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Weak final drive on cat 311B excavator

funwithfuel

Senior Member
Joined
Mar 7, 2017
Messages
5,518
Location
Will county Illinois
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Mechanic
I don't know about him, but if we're in his position I would slack the nut on the adjustment screw (of the slower motors axial pump) on the pumps control head. Insert the Allen key and give it a clockwise turn (90° at a time) ,and check how much speed it gains after every 90° turn . The machine should be boom jacked during this operation. Check the number of threads on the screw so it can be returned to normal should the operation be unsuccessful. Am guessing you don't have a flow meter.
No way would I start making pump adjustments until after I compared cycle times of every function against published specifications. We haven't been able to gauge the servo pressure applying on the spool we haven't been able to gauge the servo pressure going into or out of the foot control pedal We're just trying to narrow the guys field of view so that when he calls a technician out or if he opts to purchases gages has a better starting point then well here's the entire machine to look at. There are still too many unknown variables
 

slwbid

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Joined
Apr 20, 2012
Messages
119
Location
Trenton, ga
Thanks all.
Latiff... no I dont have as flow meter.
Does anyone have picture of these adjustment screws and allen screws you are talking about? I'm not sure where they are.
Also, I only know of one hydraulic pump on this machine. I will take a picture of it tonight.
I work on nearly everything on this excavator except the hydraulics. I'm pretty clueless about the hydraulics, except for replacing busted hoses.
 

slwbid

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Apr 20, 2012
Messages
119
Location
Trenton, ga
Additionally, if I knew what to order in the way of flow and pressure meters, I might be able to afford to do that can anyone point me to the proper meters?
Additionally, I am ver curious about the foot controls outputs and/or how to check those. For no real reason, I've always been suspicious there could be a problem there.
Thanks all.
 

slwbid

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Joined
Apr 20, 2012
Messages
119
Location
Trenton, ga
I may have indicated more ignorance about hydraulics than is warranted. I've worked with my Dad doing lots of diesel work, including complete motor rebuilds, transmissions, final drives(not hydraulic).
So I'm not afraid to turn bolts, adjust stuff, etc. I think in hydraulics, when workingvwithoutbguages, u you would want to only change a small bit at a time to make sure not blow something, test all functions ro see if problem was better orvwirse and make sure not causing some other function to degrade....and I know how to set stuff back like it was. So if I can find the adjustment bolts for the hydraulics, I'm not afraid to turn them. :)
Thanks much to all your continued help. I appreciate you guys.
 

funwithfuel

Senior Member
Joined
Mar 7, 2017
Messages
5,518
Location
Will county Illinois
Occupation
Mechanic
You dont make mechanical adjustments until you've verified your inputs are correct. You dont know that the servo pressure reaching your foot pedals is correct, subsequently dont know if servo from pedals to spool caps are correct.
Have you performed the case drain test?

Hydracheck.com is just an example of a supplier for test equipment. Figure out what test nipples you have and order accordingly. You may be able to source locally much cheaper. You'll also need break-out Ts it adds up fast.
By your pic, it looks like Parker compucheck fitting
 

heymccall

Senior Member
Joined
Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
What about putting the machine into backup mode, which sets both PRVs to a fixed value?
Put it in backup, throttle it up and see if the same side is lazy.
 

heymccall

Senior Member
Joined
Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
Go into service mode on monitor. Go to function 21.
Stall bucket dump. Observe number.
Stall stick out. Observe number.

Is they same?
 

heymccall

Senior Member
Joined
Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
Screenshot_20191010-224547_Chrome.jpg Screenshot_20191010-224046_Chrome.jpg
The number shown (x10) is the kpa of of the higher pump pressure of the two when both pumps are stroked (boom up, straight travel, etc).
The number shown (x10) is the kpa of the stroked pump when only one pump is stroked.
 

slwbid

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Joined
Apr 20, 2012
Messages
119
Location
Trenton, ga
Heymccall.
Yes they are the same for stick stall and bucket dump stall (there may have been tiny difference. They were both bouncing from about a high of 31.00 down to about 30.50
What does that tell me
 

heymccall

Senior Member
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Feb 19, 2007
Messages
5,349
Location
White Oak, Pa
That's 4500psi per pump.

Now, in same menu, stall each track at speed dial 10 in turtle (low), one at a time, and note that value.
Easiest way to stall a track is to insert a pin between the sprocket and the track frame.
 

slwbid

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Joined
Apr 20, 2012
Messages
119
Location
Trenton, ga
Heymccall
Stall tracks in turtle at 10.
When stalling a track, each side is essentially the same...right at 35 or little above.
 

slwbid

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Joined
Apr 20, 2012
Messages
119
Location
Trenton, ga
hello everyone.
I did both tests that were suggested, including the last one where I stalled tracks in turtle at 10.
When stalling a track, each side is essentially the same...right at 35 or little above.
Anyone can tell me what I should do next?
Sure appreciate all the help
Stacy
 
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