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.