New owner, old 960

[HughF]

So, I bought an old 960 from a tractor dealer here in the UK... £6k delivered, which seemed the going rate for a skid steer over this side of the pond. Tyres are good, bucket is usable, starts and drives. 3800hrs.



It spent it's early life driving a road planer so has Hi-flow hydraulics on an electrically driven solenoid valve under the footplate. Regular 3rd spool valve outlets also piped up:



Within 24hrs of taking delivery I had got it sunk up to it's belly in my field, which then necessitated some work with a tractor, a tirfor winch and a few evenings to haul it out:
I have since purchased some McLaren over-tyre tracks for it.




I've fitted a new fuel filter, sorted out the wiring which was a mess, and given it a general going over. Seems like an honest machine. Hoping to put it to good work in the confines of my barn where I can't get my tractor.

 

[HughF]

OK, so using this a bit and I've discovered a bit of an issue. It seems to lack power in forwards when it gets warm. The stick come up hard with quite a bit of resistance, so I'm not sure if it's drive motors or pumps that are the problem. It still has tons of power in reverse.

Video showing the issue:



I suppose I need to get a pressure gauge on the lines to the motors and verify I'm getting 4500psi? I notice that the charge oil filter hasn't been changed, would that cause the issue?

I'm mechanically very competent but haven't had any experience of hydrostatic transmissions before, skidsteers being rare as unicorn fart here in the UK

 

[Firefighter]

Try the filter, the motors may need rebuilt, if the drive is ok in reverse but not forward it would seem as
an issue with the motor, if its in both directions, then it probably has damaged or scarring on the valve plates
both the pump & motors would need disassembled, easiest way to check the reverse is back up against a stationary object or wall etc,

 

[HughF]

The way I see this:

1. Pressure test charge pump
2. Pressure test forwards/backwards pressure on both pumps (to validate relief valve performance)
3a. If above fails, swap relief valves between forwards/backwards and see if the machine now has power in forwards and lacks power in reverse
3b. If above passes, look at the motor being the issue.

 

[HughF]

Well, fast forward a while and 55hrs runtime later - I've put a set of relief valves in the ta1919 pumps and that's made…….. no difference

I've broken and re-welded the linkages a couple of times, and I think that's because the neutral centralisers are very stiff. I'll take them off and lube them up.

What's the next steps for the low power and noisy pumps issue? Charge pressure?

 

[Firefighter]

Well, fast forward a while and 55hrs runtime later - I've put a set of relief valves in the ta1919 pumps and that's made…….. no difference

I've broken and re-welded the linkages a couple of times, and I think that's because the neutral centralisers are very stiff. I'll take them off and lube them up.

What's the next steps for the low power and noisy pumps issue? Charge pressure?

check charge pressure, also make sure that the suction hose does not have a leak, or the screen plugged, are the boom functions normal that would probably be a good indication of the health of the hose or screen
if everything checks out i would say the hydros need to be pulled apart

 

[HughF]

Boom functions are strong as an ox, no issues there. When you refer to hydros you mean pumps, or motors?

 

[Firefighter]

Boom functions are strong as an ox, no issues there. When you refer to hydros you mean pumps, or motors?

Hydrostatic pumps, If the boom function is smooth, with no pulsation or grumbling noises, should indicate that suction side is 100%
Pull the hydraulic filters off (2) and pour them in a clean container, inspect it for any brass colored metal flakes
if you have, i would pull the pumps, u will find your problem

 

[HughF]

Engine and pumps out the back as a whole long assembly, or pumps out through the seat hole, leaving the engine in place?

 

[Firefighter]

Engine and pumps out the back as a whole long assembly, or pumps out through the seat hole, leaving the engine in place?

I usually just remove the steering assembly and floorboard, then its not a big deal to take it out the front. remove the belly pan and then powerwash everyting out really well,

 

[HughF]

I usually just remove the steering assembly and floorboard, then its not a big deal to take it out the front. remove the belly pan and then powerwash everyting out really well,

Appreciate the advice, thanks.

 

[ward]

Here in the USA I worked on a bomag roller in 1995/1996 and had to pull the hydrostatic pump apart and of course the shop guys had to go study the pump, pick up and finger the parts as it was the first one we had seen apart, the manual was in German, when I put it back together it was awful at times and jerky, after studying differnt bomag machines shop manuals one had good reassemble pictures and one of the things was the lens had 2 holes and a pin in the pump housing that clocked the pump or advanced according to the rotation of the engine I tooked it back apart and it was in the wrong hole causing the pressure to charge aginst the swash plate pushing back aginst the control lever.