Need help with power steering issue from hell

[chenderson]

I have a 1990 M998 with a power steering issue that I believe is the steering box but would appreciate some advice before I load up the expensive parts cannon. It is the older pump with integrated tank and 4 belt v pulley.

Symptoms: power steering for the most part works ok. When turning I encounter multiple spots that require increased effort, sometimes two hands to turn. Once I make it through the hard spot I can turn roughly another half a turn and there is another hard spot. This happens in both directions. Also happens on jack stands with the engine running as well as off. Hydraulic fan and brakes both work as they should.

Things I have tried with no change:

1. Changed ATF steering fluid and bled multiple times using the steps in the manual.
2. Replaced shaft from steering wheel to box thinking one of the u joints had a bad spot that only showed up under load.
3. Purchased the official military pressure and flow test set. All tested to spec using the procedure that came with it.
4. Today I disconnected the pitman arm to rule out any binding after the steering box and the issue was still there.

While I had the pitman arm disconnected I opened the hood and saw the power steering hose from the cadillac valve to the fan clutch jump every time I hit the hard spots. Again, this is with the engine not running. Could there be some valve or blockage that is causing this? I really do not want to throw a pricey steering box at it to find out its something else.

Any help would be appreciated!

 

[FlameRed]

No strange noises?

I recently replace my pump on the same platform and found it really really picky about how it wants to be bled. I must have done it 5 times incorrectly until I figured out that as part of the documented procedure, it really, really wanted to wait a couple seconds at each left and right stop. I also would check every 5 full revolutions if the reseviour needed a top off. And yes, do the number of stop to stop turns required - don't do fewer! I think it is 40?

I would have pump noises when it had air in the system. I would think that having air in the system might make a line jump? But I definately hear some strange noise effect too!

All I can say it is really picky about being bled.

 

[NDT]

Sounds like you have done an exceptional job at isolating the problem to the Saginaw gear.

 

[chenderson]

No strange noises?

I recently replace my pump on the same platform and found it really really picky about how it wants to be bled. I must have done it 5 times incorrectly until I figured out that as part of the documented procedure, it really, really wanted to wait a couple seconds at each left and right stop. I also would check every 5 full revolutions if the reseviour needed a top off. And yes, do the number of stop to stop turns required - don't do fewer! I think it is 40?

I would have pump noises when it had air in the system. I would think that having air in the system might make a line jump? But I definately hear some strange noise effect too!

All I can say it is really picky about being bled.

Thanks for the reply. No strange noises at all. I bled the system with 20 inches of vacuum for 20 minutes and no change. It has been this way for 1 year and 2,200 miles.

 

[chenderson]

Sounds like you have done an exceptional job at isolating the problem to the Saginaw gear.

Thank you. Just wanted to make sure I was headed in the right direction. I see rock auto has a LARES new steering box for $415. Will probably give that a go.

 

[chenderson]

Well, looks like a new steering box did not fix the issue. The only things left are the pump and hydro brake booster, correct? I'm going to run another pressure and flow test to see if I missed anything. Is there any reason I can't bypass the hydroboost and plug the high pressure line from the pump direct to the steering box? I think the test gauge would give me enough hose to do that and rule out the hydroboost. Just trying to avoid throwing more parts at it than I have to. At least the new steering box is nice and tight and cleaned up a little slop in the wheel. Thanks in advance for any help.

 

[Mogman]

So you still have tight spots even with the linkage removed? I cannot see how the hydroboost could give you repeatable tight spots at the same steering positions, you said it happened even with the engine off, again cannot see how the hydroboost could affect that...
But yes if you can you can bypass the hydroboost.
Take notice again just for kicks if it the steering wheel is in the same position at each tight spot, I understand you replaced some of the steering shaft but still, ever half turn sounds like a possible steering shaft issue.

 

[chenderson]

So you still have tight spots even with the linkage removed? I cannot see how the hydroboost could give you repeatable tight spots at the same steering positions, you said it happened even with the engine off, again cannot see how the hydroboost could affect that...
But yes if you can you can bypass the hydroboost.
Take notice again just for kicks if it the steering wheel is in the same position at each tight spot, I understand you replaced some of the steering shaft but still, ever half turn sounds like a possible steering shaft issue.

Yes, tight spots with the pitman arm removed, engine running or not. I also at some point removed the shaft from the steering column to the steering box and the steering wheel turned freely. The hard spots don't seem to be in consistent locations. Its almost like if you try to turn the wheel a little faster than normal it will become a hard spot. Its difficult to explain. Like some valve is bypassing pressure then returning to normal. But I would assume that would of showed up as some anomaly with the gauge attached. It's drivable but my concern is if I ever encounter a oh crap moment in snow and need to counter steer fast to correct a rear slide.

 

[Mogman]

Curious, when you have the pressure gauge attached what does it do when you get to a hard spot?
Also does the problem get better or worse when you run the engine at high idle?

 

[chenderson]

Curious, when you have the pressure gauge attached what does it do when you get to a hard spot?
Also does the problem get better or worse when you run the engine at high idle?

I don't remember exactly but I will hook it up tomorrow and let you know. I vaguely remember there was no change in pressure or flow but will confirm.

 

[Thunderbirds]

Yes, tight spots with the pitman arm removed, engine running or not. I also at some point removed the shaft from the steering column to the steering box and the steering wheel turned freely. The hard spots don't seem to be in consistent locations. Its almost like if you try to turn the wheel a little faster than normal it will become a hard spot. Its difficult to explain. Like some valve is bypassing pressure then returning to normal. But I would assume that would of showed up as some anomaly with the gauge attached. It's drivable but my concern is if I ever encounter a oh crap moment in snow and need to counter steer fast to correct a rear slide.

I really don't mean to sound sarcastic, but have you paid attention to the directional turn signal apparatus? I know mine binds up (I mean really binds up) when I get to the point the "trigger" reaches the turn signal assembly. I have gotten used to it until it fails. Then I will replace mine..

 

[chenderson]

I really don't mean to sound sarcastic, but have you paid attention to the directional turn signal apparatus? I know mine binds up (I mean really binds up) when I get to the point the "trigger" reaches the turn signal assembly. I have gotten used to it until it fails. Then I will replace mine..

View attachment 928520

Thanks for the reply. My m998 did not come with the cancellation ring as yours is pictured. After looking into them and reading the stories of them breaking I machined one out of aluminum instead of plastic. I had the binding problem even before I made and installed the cancellation ring. Good call though, I definitely could see that causing similar symptoms.

 

[chenderson]

Curious, when you have the pressure gauge attached what does it do when you get to a hard spot?
Also does the problem get better or worse when you run the engine at high idle?

Finally got around to hooking up the pressure gauge. I do not see any changes in pressure or flow when I hit the hard spots. One thing I noticed is the pressure gauge flutters quite a bit, is this normal? I'll see if I can upload a video

 

[Thunderbirds]

Finally got around to hooking up the pressure gauge. I do not see any changes in pressure or flow when I hit the hard spots. One thing I noticed is the pressure gauge flutters quite a bit, is this normal? I'll see if I can upload a video

Depending on the rate and sensitivity of the gauge, fluttering is just when pressure bottlenecks in the hose to the gauge, or the gauge itself. It happens often when I synchronize my carburetors on our Vtwin motorcycles and have the gauges hooked up. I know its not hydraulic pressure in my case, but maybe the same principal? I have to have restrictors inline and close them ever so slightly so the fluttering stops. It may or may not be the actual pressure changing, but the gauge/needle... Just a thought.

 

[Mogman]

I have seen the needle flutter on a system that worked just fine so I would say that is normal.
IIRC it was under a load, be careful and do not press too hard on the brakes as that is how I blew out a hydro-boost one time.