i bought a 303.5 mini excavator a few months back and the excavator has a problem with high case drain pressure the guy I bought it from said he had acquired it from a the owner who said that it needed a turn motor so he replaced the turn motor. Machine said it would still not turn very well after replacing the Turn Mower the mechanic told the owner that he needed to replace the main hydraulic pump. he thought that was the problem put the new pump on operated the piece equipment for about 4 hours and then blew a final drive this is where I came into the picture. I bought the piece of equipment the guy said the owner said he was not going to put any more money into this piece of equipment so I bought the piece equipment and when I purchased the machine I drained all the fluid out of it checked all the ports put in new filters fluides instaled one new final drive on it and used it for about 12 hours and then it blew another so I bought another final drive and put another new final drive on it used it about 2 hours and it blew a new final drive on the other side so I called caterpillar and they tell me to replace the swivel I purchased a new Swivel and now I still have high pressure on case drain I put a new Swivel on it and still have a high case drain return pressure I have not installed the new Drive Motors fear of destroying the new ones.I even took the turn motor off of it to check and see if maybe that might have been the problem with they turn motor removed and hoses blocked off still have high case drain pressure have not took the hydraulic control valve apart and looked inside know but have looked and see if they were any metal found none there is some seepage on a return hoses but I think that's due to the high pressure in the return system I cleaned hydraulic tank and system and checked it for metal particles but they were none visible the machine is relatively clean and has a lot of hours on it but is still very clean to be as old as it is.
Need to stop throwing expensive parts at it, and get a senoir field mechanic with lots of gages and schematics to help out. Who knows if new pump was set up properly. Maybe releifs are way out of specs. Lots of things to check. Maybe some parts are missing. Simon C
I agree with Simon. It's time to stop loading the parts cannon and get someone well-equipped with testing equipment on the machine who actually knows how the systems work. Define "a lot". Have you considered the possibility of a couple of hoses mis-connected somewhere that could be putting pressure into the case drain line.?
yes sir I wondered about that hoses being misconnected but according to the schematics I have from Caterpillar they're right I to agree with Simon about Who knows if new pump was set up properly. Maybe releifs are way out of specs. trying toget the money up now to get cat field mechanic to stop by another issue I found since I got the machine that it makes a roaring noise when you rotate the cab.I'm wondering if the brake on the cab motor is trying to engage due to the high pressure on a Case drain return causing the noise .I pulled the turn motor off looked into gears inspected and make sure grease was there every thing looked good
if the pilot accumulator has no pressure would that cause the problem
No. The only function of the pilot accumulator is to allow the implements to be lowered to the ground in case of an engine failure.
CAT sn# AFW00883 MDL# 303.5
Do you have access to some accurate pressure gauges.? You will need at least 1 x 1000psi, 1 x 6000psi. A couple more 6000psi gauges would not do any harm. I would also suggest you need an O&M Manual. You can download one from HERE as a pdf file for $52 and have it within 5 minutes. The reference is SEBU7296.
COULD Pilot Pattern Change VALVE ROLLPIN MISSING CAUSE HIGH Case drain return pressure TO BE HIGH if valve is not in right position
Happy Thanksgiving to all
o by the way i have this Manual Caterpillar 303.5 Mini Hyd Excavator Serial AFW Repair Service Workshop Manual
What's the Cat Publication Reference.? Should be on a label on the spine of the binder.
RENR3536-02
i fix it i hope good so far let you know later best i've been able to tell it was the swivel all the pressures are in with inspect now so I think it was the swivel all along must have been a bad spot in the swivel that I rebuilt or I could have just pinched a seal don't know but so far with a new Swivel I have had no problem thanks for you guys advice you pointing me in the right direction