JD 310B starting and hydraulic issues

Hi all, new here and definitely not an expert on Diesel engines or hydraulics.
Borrowed a JD310B backhoe, ran great until I put a few hours on it. Issues started with the hydraulic brakes feeling spongy then I was able to completely compress the pedal without any resistance or braking. Fluid is full and even slightly above the fill line since I thought low oil may be the problem.
Next day I started the Deere, front bucket would not lift for a good 30 mins (bad pump?). Once it did, it ran good for a few hours then once again the brakes slowly started to go out. Gave it a rest for the day,
Next few times I ran it, it took nearly 45 mins for the front bucket to lift, found out that if I turn the steering all the way to the left, the lift and tilt front bucket works much better but still slow (any idea why?) now the bucket won’t lift anything unless the front tires are turned all the way to the left, quite inconvenient.
Last time I ran it was for about 3 hours. Was grading a driveway so nothing too hard on the machine and it ran real rough for about 30 seconds with black and dark grey exhaust pouring out of the chimney then died. Started up again and ran for about 10 seconds doing the same thing. Let it rest for the day.
Tried to start it the other day and wants to turn over but acts like not enough juice. Tried 3 times and starter started smoking...
New batteries (2-6v connected in parallel) and have plenty of juice left (each 6.5v).
Checked and cleaned air filter, fuel filter looks good, cleaned battery terminals, took each out and recharged.
Need some advice from some more experienced people than myself. Any input would be appreciated, definitely not used to working on heavy equipment.
Thanks!

Where in Michigan are you located?

Are you sure the batteries are in parallel and not in series? I run 2- 6volt batteries as well, but mine are in series. I had similar symptoms as far as how the hydraulics don't function properly when my main pump on front of engine went bad. Given that it doesn't want to crank, I'm betting your pump has a major issue, or is deadheaded and creating too much resistance for starter to turn engine over. I'm far from an expert, but I've gotten quite intimate with my 310A over the past 8 years.

Also, you say borrowed...is the owner aware of what's going on?

Jackson

Yes my bad they are connected in series. owner is aware but dosent know much about the machine.

Mg will be along, hopefully.

Start with the engine, is the oil level OK, is the coolant level OK, do they both look good. Can you rotate the engine with the fan belt and fan? it should move easily a tiny bit at a time, and move another tiny bit after a few seconds. There was a big load on the engine to make it smoke and die, so you might not be able to move it. Find out why, remove the front pump coupler and see if the engine turns easier. Or pull the hydraulic pump and check it for debris.

Don't start it or run it.

Delmer said:

Mg will be along, hopefully.

Start with the engine, is the oil level OK, is the coolant level OK, do they both look good. Can you rotate the engine with the fan belt and fan? it should move easily a tiny bit at a time, and move another tiny bit after a few seconds. There was a big load on the engine to make it smoke and die, so you might not be able to move it. Find out why, remove the front pump coupler and see if the engine turns easier. Or pull the hydraulic pump and check it for debris.

Don't start it or run it.

Click to expand...

I agree about a heavy load. Be careful if you do take the 4 bolts out that attach the pump coupler to the crank drive pulley as there may be a fair bit of trapped torque that could unwind violently once some of the bolts are out. The coupler should be bolted to the crank and slips over a splined shaft on the pump, held tight with pinch bolts.

Welcome to HEF Speelk!

Wow, you have quite the load of issues going on. Lets deal with starting first.

All your issues are related in my opinion. The brake valve gets its oil from the transmission pump. The transmission pump charges the hydraulic pump.

Speelk said:

Tried to start it the other day and wants to turn over but acts like not enough juice.

Click to expand...

It should have a destroke solenoid mounted to the front left side of the hydraulic pump. It should be energized while cranking. It removes the hydraulic load on the engine for starting.

Also the batteries should be (2) 6 V batteries in series to make 12 V.

Speelk said:

Was grading a driveway so nothing too hard on the machine and it ran real rough for about 30 seconds with black and dark grey exhaust pouring out of the chimney then died.

Click to expand...

This sounds like something placed a big load on the engine. Maybe a pump going? If destroke solenoid is OK, then I would remove the pump coupler as mentioned to see if the engine starts.