420 D Cat tlb not much bucket flow

[Bruce O]

Hi folks,

Friend got a 420 D Cat tlb, probably had dubious maintenance, rubbed the tires bald but bucket pins not loose, bucket arms not beaten. Front bucket arms move really slow going up. Same with bucket roll. Backhoe and outriggers same slow speed. Plenty of oil in the sight gauge. I'll be helping when I can. I would like advice on pressure check ports, blown filter or plugged inlet screen checking.

Specs describe a variable flow swashplate pump, closed center valve, and I'm somewhat familiar except this model's quirks. Is there a check for swashplate movement?

Bruce

 

[Nige]

If you operate another hydraulic function at the same time as the bucket raise function does it speed up.?

 

[Bruce O]

My episode operating this tlb is an interesting episode worth another story. (We were safe and just loading a junk pickup on a trailer)

A couple times as I tried lifting and curling the bucket at the same time under a several hundred pound load, if I recall the front bucket dipped when the curl back pulled. But the the dead pickup no brakes and tlb no brakes, everything was so snaky it may have had a couple dynamics going on.

And the all the hydraulics so slow is hard to see behavior.

 

[Nige]

And the all the hydraulics so slow is hard to see behavior.

Sounds like some testing is in order. Post a Serial Number.

 

[Bruce O]

Thank you, Nige. I did some homework, found some function and repair manuals you posted for similar symptoms. The resolver needs to be resolved....

Previous career started in field service/ tech writer for mobile crane/excavator gear pumps/open center valve. Routing flow between cylinder rod-end to head-end, shuttle check valve for pressure priority, pilot circuits, and locking oil in on a crane boom (pressure release) made some interesting writing and circuit troubleshooting.

Finished career with axial swashplate for high speed servovalve servo-hydraulics, but my job was system operations training for judging system performance.

Just a couple weeks into retirement and I'm right back in, this time trying to describe why the "resolver" circuit is there (what it is supposed to do) That helps keep interested in following the check valve circuits. Terminology is ambiguous and read some manuals back to front.

Bruce

 

[Nige]

I did some homework, found some function and repair manuals you posted for similar symptoms. The resolver needs to be resolved....

That was where my earlier question was headed.
If you need any machine-specific information just ask. All it needs is a S/No.

 

[pittsburgh cat man]

Did you find the resolver chart?

 

[Bruce O]

Yes, I saw a couple hydraulic schematics showing several boom and bucket valves with the resolver check valves. Previous posts indicated that o-rings on the check valves deteriorate. That will be another troubleshooter possibility.

The friend (neighbor) and myself have priorities for a couple months, so I'll get some time to read up more.

Where should I look for the serial number? Thank you for the help.

 

[Nige]

Where should I look for the serial number?

See attached. If it is truly a 420D the Serial Number (last 8 of 17-character PIN) is likely to be FDP or BLN followed by 5 digits. There are other possibilities but those two are the common ones.

 

[pittsburgh cat man]

There is a chart to check the resolver network It shows how to find the bad resolver by pulling different functions in specific order

 

[Bruce O]

I had some time to just look around, there's the data plate in broad daylight. I also looked around the back end and saw what might look like resolvers. Are the filters under the cab floor?

PIN CAT0420 DVFD 09505

SN 7 BJ 73749 Arrangement 1878014

HG 208209 Arr. 1720844

Bruce

 

[Nige]

FD 09505

FDP09505 is the Serial Number. the alternatives are BLN or FDP prefix so it's obivous which one of the two it is. See the two attachments.

 

[Nige]

Are the filters under the cab floor?

Which filters are you referring to.?

Attached the parts breakdown for the front & backhoe control valves. I marked the resolver in the first section but they are pretty much the same on each valve section. Seeing as the machine is well over 20 years of age I would suggest resealing the resolver parts in all the valve sections. In some or all sections you may have to replace the ball #6 or even the shutlle valve assembly #5 if the ball inside it does not rattle when you shake it.

 

[Bruce O]

Thank you for the parts diagrams. As you suggest, if we dig into this, replacing the o-rings on all resolver circuits will be the most effective. I'd normally want to check pressures instead of shotgunning, but from the descriptions, the furthest check valve influences circuits up stream.

Do pressure gauge diagnostic ports need special adaptors from Cat? Or does Cat put a part number on something such as JIC 37 degree flare? I'm assuming it's not pipe thread. I'd need to get a 5 or 6Kpsi gauge and hose.

I was asking about hydraulic system filter location and inlet screen.

If the shuttle valves don't rattle, is it possible to clean them or check for springs, if they have springs?

Bruce

 

[Nige]

If the shuttle valves don't rattle, is it possible to clean them or check for springs, if they have springs?

There are no springs, it's just a loose ball inside a tube. If it doesn't rattle when shaken you can obviously try brake cleaner or similar but at the end of the day the ball HAS to rattle if you want the shuttle to work correctly.

I was asking about hydraulic system filter location and inlet screen.

See attached. The filter is an ultra-high efficiency type. Latest P/N is 465-6505.
There is no inlet screen on this hydraulic system.

if we dig into this, replacing the o-rings on all resolver circuits will be the most effective.

The machine is 20 years old. The O-Rings and backup rings will most likely be like rock by now, and will probably fall out in pieces.

For each valve section the minimum parts you will need are Items 4A thru 4E and 6A thru 6C. From memory each section uses the same Part Numbers but be sure to check. Depending on condition you may need some of Items 4, 5, & 6.

Do pressure gauge diagnostic ports need special adaptors from Cat?

If they are the quick disconnect type shown below then the matching coupler is Cat Part Number 6V-4143. Aftermarket versions of this P/N are also available. Female thread in it is 1/4" NPT.