Caterpillar 312B weak travel diagnosis

[CatKC]

I have a Cat 312B SN-9GR00432 which has weak travel, very weak after warming up. It will go into RABBIT (fast) mode but shifts back to TURTLE going up an incline.
The LEFT track is weaker so it tracks slightly to the left all the time.
I have replaced the swivel seals and had the hydraulic oil analyzed, the Hydraulic filters have been changed.

I would like suggestions on how to diagnose if this is a weak hydraulic pump, worn LEFT drive motor (both?) something else?

Separate inquiry, what is the function of the STRAIGHT TRAVEL SOLENOID and could this be a cause?

 

[John C.]

If there is no dirt under the travel pedals and they are moving the same amount of distance I would suggest a case drain test on each motor. Put a suitable size pin between the sprocket and track frame to lock out the rotation. Now pull the case drain hose and plug it. Put another hose on the case drain fitting on the motor and then stall the track for about a minute. Should probably be less than a quart of oil. Now check the other side the same way and see what you get. The other issue could be an out of adjustment or worn pump. That can probably be adjusted some for more power. That is best left to experienced wrenches. How many hours do you have on this machine?

 

[CatKC]

If there is no dirt under the travel pedals and they are moving the same amount of distance I would suggest a case drain test on each motor.

I have checked for dirt under the pedal, also the same track is weak FORWARD or BACKWARD.
I checked the track rotation to see if I could detect any 'binds' by lifting each track off the ground, the LEFT was slower with no load.

Weather permitting I will check the case drains, I'll have to get a fitting for it first.
If anyone has an idea about the type/size fitting I will need please let me know.
If the case drain check shows a lot of oil I 'assume' it would mean a worn motor?

As it doesn't travel straight, any idea what the STRAIGHT TRAVEL SOLENOID is used for?

When I bought it the hour meter had been replaced. Machine hours are a guess, from the 'visible' wear condition I would guess in the 4,xxx - 5,xxx hour range, but I'm not very knowledgeable about the subject.

FWIW: I know how to used the Monitor if there is something I can check there. I also have a reasonable number of 312 documents covering service, maintenance, adjustments, parts Etc. If it comes down to having to 'adjust' the pump I think I can handle it. . . . . with a little guidance on what NOT to do and the 'BUT FIRST' gotchas.

 

[John C.]

The straight travel solenoid allows the machine to walk straight by joining both pump flows when traveling and operating another function. It is easy enough to check when the travel is working normally. Just travel straight and operate the bucket and if the machine doesn't vear one way of the other, the valve is working normally. Your uneven travel should straighten out when you operate another function.

 

[CatKC]

Your uneven travel should straighten out when you operate another function.

Thanks, something I haven tried.