Hello fellas, Ive just bought myself a cat 428 1988 to use on the family farm. just a quick question about hydraulics... when you start the machine up should the hydraulics work at idle speed? as you can guess they dont... I have to rev the machine to get them going. once the hydraulics are going they work fine at any engine speed. I have changed all the oils on the machine; engine, hydraulic, transmission, final drives etc. and replaced all filters with genuine cat parts. but this did not help. any advice would be appreciated
I wish I could offer advise, but I have little experience with Cat loader/hoe hyd systems. I'm thinking they use a hydrostat pump, but I don't know if they use a charge pump. If it does, you may have a problem with the charge pump. If you could obtain a hyd schematic from a Cat dealer, it would help you a good deal indentifying what might cause your problem.
Just like a forklift, hydraulics are slow at idle but should function, the fact that you have to rev the engine indicates that there may be a weakness in the pump. In my experience I have had many machines that have had slow hydraulics and they can last for years like that but if this is a machine you depend on it might be wise to rebuild the pump and reseal the suction system as some day it might let you down at the most inopportune time.
Thanks for the advice fellas. I will try and get that hyd schematic. I was hoping there was an inlet filter to the pump that could have been blocked or something like that. I really dont want to rebuild the pump just yet..... Im skint after buying the thing!!! Thanks again
At first glance this problem doesn't make sense. You could say that the pump is losing it's prime whilst stood, but I'm pretty sure the pump is below the tank level and flooded with oil all the time. How long does the machine have to be stopped for the problem to arise? If you stop it for 30 seconds does it happen or does it have to be stopped for a day? If it really does work perfectly after you raise rpm for a short while, the only thing I can think of is one of the spools in the pump compensator is sticking. If you look at the main hyd pump, it is the small valve bolted to the side. Take it off and strip it but be careful with the adjustment screws. If you remove them, carefully count the number of turns so you can reassemble the same way. Check the spools for dirt and/or binding. Is it possible that it isn't the raised rpm that's making it work, but moving the levers around? This would make a little more sense. The pump is upstroked via a reslolver network and this is more likely to give problems.
Hello Cmark, I'm not sure how long the machine has to be stopped for, for this to happen. I will find out the next time I use it. It definatley happends after one or two minutes though. Every time I start the machine I try all the levers. The only movements are the ones with the help of gravity... Until I give it a rev.... and then everything works even at idle speed... I will definately have a look at that pump compensator. Thanks for the expertise