i've got a case 75xt that is fine when cold, but once the hydraulic oil is good and hot the unit won't turn when you move the lever's in opposite directions. also when trying to turn the green light on the display goes out and the parking brake light comes on. but driving straight it fine. any ideas where i should start looking?
Does the unit make any unusual noise? Does the hydraulic oil foam. Has it had regular maintenance? How many hours?
i haven't heard any weird noises. hyd. oil seems to stay clear. i've only been servicing the equipment for the past year. i'm not sure of the maintenance prior to me, but i would say it hasn't been the best. an oil leak went unreported for a couple of months and the operator was using a 46w hyd. oil and not 10w30. so i know that doesn't help. i've since repaired the leaks, flushed the system and put in the proper oil and HTO additive. the unit has around 6600hrs.
I would get a 600 lb pressure gage and check the charge pressure in actual operation. Since the problem occours with hot oil I suspect leakage within the closed loop system allowing the charge pressure to drop below the switch setting and turning the systems normal lite off and the system is going to park. Watch the pressure as you duplicate the conditions where the unit will not turn. You should really have a service manual to locate the test port and get the charge pump relief settings and procedures. Your piston/ block assemblies and commutator plates in the transmission assembly may have picked up some wear or the motors may have internal leakage.
unfortunetly i don't have a service manual. thats the first think i was thinking was i was losing charge psi. i'll have to look into testing it
With 6600 hours and so so maintenance the whole system is likely worn. The hydros may have enough wear to cause the problem but everything wears with use. I would also suspect the heavy oil was used to combat the problem. Most likely a set of pumps and new motors are in order. By all means get a service manual and do the pressure tests to verify. Unfortunately alot of less reliable machines give up before 6600 hours. Another thing to consider is it had an oil leak and may have run low enough to scar the pump surfaces.
finally got back to it yesterday. capped of the hydro pump, and i'm dumping charge psi on the rear pump. time for new
I dont understand your terms "capped" and "dumping". I am guessing you put caps on the high pressure hoses to the motors. Also guessing you have charge pressure to rear pump or just volume. With no output flow from the pump it should pressurize if there is charge oil. Or am I way off?
yes i capped the the high pressure ports. the pump that drives the right side holds charger pressure and pulls the engine rpm's down when stroked. the pump that drives the left side drops all charges pressure and never pulls the engine down.
With no flow out the drive lines the charge pressure shouldnt drop. I could see the pump not able to make pressure but charge pressure should be stable. There is a serious leak internally or a bypass valve for that pump has failed. I dont have a breakdown for that pump but Ill see what I can find.
i already sent the pump out for repair. just waiting on word from the local case dealer about the motors. they are on backorder no promise date yet
Found a blow up of the pumps and they do have a bypass valve besides the high pressure releif valves. Given the results of your tests I would bet the bypass on that pump had failed. Sorry I couldnt get back before you sent them out. As always everything came up all at once.
well i had a pretty good idea that i was losing charge pressure before i started but giving the prior maintance of this customer's machines before i took over i'm not suprised the pumps were bad. i'm recommending the motors be replaced as well
Tightgtp so was the pump the problem I have an 2003 75xT with 1400hrs and is having the same problem as your machine had will go forward and back but won't turn left or right and has no pushing power and parking brake light will come on when it warms up