939A1 Power Steering Bleed?

[slothman]

I blew a line at my steering gearbox this past weekend. Had to drive a half mile before we could work on it. M925A1.

Reattached the line. Added oil to max, drove it around turning wheel to both stops, and repeated for ~2.5 gallons of oil (maybe 5 or 6 repetitions?). Oil kept just spraying out the overflow valve.

I am assuming its not being bled correctly. I can't find anything in the TM on how to solve this. Can anyone point me in the right direction?

Likely need a rebuild kit at this point too - any ideas on where to source one?

Thank you!

 

[red]

Lift both front tires off the ground and turn from lock to lock with the engine running (takes about 10-20 complete cycles to do this)

 

[slothman]

Lift both front tires off the ground and turn from lock to lock with the engine running (takes about 10-20 complete cycles to do this)

I was essentially doing this, driving around an open field turning lock to lock, but it was pushing all the fluid out the overflow on the first turn.

 

[red]

You have to take the weight off to get the air out.

 

[slothman]

gotcha. will give it a try.

 

[juanprado]

I added a power stg cooler to my m923 with the nhc250. Lost a few qts as the pump went dry. I filled the pump and started it. Turned a few times lock to lock, refilled system as the cooler filled up, turned wheels a a few more times on ground and done.

I suspect you have to have another problem to have fluid being physically expelled out like that. Do your stg cylinders work ok? Did the power stg assist work ok before the hose blew?

 

[doghead]

Why did the line blow?

 

[74M35A2]

^This^. You may have something going on with your steering gear, causing the pump to pressurize the fluid continuously rather than as needed. This will over-temp the fluid, causing the fluid to expand, soft hoses to burst, etc....

Should not really have to bleed a pressurized recirculating system, it should just take care of itself as soon as the correct amount of fluid is present.

 

[slothman]

Update:

The line that blew is one of the two hard lines going to the assist cylinder, at the steering gear. This occurred while doing a pretty major step down off a slope at an angle. My theory is that the assist cylinder acted as as shock absorber and the pressure from that blew the line.

The P-S pump was certainly bad after tear down with burnt up bushings. We aren't sure when this happened as we had to drive several hundred miles to get home after failure. (We had tried filling it and bleeding it in the field with no luck).

We replaced the PS pump and jacked the front end up and did 30-40 end to end turns while running, some bubbles came out, but fluid level stabilized and still no power steering. The fluid / pump are not getting hot. Before level stabilized, the level would increase/surge (and slowly decrease following the surges) while turning from the right to the left, but not from left to right.

The plumbing on the system makes me think that the gear should work regardless of the assist cylinder's functionality.

 

[74M35A2]

There is valving in the main driver side steering gear box that determines if the pressure from the PS pump is utilized or simply recirculated. Sounds like this could be your issue, if you believe pump is OK.

 

[slothman]

replaced the steering gear. my old steering gear seemed ok (sans lots of metal flakes from the totaled pump).

no change.

that puts me at replaced pump, replaced steering gear.. no external leaks on assist cylinder.

If we disconnect the lines at the asst cylinder side and run the engine should fluid spray out? it only comes out when i turn the wheel.

we've flushed the fluid twice now at the asst cylinder side. bled it with wheels up turned end to end.

 

[slothman]

bump. replaced assist cylinder. still no power. bled and filled system. blew all lines out with compressed air. flushed. ???!? maybe the pump i got was bad?