Drive problem

[dines1978]

I have a 1988 642b and i just had the pump rebuilt. After installing the pump and filling the system with fluid I took it for a test drive. Everything was fine until I made my third turn and headed back to the shop. About half way there the left side seemed to lose alot of power. Now I have no reverse on the left side and forward feels weak. I have swapped the replenishing valves and it made no difference. I had the left drive motor rebuilt and it made no difference. With the loader lifted and block I get drive in both directions on both sides. When it is on the ground I have no reverse on the left side. Now, if I lift and block the loader I can not turn the wheels by hand on the right side. On the left side I can turn the wheels forward by hand easily but reverse by hand is difficult. I don't believe I should be able to turn these wheels at all by hand with the loader turned off, Correct? Anyway, I don't know where to go from here. I don't want to pull that pump again. Any ideas or in put would be great. Thanks

 

[OldMachinist]

You shouldn't be able to turn the wheel by hand if there's oil in the motor. The only thing I can think of that you haven't tried is to swap the motors and see if the problem follows the motor. If it doesn't its the pump and if it does its the motor.

 

[Tazza]

You shouldn't be able to turn the wheel by hand if there's oil in the motor. The only thing I can think of that you haven't tried is to swap the motors and see if the problem follows the motor. If it doesn't its the pump and if it does its the motor.

How long have you run the machine since you installed the re-conditioned pump? I just did this on a 743 yesterday, it runs the same pump. How did you get oil back into the pump to prime it?
OM is spot on, the motors when full of oil will NOT move by hand. When the system is full of oil, without air bubbles the wheels should be solid, but if you get an air pocket in the motor it will spin easily. With air, you will find one direction it may lock up but the other it will still move then eventually stop.
I'm thinking you haven't purged the air from the system yet or the system wasn't primed correctly and *possibly* damaged the rotating group or wear plate due to lack of oil. I fill the tank with oil and extend the lift rams out then operate the pedal to draw oil through the pump. Move them full stroke back and forth operating the pedal, this helps get more oil into the pumps. I then start the engine for a few seconds at a time till the pump has re-filled the system.
It will take ages to get all the air out of the cylinders and lines, so expect weird operation for a while.

 

[dines1978]

You shouldn't be able to turn the wheel by hand if there's oil in the motor. The only thing I can think of that you haven't tried is to swap the motors and see if the problem follows the motor. If it doesn't its the pump and if it does its the motor.

Ok, I swapped drive motors from side to side today. My problem followed the drive motor. I called the dealer, they rebuilt the motor for me, and asked if they changed or even checked the shuttle valve. His reply was simply, no but if you bring it back we can take another look at it. Is it normal not to replace the shuttle valve when rebuilding a drive motor? I even told them I had no drive in one direction with that motor, shouldn't that have been the first thing to check? What are your thoughts? Thanks

 

[Tazza]

Ok, I swapped drive motors from side to side today. My problem followed the drive motor. I called the dealer, they rebuilt the motor for me, and asked if they changed or even checked the shuttle valve. His reply was simply, no but if you bring it back we can take another look at it. Is it normal not to replace the shuttle valve when rebuilding a drive motor? I even told them I had no drive in one direction with that motor, shouldn't that have been the first thing to check? What are your thoughts? Thanks

Its not nrmal for the shuttle valve to get replaced, but i always remove it and give it a good clean so you can look for obvious problems like broken springs or bad wear on the sealing faces.
Loss of drive in one direction could be a bad seal too. There are 2 plastic/nylon seals that seal against the 2 main inlet ports. If they were not installed correctly the oil could be passing from the high pressure side to the case drain on the outer section of the seal. If it was the inner one, the oil would simply flow back to the other port and you would have a lack of power in both directions.
I hope some of that made sense, its a lot easier to follow if you know what the internals of the motor look like.

 

[Louis]

You shouldn't be able to turn the wheel by hand if there's oil in the motor. The only thing I can think of that you haven't tried is to swap the motors and see if the problem follows the motor. If it doesn't its the pump and if it does its the motor.

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