Broke by Model 48 Backhoe

[MMH]

I have a 4500 tractor & a Model 48 backhoe. The backhoe has seen allot of heavy use but is was doing some very light work today. My son was operating it and heard a 'pop' right after he dumped a bucket of dirt and started to swing the boom back towards the hole. After the 'pop' the swing would not work in either direction. In addition, the boom in place (in the swing direction). The tractor back end was uphill & gravity would cause the boom to swing sideways. We could push the boom by hand to center as well.

My guess is that one of the cylinders blew, but want to make sure that it is not the valve or something else. What is the best way to check it out?

 

[beenthere]

With a pressure gauge maybe?

 

[sisupower]

I have rebuilt those valve stacks several times. But could be a cylinder

 

[sisupower]

You will be able to push the backhoe around by hand cause the way the valve stack is. Look under valve stack. Should be some cups under these for each valve. Are any of them leaking?

 

[MMH]

You will be able to push the backhoe around by hand cause the way the valve stack is. Look under valve stack. Should be some cups under these for each valve. Are any of them leaking?

I would assume that the valve stack is directly under the levers - correct?

 

[sisupower]

I would assume that the valve stack is directly under the levers - correct?

Yes it is. Probably have to remove a cover to see it

 

[texasranger556]

Are you getting any sort of response when the swing lever is held all the way left or right? Hydraulic relief valve squeal? I would think if something in the swing cylinders broke, you would most likely get an oil leak in addition to delayed motion. The spool valve or linkage coming apart seems most likely.

 

[MMH]

Yes it is. Probably have to remove a cover to see it

Removed cover and plate that has the swing bumpers on it. The valve stack as six valves and a 'feeder' body where fluid from the pump comes in. The suspect valve is in the middle of the stack. Do I have to remove the entire valve stack before pulling the individual valve bodies apart? It looks like there are two long thru bolts holding all the valve bodies together. Is it a matter of removing these bolts and pulling the individual bodies apart?

If anyone has a service manual or additional advice, it would be much appreciated.

 

[sisupower]

Removed cover and plate that has the swing bumpers on it. The valve stack as six valves and a 'feeder' body where fluid from the pump comes in. The suspect valve is in the middle of the stack. Do I have to remove the entire valve stack before pulling the individual valve bodies apart? It looks like there are two long thru bolts holding all the valve bodies together. Is it a matter of removing these bolts and pulling the individual bodies apart?

If anyone has a service manual or additional advice, it would be much appreciated.

Yea I remove the valve stack and put it in a bench to pull apart. Remove the through bolts and it comes apart section by section. Mark all you hoses good for easy of installing back. Take pictures of the way hoses are routed.

 

[texasranger556]

Perhaps stating the obvious, but the linkage is all attached and working? Any fluid leaks?

 

[MMH]

Perhaps stating the obvious, but the linkage is all attached and working? Any fluid leaks?

No fluid leaks and all linkages OK. Not stating the obvious at all. I would be embarrassed to admit how many times I did things the hard way because I overlooked the obvious.

 

[texasranger556]

Before pulling the valve out, I'd pull a line off at a swing cylinder or the output of the valve to verify the valve is at fault.

Sisupower sounds like he's dealt with a similar problem before so you're probably headed in the right direction if you already started pulling the valve.

 

[MMH]

it was a broken cylinder. The nut that holds the piston to the rod totally backed off and then the piston came off. Actually the nut backed off until it was only on by two threads which then sheared. There was plenty of blue loctite on the threads so either the nut was not properly torqued, or oil/grease was still on the threads when the loctite was put on. I cleaned up the ends of the threads & chased them. All other parts (seals, piston, etc.) seem OK. So I am going to reassemble & assume that all will be OK. Even if it is not, I have nothing to lose - no parts just my time. I will properly degrease, apply loctite liberally, and torque the s**t out of it!

 

[sisupower]

Good!!

 

[texasranger556]

I guess that makes sense, the oil would have a direct path through the center of the piston so no restrictions at all.

On my loader one of the bucket cylinders was leaking and allowing the bucket to dump by itself in about 20 seconds. Since both cylinders are tee'd, it's not obvious which was leaking. If you dump the bucket all the way, disconnect the retract hose on the right cylinder (or left, up to you), then with the tractor running try dumping slowly. If oil comes out the hose, it's the left cylinder, if it comes out the cylinder port it is the right cylinder that needs rebuilt. Could use a similar method to troubleshoot parallel swing cylinders.

Glad you found the problem!