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Cat 420D Backhoe S/N FDP 8867. Signal oil pressure is 250…

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Cat 420D Backhoe S/N...

Cat 420D Backhoe S/N FDP 8867. Signal oil pressure is 250 psi. Everything is creap slow Have removed and checked valves - resolvers - components with factory manual. R & R pump including pump components. Pump appears to not be stroking. We have checked signal network from one end to the other. No improvement to signal pressure at all. The pump appears to be unable to generate minimum signal pressure. Do you have any suggestions?

Mechanic's Assistant: What is the complete model and serial number of your machine?

Caterpillar 420 D Loader ? Backhoe. Serial Number FDP 8867.

Mechanic's Assistant: Sometimes things that you think will be really complicated end up being easy to fix. The Heavy Equipment Mechanic I'm going to connect you with knows all the tricks and shortcuts.

What is fee? I'm doing this for my son.

Mechanic's Assistant: You just pay a $5 deposit now and the rest only when you get a reply from the Heavy Equipment Mechanic. All of this is 100% satisfaction guaranteed, so you can get a refund if you're not happy for any reason. Anything else you want the equipment mechanic to know before I connect you?

No. Thanks.

Submitted: 7 months ago.Category: Construction and Road Equipment
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Answered in 3 hours by:
10/1/2017
Mechanic: catmastertech, Technician replied 7 months ago
catmastertech
catmastertech, Technician
Category: Construction and Road Equipment
Satisfied Customers: 2,495
Experience: Field service technician for CAT 19 years.
Verified

Hello,

Did you Replace the pump with a new one?

Did you reseal the resolvers in the loader valve including the one in the inlet section?

Did you check the flow regulator valve of the inlet section by disassembling it?

How many hours are on this machine?

How is the steering?

Do you get any response when you use two functions?

Do you have pilot pressure?

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Customer reply replied 7 months ago
Pump has not been replaced. Upon disassembly and inspection internal components looked really good. Resolver balls and seals have been replaced. This was done while various valves were removed for disassembly and inspection. The flow valve was also disassembled and components inspected. The hours showing on the meter are 4224 hours. The steering is as slow as everything else. My son and I have tried every combination you might imagine and the are no increase in function speed or signal pressure increase. The manual does not make any reference to pilot oil pressure. This is the term I am used to instead of signal oil. The loader valve is mechanical and the backhoe valve is pilot operated if it makes any difference. We have a good many hours working on this tractor. My son was a Cat tech on the road foir about 14 years and I have been fighting this iron over 50 years myself. This inquire is all my doing. Sometimes a new direction is needed. At this point I believe that pump will have to be replaced to increase the signal pressure. If there is a way to establish that need before all that money is spent, I would feel better. Thanks for your help. LFK
Mechanic: catmastertech, Technician replied 7 months ago

I stay out on the road mostly too and like most techs, we don't have many issues with the 420D that has not already been updated and fixed in the past.

One issue I understand was present but, not reported much was the pump swash plate bearing retaining screw backing out and jamming the swash plate. This became a big issue on the E model but, a few D models also used this same pump. If your pump had the half shell bearings (like the main bearing set) this would have the retaining screw. Since you inspected the pump, I assume this was checked.

One issue I had recently was debris in the loader inlet flow control relief valve. Since you have already inspected this too, I am not sure of which way to point you. Try turning off the pilot control and also try blocking the line to the loader quick coupler if you have one.

The pilot pressure for the rear joysticks appeared to be connected to the load signal in one of the manuals I was reading but, it is not shown in the schematics. This may just be a typo and not related to your machine.

You have done everything I can think of and I also research for newer service magazines about this and I did not find anything.

I will OPT-OUT of the question so others can see it and maybe they have had this issue in the past and can help you better.

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Mechanic: Dan, Technician replied 7 months ago
Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 6,721
Experience: 17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
Verified

Hi Lee, My name is***** you still need further help with this? I was field service for Cat as well in the past but currently independent.

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Mechanic: Dan, Technician replied 7 months ago

Hi, Did you get this resolved?

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