test will work on the ripper cylinders though.
It’s looking like a piston sealing issue to me.
If the machine was rebuilt 5k hours ago I would be interested to hear if the seals used in the cylinder were OEM or "will-fit", although TBH 5k hours on a set of dozer blade lift cylinders isn't bad.
I have had those piston reliefs hang up or separate before causing drift also, sometimes destroying the cylinder. I would think you could do a 2 person operation by holding the blade lift cylinders in position halfway and listen for a oil bypass. The ripper cylinders I assume have lock valves or are piped through a lock valve set up. 90% of the time on ripper cylinder drift I have run across has been piston seal leakage.
Same here. TBH I had completely forgotten that the D6T blade lift cylinders were equipped with them. See #5. I should've checked before posting last night.
Hi there the blade cylinder drift really just appeared overnight working in some fairly rocky conditions. would it be best to just strip the cylinder down and have a look ?
Maybe. But I wonder if you could raise the blade up, maybe half way, and hold it with another machine, then cap off the bottom line on each cylinder. Let go of the blade and see what happens. If it drifts down with a capped line, you know you have bypass on each cylinder as you've isolated the cylinder from the rest of the system. I'm not familiar with these hydraulics so no idea if that'll work but trying to give you a way to definitively answer what the problem is before you randomly throw parts and effort at it.
Is it just one blade lift cylinder or both.? Your OP gave the impression it was both. I was thinking of raising the blade cylinders halfway up, then hooking a chain block on to the back side of the blade. Then remove the lines feeding the rod end of the lift cylinders and cap the port on each one. Then lower the chain block until the weight of the blade is again on the cylinders. If the cylinders continue to drift under those circumstances then they are coming off, because either the piston seals or the piston relief valves are leaking. I wouldn't go to the effort of removing cylinders unless I knew for sure there was something wrong inside tem.
Hi nige it is both of the lift cylinder's the blade will drop from fully raised to ground level in around 2 minutes. I’ll try and get some caps tomorrow for the cylinder ports.
Hi there guys after caping cylinders and still having the blade drop slightly we decided to open up the cylinders and found small pieces of metal imbedded in the seals an one of the barrels has some score marks in it so looks like the cylinder barrel will need replacing.
Nothing missing from either of the pistons, or anything else in the cylinders for that matter.? If the answer is no, look in the quick drop valve under the tin cover on the top of the hood. It's the next component in line beyond the blade cylinders. Don't go firing it up again until you find where the metal came from.
Hi Nige pistons are both in great condition. I’m going to start pulling lines and cleaning everything. Is there any common cause of this issue that you could think of. And would you know if there is an option for oversized seal kits for the lift cylinder? Thanks
Not really. Every failure tends to be different. I suppose it now throws the “overhaul 5k hours ago” in the picture. First question I would think is what was replaced in the hydraulic system vs what was not. 2nd question would be were the parts used OEM or aftermarket.? Pull the hydraulic filter and do a cut of the media. If you’ve never done it before there are videos on YouTube showing how it’s done. Post photos of everything you find. It will give an idea of how much debris is floating around in the system and how big your cleanup job is going to be. Offhand no. I’ll have to look. TBH if you have gouges in the walls of the cylinder barrel honing is probably not going to clean them up within permitted limits The largest oversize for honing and seals to fit is only 0.030”. Did you look very closely at those piston bypass valves to eliminate the possibility that the metal came from there.? Post some photos of what you found.
What is the possibility that what you are seeing is contamination from a previous failure?
Always possible. @Jbc92 - have there been any repairs to the implement hydraulic system recently.? By recently probably within the last 6-12 months.? I guess it depends how many hours the tractor has clocked in that time.
Here's a link to the best VIDEO I know of regarding cutting/inspecting a filter. Yes I know it's an engine oil filter but the principle is the same.
Nearly all the metal appears to be in the left cylinder stuck to the seals very little pieces in the right cylinder hydraulic filter has very little metal in it. View attachment IMG_4061.jpeg
I'd be having a very close look at the bypass valve in the piston on that lift cylinder.
Hi guys there is history of the left rod being replaced around 12 months ago maybe something was missed when they were in there. What is the process for removing the bypass valve I’m assuming just unscrew it?
Yeah, they missed cleaning the system well enough. The lift cylinders are tied together................so they can cross contaminate. You and your guys have a lot of clean-up to do to prevent another failure soon.
Ha. The thick plottens….. They are pressed in. Personally I’ve never been able to get one out without destroying both it and the piston.
If the cleanup now isn’t done right you’ll be looking at another failure in a few months.
Hey guys thanks I have a couple of new lift cylinders coming in for the machine. How would you guys recommend cleaning the system I have pulled most of the lines so far would you recommend opening and cleaning the valve block assembly?
If you want to do it right everything has to come apart. Pump, cooler, control valves, right back as far as the ripper cylinders. Plus every hose in the system will need to be sponge gunned.