CAT 301.8 stick comes slowly in on its own

[pete40]

I've had this problem for about a month now. While walking or working the machine in any way without pushing the stick outwards, it will slowly come inwards on its own. Not strong enough to go against gravity but close to it. There is obviously either some sort of bleed off, or into it, to make it do this.

Any ideas out there where to start trouble shooting this problem?

 

[Per Eriksson]

Internal leakage in the cylinder is the first thing to check.
Stick out as much as possible with a full bucket in the air and shut the machine off and listen for oil bypassing the seals in the cylinder.

 

[pete40]

Thanks per, will try that tomorrow.

 

[pete40]

What sort of sound should I hear there? Any specific type?

 

[uffex]

Good day
The attached may be helpful.
Kind regards
Uffex

 

[pete40]

Thanks uffex. I might have to check their (exatech) library a bit more. And get some plugs. Assuming it is the seals, is this something the average (bush mechanic) can do or best to take it of and let someone else fix it?

 

[pete40]

The squeal, hiss is definitely from the clyinder. It's coming in more quickly all the time now.

 

[uffex]

Good day Pete
I suggest that you also check in the opposing direction if the cylinder holds tucked into the machine seals are less likely more probable a shock valve. It is always better to absolutely sure before you start tearing down components, gambling belongs with bookmakers.
Kind regards
Uffex

 

[pete40]

Good day Pete
I suggest that you also check in the opposing direction if the cylinder holds tucked into the machine seals are less likely more probable a shock valve. It is always better to absolutely sure before you start tearing down components, gambling belongs with bookmakers.
Kind regards
Uffex

Don't quite get what you mean. You can see in the video, with engine off, it falls rapidly to a point where it wont go up hill, or in any further as that would be against gravity. It does not slowly go "out".

 

[pete40]

Good day Pete
I suggest that you also check in the opposing direction if the cylinder holds tucked into the machine seals are less likely more probable a shock valve. It is always better to absolutely sure before you start tearing down components, gambling belongs with bookmakers.
Kind regards
Uffex

At the moment if I push out on the stick, then stop, the stick will gradually come in on its own accord. If I pull in on the stick and stop, the stick continues to come in on its own, it does not travel on its own outwards.

 

[Vetech63]

Uffex is wanting you to check for drift in both directions, stick out and in. Get the stick straight down with the bucket just off the ground then pull the stick in all the way. Does it drift outwards?

 

[uffex]

Good day Pete sorry for the confusion the only way to diagnose from a distance is to use proved methods that needs you to be eyes & ears so to say. Unfortunately, I do not have a hydraulic schematic for your machine, but it is a strong possibility that the arm circuit has a creep prevention valve installed to the arm in. This would give only two possible cause's for arm in creep 1/ shock valve 2/ Cylinder seals. If the arm only creeps in one direction it is more probable you have a shock valve issue, as this is much easier to change than cylinder I suggest checking that out.
Repairing a cylinder in the bush would not be as easy as taking into a shop, sometimes taking these apart can be problematic, you can read information regarding cylinder repair at the library, often what gets overlooked is the cause in a rush to make the cure.
Keep safe
Uffex

 

[pete40]

Ok. I get it. I don't want to do work for no reason either. The arm (stick) does not travel outwards on its own. I'm not sure I have a valve. Here's the pages from my parts book. It's not shown there. If there is a valve, where would it be located? I could show the relevant page/schematic from my book.

 

[Vetech63]

Items 23 and 24 is your circuit reliefs

 

[pete40]

Items 23 and 24 is your circuit reliefs

Thanks Vetech. The way I read it, 23 and 24 are attached to the Boom valve(2). My problem is related to the Stick valve(7). This has item 20 attached either side, labelled as "Valve AS".

 

[Vetech63]

Thanks Vetech. The way I read it, 23 and 24 are attached to the Boom valve(2). My problem is related to the Stick valve(7). This has item 20 attached either side, labelled as "Valve AS".

Yeah! I had boom stuck in my brain lol

 

[uffex]

Good day Pete
The illustrated does not appear to have creep prevention valve, if you follow the lines from the arm cylinder back to the
MCV and there is nothing between, then for sure it will be just shock valve that seals the arm in. I suggest take the easy first switch the two shock valves 20. If the situation remains test the cylinder as information. If the cylinder is good it must be the main valve segment
Be sure to loose the residual pressure before you dismantle any parts.
Stay safe
Uffex

 

[Per Eriksson]

Here's my take,
If you clearly hear a whoosing sound from the cylinder and not the main valve inside the machine then it's the cylinder seals even if it isn't drifting outwards.
This is due to the fact that for the stick to drift out the stick cylinder rod has to go in and that would mean oil would have to leave through the line reliefs and that won't happen until the pressure inside is above their setting which most likely wont be reached with the stick suspeneded in the air.

 

[uffex]

Good day Per
Been in this discussion before, your theory holds good in a fluid tight system, but the design of spool valves are not fluid tight all of those leak some especially those without creep prevention valves which I guess is the case with this machine.
Kind regards
Uffex

 

[Per Eriksson]

With the stick drift rate he showed in the movie I'm fairly certain that the leakage rate around the spools are of no relevance.