When good hydraulics go bad...

[john_bud]

Howdy,

I thought there might be some interest in seeing what is inside a hydraulic cylinder that "went bad". First off, the cylinder worked and did not leak a drop. But, it wouldn't hold a load and was sluggish. All symptoms of an internal leak.

Different cylinders come apart differently, these have a screw in gland and nut. Unscrewing with the rust, dirt, paint and junk was "fun"!

Here is a pic of the cylinder with the rod out. It's big brother in the background was too much for me to do so it went to the hydraulic shop. Even they had trouble getting it apart.

Next is the piston that seals the hydraulic juice in both directions allowing the double action to occur. This is also the bad boy that was leaking.

Exploded view of the packings

Hey, something looks bad... can you spot it, too?

Bad vee packing ring

This is the packing that keeps the fluid from shooting out by the rod, called oddly enough, rod packing. String is holding them in one piece.

Here is a pic of a finished cylinder. I kinda cheated here, this is not the one that is shown in parts... but it is the same diameter and all.

Well, that's about it. Any questions? No? Good, now you can rebuild your own cylinders. Have fun!

jb

 

[markct]

yea hydraulic cylinders realy are pretty simple inside, the thing that gets most people is the huge amount of tourque that is needed to unscrew the gland and the nut on the end of the piston. i do alot of cylinder work at my job as a mechanic at a garbage company, some of the cylinders we have needed a 10 ft pipe on a 1 inch drive breaker bar to unscrew the nut on the end of the rod, the last one i did took a 2 3/8 socket and two guys hanging on the pipe. once you get into cylinders over about 3 inch bore is when it gets into heavy tourques, but even so once thats overcome its just a simple matter of picking out the seals and making sure to put plenty of lube on the new ones. i have noticed that usualy a cylinder thats being rebuilt for the first time comes apart easier than one that has previously been rebuilt by a hyd shop, i have often suspected they tend to overtighten everything a bit with there hyd wrench table to make it more likely the average folk will have to take it back to them the next time. i have had some cylinders that took a pull from a forklift or come along on the breaker bar to unscrew them

 

[TwinWillows]

A question from someone who's never seen the actual disassembly process.. How do you hold the clyinder so as to get all that torque into the fitting? I can't picture any bench/vise resisting the turning moment created by a 10ft cheater bar much less that created by a comealong or tow motor?

 

[john_bud]

Good question!

I didn't need that much power to get mine open, but it was close! The cylinder has external fittings that can be used to resist the spin, or as I did you can put a pin into the cross tube and wedge that in the vice.

The one pictured needed me with a 3' cheater on an 18" wrench doing a squat (which picked up the workbench) while a buddy used a drift and 24 oz hammer to tap the gland nut after it had been heated with a torch. All this was after cleaning off the paint, dirt, grime and stuff from the grooves. In the pictures, the larger cylinder kicked my a-s. It was taken to the local hydraulic shop and they had trouble with it.

Cost breakdown - doing it at home is between 16 and 60 bucks depending on the cost of the seals. Large range, eh? Local hydraulic shop components are about 60, online much cheaper! The one that the hydraulic shop did was about 200 bucks. (ouch! owww owww whimper whine....) Actually, the local shop was very helpful and fixing the cylinder thru them is still cheaper than getting a new one. You get what you pay for, and that help is cheap even at the premium listed.

I got a tip that they come apart easier if they are loosened while still on the machine. I will try that next time, for sure.

Here are two places to get packing components.

Baum Hydraulics

H D distributors.

The second one you need to sign up, then when "approved" you can order.

Prices are similar with each being cheaper on some things and not others.

As a DIY project - it has been easier to do than to write up and post. (Except for the unscrewing....)

jb

 

[dfkrug]

To unscrew the nut, I put a long rod thru the pin end and
park my tractor on it. Then I take a breaker bar to the
other end.

As for overtightening, MARKCT is prob right that the shops
put too much toque on them. I suspect they use a large
pneumatic wrench (3/4 or 1" drive). Mine is only 1/2"
drive and does not cut it.

This is also a problem with the lug nuts on your tractor.
Have you ever tried removing them?

 

[Richard]

nice pics, thanks.

Different question, you said if it's not leaking and not holding a load, it has an internal leak.

What if it won't hold a load and it's been freshly repacked (by the dealer). Would it then be fair to think the valve pack might need some new seals too? (This is a JCB, 1550-B)

If the backhoe control pack (or what ever it's called) does need some new valves/seals/other... any rocket science involved there or could a reasonably intelligent backyard mechanic tackle the job?

 

[markct]

</font><font color="blue" class="small">( question from someone who's never seen the actual disassembly process.. How do you hold the clyinder so as to get all that torque into the fitting? I can't picture any bench/vise resisting the turning moment created by a 10ft cheater bar much less that created by a comealong or tow motor?
)</font>

well the short answer is with whatever is heavy and nearby, sometimes they can be held in one end of whatever it is they mount to, thats how we do the sweep cylinders on garbage trucks, other times you can often pin them to the hitch of a truck or tractor, and on some smaller ones a chain pipe vise on a heavy bench will work, or i have even welded tabs to pin the cylinder directly to my welding bench. i have also chained them to the forks of a forklift and put a bar thru to prevent them from turning. basicly just whatever is heavy and secure, most everyone has a tractor with a drawbar, or a pickup with a reciever hitch so thats usualy a good place

 

[john_bud]

Richard,

There is a way to test to see if it is the cylinder or the control valve leaking. Fully extend the cylinder in question. Unhook the hydraulic line that would retract the cylinder. Then use the control to extend the cylinder and observe the open port. If you have fluid coming out, the cylinder seals are bad. If no fluid comes out, (and the cylinder droops under load) you probably have a leak in the control valve.

You much much much prefer the cylinder to leak! Cheap and fast to repair. The control valve leaking may mean the spool and it's housing are worn or scored. They can be repaired, but that is by welding them up, machining back to size, heat treating, and chrome plating. ($$$$) I would get a repair quote and compare that to a used control valve.

Oh, the dealer repairing it may or may not mean much. The cylinder I am repacking now had a short vee stack put in. The piston bottomed out before the vee's were compressed. In fact, there was about 0.050" of visible gap between vee's and the piston. The packing was replaced at some point, but pointlessly if you know what I mean!

The new packing is also 40-50 thousanths short. I spent an hour at the local hydralic shop today getting shims ordered. Doing it right isn't always easier up front, but it pays off down the road.

I am not an expert on this, maybe an expert can chime in and correct any mis-info or clarify.

jb

 

[markct]

what may have happened is that in the past someone had the wrong seals so they machined the piston to fit, theres a local hydraulic shop thats notorious for doing this, the problem is that then next time ya go and order a kit for it the parts dont fit

 

[john_bud]

Mark,

Yeah, this old tractor has been around the block and hit every mud puddle! I got the packing installed today (not using shims as the service guy talked me out of them), the rod is easily hand rotated and moved up/down in the cylinder. Doh! I will be making some shims for it tomorrow.

Also, got the bigger 4" diameter cylinder back from the shop. My a-s is still burning from the reaming. When the counter guy told me they had trouble opening it, I didn't realize they were milking the bull all day with it at 72 an hour and charging me! They also must have thought I have "a real purdy mouth" as they hit me for full retail on the packings. Not happy with those guys at this point in time. I did a quick look up and can get the exact same parts from HD distributors for about 35% less. Needless to say, they won't get a crack at the other 4" cylinder. There is a new adjustable pin wrench on its way to my front portch in a big brown truck.

jb