D3B w/backhoe Need help please.

Not really up on D3's but sounds very much like you have a hydraulic blockage which is loading up and bogging down the engine. No, not likely to be caused by plugged transfer pump screen.

Also a word of caution...could mean you are generating some extremely high pressure......are there quick disconnects involved?....check for a faulty coupling.

Hey Bob/Ont...need a little help on this one.

First off move the cable that controls pump out put and see if it helps. Also try the controls for the blade and the hoe and look for some action to see if they are getting flow. Pay attention for engine unloading and you will find problem. Then the hoe quick connectors are a great source of trouble if they are old. Look for wear caused by the locking balls in the retaining groove.. If the groove is worn or the spring inside of the down stream coupler is weak the check valves will not unseat and allow oil flow down stream. Quick connectors have check valves sealing the ends when you take them apart. To unseat both of them so the oil can flow the connectors must be properly seated together and the springs behind the check valves must be of equal strength. I have had one spring retaining ring slip out and almost blow a pump apart while flow testing it. Luckey it was a piston pump and could blow the barrel off the port plate.
Later Bob

Thank you for your replies. I will check for those problems.

Does anyone think this could be a torque converter problem? It moves just fine when it is running, I mean until it dies. A friend of mine suggested that it could be a torque coverter issue and that I should have a look at the scavenger pump screen.

I have seen a badly leaking torque do that but it was in a seperate housing and couldn't drain. Your's is in the front of the trans and drains back down without a scavenge pump. Play with the hyd controls while it's still running and look for movement of implement as the engine runs free. Have you got the LH engine side cover off to have a close look and listen to the pump? Make sure the cable is hooked up and actually moving something. It sounds like you have a fixed displacement pump deadended some place before a main relief valve.
Later Bob

bob

I fired up the machine, warmed it up, and opened the throttle. the machine did not miss a lick for over an hour. after that, when it did act up, it wasnt as severe and it would recover and repeat about evey five minutes. I believe that valve on the hydraulic pump is full open with the cable pushed all the way in. All the blade functions work great and have no effect on the engine when operated. I do have an open hyd circuit via the backhoe supply/return I feel reasonably sure that the hyd and fuel systems are not my problem.

Previously when the problem occurred I was operating the crawler under normal conditions- dozing, traveling etc. Under these conditions, when the engine rpm would drop off it would not recover and eventually die.

The machine has 6300 hours. I was looking at the top of the filter housing under the floor boards between my feet. Im not positive , but it looks to be the trans filter. It could be the original as the paint on the cap screws is fairly well intact. In your opinion, could that filter cause these symptoms? Thanks, Rob

I'm looking at my D3 79U series parts book and it does not show an external transmission filter .....just the suction screen in the transmission. Does show a hydraulic system filter. Also the hydraulic pump with the cable valve is a wobble plate piston pump with servo valves. Plenty of sources for problems.

Bob I can post these parts diagrams if you think it would be helpful.

Please do. My parts book and service manual are in the mail. Thanks

Okay Rob and OM, there are two transmissions. The 3F 1R with only a screen and the 3F 3R with a suction screen in the bottom and a filter under the floor plates that Rob mentioned. Your last post paints a new picture. If the blade and the hoe both work when the selector cable is moved to each position then it's not likely the hyd system. Check this out and also have a look at the connectors for wear and come on back. Keep in mind worn connectors can sometimes work and sometimes not work depending where the locking balls are in the groove. This causes some head scratching with the piston pump that doesn't have the selector valve. The main valve returns oil to the tank through the hoe valve and it gets blocked so nothing will work on two of the three circuits.
I doubt the trans is loading the engine down but change and cut open the filter to see if it's clean.
Later Bob

Thanks Bob,
I'll save the parts posts for now....probably just add to the confusion.
I'm still betting on an intermitent coupling problem.

Rob, you never did say what model D3B this is....can you post?