Bobcat 331 drive motor loss

[catdozer]

I have a bobcat 331 excavator and on the left side the track just loses power sometimes, then play with the lever and works fine for a bit. Push some dirt and also has a lose of power again. I'm pretty well thinking it's the drive motor, but could it be something else? Any help would be greatly appreciated.

 

[SSdoxie]

Cat,
The model 331 was bulit for a number of years and went throught quite a few design changes without changing the model number. Give me your serial number so I cand look up what pump, motor, and control system you have. If it is one fo the latest versions, it might be just a control linkage problem.

 

[catdozer]

Cat,
The model 331 was bulit for a number of years and went throught quite a few design changes without changing the model number. Give me your serial number so I cand look up what pump, motor, and control system you have. If it is one fo the latest versions, it might be just a control linkage problem.

I can get the number tomorrow. but I do have the manual and the numbers are 512913001 thru 512915199 and that it. Now I made hoses for the two large lines and crossed them to the other side to see if it was a pump or motor but it still stalls out on the left side.

 

[catdozer]

i got the S/N today 512914912. we tested it for awhile today. and it was the right side acting up. so it must be the pump then. since its the other side stalling after we switched em. i would still like your opinion SSdoxie.

 

[SSdoxie]

Your 331 is less complicated than the later models. Uses fixed displacement gear pumps and mechanical linkage to the control valve. Swapping the hoses they way you did and still have weak drive in the same motor would indicate motor is by-passing oil.

It could be a sticky spool valve or check valve in the end cap that allows it to regain some power when you move the lever forward & reverse. May want to try taking the end cap off first, clean & inspect there before remove complete motor.

 

[catdozer]

Your 331 is less complicated than the later models. Uses fixed displacement gear pumps and mechanical linkage to the control valve. Swapping the hoses they way you did and still have weak drive in the same motor would indicate motor is by-passing oil.

It could be a sticky spool valve or check valve in the end cap that allows it to regain some power when you move the lever forward & reverse. May want to try taking the end cap off first, clean & inspect there before remove complete motor.

it wasnt the the same drive motor that was stalling, i didnt use it enough yesterday to see which drive it was. but using it enough today it was the opposite side acting up. it was the left side stalling. switch the hoses on it now it was the right side stalling.

 

[SSdoxie]

I suspect it is back at the gear pump(s). There is a 3 section gear pump assembly, mid-section #2 and section #3 (counting from engine out) are the pumps for motors, 1 for the right & 1 for left, once oil flows through the trave motor spool of the control valve the oil enters a parrallel passage the feed all remaining digging functions. Between section #2 & #3 is are 2 plugs, these are check plugs that allow oil from pump #1 to enter when you go in 2 speed. If the the check for left drive is leaking you will loose drive pressure on that side. Remove both check plugs and inspect them close. If no problem found there, it would be best to use flow meter on each section to see if 1 section is worn.

 

[catdozer]

I suspect it is back at the gear pump(s). There is a 3 section gear pump assembly, mid-section #2 and section #3 (counting from engine out) are the pumps for motors, 1 for the right & 1 for left, once oil flows through the trave motor spool of the control valve the oil enters a parrallel passage the feed all remaining digging functions. Between section #2 & #3 is are 2 plugs, these are check plugs that allow oil from pump #1 to enter when you go in 2 speed. If the the check for left drive is leaking you will loose drive pressure on that side. Remove both check plugs and inspect them close. If no problem found there, it would be best to use flow meter on each section to see if 1 section is worn.

Ok do I have to take the pump off? And can I hook up to what looks like quick connects?

 

[SSdoxie]

Ok do I have to take the pump off? And can I hook up to what looks like quick connects?

The couplers at the pump fittings are for reading pressure at each pump. You could start there, take a reading with track stalled ( put a bar through the track spocket so it cannot trun) then disconnect the motor lines and plug ends of the hoses with steel caps and try again. If max pressure is low in both tests would indicate pressure loss at the pump. But inspect those 2 check valves at the pump first. I came across one last week that had other problems but also had the similar loss of drive you have, one of the check valves had blown o-rings on it.

 

[catdozer]

The couplers at the pump fittings are for reading pressure at each pump. You could start there, take a reading with track stalled ( put a bar through the track spocket so it cannot trun) then disconnect the motor lines and plug ends of the hoses with steel caps and try again. If max pressure is low in both tests would indicate pressure loss at the pump. But inspect those 2 check valves at the pump first. I came across one last week that had other problems but also had the similar loss of drive you have, one of the check valves had blown o-rings on it.

We blew a gauge, fed up I just dropped it off at the dealer, he met me there and put it inside. he said I may have blown an o-ring also, but we'll find out. Im very happy and very appreciated that you helped me. I must asked are you a mechanic, cause you are very good with your bobcats !