Hydraulic Cylinder Replacement

[BenTh]

I ordered a replacement hydraulic cylinder today from PT for $120. Also ordered 4 seal kits for the other cylinders at $12 each.

While I take JJ's point about not fixing stuff until it is broken, I'm thinking that rebuilding the cylinders comes under the header 'preventive maintenence' since this is an old machine. Last thing I'd want happening is another cylinder jamming, especially as all the other hydraulic actions have two cylinders controlling them. If one cylinder jams and the other is still actuating, I might get stuff bending that I don't want bending! Refurbishing this machine may end up being a winter project.

Sedgewood: Thanks for the tip regarding the hose fitting. It would be unpleasant to find that out the hard way!

 

[BenTh]

Well I received the new hydraulic cylinder today, along with the rebuild kits from PT. The rebuild kits are basically seal kits with replacement seals for the cylinders. It turns out that all of the cylinders have the same seal kit (at least on my PT 1418.) So, I have some rainy day projects rebuilding the other cylinders. After that I'll probably start going through the rest of the mechanicals to make sure that they're solid.

Question regarding connecting up a new or rebuilt cylinder: What do you do about air in the lines or in the cylinder for that matter? Do the gear pumps and cylinders push out the air naturally into the resevoir as you work them or is there a recommended procedure for bleeding them?

Thanks,

Ben

 

[davesisk]

Good deal, Ben. I don't know how you'd check the rest of the cylinders for a loose piston nut short of taking them all apart and visually examining the rod and piston (and at that point, you might as well install the new seals).

You don't have to bleed any of the cylinders or anything else on the pressure side of the pumps...they will push the air out of the lines and into the reservoir. Just install the hoses and work the tilt operation on the joystick a few times...they'll fill right up. The only thing you ever have to bleed is the suction side of the tram pump (the side coming from the bottom of the reservoir and through the filter). You would normally have to bleed the gear pumps I think, but to my understanding the tram pump supplies charge pressure to the tandem gear pumps, so air gets pushed through them quickly without doing any damage.

Good luck,
Dave

 

[J_J]

Try this. if you install new or rebuild your cylinders. Connect the two bottom lines on the lift cylinders. start the machine, and raise the arms. This will fill the backside of the cyl. With the arms still up, connect the top lines, and when you lower the arms, the top part of the cyl will fill with fluid. With the tilt cylinder, push the cylinder all the way in, and connect the bottom line. Activate the tilt, and extend the cyl. then connect the top line. Then, work the lift and tilt cylinders through several cycles. I think most all the air will then be removed. If it feels spongy, you still have air in the system.

 

[BenTh]

Dave, JJ, thanks for the info.

JJ, sounds like your technique is a good way to get started. That should take most of the air out of the cylinders. I assume what little remains will work out on its own.

You mentioned that you'd rebuilt cylinders in the past. Any tips on doing the rebuild? I assume that you want to make sure that seals are all prelubed during assembly with at least the hydraulic oil. I believe you also mentioned using Lock nut fluid on the threads. Is this the same as Loctite?

Dave: As far as loose nuts go, I'll find that out during the rebuild. What I'd like to do is work through rebuilding the remaining cylinders given that they're 15 years old and it's probably about time for them to get rebuilt if they're going to continue working reliably for the years to come. Plus, that first failure was scary, having hydraulic cylinders pushing against each other with only bendable metal in between sends chills up my spine. I figure I got lucky this time with only a small bend, probably inconsequential bend in the pivot arm.

Ben

 

[J_J]

Locktite is the word I was looking for. Again, I would not tear a cylinder down just to rebuild it, but if you have to, secure a clean working area. Drain all the fluid from the cyl. Take of the end cap of the cyl with a large pipe wrench. Pull the rod and piston out. You should see, starting at the threaded end. A nut that holds the piston on the shaft, a piston with 2 or 3 o-rings, and the end cap that has a seal and a wiper. take the end nut off, slide the piston off, and slide the shaft out, Do the end cap first, it has a seal and a wiper.
Lubricate all parts with oil, and replace the parts one for one. The wiper has to go in a specific direction. As you take the wiper off, notice the direction of the lip on the wiper, and replace it the same way. slide the rod through the end cap and then slide the piston on and use Locktite on the nut. After replacing all the seals and o-rings, lube everything good and insert the rod asembly in the barrel of the cyl and tighten end cap.

To get the o-rings off, do not use anything metal, use a strong piece of pointed plastic, so as to not leave burrs on the piston.

 

[BenTh]

JJ, Thanks for the pointers...especially about the piston. It wouldn't be hard to take that off without noticing that it wasn't symmetric and then wondering only later, "which way did that thing go on?"

I'd like to push you further on the rebuild issue. That is, if you wouldn't mind, could you elaborate on the </font><font color="blue" class="small">( I would not tear a cylinder down just to rebuild it )</font> comment.

The reason I ask is that it doesn't seem unreasonable to me to rebuild something like this to extend its service life, being that it is so old. I don't have any way to check its condition other than taking it apart (as far as I know and I'm new to hydraulics in general), and if I take it apart, I might as well put in the new seals. And, of course, my overall goal is to try to make sure the cylinders are all in good condition and not have another issue with them. Chances are that if I'd caught the issue with this cylinder before it had happened, I wouldn't have had to replace it.

As I said, I am new to hydraulics so I wouldn't be surprised if I am missing something, and would appreciate your comments.

Regards,

Ben

 

[Gravy]

Ben,

FWIW, I don't think it's unreasonable to do preventative maintenance overhauls to your cylinders in the off season. The parts cost isn't totally outrageous, and I think it's better to learn this stuff during the doldrums, rather than when you're in the middle of a job.

While "don't fix it if it ain't broke" makes sense, so does "a stitch in time saves nine". We all have to figure out what balance between the two makes sense for our individual situation.

Good luck, and have fun!

Gravy

 

[J_J]

If you are prone to do preventive maintenance on things, then it would be natural for you to do the cylinders. For most people, if it is working ok, leave it alone. There are only a couple of people on this forum that has had to rebuild a cylinder. An analogy might be, because one tire goes flat, would you break down all the tires to look inside. For the
most part, preventive maintenance is done on things for safety reasons or on parts that are prone to break down.

Consider this, that after rebuilding, it might start leaking, whereas, it didn't leak before. A few on this forum has replaced all the hoses. I only replace when I see a problem.

Hydraulics work very well unless abused. Filtration is the best preventive maintenance one can do.

I am thinking is your case, the nut somehow worked itself loose and caused that problem. I have known this to have happen before, on other hyd cyl , but yours is the first for the PT that I know of.

 

[BenTh]

JJ, Gravy: Thanks for your comments and insights.

When I bought this tractor, I knew it was going to need some work. When I bought the tractor, Dave and I had a difference of opinion on what state the tractor was in. When I looked at the tractor, I saw a project. When Dave looked at it, he saw a refurbished tractor, ready to go. That's why I wouldn't pay top dollar for it (though some may say I did!)

While one busted cylinder doesn't make me right and Dave wrong, I'm approaching this as a project, to get the tractor back to the point where I, myself, see this as a refurbished tractor, meaning, almost as good as new. To that end, I'll probably end up doing a lot of unecessary work. That way I can paint it if I wish and know that it both looks good and IS good.

So, raise bayonets...Charge!!!
(And let's hope that I have more luck than the Light Brigade /forums/images/graemlins/smile.gif )

Ben