Non-Hydroboost Power Steering and Brakes Linked?

[510man]

I searched and didn't find this issue. Hoping someone has already sorted it out.

I have '99 Suburban C1500 with a 350. I'm having an issue where my power steering quits when idling with my foot on the brake. Think parallel parking type stuff. The power steering returns when I release the brake pedal. Truck drives fine otherwise.

This is a traditional brake booster system. No Hydroboost. The factory variable assist has been removed. Thus, the truck has a 1996 style PS pump, valve and hoses so no variable assist.

I thought non-Hydroboost PS and PB systems were independent closed systems where one can't effect the other. Evidently, I'm wrong.What ties these systems together?

I thought my PS pump was going bad. Replaced it with a new one (not rebuilt) and have the same issue. I'd prefer not to continue down a path of guessing and parts swapping.

Suggestions? Thanks for any help.

 

[exp500]

Has your steering gear been tightened to reduce play? Have you verified Idle RPM?
Recommend you remove the relief valve on the pump and clean it. Flush P/S system.
What pump was the replacement?

 

[510man]

Bought the truck new. Steering box has never been touched. I'm not following the association between play in the steering box and disabling the PS boost. RPM doesn't change the problem. Happens at idle. I can shift to neutral or park, rev the engine to 2k, and no change until I release the brake pedal. I may try cleaning the relief valve. A new one came with the new pump. Flushed the system, installed new hoses and a PS filter too. Rebuilt pump was an AC Delco. New is a Cardone. Both exhibit the same problem. Hoses and valves replaced both times.

 

[east302]

Short of rpm, they are independent.

Just to clarify - did you have the issue before the EVO delete and switch to the 96-under pump?

 

[exp500]

I asked about steeringbox adjustment because if too tight the recirculating balls don't.
How about a vacuum leak at the master vac? Check Vacuum nipple and spray around booster with engine running. Thinking low Idle here.
Does pump make noise when parking/slow? Foamy oil? Using ATF? Pressure line kinked? Especially at steering box, seen that a few times.
You could remove valve from old pump, clean ball and install in new pump also, less crawling around. Take Pics of valve assy. components. There are alot of different ones. That controls both pressure and flow.

 

[east302]

You could remove valve from old pump, clean ball and install in new pump also, less crawling around. Take Pics of valve assy. components. There are alot of different ones. That controls both pressure and flow.

Probably getting into the weeds here, but that’s what I had to do to get an aftermarket “EVO bypass equipped” pump to work on my 98. Of the three pumps that I’ve seen, they all used a valve without the shim under the nut like the EVO ones.

Noting that the 97-00 GM bypass kit didn’t include the valve, it implies that GM didn’t intend for it to be replaced and that the aftermarket part manufacturers just don’t sweat the details.

Here is the valve from an EVO-equipped pump on the right and one from a bypassed aftermarket pump on the left .



I couldn’t get power steering with the one on the left unless I raised the engine speed, a symptom that this poster doesn’t seem to be having making this, likely, irrelevant.

Having three 98 models, I just swapped the valves out when the pump went and they’ve worked fine with both 96-under and 97+ Saginaw boxes. The 96-under box is my favorite for heavier steering feel, though. It returned the same heavier feel with or without functioning EVO.

I wish I knew why

 

[510man]

Short of rpm, they are independent.

Just to clarify - did you have the issue before the EVO delete and switch to the 96-under pump?

I did not. I didn't have it post conversion circa 2012 for many years. Conversion worked perfectly for a long time.

Variable assist applied sporadically on the Tail of the Dragon will make you change your shorts. That's what caused me to convert but that's a conversation for another thread.

 

[510man]

I asked about steeringbox adjustment because if too tight the recirculating balls don't.
How about a vacuum leak at the master vac? Check Vacuum nipple and spray around booster with engine running. Thinking low Idle here.
Does pump make noise when parking/slow? Foamy oil? Using ATF? Pressure line kinked? Especially at steering box, seen that a few times.
You could remove valve from old pump, clean ball and install in new pump also, less crawling around. Take Pics of valve assy. components. There are alot of different ones. That controls both pressure and flow.

Good suggestion to check for a vacuum leak. I believe that's all original so it's old. No noise and no foam. Running PS fluid vs ATF. No kinks in the hoses. The original valve was an EVO and it's long gone with the core return when initially converted.

I did order a 1996 valve from GM. The new pump came with a valve installed so I never used the GM valve. Special order so I couldn't return it. I may try installing it if I can find it. I know I still have it somewhere.

 

[510man]

Probably getting into the weeds here, but that’s what I had to do to get an aftermarket “EVO bypass equipped” pump to work on my 98. Of the three pumps that I’ve seen, they all used a valve without the shim under the nut like the EVO ones.

Noting that the 97-00 GM bypass kit didn’t include the valve, it implies that GM didn’t intend for it to be replaced and that the aftermarket part manufacturers just don’t sweat the details.

Here is the valve from an EVO-equipped pump on the right and one from a bypassed aftermarket pump on the left .

View attachment 368429

I couldn’t get power steering with the one on the left unless I raised the engine speed, a symptom that this poster doesn’t seem to be having making this, likely, irrelevant.

Having three 98 models, I just swapped the valves out when the pump went and they’ve worked fine with both 96-under and 97+ Saginaw boxes. The 96-under box is my favorite for heavier steering feel, though. It returned the same heavier feel with or without functioning EVO.

I wish I knew why

So you are using the EVO valve on the right on a non-EVO pump, correct?

I never put the EVO valve in the non-EVO pump. I did try ythe EVO pump with the sensor unplugged. That resulted in full assist all the time. That sucked to drive but it was consistent and got us home for the Tail Of the Dragon without landing in a ditch......or worse.

 

[east302]

Yes, it has the valve from the EVO pump in the non-EVO pump.

So you put the non-EVO pump in around 2012 and had no issue. Then this started so you swapped that pump out with no improvement, right?

Since you had the problem before and after this recent pump swap, I’d be tempted to rule out the pump unless it’s a different problem with, coincidentally, the same symptoms.

Spitballing here, but is there a pressure switch on any power steering line? I doubt that GM used one, but remember having a Ford that had a switch that would adjust pressure when the a/c was used.