New member but long time lurker, recently picked up an 04 cat 304 mini not running for super cheap and am working my way through some issues now that i got it running. And need some help/advice in getting it back in operational shape. let me start off by saying the machine was half torn apart when i bought it so i have no real way of knowing what worked or not beforehand or what the original problem was that caused it to be taken apart other than service records since new, which is why i only paid $3k for it. The machine currently has one pretty significant hydro fluid leak from one of the "valves" (not sure what to call it) in the main block under the cab that appears to run to the aux hydraulic pedal/thumb. Boom, stick and bucket function as normal with apparent full power but there is absolutely nothing in the way of cab swing/turn or track movement of any kind. The blade does raise but extremely slowly and does not have enough power to lift the machine. Additionally the swing boom has no movement/response of any kind. Also found a completely frayed/broken harness connector today and can't seem to determine what its for or what it connects to. I have worked on cars and trucks pretty much since childhood so i know my way around a wrench but my knowledge on the equipment side of things is admittedly lacking. Where should i start with tracking down these issues? What is that leaking "valve" called technically so i can source a replacement? What the hell is that connector/harness for? I'd appreciate any input as I'd like to get the machine operational sooner than later for a retaining wall project. Thanks
Good day Suggest you make fixing the leak first on the agenda - the description suggests that you have a pump - or relief valve issue as the problems relate to that kind of combination. If you are not so confident it may be better to get some help. Kind regards Uffex
I appreciate the insite, from my limited research thats also the direction i was pointed in. I have a buddy thats a service tech for volvo and does this day to day for work with a take home service truck so he offered to come take a look aswell but was unsure if the symptoms clearly pointed to one thing over another. Im gunna stop at our local cat dealer today and see if i can't get the leaks stopped and get a schematic/breakdown for the hydros and wiring harness.
Sounds as if you are on the correct way a hydraulic schematic is always the best document help you can get. Good luck
I had to guess on your serial number prefix but here's a schematic for a 304CR prefix NAD
Many thanks this is exactly what i was looking for and cat couldn't seem to understand. Def gunna take some time to go through making sure everything is actually going where its supposed to before i can start diagnosing. NAD is the correct prefix. You don't happen to have one for the wiring harness under the cab aswell do you?
A Service Manual might also be a very good investment if you got the machine for (relatively) cheap. The Cat publication reference is RENR6660. Can't see one on eBay at the moment but these guys do a CD version of the genuine Cat manual for $365. https://www.servicemanualpro.com/?page=Products&searchbox=NAD
Good day As I have interrupted the schematic pump No3 provided the fluid for the slew - swing and blade I suggest test the pressure of the circuit dead end the blade wind out and then in with the relief valve No.25, I cannot see the connection to the tracks - crawlers maybe this is a separate issue. Tak Per for the schematic. Kind regards Uffex
Well as an update im pretty sure i got my leaks sorted out. Both were coming from improperly installed o rings that had been squished. New problem for today is after i got the o rings replaced i cant get the machine started♂️. Cranks fine like it wants to go, get smoke from the exhaust but just wont fire. Checked the filter and this is what came out I swapped the filter cleaned up the filter head and still got nothing coming out of the electric pump other than little dripples. I blew out the lines going back to the tank with shop air and now have fuel at the pump but have to charge the battery before i try to start it again. Im assuming all that crud is rust/paint from the tank and its going to need a good cleaning.
Good day Maybe a full strip inspection and service is called for - it may be worth getting the hydraulic fluid checked while you are at the machine, may be why thee machine was in the bargain basement. The debri would suggest something other than rust/paint - fuel especially for smaller machines get filled from all sorts of containers often little care taken. Kind regards Uffex
Interesting update, i had some time at lunch today. So i drained and flushed the fuel tank hooked everything back up and did get it started however it took more cranking than i would think is normal. Then i had absolutely no boom, stick or bucket functions at all which didn't make sense to me as they were all working fine 2 days ago. Checked all the fuses and found a blown 20 and a 10. I dont know what they are for as the cover is missing but when they were replaced i got all my previously working hydraulic functions back and all my leaks are now fixed also figured out that the broken harness connector goes to the floor mounted 2 speed switch. Maybe now i can actually get around to figuring out why everything else doesn't work lol.
You want an electrical schematic as well..?
Absolutely if you have one available
No worries. To identify the correct schematic I already know it's NAD-prefix but I also need to know if the Serial Number is above or below 1634.
NAD01193. Very strange update but i changed the oil today over lunch and figured id run some good fuel through it after the tank cleaning and my swing miraculously came back. Its super slow and nowhere near where it should be but it does now swing. Still no swing boom and no travel functions but its like the longer i just let the machine idle the more things strangely come back to life. My buddy that works for volvo is coming Sunday to do some pressure tests so i should have some solid info to report back with next week.
Someone put some far-too-heavy hydraulic oil in it and it takes time to "thin out"..? Schematic on the way.
the gear pumps on them are known to go bad in atleast one section.
I kinda half thought the same thing. When i picked the machine up it only had about a gallon of fluid in the tank due to the leaks and the guy i bought it from gave me 4 5 gallon pales of that cheap tractor supply Traveller iso46 fluid just to get the boom high enough so i could get it winched on the trailer. I had intended to replace every fluid in the machine once i knew it was viable/worth the expense and i was going to keep it. Seller said thats what he has always used in the machine since he's owned it but i believe the spec for the machine is much lower with regard to hydro fluid weight.
You'll have to forgive my ignorance as im not extremely familiar with the workings or terminology of these machines and their hydro units. Which gear pump are you referring to? Like one of the drive motors for the tracks?
This one............ To be more accurate the gear pump #43 which is the small one on the back of the main piston pump and is non-rebuildable. If it is foobarbed a new one is less than $100.
Been super busy with work the past few weeks so i haven't had a chance to get much done on the machine until today. I had my buddy from volvo come take a look at it we got most of the electrical gremlins sorted out. Now everything electrical works with the exception of the water/temp guage. He feels that there is a good possibility the machine is airbound due to being run with next to no fluid. Or the pilot pumo is junk as others have suggested. He thinks this because when checking for pilot pressures he cracked one if the lines loose on the block for travel while having me put very light pressure on the pedal and a massive amount of air came out and then the track jerked forward under full power for about 3 seconds and stopped, which is the only track movement I've had with this machine since buying it. The machine barely has enough power to swing right but when swinging left moves better/faster, although still nowhere close to where it needs to be. Is there a procedure to bleed the hydro system? Should i consider cracking all the lines loose one by one and trying the individual functions to attempt a bleed? Could something else cause air to enter into the system when it shouldn't?
Good day Please see attached maybe helpful. Kind regards Uffex
So to update everyone I've finally made some good progress on the machine. The short answer to my issues was 2 hoses off the travel block that were swapped. Everything now functions but what i thought was the pilot pump is looking like a swing pump that also is the supply for the main swing, swing boom, and blade all of which are still very slow and weak. Gunna dig into it more this afternoon but as of now technically everything works and the machine moves.
Ok guys this should hopefully be the final update on this issue/problem. After getting the swapped hose issue sorted out i had my buddy from volvo come down to do some pressure testing. We confirmed that the small gear pump off the main pump is infact directly tied to the slew, swing/offset boom, and blade circuits. As mentioned before these functions were all extremely slow and weak. When pressure testing that pump it only put out 180-200psi and from my research should have been around 400psi. I called CAT and they could have it to me next day for $104 out the door. Well today i swapped it out and am happy to say the machine appears to be fixed. Only thing left to have it fully functioning is to order a new 2 speed switch that i may or may not have mangled in the teardown process. I suspect the gentleman i bought it from was honest in saying that he blew a hose underneath the machine and could never get it figured out. as a result i think he ran that smaller pump dry damaging it. His mechanic or whoever took the machine apart and when putting it back together not only crossed some hoses but pinched a few o rings causing the machine to now not move, **** fluid, and have weak functions which ultimately were not expensive or very time consuming to rectify after identifying them. Thank you for all the advice, opinions, and suggestions as they were all extremely helpful. The $3k caterpillar is now back in action for under $1k
Always nice to hear a success story. It can be a real hair-tearer when you weren't the one who pulled the machine apart so you have no idea what was done before you got your hands on it.
Hello Nige - I was snooping around this post about Cat304cr, on account I have some electrical spaghetti to sort out myself, on machine NAD04265 - Any chance you have that schematic you're referring to here that you can share (again) ? TIA - gibbs
Keep an eye on your messages. It's a different schematic because your machine is a higher Serial Number, but it's on the way.