I've got at 96' 938F CAT wheel loader. No power steering when cold. Once the hydraulic fluid has warmed up power steering begins to work, even then engine has to be reved up for it to work. I have changed the hydraulic filter, and noticed the hydraulic fluid is becoming aerated. This problem seems to have come on suddenly and has not improved. Any ideas or suggestions would be a great help.
Narrow the field down a bit......... there are 5 different versions of the 938F. Post a Serial Number for correct information that relates to your particular machine. What weight of oil are you using in the hydraulics
Sorry, I believe it's a 96' model. Machine # 1KM01150 Currently using generic brand 303 hydraulic fluid. Also, a few months ago the brakes would intermittently quit working. I've since replaced the accumulators, as they were leaking, with no improvement. I don't believe this issue to be related, however I need to get the brakes working also.
Your machine was manufactured on 17th August 1995. "Model Year" really means nothing with Cat equipment, Serial Number is far more important. The same model could be in production in up to 5 plants all over the world at the same time, each one would have a different S/N prefix and with potentially slight differences in component parts and how they function despite all of them having the same model number decals on the outside of the machine. As an example there are 3 different System Operation documents for the 938F Steering System. Attached is yours.........you need to study it and understand how the system works before you go off troubleshooting. The Test & Adjust is also there. How many total hours on the machine..? Now to your "generic brand 303 hydraulic fluid". 303 relates to a Deere spec for a 20-weight tractor oil that has been obsolete for more than 40 years. https://www.tractorlife.com/2018/06...-the-dangers-of-303-tractor-hydraulic-fluids/ You say that the operation improves as the machine warms up. If it's a while since the oil was last changed then maybe it might be worth switching to a decent-quality SAE10W (ISO AW32) hydraulic oil and some OEM filters. I'd also suggest to cut the old filters open and examine the interior for any particles, metallic or otherwise. Last thing. Do you have an Operation & Maintenance Manul for it..?
Thanks very much for your help and all the information. All I have is a parts manual for this machine. I cut the filter open, no debris, metal or otherwise. The fluid is dark grey in color. I will start by switching to the fluid you recommended and let you know if there is any improvement. Thanks again.
You may find it difficult to replace the contents of the system in one hit. Draining the tank alone won’t cut it, you may have to start opening up lines to get more of the oil out. Either that or you may have to change the oil more than once. Pay attention to the suction side of the steering pump, if the fluid is giving the impression of aeration then you could have an air leak between the tank and the pump inlet. I’ll post a link later where you can download a genuine Cat O&M Manual in pdf format for less than $50. You never mentioned how many hours are on the machine.
The gauge cluster has been replaced recently. I'll try and find out how many hours were logged. It only indicates 40 hours now, as most of the time the machine is operated with the fuse for the cluster/action alarm removed. Only has code 030 0'110.08 stored and the action alarm sounds and the accumulator light flashes. I've changed the hydraulic fluid and filters, no improvement with steering or brakes. I'm about to go and check pressures for the power steering system. I'll let ya know what I find out.
You said that you replaced the accumulators. Did you charge the replacements with nitrogen because AFAIK they are sold uncharged because of the regulations regarding transport of charged compressed gas cylinders.
Here's the troubleshooting procedure for your CID110 FMI08 Diagnostic Code. Although it has nothing to do with the steering I would suggest you fix it first before proceeding further because it will enable you to have the Action Alarm permanently live to assist you with troubleshooting.
There is a load sensing rotary axle piston pump supplying that system and some pretty complicated valves and circuits to try and troubleshoot that type of problem. If after following what Nige has told you and the problem doesn't get any better I would suggest you contact a qualified mechanic, preferably at the dealer, to do more extensive troubleshooting. While help from here is invaluable, nothing beats an experience ear and hand on site for a cost effective repair. Good Luck
Thanks for all the help. I replaced both hydraulic pumps. The large pump which operates steering and all cylinders, and the small pump that bolts to the large pump for the brakes. All seems to be working properly now
Would certainly work on changing and filtering that oil, all that trash from failed pumps is floating around in there. You mentioned it looked gray, do you think it was water or metal as oil should look like oil.
Changed filters and fluid a second time after pump replacement.
Hows the oil look after that and a good hard run? Have you done any sample testing to see if there is anything left behind?
If you are using the standard Cat 1R-0722 (33 micron) element in the hydraulic tank, get yourself some 139-1536 (6 micron) elements. Run for no more than 50 hours or until the filter plugs, whichever comes first. If the filter plugs in less than 50 hours, change it and repeat the process. Until you can get a 139-1536 element to go at least 50 hours without plugging you can't consider your system as being anywhere near "clean". TBH I'd use the 139-1536 as a service filter and change it every 500 hours once I'd got the system clean, but that's just me. The 6 micron elements are double the price of standard, but how much did your new pumps just cost..? I'm willing to bet somewhere in the region of $4k. You can buy a lot of filter elements for that sort of money ......
I think the JD 644E uses a 23 micron filter, I'd love a 6 micron filter for warmer weather. Cat has way more filter options.
IMHO it's knowing what options exist and then making use of them when circumstances dictate is the key thing. There is also a half-way house 20-micron element available, Part Number 1R-0774.
BGood morning Mr. Nige...do you have the electrical schematics for the 938f prefix 1km? The machine isn't moving and I don't have the electrical diagram for it...I would greatly appreciate your help.
I do have a copy. Check your message inbox.