Pressure on quick connects

[Woody65]

I just recently purchased a 2005 Bobcat 331 excavator. I purchased a thumb to attach to it and after getting all the hard stuff accomplished I went to connect the quick couplers and had no problem with the male fitting but cannot get the female coupler from the thumb to connect to the excavators male connect. I tried disconnecting the lines from the thumbs hyd cylinder, moved all of the joysticks and hyd levers around after shut down to try and release the back pressure to no avail. I can connect the two hoses from the thumb cylinder together. When I try to push it on it gets about 3/4 the way on and I run into back pressure. I am pushing so hard that the boom arm and dipper are moving back and forth. Any suggestions?

 

[ovrszd]

Are you saying with the hoses disconnected from the thumb cylinder it still won't couple?? If so, would have to be in the connector somehow. Are you sure your couplers are the same type?? There are variations. And some of them will not mix. Uncouple everything and look at them carefully. That would explain why they will couple into each other but will not couple to your machine.

Let us know what you come up with. Got my curiosity up for sure.

Pics of the couplers would be nice too.

 

[crackerjack222]

Shut the machine down, move the hydraulic controls back and forth to relieve the pressure in the system. Use a wrench or other blunt metal object to press on the center of the connector. Have a rag wrapped around the connector to catch any oil that squirts out. Now you should be able to make the connection.

 

[DT86]

To me it sounds like it could be a bad fitting or still have pressure on the excavator side of the connection.
Are we talking about flat faced couplers?

 

[Woody65]

The couplers are the same because the male one connects to the female one on the excavator fine.

I did the shut down move all the joysticks around to no avail.

They are flat faced couplers.

I have heard of back pressure but this seems extreme.

 

[Bladehauler]

the skid steers have a pressure relief valve built in so on shut down you turn the key all the way to the left and hold it for a few seconds to drain all the pressure, I wonder if your 331 has the same setup ?

 

[Woody65]

My son in law just came over and between the two of us pulling and pushing it went on. We really had to monkey with it but once we got both of us on it the 450lbs won the battle. The thumb works great but I have to modify the bucket a little to get it to close all the way. So much for a pin on no welding required attachment. Thanks for all your suggestions.

 

[Woody65]

the skid steers have a pressure relief valve built in so on shut down you turn the key all the way to the left and hold it for a few seconds to drain all the pressure, I wonder if your 331 has the same setup ?

You must have posted while I was outside with my son in law. I will remember that for the next time. Thanks.

 

[Cord]

That machine has pilot controls so the circuit has to be energized to relieve the pressure. That said, I often have to crack a fitting to relieve the pressure. It doesn't seem to much pressure before you can't make the connection. Sun beating on the cylinder is enough. Sometimes you can try pulling on the attachment while a second person tries to make the attachment.

 

[ovrszd]

I thought the OP originally said he had removed the connections from the cylinder?? I must have misunderstood.

Next time, and there will be a next time, loosen the hose connection at the cylinder or loosen the coupler connection from the hose and relieve the pressure. The pressure problem was evidently in your thumb cylinder rather than the machine. Flat face couplers are harder to drain pressure off without doing damage to the coupler mechanism.

I learned long ago to uncouple hot, recouple cold.

 

[MNBobcat]

You must have posted while I was outside with my son in law. I will remember that for the next time. Thanks.

A few things I have learned...

There is more to it then that. On the Bobcats, you shut the engine down and turn the key all the way to the left but you also have to wiggle the foot pedals (rock them back and forth) to actually bleed down the pressure. The key alone doesn't do it. You continue to hold the key to the left when you're wiggling the pedals.

Oh, and when connecting/disconnecting hoses when the machine has been sitting for a while its best not to first start the machine. The pressure will frequently bleed off while it sits so its usually almost always easiest to work with the hoses when the machine hasn't been run for a while.

Don't leave the bucket or attachment in the air either...that will hold pressure on the hydraulics. Set the attachment down when you shut the engine off.

 

[Woody65]

I thought the OP originally said he had removed the connections from the cylinder?? I must have misunderstood. Next time, and there will be a next time, loosen the hose connection at the cylinder or loosen the coupler connection from the hose and relieve the pressure. The pressure problem was evidently in your thumb cylinder rather than the machine. Flat face couplers are harder to drain pressure off without doing damage to the coupler mechanism. I learned long ago to uncouple hot, recouple cold.

After not being able to connect the one hose, I did remove both hoses from the thumb cylinder thinking pressure had built up in the cylinder after I connected the first hose. With both hoses connected to nothing I attempted to connect them to the machines quick connects. One hose went on as usual but the second one would not go past about halfway onto the machines quick connect. The pressure was coming from the machine.

 

[Woody65]

A few things I have learned... There is more to it then that. On the Bobcats, you shut the engine down and turn the key all the way to the left but you also have to wiggle the foot pedals (rock them back and forth) to actually bleed down the pressure. The key alone doesn't do it. You continue to hold the key to the left when you're wiggling the pedals. Oh, and when connecting/disconnecting hoses when the machine has been sitting for a while its best not to first start the machine. The pressure will frequently bleed off while it sits so its usually almost always easiest to work with the hoses when the machine hasn't been run for a while. Don't leave the bucket or attachment in the air either...that will hold pressure on the hydraulics. Set the attachment down when you shut the engine off.

I did not know about turning the key left and manipulating the pedals. I tried to just move around the joysticks. The machine was sitting for about a week with all the hydraulics on the ground. If I would have known about the key maneuver I think I would have had no problem. Thanks again for the tip.

 

[rswyan]

I just recently converted all my QD's to the skidsteer flushface type ... so brand new couplers and all appear to be of the same brand/manufacturer.

One thing I have noticed is that they seem somewhat sensitive to alignment ... get them slightly cocked and you're going to have an issue.

I can eliminate pressure as a possible cause, since this was with couplers which were not connected to anything and had never been installed.

 

[rswyan]

I just recently converted all my QD's to the skidsteer flushface type ... so brand new couplers and all appear to be of the same brand/manufacturer.

One thing I have noticed is that they seem somewhat sensitive to alignment ... get them slightly cocked and you're going to have an issue.

I can eliminate pressure as a possible cause, since this was with couplers which were not connected to anything and had never been installed.

 

[TomSeller]

Flat faced couplers are sure nice when it comes to keeping your connections clean, but without that built in relief of a skid steer, ag couplers allow simple pressure relief by tapping the male end on something. Wipe up and go.

 

[ovrszd]

After not being able to connect the one hose, I did remove both hoses from the thumb cylinder thinking pressure had built up in the cylinder after I connected the first hose. With both hoses connected to nothing I attempted to connect them to the machines quick connects. One hose went on as usual but the second one would not go past about halfway onto the machines quick connect. The pressure was coming from the machine.

Ahhhh,, got it now.

 

[ovrszd]

I did not know about turning the key left and manipulating the pedals. I tried to just move around the joysticks. The machine was sitting for about a week with all the hydraulics on the ground. If I would have known about the key maneuver I think I would have had no problem. Thanks again for the tip.

My FEL 3rd function is operated electronically. The only way to relieve tractor pressure is to shut off the tractor, then turn the key back on without starting the engine, then cycle the open/close buttons to relieve the pressure. Without that knowledge I'd have problems frequently.