1256 Power Steering

[redgreen93]

Have a 1256 that gets you sparingly but somewhere along the line now lost power steering. Covered a few different times on multiple forms but I guess where I'm stuck is it doesn't seem to fit the bill for a normal MCV valve or pump issue. Jacking front end up, everything really turns smoothly so not mechanically binding. Down to the hydraulics, oil filter changed and overfilled the oil. From there I pulled the 5/8 inch plug out the back of the MCV valve and started it, good strong gush of oil out. Also took plug out of steering valve and confirmed oil flow there as well and loosened line going up to front bolster and oil there as well. Seems pump and valve are outputting but no gauges at the moment to see what pressure. The odd part here is even if it was a weak pump, brakes and TA work great, it is strictly the steering. What other checks have you guys ran across that I am missing?

 

[Janicholson]

Cylinder bypass can make that happen. Jim

 

[rustred]

the tractor vet will clue you in soon with a story.

 

[caterpillar guy]

You don't say if it is only one way or both ways if one way then look at the pilot valve down by the starter. It can have the piston stick or cap leak. Otherwise it has to be a flow issue whether it is a hose or cylinder. Could also be a hole in a line leaking would lose both flow and pressure.

 

[redgreen93]

(quoted from post at 07:54:12 05/02/21) You don't say if it is only one way or both ways if one way then look at the pilot valve down by the starter. It can have the piston stick or cap leak. Otherwise it has to be a flow issue whether it is a hose or cylinder. Could also be a hole in a line leaking would lose both flow and pressure.

Good point, should add it is the same in both directions. No external leaks, being a 56 it has the front bolster rather than a cylinder and I'll be honest I'm not totally familiar with those internals. Is a bypass or similar issue common with the bolster?

 

[redgreen93]

Being a 56 it has the front bolster rather than a cylinder but I guess I'll plead ignorant on the bolster internal workings. Is a bypass still something likely there?

 

[pete 23]

First thing to check is relief valve in bottom rear corner of mcv. It has an
o ring on it that often disintegrates. Or ,something may be stuck in the
relief valve holding it open.

Also, if it has clutch booster that is the port that feeds booster and if
that elbow is not screwed in as far as you can before tightening the o ring
retaining nut, it will blow that o-ring.

If you suspect cylinder leakage in bolster, you can take the leak off line
off in front of radiator on that bearing cap, that is hooked to oil cooler.
PLug oil cooler line and then turn wheel to see if oil keeps shooting out.
You are going to get some at first and then some small leakage if it is ok.

 

[caterpillar guy]

The front bolster steering is just a rack with a gear vertically to fasten the arm to for the tierods. The piston is on the ends of the rack. being pushed each way with the turns of the wheel.