Cat 416b backhoe

[bennett]

Good day looking for advice on a 1993 cat backhoe, the front bucket won't lift have removed all valves to check for blown orings, they all look good could someone help me with finding the cause because at this point im stumped at this one,

I found if I give e it fuel it would lift half way and stay in natural, but only for a few attemps Then it just started dropping if I didn't hold back on the leaver, then at one point the leaver stuck in lift mode, Have had no luck in fi ding the issue with the lift valve

 

[Nige]

Have you checked whether the lift cylinders are bypassing oil around the piston.?

Do the bucket tilt and all the backhoe functions operate correctly.?

 

[bennett]

Yes have checked the cylinders seam to be good,

Also yes all other functions work fine bucket tilt and backhoe, have the hydraulic valve off now and checked the two lower valves and i notices one of them had a lot more play on the check valve, would that make a difference?

 

[Nige]

Yes have checked the cylinders seam to be good,

Not exactly a vote of confidence. You need to know for sure that the cylinders are not bypassing before turning your attention to the control valve. How exactly did you check them.?

have the hydraulic valve off now and checked the two lower valves and i notices one of them had a lot more play on the check valve,

Can you post some photos of what you are looking at.

 

[bennett]

Yes im sure the cylinders are working fine e no blow by, I will post pictures tomorrow when I get a chance

 

[Nige]

If you attempt to operate any other hydraulic function on the machine at the same time as the bucket does it work normally.?

 

[bennett]

No it dont the only way I can get it to lift half way is by having the rpm up

 

[Nige]

No it dont the only way I can get it to lift half way is by having the rpm up

my money is on failed piston seals in the lift cylinders.

 

[Simon C]

my money is on failed piston seals in the lift cylinders.

Sometimes the extra flow with the engine revved up will lift it, but has a proper leak by-pass test been done with the engine fully revved and lever pulled back to force oil to leak if there is a problem.
Post a picture of your cylinders and explain how you tested it.
Simon C

 

[bennett]

Yes with the engine fully reved up when you pull back the leaver to lift it would lift half way but you could hear the oil bypassing back to the valve with the leaver all the way back, I didn't test the cylinders my self the were done by another mechanic and he said they were fine,

 

[bennett]

I have also check the cylinders my self before thers was no obvious signs of any oil leaking from the cylinder they was complete dry and clean, to my knowledge if oil was leaking from the cylinder you would have leaking oil sign from the cylinder, would i be wrong there

 

[bennett]

From what I have checked if you look at the diagram # 17 the spring on both the lift and tilt when I pull the valve they both have no pressure on them when I put the plug back in now not sure but I am wondering if the spring has collapsed and the valves not working right.

 

[HarleyHappy]

Just because the cylinders aren’t leaking externally, doesn’t mean the cylinders aren’t leaking internally.
Therefore, if you were trying to lift and had to increase RPM’s and fluid was leaking by a single or both pistons, you would create head pressure.
Probably stopping them halfway up.
You can look on here how to check the cylinders but the easiest and fastest way is to disconnect the top hydraulic line on either side and see if oil is blowing past the piston.
I believe this should be done first on both sides before doing anything else.

 

[bennett]

Yes I have messaged the guy checking them he he's let me know the ones he checked is fine and checking the other one now to confirm both are working

 

[Simon C]

Yes with the engine fully reved up when you pull back the leaver to lift it would lift half way but you could hear the oil bypassing back to the valve with the leaver all the way back, I didn't test the cylinders my self the were done by another mechanic and he said they were fine,

A cylinder by-passing does not have to leak 1 drop of oil out but can bypass 2 gallons in only 3 seconds if bad enough. Need to do as Harley Happy said and post a picture of it in case you have got something wrong. As Nige said betting your cylinders are gone. And even if only one is gone most times the second will blow right away after or not long after.
Simon C

 

[bennett]

Good day, have had the cylinders rechecked and the guy says that they are good did the presure test on them he said and are good,


So back to the valve banks for the lift loader have checked all seals and seam fine just replaced orings in the lift leaver to make sure but the check valves orings seam fine but there's a lot of play in one at the top with the one oring dont think that suspose to be that way, Also in the pics I have the top valve banks off one has presure on it when taking out the plug but the others have no presure downward on the spring been trying to upload some pics but it won't let me will try later to get some pics on here

 

[Nige]

Whenever digging into one of those valve sections I would always suggest to replace all the O-Rings and backup rings that are fitted on the shuttle valves #22 & 23. There must be about a dozen of them all told.

Also check that the ball inside the shuttle valve #23 is free to move (it should rattle when you shake the valve) and the ball #24 should be perfectly round and undamaged.

I’ll see if I can come up with a spec for the spring #17.

While you’re at it tell us a little more about how the problem came about. Did it literally go from good to bad overnight or did it get slowly worse over time.?

 

[bennett]

 

[bennett]

Ok so wondering about that the valve #23 one has a little play and can hear the ball the other has nothing and sticking g when shaking, and for the other orings was at cat today to get them and like always they have nothing in stock, I do have both check valves on order and plan on replacing them with new just because I dont trust the ones I took out,

and has for the issue it happend right away no warning at all went in to lift some fill and was doing nothing unless I give it full fuel, Thats what stumped me it was strange but like all hydraulics some ti.es you could chase it for weeks to find the problem.

 

[bennett]

Good day, Just want to give an update on the issue with cat backhoe and how the fix went, so has i mentioned the bucket would only lift half way with full throttle, removed valve body replaced all orings most were still good, the culprit though was this valve, now you say the orings are good and yes they were it sa ceased so the tip had no play and the bearing would not move. So replaced with new and working fine again.