Mobilewrench
Senior Member
Serial number (provided by customer. No tag on machine). 94N02917.
As the title says, the complaint was that the blade would lower but not raise.
I tend to shy away from this older stuff because I prefer to only work on machines that people actually use to make money, you know... Production machines. I also shy away from customers trying to use 50 year old machines to make money. So, I am a bit ignorant about these hydraulic systems.
But a friend asked me to look at it so I did.
My friend has a g series d7. So he already knows more about this than I do.
When I finally shoehorned a bit of time to look at it, it turns out that they were able to lift the blade and turn the machine around... So it seems to be an intermittent problem or a cold vs hot oil problem.
His theory was oil bypassing the piston seals so he had the actual owner buy seal kits for me to change.
Personally, I never rely on someone else's diagnostics. And rely even less on customers providing parts.
So, anyway, rolled up and met my friend on the job site the other day and decided to do a few checks on the machine before starting to tear things apart. (Please remember that I am pretty ignorant when it comes to this vintage of machine)
Since everything was working when I got there, had him do a few cycle times on the blade lift circuit. A few raise and stop and lower and stop cycles on the circuit to see if there was drift or failure in the lift function.
Also had him blade down to raise the front of the machine off the ground to try to determine if the cylinders were actually bypassing.
This is maybe about fifteen minutes in operation, so I assume we are close enough to operation temperature. There is no drift, machine is rock steady with weight on blade.
This is where things go a little side ways.
I have him lift the blade and hold it against relief. Then lower the blade a little. Now I have drift. Lower it more; no drift. Lower it more; drift.. So, tracks are back on the ground now. I tell him to raise the blade again. Blade will not raise. Just a tiny jerk and that is only the slop in the pins.
This is where my ignorance is blinding me.
In my mind a low power circuit on a cat is either a resolver issue or a pump not stroking issue. So I ask him to raise the ripper and hold it against relief to stroke the pump and the try the blade raise.
This is where things get confusing.
He holds the ripper up against relief. He tries to raise the blade.
The blade goes down and lifts the front of the machine off the ground until this hydraulic line blows.
As the title says, the complaint was that the blade would lower but not raise.
I tend to shy away from this older stuff because I prefer to only work on machines that people actually use to make money, you know... Production machines. I also shy away from customers trying to use 50 year old machines to make money. So, I am a bit ignorant about these hydraulic systems.
But a friend asked me to look at it so I did.
My friend has a g series d7. So he already knows more about this than I do.
When I finally shoehorned a bit of time to look at it, it turns out that they were able to lift the blade and turn the machine around... So it seems to be an intermittent problem or a cold vs hot oil problem.
His theory was oil bypassing the piston seals so he had the actual owner buy seal kits for me to change.
Personally, I never rely on someone else's diagnostics. And rely even less on customers providing parts.
So, anyway, rolled up and met my friend on the job site the other day and decided to do a few checks on the machine before starting to tear things apart. (Please remember that I am pretty ignorant when it comes to this vintage of machine)
Since everything was working when I got there, had him do a few cycle times on the blade lift circuit. A few raise and stop and lower and stop cycles on the circuit to see if there was drift or failure in the lift function.
Also had him blade down to raise the front of the machine off the ground to try to determine if the cylinders were actually bypassing.
This is maybe about fifteen minutes in operation, so I assume we are close enough to operation temperature. There is no drift, machine is rock steady with weight on blade.
This is where things go a little side ways.
I have him lift the blade and hold it against relief. Then lower the blade a little. Now I have drift. Lower it more; no drift. Lower it more; drift.. So, tracks are back on the ground now. I tell him to raise the blade again. Blade will not raise. Just a tiny jerk and that is only the slop in the pins.
This is where my ignorance is blinding me.
In my mind a low power circuit on a cat is either a resolver issue or a pump not stroking issue. So I ask him to raise the ripper and hold it against relief to stroke the pump and the try the blade raise.
This is where things get confusing.
He holds the ripper up against relief. He tries to raise the blade.
The blade goes down and lifts the front of the machine off the ground until this hydraulic line blows.
