Power steering fault, help.

[Patrolling Paddy]

I'm having some issues with my power steering at the moment and have been tinkering but would like to get your thoughts.
It's a 94 TD42 GQ coil cab and a few years back I converted to a GU steering box (among other things) and it has been going strong. I have since gone to 37" sticky treps with -44 offset rims and I think that has stressed it to the point of failure.
The box came from the wreckers as on 4/04 GU tray back box #104 if that makes any difference.

The steering has always been heavy with the big wheels but recently it started getting past heavy and started to hit Armstrong, like it was low on pressure or something and now after the last comp I can't get anymore than about 1/4 turn if I'm sitting still and it is very difficult to get more than 1/4 turn when moving.

The kingpins are good, wheel bearing are good, drag link is good, tie rod is good. If I disconnect the drag link from the pitman I can freely turn everything by hand so I am comfortable that the front end components are not the cause.
If I jack the wheels off the ground I can turn the steering without it locking up but it does take a little effort, not excessive but it feels like it should if the wheels were on the ground.
The pump is flowing well and I am seeing a good strong return flow at rest. The pump hits 1250psi on relief which is normal.

I'm now thinking the power piston in the box is knackered and I think I will try for another box, what are your thoughts?

What is the best box # for heavy duty (ab)use

[Evo]

Could very well be something in the box has let go and is restricting movement in the box especially under load.
Maybe a sudden shock to the steering while at comp?
If you can find the same box again (seeing as you didn't have issues for a while) just to get you going and pull this one down to have a look-see.

Evo

[liftlid]

Sounds exactly like the air lock problem mine had when I replaced the pump, did you roll the truck ?

[Patrolling Paddy]

Not been rolled.
To bleed is just lock to lock from what I can find, how did you sort yours out?

[liftlid]

Mine kept locking up whilst driving, jacked up drivers wheel and turned side to side, did this several times before it came good, I've got a gu box on a gq, I wondered if the air collected in the pipes not the box???

[Patrolling Paddy]

Well I just wrote another response but it disappeared on me, damn iPad.

While fault finding I have had the system apart, replaced the return line, replaced the oil a few times and bled it through aswell and no change to the problem. I even put the old GQ box back in but I think that is completely dead cause I had no power at all from that one, couldn't even get pressure, it has been sitting in the shed for about 8 yrs though.

I think it might be time to head to the wreckers and get another box. Are any of the box # better than a 104?

[Patrolling Paddy]

I'm not thinking a mechanical failure of the box as it still turns by hand if you turn the pitman arm. The worm gear could use a tweek as there is a small amount of backlash in the gears I can feel but this shouldn't affect the power assist at all.
I might just pick up another box and see how it goes, then pull this one down as suggested and see what I can find.

Sudden shock to steering could be anywhere from the start line to the finish line as the poor thing cops a hiding, however it was developing prior to this comp, it could have even been a faulty box from the wreckers that got sent over the edge with the big wheels, large offset and diff lock combined with the conditions it survives (well mostly survives).

[Patrolling Paddy]

New box is in and no joy.
The pump is making the right pressure but as soon as it is under any load it won't turn the wheels.
Any idea what the best replacement pump would be.

[Parksy]

Have you tried bleeding from the bleed nipple on the steering box?

[Patrolling Paddy]

No bleed nipple on the GU box. The old GQ box had one but not the 2 GU boxes I now have.
If I jack one wheel up (either side) the steering turns like it should. Lock to lock back and forward repeatedly and no joy as soon as both wheels are on the ground. If you turn really quick with a wheel up it flutters a little bit too I noticed this arvo.

I'll try again to bleed some more but I just don't know anymore.

Pressure gives the force behind the power assist and the flow should be what keeps up to the movement and speed of turning. I doesn't matter how fast I turn the wheels it only makes about 1/4 turn before it says no more and the pump hits the relief pressure.
If it is making pressure it should turn but maybe something else is happening, I just can't work out why 2 boxes are doing the same thing.
I'm going to disconnect all the steering components and see if I can find anything binding at all, I can turn the wheels by hand so I'm not expecting to find anything but this is just giving me the $hits now.

[Parksy]

That's strange about the lack of bleed nipples. My gq and gu steering boxes both have bleed nipples.

[Patrolling Paddy]

Anyone pulled these pumps down before?
In the end of the spool there is a little gauze filter and when I try and blow through it nothing happens, not sure if is supposed to be a through hole but it seems odd to put a filter on a blank.
Maybe the spool should shuttle to allow more flow or something. Can't get my head around it at the moment.

[Evo]

None of the lines taken a beating from a foreign object, etc?
Hence restricting flow under load more-so than with free load?

Evo

[Patrolling Paddy]

The pressure line looks good from the outside, the box to tube line appears to be good, tube looks good I can't see any damage and the tube to res is new (I couldn't get the hose off so had to cut it free). Now that's all external inspection and I can't see inside but the return flow unloaded looks good so I don't think I've got an internal hose issue.

I think that the free flow will be more than the loaded flow given that loaded that flow is turned into pressure.

This is a pain in the a$$. Thanks for the input guys it is appreciated

[Avo]

Anyone pulled these pumps down before?
In the end of the spool there is a little gauze filter and when I try and blow through it nothing happens, not sure if is supposed to be a through hole but it seems odd to put a filter on a blank.
Maybe the spool should shuttle to allow more flow or something. Can't get my head around it at the moment.

I have pulled mine apart,did you strip it right down..when I did mine the little vanes only go in one way..i put them in the wrong way and had similar problems...just go and welcome a few more members and download a manual mate..there's pretty good pics of the power steering pump in there.

[Patrolling Paddy]

I haven't committed to pulling it right down as yet cause I don't have the seal kit, I pulled all the relief spool spring etc as this is the bit that controls why the pump does.
The vanes and rotor are not really serviceable other that strip clean and install, replace if not right. The pump seems to push oil and pressure until it come under load and then it gives up, it still produces full pressure but doesn't provide power to the power steering. The internals might not be right but they still seem to be functioning.
I might try and pull the gauze filter out of the spool and see if there is anything blocked behind that.

I'm looking at a new pump anyway now so what have I got to loose either way. It seems to be cheaper to get an am pump than a service exchange stock one, other than needing to make a bracket and get new hoses.

Well back to the shed

[Patrolling Paddy]

Well behind that gauze is the relief. Don't mess with it is the advice I will give at this point.

[Avo]

when I bled mine after replacing the pump mate I had jacked my car up with both wheels off the ground..grab a wheel and turn from lock to lock really quickly,i did this about 10 times,refill resevior and did again..when I turned wheels slowly using steering wheel it didn't work...hope that helps..

[Patrolling Paddy]

Well I picked up a 04 GU pump this morning, I'll put in today and try the bleed trick.
The GU pump looks the same from the outside but when you look into the pressure fitting the port is about 4-5mm and the GQ one is only about 2mm so this should help, from what I can see of the spool it looks different too. Not pulling this one apart though.

[Patrolling Paddy]

Installed bled and going. Not overcome the stationary steering but it seems smooth and easy when moving. Gotta take it for a drive and see how it goes under stress. With the damper and spring disconnected I turned the wheels for about 5 minutes before trying to turn from the cab, doesn't seem that it made the problem go away but this pump is better than the old one.
Going to look at getting a psc pump and fit that up.

[Patrolling Paddy]

Put my 35s back on with the -22 offset and the steering is heaps better. Still not right but heaps better.
Going to strip the front end and see what is going on. Now starting to look more at kingpins, it was suggested earlier but because it turns freely without load on the tyres and I can turn it from the tyres freely I haven't convinced myself it is mechanical yet but given the kingpins would be affected by load, particularly with the wider offset they may be compromised under load but nue yet failed? There is not crunching, grinding, binding or anything else that I can find yet.

I was getting only 1/4 turn before it would stop and now with the 35s, new pump and new box my 2yr old boy can turn it 3/4 before it stops, this is consistent and doesn't really change. Feels heaps better so I'll strip the front and see if I can find any sinister sneaky faults that seem to be the underlying issue. The pump had some issues anyway, when I pulled the relief apart I found that the ball had scoring/grooving from where it had been passing/relieving heaps so I think it was starting to relieve early and wasn't getting proper pressure/flow before the relief fully opened. I don't think there is any problems with my box so I will refit it later too.

Cheers for the info so far guys, I'll update when I work out what else is going on, it will take a few weeks now as I'm back on roster Tuesday.

[Patrolling Paddy]

Well here's an update for you all. Pulled the front end to bits and found both CVs were bound up and the kingpin bearings were ok ( if I wasn't having issues I wouldn't have changed them). Thought this was a likely cause so went shopping and got some new stuff.

New (second hand) CVs
New swivel hub kit
New wheel bearings
Disconnected the front drive shaft as the uni's are dead too.
Tie rod ends are good
Drag link ends are good
Diff lock seems good too

Already done
Changed steering box
Changed steering pump
Checked steering pressure is spec

The steering is the bloody same
Looks like I'll be checking something else for binding, don't know what else is left.

Think I'll be looking into the PSC aftermarket pump running 1650psi and see how that goes, after that it's ram assist.