Cat 235 excavator weak slow stick and only full speed swing

Our ecovillage'srecently adopted 1976 Cat 235 sn:32K855 has a slow stick and resealing it didn't help nor did the procedure to remove air from the pilot oil system at the five and three stem valve groups. My service manual is also pretty poor at helping an amateur troubleshoot it. I am guessing it may be a problem in the stick or stick crossover valve in the 5 stem valve group... but who knows? It also has no sensitivity to the swing and just goes full speed which is going to make fine work tricky and everything more dangerous. Previous newbie owner took apart the left side pilot valve group that the associated lever control goes into but didn't find anything obviously amiss. Wondering if I should just try replacing that group though.

Would really love to hire someone that knows this machine in the Rhode island area to come fix it up with me this week or later when I move it up to southeastern VT to build a permaculture ecovillage incubator. Any help would be appreciated even if it could only be lending a brain to my hands through zoom this Friday.

Should probably be a separate thread, but I also just purchased a motorless Cat 235B that I am trying to put a cat 3306DI sleeve metering cat engine in off a mep-007b military 100kw generator and hoping I found a pro who can convert the fuel pump and governor enough to make it work but that remains to be seen. I am worried I may be at it awhile getting it running again. It is in Tiverton RI. May have the old block and generator engine for sale soon if this doesn't work and will be in need of a used 3306DI engine. Thanks y'all!

What is an eco village? Do tell.

One day I will live in Rhode Island. I will marry a round American women and raise rabbits. She will cook them for me. And I will have a pickup truck,.... and maybe a recreational vehicle. And drive state to state. Do they let you do that?

An ecovillage is a thoughtfully designed micro-society where people live and mostly work together in comparative harmony with the earth while attempting to model and evolve the systems and culture that might be needed to solve the myriad of crises that are harming us and the earth. Permaculture and self-organizing group management systems like holacracy/sociocracy are often key aspects of ecovillage life as is the sharing of vehicles (i.e. you might not get to have your own exclusive pickup or RV). Examples might be Findhorn or Tamera in Europe, and possibly Earthhaven in North Carolina or the Dancing Rabbit cluster of communities in Missouri.

Good luck @Coaldust with your RI dream. There are plenty of round women there but you may be harder pressed to find one to cook those rabbits up for you that hasn't already been snatched up. As to your question about having the freedom to travel, it's not as easy as it used to be and camping for free has definitely gotten more challenging. As to the legal and bureaucratic side of things, most of the time the federal and state governments will permit you to drive state to state if you follow all the rules and pay for all the permits but the more traditional "right" of freedom to responsibly travel has been largely lost although there are still a few activists working to restore it. I was one of them for awhile a decade or so ago and even took a case all the way to a lower court although I lost when the judge remarked it was above her pay grade and I would have to take it up with the NH superior or supreme court, a daunting and costly task. The freedom was probably being curtailed as early as the emergence of the first professional police force in the 1800's in Boston, but more dramatically during the prohibition era of the 1930's https://slate.com/news-and-politics/2020/01/right-to-free-movement.html.

Would be lovely to get some help with my excavator questions too though if anyone has a second. Happy to trade value for valuable advice received too!

One other thing about the Cat 235 is that the stick is much slower during the final 20% or so of extension out and fully retracts much faster. Full cycle time out is about 18 seconds even at a pretty high throttle and the spec is something more around 4-5 seconds if I remember correctly. The hydraulic oil also doesn't look perfectly clear, but I'm skeptical it needs a full change and that it's probably just some entrained bubbles mostly and hopefully not much moisture.

Bob,

It’s helpful to provide the serial# and hours with these types of questions. Head on over to the new member forum and check it. Welcome to the HEF!

I recommend looking through the archives. We’ve had some recent 235B slow stick discussions. There has been an upswing in new guys with old, worn out 235B’s joining the community.

Whoduthunk the 235B would make such a strong comeback in Q4 22? So, which malfunction do you want to tackle first?

Thanks Coaldust. I would like to work on the slow stick first and my search in the excavator forum didn't turn up anything so I will search the new member forum or elsewhere but it seemingly won't let me search with short words like 235 and I can't find the thread you mention anywhere. Can you post a link here or school me on searching properly? I provided the serial number for that Cat 235 in my first post and the hours are unknown and the Cat 235B is 7WC00800 and also unknown hours.

The HEF search function is a bit clunky to say the least, and often does not turn up results you know are there. Try using the following format in a Google search -
"[put your search term here] site:https://www.heavyequipmentforums.com"

I’ll take a look. Google works better for searching old threads. Use heavy equipment forums in the key words.

Ok, we can totally do this. Easy stuff, first. I would pull hyd filters and see what evidence you can find. The return filter may be packed full of stick cylinder seal material.

Edit- beat by Nige.

Coaldust said:

I would pull hyd filters and see what evidence you can find.

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I'd also suggest to cut them open if there is nothing obvious on view on the outside.

This is probably the best filter cutting demo on Youtube. Ignore the fact it's an engine filter, the process is the same whatever filter it is.

I'm just a farmer-grade mechanic, but my first thought is to check the relief valves on the valve banks to see if those are opening early. At the very least, that might help with the weak stick.

The other possibility is the piston packing inside the stick cyilinder is failing, and the oil is bypassing though the piston. Try 'stalling' the stick for a couple of minutes while logging the temperature of the cyilinder - if the temperature steadily climbs, your cyilinder needs a rebuild.

If your oil is a murky white color, it has water contamination. At the very least a oil filter cart with a set of water absorbing filters can try to save it.

One other thing to check is your tank inlet screen. Especially with a excavator that old, there is a good chance it has some crud embedded in it.

Get yourself a hydraulic pressure guage and plumb it onto the output of the pump to check the pressure of the circuits.

There is this floor pedal to the right of the chair you can lock down that activatges part number 8J5880, the pump selector valve group which combines the two pumps for stick out and boom up, seems weird they wouldn't also want an option to combine for stick in. I wonder if not having that locked down could cause the slow stick extension and perhaps a slower boom raise although it didn't seem too slow to me. Still wouldn't explain the weak stick in movement though. Can't test all of these things until Friday unless a friend down there helps me out.

So the prior owner changed the hydraulic filter back in February and says he found metal in it and noticed that the gear driven pump (the swing pump?) had been changed and suspected that was the source. My priorities now are to engage the pump selector floor pedal and see what effect that has on the stick out and boom up, check the pilot pressure (335 +/- 25psi), check if the spool in the pilot valve that controls the swing or stick has turned in the bore of the body or does not move freely (not sure if I could figure this out without help), check that the spool in the stick main control valve moves freely and is centered (pg 68 and maybe for swing too?), check that the summing valve is working correctly (pg 66 and maybe the underspeed signal pressure check on pg 65 too), check engine rpm during swing function 1930 +/- 50rpm (but the lock pin handle to stop swing movement doesn't seem to be movable with normal force so find some other way to prevent rotation?), and check engine rpm for rear pump during full extension and retraction of the stick cylinder (1825 +/-50rpm), and for full boom and stick (1720+/-50rpm), check leakage rate of rear pump (pg 67), check pressures in oil outlets for pilot control valve for stick and swing movement (pg 67-68), check relief valve in main system oil (3600+/-100psi for boom and stick pg 68-69). Just repacked the stick cylinder so doubt that it is failing already and oil is bypassing through the piston, but I guess I could do the stall check anyway?

Bob Rolen said:

So the prior owner changed the hydraulic filter back in February and says he found metal in it

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In that case I’d suggest to pull the filter again and cut it open. If there is a significant amount of contamination in it then you may be in for some more disassembly and cleaning work. It’s entirely possible that your cylinder speed & swing problems are down to contamination.

If metal contamination is suspected, I'd look at bringing in a filter cart to clean the oil and flush the main reservoir out.

Puffie40 said:

If metal contamination is suspected, I'd look at bringing in a filter cart to clean the oil and flush the main reservoir out.

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Agreed, but it's the possibility of contamination stuck in valves, etc, that likely won't come out how ever long the machine is run. That's why I mentioned "some disassembly may be required", and the "some" was very tongue-in-cheek. It might be that every valve on the machine has to come apart to get the system clean.

Nige said:

That's why I mentioned "some disassembly may be required", and the "some" was very tongue-in-cheek. It might be that every valve on the machine has to come apart.

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If you had to guess, which valves are most likely to have something stuck in them that could be causing the slow stick extension or full speed swing? There are a near infinite number of valves on this machine.

Bob Rolen said:

There are a near infinite number of valves on this machine.

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I don’t do guesses and you’ll probably end up disassembling/cleaning each & every one of them. That’s what happens when a hydraulic system gets contaminated.

Bob Rolen said:

If you had to guess, which valves are most likely to have something stuck in them that could be causing the slow stick extension or full speed swing? There are a near infinite number of valves on this machine.

Click to expand...

I guess the first place to start would be the main control valves directly connected to the two functions having problems. After those are cleaned, just work backwards until you get to the pump.

You should probably check swing motor case drain also. If the swing pump failed it may have taken the swing motor with it.
Stick weak in one direction is probably a weak line relief valve at the stick control.

It was a broken centering spring in the swing valve. Easily accessible and should be a simple fix. Also seems the pump relief pressures are a little low and the engine could be lugged down a bit more, all of which sound like they should be easy adjustments to make if I can get an appropriate pressure gauge with the disconnect fitting and hose. 6000psi and maybe another 600psi one for the pilot valve. Anyone have any recommendations on where to get those? https://www.ebay.com/itm/3850441522...rWyujQiTan3S3bR7vHHRSjpf4eI=|tkp:BFBMguHI_aRh and an extension hose?

Who do you go to for hydraulic hoses? They should have the guage and the fittings you need to set up a pressure tester.

In theory grease gun hoses should be enough for a pressure guage as the guages dont need much volume, but make sure those have the appropriate pressure rating written on the side.