Backhoe boom wants to drop when trying to raise it while bringing the stick in?

[chad22]

Hi. On my home made backhoe. It's digging great. But I have another problem that starts out after the the pump is running for a couple minutes.

When trying to bring the boom up and stick at the same time the boom wants to drop. This happens whether I have a load in the bucket or if it's empty.

I was wondering. The backhoe sat outside in the rain and the hoses to the tank were left out (uncovered) and I think water might have entered the fluid.

I never changed out the fluid and was wondering maybe "contaminated fluid" could be the cause of the boom lowering and sometimes not wanting to raise back up.

It raises better when I have the stick all the way in.

But sometimes I can't even get the boom to raise the stick out the hole. Unless I move the lever to the valve back and forth and even then it's slow.

I let it sit for 30 minutes or so and it raises right up out of the hole.

I'm going to town today and gonna pick up some fresh fluid. But thought I would post this to see what ya'll think?

And oh yeah gonna hopefully get a pressure gauge and the fittings to tie it in.

Thanks

Chad

 

[leonz]

Hello Chad,

Your problem sounds exactly like the valve spools are leaking/bypassing and its a case of replacing the valve body.

I would remove the valve body and the suspect cylinder and have reliable hydraulic shop test them for you as the labor cost would be worth the time.

 

[J_J]

Does the boom and stick circuits work using one spool at a time?

Apparently there is something taking pressure from the weaker circuit, meaning the pressure in the stick circuit may be low, and the pressure in the boom circuit be higher. If you are using both spools at the same time, release the stick spool and see if the boom stops.

I think the boom will take more pressure to get it moving.

I think that if you had a gage in the circuit, you could see what is happening.

Each spool activated will reflect the pressure on the gage.

 

[chad22]

Does the boom and stick circuits work using one spool at a time?

Yes. I can move the stick in and then just raising the boom it won't drop back down. The dropping back down just happens when operating another valve such as the "Stick valve".

But it still takes some effort to get the boom to raise back up. It will go down just fine and can even lift the hoe off the ground. But when raising it, I have to move the valve lever back and forth or operate the valve, wait a few seconds and operate it again. And it usually takes about 4 or 5 tries to get the boom fully raised.

If you are using both spools at the same time, release the stick spool and see if the boom stops.

I tried that and that's exactly what happens. The boom will stop lowering and will want to start rising. But then again it takes some effort to get it to raise back up.

I'm kinda wondering now that my pump is just too worn out. I mean it was working for a bit when I put those new seals in. But then started degrading again.

May just go ahead and order a new pump. And hopefully solve the problem.

We went to town and got the fluid. "My dad paid for it". He insisted so I let him. lol

I was gonna go ahead and change the fluid out and see if it fixes the problem, but might just wait until I get the new pump. So I know that the fluids are fresh with the new pump.

Was gonna get a pressure gauge but the stores around here are out of stock. Probably just order one when I order the pump.

Thanks

Chad

 

[chad22]

I changed the fluid out. But still nothing. This makes me sure it's the pump. I held the boom lever in the up position and it just wants to fall back down. This shows me it's not getting enough pressure.

So I think the pump is bypassing or has an internal leak somewhere.

But oh well the fluid did need changed though as it was all milky and had water in it.

I did check all the connections to ensure they were no leaks and there are none on the hose connections.

So I'll just pony up the cash and order a new pump as this backhoe is really needed this spring. Gotta dig in my water line to the trailer house, redo my parents water line from meter to house, and finish digging up and replacing a ladies sewer line.

She was just gonna try to clean it out in that one spot but decided to go ahead and fix it for good.

We did dig for awhile but didn't find the sewer line where it was marked. So were just gonna try and find it this spring. "hopefully find it" We might have the whole yard dug up. lol

Anyway I appreciate the help in diagnosing the problem. Just wish I could have gotten a pressure gauge yesterday. But I'll just order one when I order the new pump.

Chad

 

[J_J]

I would put a hyd gage on the system and test it out first.

Max out each cyl one at a time, and if they all read the same, then you could suspect the pump, or the setting on the relief valve.

One cyl could have bad seals.

Do you have a clear flow back to tank?

If you put the boom up and the spools are in neutral, that puts a block on the cyl, and if they move, the seals are leaking..

 

[chad22]

The Boom will stay up in the air as long as you don't move the valve. Also when maxing out the cylinder there seems to be no load on the engine.

The pump does seem to have great flow. But seems it's just not building up any pressure.

I've adjusted the relief valve and it just doesn't help any.

I'm gonna go ahead and put one of these DuroMax 16 Hp., 1'' Shaft, Recoil/Electric Start Engine - XP16HPE XP16HPE new engines on the backhoe, and a different pump mount as well as a cheaper pump. Then use the current engine for my old sears lawn tractor.

I was gonna go with a haldex pump like I originally had. But was looking at this one on surpluscenter. https://www.surpluscenter.com/item.asp?item=9-7767-B&catname=

I can buy the pump and mount for what northern wants for the haldex pump.

Right now the boom won't lift back up at all. It's currently sitting in my water line trench. And probably will stay there till spring. At least it'll keep someone from falling in the 5 ft deep trench. "like me" lol

Chad

 

[J_J]

Just a little curious how you adjusted the relief valve if the pump will not build up good pressure.

Did you swap the hoses around. Boom hoses to the bucket cyl, etc to check pump and valve. .

Do you have one good cyl that works. Move the hoses to different spools and check pressure.

I think I would raise the boom and bucket out of the mud and water, and place a 4 x 4 across the ditch and lay the boom, stick, bucket on it.

The 16 HP engine can power an 8 GPM pump at 3000 psi, at 3600 rpm.

 

[chad22]

Just a little curious how you adjusted the relief valve if the pump will not build up good pressure.

Well at first I thought it might be the relief valve set too low. So I played with adjusting it in an out to see if the boom would raise any better. It did help just a wee bit. But hardly any difference at all.

I forgot to mention the swing cylinder does the same thing as well and sometimes doesn't even want to move.

I have also noticed that it doesn't want to hardly curl the bucket in and out or move the stick in and out anymore. So I'm pretty sure it's the pump that's the culprit.


I don't remember if I mentioned this or not. Sorry if I have. But the boom suddenly started lowering when the lever is in the raise position.

Instead of raising like it's supposed too it it goes the opposite direction. (down) lol

So basically when trying to raise the boom it wants to lower down.

But now thinking about it. Wouldn't that be something to do with the valve? In a way it sounds like the valve is bypassing fluid when the lever is moved. Cause shouldn't it just stay up and continue to move or not move at all. Even if the pressure in the pump is weak?

Once the weather clears, I'll try switching hoses around too see if it helps any. I've ordered a pressure gauge so hopefully it will be here soon and I can get the pressure reading.

As to the bucket and stick in the hole. I think I will move it out of there. If I have too. I'll slowly lift it out with the tow truck. Probably do that tomorrow

Chad

 

[J_J]

It might be that the down pressure on the boom cyl could generate more pressure than your pump, and the fluid from the cyl would flow out.

I should ask if the boom cyl is on top or bottom of the boom.