Last week my vacuum pump went out. I swapped it by separating the ps pump and vac pump in the truck and just pulling the vac pump out (probably a mistake in hindsight).  Once I got things back together I had vacuum but now no power brakes (hard pedal) or steering.  I had a spare (unused reman) ps pump so I swapped that and went through the procedure for purging air from the system but I still have zero power brakes or steering.  I also flushed the old fluid by routing the return lines into a bucket and noted lots of flow so I know the pump is pumping.  If I do the purge procedure slowly and at idle only nothing special happens but some combination of raising the engine rpms and moving the wheel rapidly causes the pump to belch fluid. Does this indicate that I still have air in the system or some other problem?  I also noted, while experimenting, that there is very little return fluid from the hydroboost line, mostly just from the steering rack.  I don't know if this is normal though.  BTW, I suspect that my old ps pump was probably fine and that I may just not have had it fully seated in the vacuum pump when I re-assembled it.  Is there something that could be wrong with the re-man pump that could be causing the problem even though there seems to be plenty of flow? 

 

I've read quite a few posts about similar problems but mostly people just seem to keep swapping parts until it starts working, flush the fluid, or keep purging air.  Is there a better way of properly diagnosing exactly what is wrong?  Any help would be much appreciated, I'm about out of good ideas and really need to get this thing back on the road and myself back to paying work.

 

Normally... I do this with only the steering box return routed to the waste container. Now with the reservoir full with the front axle lifted off the floor now rotate the steering from lock to lock without the engine running. The steering box will naturally pull a vacuum sucking the fluid on one side of the piston the dumping flow when compressing. Typically takes about a full quart to prime and clear the lines. Then hook the return line back up and do the purge again till the foam quits then you are ready to start the engine. 

Thanks Mopar1973man.  I gave that a try and it seems like a good technique.  I worked through about 1.5 - 2 quarts like that but it doesn't look like I've actually resolved anything.  Any other suggestions?

Might check shaft alignment too make sure your dogs are lined up into the slots of the vacuum pump. Make sure the pump shaft isn't damaged.

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Thanks.  I was pretty careful with that and the pump is clearly pumping.

 

3 hours ago, RayNAz said:

BTW, I suspect that my old ps pump was probably fine and that I may just not have had it fully seated in the vacuum pump when I re-assembled it. 

 

Can you explain with more detail.  It is possible that the coupler has been damaged if the pump was operated without the pump being fully seated.

 

Also, just curious, what was the failure of the vacuum pump?  Other than a leaking shaft seal, they are fairly bulletproof. 

 

- John

Edited December 15, 2024Dec 15 by Tractorman

1 hour ago, Tractorman said:

 

Can you explain with more detail.  It is possible that the coupler has been damaged if the pump was operated without the pump being fully seated.

 

 

My main reason for not thinking that the coupler is damaged is that the PS pump is pumping.  I just don't see how it could be pushing fluid around if that connection was badly damaged.  Am I wrong about that? 

 

More detail:

When I replaced the vacuum pump I separated it from the PS pump in the engine bay and just removed the Vac pump.  As you may know getting them aligned properly in the engine bay during reassembly is challenging.  At no point did I remove any PS lines so there isn't much else that could have gone wrong with the PS side of things at that point.  I really should have disconnected the high pressure line at that time to see if it was pumping at all but I didn't because I thought I'd end up making a giant mess (boy has that ship sailed:) and I knew I had a spare PS pump on hand.  When I decided to go ahead and change the PS pump I pulled both pumps out together and did the assembly out in the open.  I didn't notice any damage to the coupler at that time.

 

1 hour ago, Tractorman said:

Also, just curious, what was the failure of the vacuum pump?  Other than a leaking shaft seal, they are fairly bulletproof.

 

Last week I was on a trip out of town and on my way back I noticed that the interior vents were stuck on defrost.  Tried Cruise Control and that didn't work either.  I expected to find a broken/damaged vacuum line but they all looked fine (or at least as fine as they've been on this truck).  I then detached the line between the Vac pump and the T-connector on the firewall and there was no vacuum coming from the pump side.  Good news is that replacing the vacuum pump did fix that problem.  This was a reman vacuum pump that I had swapped about 2 years ago.  That time it was due to the infamous leak.

@RayNAz, thanks for providing more detail.  I still need some clarification of the initial replacement of the vacuum pump. 

 

6 hours ago, RayNAz said:

Last week my vacuum pump went out. I swapped it by separating the ps pump and vac pump in the truck and just pulling the vac pump out (probably a mistake in hindsight).  Once I got things back together I had vacuum but now no power brakes (hard pedal) or steering.

 

I am interpreting this to mean that the power steering pump and hydraulic system fluid were undisturbed during the replacement of the vacuum pump.  Is this correct?  If it is correct, then the power steering and power brakes should have been operational immediately upon startup.  The fact that they didn't operate on startup indicates there is a problem with the coupling.  If you did something different during the repair, please let me know.

 

- John

Edited December 16, 2024Dec 16 by Tractorman

19 minutes ago, Tractorman said:

@RayNAz, thanks for providing more detail.  I still need some clarification of the initial replacement of the vacuum pump. 

 

 

I am interpreting this to mean that the power steering pump and hydraulic system fluid were undisturbed during the replacement of the vacuum pump.  Is this correct?  If it is correct, then the power steering and power brakes should have been operational immediately upon startup.  The fact that they didn't operate on startup indicates there is a problem with the coupling.  If you did something different during the repair, please let me know.

 

- John

 

Yes, at that point that was likely the problem however like I said, I then proceeded to take both units out of the truck, carefully attach a new PS pump to the vacuum pump and reinstall the entire assembly.  At this point the PS pump is pumping.  If I redirect the return line from the rack into a bucket and start the engine then it spits out fluid quickly. If the coupling wasn't currently attached then I don't see how the PS pump would be able to pump anything.

29 minutes ago, RayNAz said:

If the coupling wasn't currently attached then I don't see how the PS pump would be able to pump anything.

 

Couplings can fail completely, or partially.  If there is only a small load on the pump, a failed coupling could easily drive the pump, but the moment a larger load is applied, the coupling could begin to slip.  I am not saying that this is the problem, but it can't be overlooked, especially since you mentioned at one point the you may have not had the pump fully seated during your first repair. 

 

Again, back to your first post, I am looking for you to confirm that no power steering fluid was lost during your first separation of the power steering pump from the vacuum pump.  If no power steering fluid was lost, then the power steering pump would operate normally as soon as the engine was started.  No bleeding of the system would have been necessary.   Example of detail that I am looking for:  "I removed the hoses from the pump / reservoir during the repair and lost power steering fluid" or, "I did not remove any hoses from the pump / reservoir during the repair and I did not lose any power steering fluid".

 

- John

Edited December 16, 2024Dec 16 by Tractorman

12 minutes ago, Tractorman said:

Again, back to your first post, I am looking for you to confirm that no power steering fluid was lost during your first separation of the power steering pump from the vacuum pump.

Correct.  The first time I did not remove any PS lines and didn't lose any fluid.  I agree, it should have just worked after re-attaching it to the new vacuum pump.

 

18 minutes ago, Tractorman said:

 

Couplings can fail completely, or partially.  If there is only a small load on the pump, a failed coupling could easily drive the pump, but the moment a larger load is applied, the coupling could begin to slip.

 

Do you know of any good way to test for that?

Been thinking..., Get the unit back out onto the bench (I know - you will really be looking forward to that)  Remove the power steering pump.  Using a depth caliper, confirm that the couplers are engaging properly. 

 

If all seems well with the measurements, then I would try this since the jaw coupling hub is pressed onto the vacuum pump shaft : 

 

Place the vacuum pump unit in a vise.  Make a suitable tool that can be operated with a wrench to engage into the jaw coupling hub.  Have helper hold the gear from rotating with the use of a strap wrench.  Using the newly made tool and the wrench, try to rotate the coupler in the opposite direction of normal rotation to see if it slips.  Use your best judgement on how much force to apply.  If it slips, you have your answer.

 

- John

 

Gotta keep in mind air is compressable, the pump needs to reach at least 4,500 PSI to do its work properly. Is it possible you have a foamy power steering fluid? How about a bad pressure regulator in the pump that is stuck in full bypass? Being both the steering and brake booster are both affected it's back to the power steering pump, typically. Now, the typical neutral position for both steering and brakes should return full flow to the reservoir again. During use of the steering and brakes the pump should increase pressure and hold for brakes and steering to function in high-stress environments (panic stop avoid deer).

8 minutes ago, Mopar1973Man said:

Is it possible you have a foamy power steering fluid?

Possibly.  I've done the bleeding quite a few times so it should be out but....   I've noticed that when I get more aggressive with the turning of the steering wheel (ie turning it more quickly then it will burp fluid out of the pump.  I don't know if this means that that I still have air in the system or if it indicates something else wrong.  It also still bothers me that during testing I was getting lots of return flow from the steering box but very little from the brake return line.  I don't know if this is normal though.

 

17 minutes ago, Mopar1973Man said:

How about a bad pressure regulator in the pump that is stuck in full bypass?

How could I tell?  If I follow Tractorman's advice to take out both pumps and inspect/measure the coupling I may swap my old PS pump back in since it WAS working before the VAC pump swap.

 

25 minutes ago, Mopar1973Man said:

During use of the steering and brakes the pump should increase pressure and hold for brakes and steering to function in high-stress environments (panic stop avoid deer).

 

Thanks, do you know of a good description of the operation of the system?  I'm a relatively analytical type and I feel like if I understood it's operation better then troubleshooting it would be more straight forward.  Also, I noticed when installing the new PS pump that the diagram I had of the lines showed the return lines from brakes and steering were backwards from how the old pump had been installed.  Does it matter?

Tractorman,  Thanks.  Not looking forward to it but I don't have any better ideas and it needs to get fixed. I'll probably take today off truck repairs an instead fix my backup car (01 Cherokee).  It developed a disturbing noise coming from the front driveshaft/transfer case area.  Possibly bad U-Joint.  I'll just pull that drive shaft for now so I can get around more easily.  I can tackle the truck again Tue or Wed.

I think it will be good for you to take a break from this - should help to clear your mind.  In the mean time I will attempt to offer an explanation of how the power steering / brake hydroboost system works.

 

The power steering pump and its integrated flow control / relief valve are fastened to the reservoir.  The power steering pump is a fixed displacement vane pump. 

 

The flow control valve portion of the integrated flow control / relief valve ensures that there is always about 3 gpm of power steering fluid flowing, regardless of engine rpm.  This steady flow of fluid gives the steering a good feel under all operating conditions. 

 

The relief valve portion of the flow control / relief valve is set at about 1450 psi (not the 4500 psi previously mentioned).  Its purpose is to set a maximum pressure to allow work to be done and to also protect the pump and other components within the system.  Since pressure is directly related to resistance to flow, the pressure in the system will always vary and will only reflect the work being done by steering or brake applications at any given moment.  Most of the time the power steering pump is operating at a pressure far, far lower than the power steering relief valve setting.

 

Power steering fluid leaves the pump at 3 gpm and passes through the brake booster control valve at 3 gpm and then passes through the steering gearbox control valve at 3 gpm and finally arrives at the reservoir at 3 gpm.   There is always 3 gpm of power steering fluid flowing through the system regardless of engine rpm and regardless of what components are being operated.   The ONLY time fluid flow will be stopped is if the pressure of the fluid is forced to rise above 1450 psi - then the fluid will return directly to the reservoir via the internal relief valve.  So, actually the pump will still be providing 3 gpm of flow, but the flow will be returned immediately to the reservoir.

 

The brake booster has a small nitrogen pre-charged accumulator that holds a charge of hydraulic fluid in reserve to provide a couple of brake applications in case of power steering pump failure.  The brake booster has a priority control valve to hydraulically charge this accumulator immediately with power steering fluid on engine startup - probably less than one second to charge.  The brake booster also has  a control valve that uses some of the power steering flow to assist with brake applications. 

 

As far as a description of the hoses, there are two high pressure supply hoses in the system.  One high pressure hose leaves the pump and connects to the brake booster, the other high pressure hose leaves the brake booster and connects to the steering gear box. 

 

There are two low pressure return hoses in the system.  One hose leaves the brake booster and returns fluid to the reservoir, the other hose leaves the steering gearbox and returns fluid to the reservoir.  The brake booster return hose will flow very little fluid - some from calibrated valve internal leakage and the occasional spurt from the release of the brake pedal.  The steering gearbox return hose will always be flowing 3 gpm.

 

The main reason there is much mystery regarding getting the air out of the system when replacing power steering components is that the small amount of fluid in the system gets recycled very quickly.  The power steering pump is flowing 3 gpm and there is only about 1/2 gallon of fluid in the system.  So, that means that the fluid leaving the reservoir is being returned to the reservoir in about 10 seconds.  Any large globs of air do not have enough time to get removed to the surface while in the reservoir if the engine is running.  This is why placing the front axle on jack stands and manually turning the steering wheel slowly from stop to stop without the engine running is the recommended practice.

 

4 hours ago, RayNAz said:

I've noticed that when I get more aggressive with the turning of the steering wheel (ie turning it more quickly then it will burp fluid out of the pump.

 

Do you mean "out of the pump" or "out of the reservoir"?  Is the fluid being forced out around the cap?  Is the cap installed?  Aggressive turning of the steering wheel will make the flow pulse because the abrupt additional displacement of fluid from the cylinder in the steering gearbox will be added to the flow.  So, what you are seeing could be normal. 

 

Hope this helps.

 

- John

 

 

 

 

I'll admit it was a grab for memory on pressure value. My bad.  4500 is injector pop pressure again my bad. 

 

As for the burp back typically that is because of air is trapped and and displacing the fluid. Repriming a system typically is a bit frustrating but patience is key. It a matter of run and settle time to work air out of the system. If the pump is truly pumping then its a matter of clearing up the air and getting just power steering fluid through the system. 

19 minutes ago, Tractorman said:

Do you mean "out of the pump" or "out of the reservoir"?  Is the fluid being forced out around the cap?  Is the cap installed?  Aggressive turning of the steering wheel will make the flow pulse because the abrupt additional displacement of fluid from the cylinder in the steering gearbox will be added to the flow.  So, what you are seeing could be normal.

I should have said that it's being forced out from aroun the installed cap.  It's not a large volume.

 

Thanks a lot for the description of the system. 

 

Do either of you think that I'd see anything useful if I replaced the return lines (temporarily of course) with clear tubing?  I'm guessing the air isn't too visible under even the return line pressure.

I don't see any benefit using the clear tubing.  Once the engine has been run, there are literally thousands of tiny air bubbles in the system.  The air bubbles will dissolve faster as the fluid warms or slowly each time the engine is turned off, but they will work themselves out.  You are worrying too much about things that are not important.

 

So, back to the drawing board.  Are you saying that when the front axle is on jack stands and engine is running that there is no power steering assist at all? and no brake assist at all?  Are you keeping the reservoir constantly topped off when you are doing this test or other tests?

 

Try to think this through before you make your next move, so that your next move will count.  We are here to help (or hinder) you.

 

Also, to answer a question that I forgot to answer..., on my truck, the return line from the brake booster is closest to the engine block when the pump is mounted.  I don't think it would matter for the problem you are having, but by design there could be better mixing of fluid in one return port vs. the other.  

 

- John

It doesn't matter which return fitting on the pump the power steering or power brake return hose goes to; they both empty into the reservoir there for are interchangeable.   

 

As @Tractormansaid there is no benefit adding clear return tubing.

 

I've seen it take 2days for the entrained air to vacate the system so be patient.

Update:

Work intruded for a while but I had some time today to take another shot at this.  I started by removing both the VP and PSP from the truck, separated them and inspected the dogs on the VP and the matching ones on the PS and they looked pristine.  No shavings, dings, etc.  I re-installed both, this time using the origional PS pump since I know it worked before this whole fiasco started and frankely it looked like a higher quality part than the reman/new unit I had installed.  As an experiment I routed the return from the steering box to the filler of the PS reservoir, pointed a camera in there and observed a reasonably constant flow while the engine was running.  I did note that if I pressed and held the brake for 10+ seconds the flow from the steering box return would slow to a drizzle.  Not sure if that's normal.  I then re-attached the return and went through the air purging process.  This time I left the cap off the filler and pointed a camera in there so I could observe the bubbles generated while I worked the steering back and forth.  I never really got to the point where small bubbles weren't being generated but I did at least get to the point where it stopped burping large bubbles.  I put it on the ground and took it for a drive but still no power steering or brakes at all.  Got back, raised it back up and observed the filler while working the steering back and forth and noticed lots more bubbles including some fairly large "burps" and I did so.

 

At this point all I can think of are:

 

1. I just have a lot of air and have to keep trying to purge it.

2.  I have some source of air intrusion, would pretty much have to be from the return line from the hydroboost since the return from the steering box seems to have constant flow/pressure and would probably show a fluid leak.

3.  That pressure regulator in the pump has gotten stuck open and even though I have flow the pressure is too low to do the job.

4.  I damaged or clogged the high pressure line at some point with the same result as #3.

 

I plan to pick up a new high pressure line (pump to hydroboost) as well as some new return line but it sure would be nice if I could measure pressure being output by the pump.  Any thoughts on how I can do that?

 

Any suggestions welcome.

On 12/16/2024 at 8:17 PM, IBMobile said:

It doesn't matter which return fitting on the pump the power steering or power brake return hose goes to; they both empty into the reservoir there for are interchangeable.   

 

As @Tractormansaid there is no benefit adding clear return tubing.

 

I've seen it take 2days for the entrained air to vacate the system so be patient.

 

Thanks.  In general, does it come back a bit at a time or all at once?  As far as I can tell I have zero power to the brakes or steering.  I'm also not really feeling or hearing any feedback from the pump through the steering wheel. 

37 minutes ago, RayNAz said:

In general, does it come back a bit at a time or all at once?

There should be power steering and brakes immediately all though it may be jerky and noise from the system due to the entrained air and slowly go away in a day or two.  There is flow so the pump is delivering fluid but is there pressure?   I think you have "3.  That pressure regulator in the pump has gotten stuck open and even though there is flow the pressure is too low to do the job."  If the high-pressure line/hose was blocked there would be very little flow and the pump would be making a noise as if the steering wheel had been turned to full left or right with no let up.   You may want to remove the pressure relief valve and inspect it.