New to the fourm. New to me cat 235b. Bought it, was super stoked to finally own a machine. Got it home, put an hour on it and blew a hydraulic hose, replaced with new hose and filled the hydraulic fluid. Took about 5x 5gal buckets. Fired her up and let her run for aprox 15 min. Slowly started using the boom, bucket, thumb ECT.. Went to pull her off the slope/start of the driveway. She moved backwards for about 10 feet (slowly).. Felt under powered. Tried to move forward and wouldn't move, tried to go backwards again no go..Any idea of what it could be? Everything else seems to work as it should.. All worked good prior to blowing the line, she did sit for a good 6 months. Checked fluid. looks a little cloudy/ milky. Fluid level looks good but after I tried to run her again I could get it to move about 6 inches under full throttle and full load then stop and bog down the engine. Figured maybe air in the system or air lock in the pump. Tried to bleed the pumps but fluid comes out right away. Did noticed one small leak on one of the rear pumps, it's a very slow drip, looks like from the seal? Cracked a line on the top of the final drive both sides to see if I got any fluid, I did. Then left them cracked started it to see if it would build pressure / squirt or leak a lot more under load, and got no difference. Not sure what line it was but it was on the top, return line or feed? New to the machine and have no idea what I'm looking for. If anyone has any ideas I'm all ears.. Thanks
Which hose did you replace?
It looks to be a hose that runs to the furthest pump at the rear, looks like a bigger pump at the rear, 1 smaller one in the middle then another one of the same size on the right, its a hose that bolts to a steel line with a flange. It blew because it was rubbing against another hose and wore a hole threw the side. I can take some pictures of the exact hose tomorrow morning but as for a name I have no idea .. Lots of hoses and I'm new to this stuff. Need to get a service manual asap.
Roger that. “Went to pull her off the slope/start of the driveway.”. Slope huh? I’m going to say the pump(s) didn’t pick up oil. Going to have to bleed the air out. Maybe use compressed air/nozzle and a rag to push oil into the pumps. Try disconnecting the case drains when you do this. It’s going to be messy. Run the case drain hoses into a bucket. If you have a helper, crank the the engine when you do this. But, don’t start it. Report back. Good luck.
I was wondering if that would cause that as the pumps are at the back as I was heading down the hill so wondered if they didn't get gravity fed the fluid. Appreciate the advice! Now for the case drains, what one is that going to be the smaller one that is on the boom that returns the fluid? Or the one on the travel motor? Is this line going to be under pressure?
Yeah, the smaller ones on the bottom of the main pumps.
Another thought, sounds like the track brakes are engaged. These 2 lines need pilot pressure whenever track movement is commanded...
I’ve had to rescue my fair share of 235b’s from bad places back in the day. Never in a driveway, though. Good luck. Those machines kept me busy with hundreds of hours of field rate OT & travel time and paid the mortgage. I haven’t touched one or even seen one, seems like forever.
The milky oil was probably entrapped air from the pumps cavitating. The fluid should clear up. I bet those pumps were screaming for mercy.
Sorry I was wrong, the hose I replaced was a lower hose that goes to the middle pump.. Here is a few pictures of the hose and what pump it goes to. (pointing at it with a breaker bar) As for the case drain hose.. I'm so lost as to what line this would be. I assume Its the smaller one like you said but looks like the smaller line jumps from one pump to the other at the bottom, so I'm assuming I need to hook up a line to both pumps and crank but no start and let bunch poor out into a bucket(s) Figured I'd want to let air out the top to let it fill with fluid vs from the bottom and fluid draining out. but I know nothing when comes to hydraulics. I'd hate to disconnect a line thinking I'm purging air out but little do I know I'm sucking air in.. I know to you It is fairly straight forward but to me Its like showing a little kid how to ride a bike for the 1st time. If possible plz circle the lines I should bleed. I'm afraid to do more damage than good. I can tackle most projects my self(fairly mechanical inclined) but this is not a cheap thing to fix so would hate to mess something up.bp Below the 1 rear pump has a small drip. Not sure if that's damage from running it not knowing it had air in the system? Edit: I think I'm picking up what your putting down.. Take the line off 1 pump at a time, push air into the tank with compressor while the bottom is draining that will allow less pressure build up and let (push)oil into the pump. Then repeat to the next pump?
The leak isn’t related. Oh’ I hear ya, brother. That’s an expensive & intimidating machine to begin your hydraulic education with. Lol. I may be way off, but in my world that’s about $40k worth of hydraulic pumps. Yup, that jumper line you describe is the case drain. Just might need to drain some oil to break the air lock and get oil moving to the pumps. Might even overfill the reservoir by a few gallons. Wish I was closer to help.
Ok going to try to tackle this procedure. One thing I did notice is when I filled it up. Ran it to warm it up moved it that 10 feet noticed it was weak pulling up the slope, figured it sucked some up into the lines and that's why it was weak.. So I shut it down, checked the fluid and was slightly below the add line, ended up taking another 5 gal bucket, that brought it up to full.. Tried to move it again. No go.. Today I went to tinker with it and noticed it's well above the full line, Its actually nearly to the top of the tank to where I can see it, slightly covering the filter screen. What would cause that? Also you mentioned it might fill it over full on the tank after doing the bleeding. Where would the fluid come from to over fill it once that air lock was released? Would the air not be taking up room in the pump that should be full of fluid? Wouldn't the tank go down a little after it floods into the pump? Sorry for all the questions or if I'm sounding like a idiot here lol just wanting to ask all the questions needed to make sure I'm not creating a paper weight here lol that my friend scares the s#!* out of me lol I really appreciate the time you have taken to answer my questions and helping me understand what it could be and fingers crossed that's all it is and I didn't already do more damage.. Also how will I know if and when the pump is full of fluid? Assuming I'd have air hissing out while it's cranking and draining from the cranking/ pushing air into the tank and that would be a good thing.. But if it doesn't do anything other than drain fluid then it's possibly pushed /whipped air further into the system like down the drive lines or am I way off?
just finished the procedure, when I went to open the cap on the hydraulic tank it was even more full than earlier today and has sat for about 3 days now. It was about 2 inches from the top. Found that odd.. I decided to do it anyways as I'm not starting it and figured I'm about to puke a ton of fluid out the case drain and had no cap on so wouldn't build to much pressure in the tank other than what I'm about to force into it.. So as it went... finished disconnecting the case drain, cranking it over while blasting air into the top of the tank, it would build pressure out the case drain as expected, and held pressure in the tank while doing my best to cover it with my hand and some shop towels.. After holding it for a minute or so leaking out slightly from my hand I lifted my hand and just puked out. Covered it back up, waited a couple of more min.. Puked out again.. Got the cap on quick.. Waited 5 min scratching my head.. Tried it all again.. 2nd time I noticed it started to bubble air back into the tank while it was sitting. Figured that's a good thing? Return like pushing air out bubbling into the tank? Did this 3 more times till I did not hear anymore air bubbles in the tank. At this point the fluid is a C hair below the full line.. Now I did not start it or see if the final drives are working again as I'm still unsure if that's what I was wanting to happen? Afraid to run the pumps dry anymore than I have. She's old and would hate to have her grenade on me with in 1 hour of run time. Coaldust my friend you Have been the only help IV had. Couldn't thank you enough for all of your input. Sorry for the novels, just trying to give as much info as I can so I can give the best idea of what's happening.
Wave a cutting torch in its face to encourage best behavior. A good threatening works wonders.
How much of a slope is it on? How is the boom sitting? That might be why the reservoir level is wonky. Sure be nice if you could get it moved to level. Give her a spin. Fire that biotch up and see what happens. If the pumps sound like machine guns or like a monkey with a hammer and a bag of marbles, shut er’ down. That’s cavitation. just slowly move the boom, stick, bucket to work the air out. Slow is key. Don’t bottom out the cylinders. Cause’ air will get super heated when compressed and burn your hydraulic seals. Double check the reservoir level. Then slowly work the travel motors. When you get it moved to a suitable location, inspect all the hoses and replace as needed, or this will become a continuous cycle of blowing 40 year old hoses.
Its no longer on a slope, that 1st 10 feet I managed to get it to move was off the slope onto flat ground. Did that procedure but had no luck. Nothing changed. Any other suggestion on what to look for next? Going to crack the break line to see if I get any difference under load.
Let’s start over. Any hydraulic functions at all? Or, just the travel issue you described? Pumps sound good?
It sounds from the first post: "Everything else seems to work as it should.. " that some of it is functioning?
MachineMike musta got it working. He’s too busy hoeing around to give us an update. Hoeing? Is that even a word?
We used to call them " Hoe Operators".
Sorry for the late update guys. Been working to much to have time to mess with it. As of couple of days ago I had a friend come have a look. Here's what we found. Went threw pressure testing pumps, break line, cab pressure, found a few not getting much pressure. Decided to pull some filters check for metal flakes from any damage to pumps. What we found is some filter particles in one of the filters. Pulled the last big can that has 3 big filters in it, got 2 out, go to pull the back 3rd filter. And see that only half of it is left, other half missing.. Next we check a valve that pressures up the break line. Find bunch of filter fibers plugging up the small holes in a valve for the tracks. Wooh found our possible source but still not excited as I would like to be. Now I know the whole hydraulic system is contaminated with all these fibers, rubber, and hard inner plastic from the filter.. Praying it did not get to the pumps, but obviously some has as we found some in a filter that would have filtered fluid from after the pumps. Now we got some schematics of the system. And see that the hydraulic tank has a baffle/filter like thing inside, so decided to drain the tank, back feed the cooler try to flush any out, found some bits in the cooler, we then split the tank and clean it out. Found a bunch of rubber, plastic and fiber filter material at the bottom as we expected. Pulled the baffle out and found most of the missing filter. Hard to tell how much we got as it's all broke down to small pieces. Thank F for the baffle. Or thank the guy who decided to add that to the design lol Now I got 2 new drums of fluid, new filters, re sealed the tank, filled it up, bled the case drains, put everything all back together. Fire her up. She moves! .. BUT.. Now she is lacking power in all functions. Before the other functions all worked with no hesitation no lacking power. Only thing was the tracks not working. Now all functions do not have the power they did before we cleaned out what we could. The tracks move, all functions move, but she's moving like she's at 1/2 throttle when she's at full throttle. So nice the tracks move but now have lack of power. I know the proper way to clean the system would be a lot more in depth and I'm on a budget to do anything with the machine so I can't afford to clean out every hydraulic line one by one. I know some gremlins might come back to haunt me. That being said I'm assuming the new filters will pick up any other stuff that will make it threw the system. We checked pressure of the pumps and specs call for 4000psi and were getting 3900 on one pump and 3800 on the other. Specs I think say give or take 50-100psi. Today we are going to try to check a few other things possibly re clean that valve again. Keep you all posted soon.
Pay close attention to your pilot system. It sounds like you have air. air can be very dangerous in the pilot system as it acts like a spring and can hold spools open when not commanded. On each side of each spool is the pilot pot. On top of that is a bleeder/test port. Crack some of those while activating the spool a little bit and see if you get bubbles. Some times adding a clear tube helps see air much better. You may need to visit several pilot areas to bleed. Many people confuse a lack of 'power' and lack of 'speed'. It sounds like main pump pressure is reasonable so you should be getting decent power but if spools are not opening all the way, you will see a lack of speed.
Ok, I will check and try this procedure. And report back. Thanks
Helping Machine mike with this project. Am an equipment mechanic but this 235b is before my era and cat literature is not as easy to follow on these units. Initial failure was machine on slope but couldn’t track. All other functions were working. Found unit had no brake release pressure and oil in tank was white/milky/dirty. Pulled some filters and found: Main return filters(3) -1 imploded from being plugged from contaminated oil(munched filter/munched rubber/debris-no metal) - Looking like complete hydraulic contamination. Pilot filter- bypass jammed open from munched filter/ rubber chunks and dirty oil. No metal flakes. - Clearly contamination made its way into pilot circuit. Case drain filter- dirty oil from munched filter/ no metal flakes Not sure how tough these pumps are but they look like beasts and they were definitely playing garburetor for a bit. First intervention involved draining/splitting tank/ getting rid of as much of junk oil as possible. Removing debris from return baffle pipe(full of rubber/paper filter/ plastic core pieces of inner filter). Cleaned out hydraulic cooler, new filters,new oil. Since pilot filter was bypassing we removed pilot pressure relief valve(full of munched filter), track brake valve and main relief valve to clean. Bled pumps, ran unit, got brake release pressure back and was able to walk it off slope. …..Couldn’t drive away fast enough.. hah Current problem is all functions are weak/ machine is sluggish. Not enough hydraulic power for digging. Can walk machine but struggles to counter steer. Looking for air or debris problems. Praying pumps are good! Checks done so far from cat literature: Track Brake Release pressure- 310psi Pilot pressure under cab- 320-340psi (gauge fluttering) Pilot pressure at filter- Low idle 350 High idle 675psi (Can’t find cat spec for this) Main pump rear- 3400-3600psi for hoe 3900 psi for track Main pump front-3400-3600psi for hoe 3800 psi for track Pumps appear to be working Bled control valve at all bleed screw/test ports on the control valve while functioning. Didn’t see any air come out. No change to operation Teed into main pumps destroke servo line, running 150psi at 2000rpm. Off of cat spec. This comes from what there calling an under speed valve As well as a summing valve. I’m not too familiar with this setup. Next steps were looking at: - Looking at running unit with servo destroke line disconnected to see if we get any more power out of hydraulics - Perform pump case drain test - Remove summing valve, combiner valve, under speed valve and searching for debris/ contamination Any tips from anyone who’s got some more experience on these things would be great! -Any other bleeding spots i should try out? Under speed valve/summing valve tips? Location on machine of the pump selector valve (couldn’t find this during bleeding air procedure)?
What an interesting twist of events. Never would have suspected a munched hyd filter. I would like to ask about identification of the particular brand of filter you found. But, I won’t. Because if I did ask that question, this thread would go sideways so incredibly fast. We would start talking about genuine Cat vs Wix, yada, yada. So please disregard and continue with regular schedule programming.
BTW, Thanks for showing up, anyways and helping MachineMike. You are not the hero we deserved, but you are the hero we needed. My goodness. Shame on the mess. A catastrophic hyd syst contamination incident like that is a heartbreaking situation. Only one fix. Anything else is a non-stop attempt to repair one jammed up relief valve after another, chasing demons for weeks, bleeding labor. Can’t guarantee any of the repairs. Nobody is happy. Endless chain of broken relationships, broken dreams and sadness. A once jubilant event of purchasing your very first 235B, to be emotionally shattered after tracking it off the lowboy. Now, all you have is a hydraulic stain on the fresh asphalt and a monument of rusting iron in the backyard. Hope is eternal or something like that. All is not lost, send me a signed purchase order, a credit card number and a plane ticket. I’ll fix up that ol’e Caterpillar. wonder if MachineMike has a spare bedroom?
You are on the exact right path by disconnecting the destroke lines on the pumps. That should put them at full stroke, then test. If you have full function back, then we know some things for further discussion. It might be worthwhile to test just one pilot pot on the main valve under full stick just to confirm that full pilot pressure is being provided to the spools. That means they are likely moving to max throw unless bound up, which sounds like you could not rule out entirely based on events. I'd probably go right to the destroke lines as I think that is where some issues are and you can test at true full stroke. See if she tracks straight, has speed/power, etc.
Checking case drain would be a good follow up. Especially if it doesn’t track straight. Might provide some indication of the garburetor health.
Checked pilot pots during functioning for boom lower/ track functions. Fully stroked have 300psi pilot signal going to main control valve. Disconnected servo destroke line to pumps and tested unit. ....... didnt know tracks moved that fast in the 70s. hah. With pumps at full stroke unit tracked fast and countersteered what i assume is normal. Machine is tracking straight as well as stronger boom function. If rpm is too low when functioning a circuit over relief it will even stall the engine. Sure appears that the pumps still have some jam to them, just the pump control circuit isnt functioning properly. Decided i should get a little more in depth with cleaning this pilot circuit/pump control system apart. Reinspected pilot filter (no debris) Pulled underspeed valve and disassembled. Found small plastic debris/ filter fibres against/ around underspeed needle valve. Reassembled and tested, no change. Have to stop the workey to spend the weekend eating turkey but next steps we plan to: Remove, clean/ re clean pilot relief valve, track brake valve, summing valve, combiner valve, main relief and increased lift valve (machine equipped with, however wiring cut off at solenoid flush) Any tips on how to set up pump control circuit on these units. Underspeed valve/ summing valve when i get there. A little hard to understand cat literature/ pictures. Thanks
Been too long for me to remember without a refresher, and all those books are packed away right now. The only thing I will mention here is you keep cleaning/inspecting, but you need to really study assemblies and take NOTHING for granted! Like assembled wrong, missing parts, etc. It is very clear to me the machine was not maintained, and with that usually comes hacks/idiots. They will sell tools to anyone and I just HATE going in AFTER someone else. Sloppy seconds? lol. Anyway, Usually equipment is ignored. Then it breaks because it is ignored, and the owner and his idiots don't have a clue so they start jacking with everything to a point it's probably worse than previous, so they put that slick penny up for sale with the words "runs great". You may need to adjust some valves, not just clean them. You know how many carburetors I have been in where idiots went before!? Floats upside down, needle settings way outside of normal, etc. Just saying. Use pressure gauges and always mark/count revs on any adjusters so you can return to where it was. Lastly, document the changes! People don't do this, then it will come up again and no one remembers.