Hello i have a problem with a cat 311 excavator. I believe its a 9lj grey market machine. The left final drive all of the sudden quit pulling as fast as the right, forward and backwards. It is still strong as it will burry itself in the ground just slow. I can make it speed up normal if i slightly hold the right pedal and slightly use another function on the boom. I have 4500 psi on front and rear pump. With either track pinned. Have not tried a case drain but wouldnt think that would be the issue since i can make it speed up with other controls. Dont have a guage pulmbed for pilot pressure but i swapped the pilot lines on either travel circuit. Travel pedals reversed but the same drive is still slow unless i slightly use other functions. Oil is clean as brand new penny. Bucket boom and stick super strong. Swing might be a tad slower but im not quite sure. Pulled all 3 travel spools main relief and travel circuit check valves. Also if i put it in rabbit mode it speeds up but still not quite as fast as the right side. Although i can make it track faster by slightly using other controls. I also rebuilt the swivel in which there was no need, the swivel had evidentally been replace at some point and seals were in great shape. Also the right side does have a slight intermitant delay to go in gear. Have been told by many people could be something in the control valve. Sorry post is long but i figured i would put it all out there. Any response would be greatly appreciated.
Hello. From your story I understood that if you drive straight with both tracks, the left track lags behind, and the excavator turns left, and when you engage other operations, the left track starts moving equally with the right one and the excavator starts driving straight? If so, then the problem is either in the left track distributor section, or in one of the pumps. When you drive straight with both tracks, each travel motor is driven by oil from a separate pump and from a separate distributor section. But as soon as you engage any other function, all the oil to the travel motors goes equally from one rear pump, through the forward travel spool. The left hydraulic motor is driven by the rear pump. The right hydraulic motor is driven by the front hydraulic pump. If the left hydraulic motor is lagging, then it is possible that the problem is in the rear pump, the performance is reduced. Have you changed the pilot lines only on the pedals? Have you tried changing them on the main control valve?
Thank you for the response. I swapped pilot lines at pedals and the control valve same thing slow left final. It almost seems that the pump isnt stroking up to turn the final i have oil pressure but no volume. That track is strong and turns machine just slow. Im going to check the negative flow line with left drive in gear when i get home. I disassembled the regulator on rear pump and resealed. All linkages spools and springs looked fine. As for the left side kicking up to speed when slightly working another function do you think front pump is some how mixing with rear oil in control valve to speed the left drive up?
If you want to post up the full Serial Number I can probably track down the test & adjust procedure for the pump control. IIRC the use of the implement function at the same time as the travel strokes up the other pump so that would explain why when you do that the LH track speeds up to the same speed as the RH track. The flow from the two pumps is being combined.
If it's a 9LJ-prefix machine then it's not grey market. The grey market version of the 311 is the 5PK-prefix machine. However from a technical point of view everything that applies to the 9LJ machine applies equally to the 5PK. See attached which may be of some help.
You a right nige, it is the 5pk it has japanese or chinese lettering all over it. I will let you know the full serial number when i get back home this evening. Thanks
The SysOp and Test & Adjust for a 5PK will be the same as for a 9LJ machine. Those were the attachments I posted above. The only caveat is that there is a Serial Number break on both machine ranges. Anything 5PK1-1000 is equivalent to 9LJ1-261, and anything 5PK1001-Up is equivalent to 9LJ262-Up.
I have had a few machines with these symptoms that responded well to a small pump regulator adjustment. You will need to loosen the large locknut on the picture shown of the rear pump and turn the adjustment screw in 1/8 of a turn at a time to see if it helps.
Thanks, i tried the adjuster clock wise and counter i dint do anything to the final drive noticeable. The serial is 5pk00267. When ever the left travel pedal is pressed either direction and swing function is engaged travel stops. The engine never loads up on either function. Unless lightly pressing right travel pedal. Could this happen to be rear pump failure? Wwhen right pedal slightly pressed the mixture of oil between front pump rear pump feeding the travel circuit, the left final drive is slightly being fed by mixture of front pump oil?
Sorry for not adding that while using swing and left travel, slightly touch right travel pedal right final drive will engage full speed.
So for all parts & service information you should use a Serial Number somewhere between 9LJ1 and 9LJ261.
Geez.. i meant the left final will engage full speed..
That confirms what I said before (check out the SysOp document in Post #5 above), that when you use another function both pumps will sum up their output to drive everything, which "restores" the LH travel speed and makes it exactly the same as the RH.
Not exactly. In Straight Travel mode, there is no full summation of flows from two pumps. In Straight Travel mode, both travel hydraulic motors receive oil through the Straight Travel Valve mainly from the rear pump. It is the Straight Travel Valve that allows for equal distribution of oil between the right and left travel circuits, so the machine should drive perfectly straight. All other equipment during Straight Travel mode receives oil from the front pump. And only the remaining oil from the front pump is distributed evenly between the hydraulic motors through the Straight Travel Valve. In fact, both tracks in Straight Travel mode are driven by one pump. Therefore, the problem should most likely be looked for in the rear pump. It is unlikely, but the problem may also be in the control valve of the left hydraulic travel motor. I wrote about this above in the post.
Ok i will look into it and let know results. I appreciate it.
Got her fixed. Figured i would let know so future folks could see this thread. It was the pumps. Pulled and rebuilt them just fired it back up today. Didnt see anything terribly wrong with pistons but the shafts and swash plates were toast. Thank everybody for there replys. Im sure be hearing from me again but hopefully not haha.
Was the rear pump more worn than the front? I hope your excavator is now running straight?
Its tracking straight. Best i could tell both sides were in bad shape. But the rear pump gave up sooner resulting in slow left track slow swing.