HOW TO DO AN ADVANCED SEARCH.

Mon Jul 08, 2013 3:56 pm by Admin


For the benefit of 944Hybrids users there are two search functions available for you to use.
The purpose of this sticky is to explain the "Advanced Search" function because it is much more powerful and is the best choice when researching information.

When you log on to the site a list of options is shown in a line at the top of the page. One option is labelled "Search", use this option (NOT the search box lower down on the right).

After you click on the upper search option, a drop down box appears. At the bottom of this box is a radio button marked "Advanced …

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Post  87944turbo on Sat Jan 05, 2019 1:22 pm

I recently completed the engine swap on my car and am now having issues with the hydroboost. I had started it and let it run several times w/out issue. Recently, the PS pump started making noise. It will sound like this maybe 10 - 15 seconds after I start the engine.

https://www.youtube.com/watch?v=E_BPTTAjQ4M

Bleeding the system is a little different for my setup, since I don't have a PS rack. I have that port capped off on the hydroboost regulator. I simply would fill it, start it, check how much the fluid went down, and refill. Fluid level at this point is stable.

Also, when it starts making noise like this, it heats up really quickly. I shot some temps of the fluid w/a hand held thermometer and temps were over 100 degrees F.

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Post  spence on Sat Jan 05, 2019 2:19 pm

That sounds like cavitation. I actually had that problem too. Turned out to be an adapter fitting I used to feed the pump had a step machined into it. I drilled the fitting out to a full 1/2" thru and the cavitation went away.
I don't think you should've capped the ps line even though your not using it. Run it back to the reservoir. I'm not sure if that would cause the problem your having or not.

Is your fluid full of bubbles?
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Post  87944turbo on Sat Jan 05, 2019 4:12 pm

I haven't examined the fittings, but it does seem like there must be some sort of restriction somewhere?  I'll check on that, starting with the outlet from the pump.

Yeah I went back and forth on capping the PS line.  

BMW Hyrdoboost Questions 80-h31_hb_flow_diagram_7bdd3ecbdf75cf5ef05a8f16cb2931839f3ddda6

I was using this for reference.  And it looked to me like the line going to the PS rack is a high pressure line (shown in dark red on the diagram).  I was worried that if I plumbed it directly to the reservoir, I would be sending high pressure fluid to the reservoir." />


Last edited by 87944turbo on Sat Jan 05, 2019 5:58 pm; edited 1 time in total

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Post  spence on Sat Jan 05, 2019 4:19 pm

I'm running a mustang hydroboost and a manual rack. I ran the ps line back to the reservoir. That ps line is a high pressure line; but that fluid needs to go somewhere. I bet that's your problem. That line wouldn't be under any pressure anyway unless you restrict it (Turing your wheel). Since you dont have anything hooked up to it, it just acts as a return line.
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Post  87944turbo on Sat Jan 05, 2019 6:06 pm

Thanks for your help! Are you using the LS style pump and reservoir?

I really wish there was a way to add another return port to the reservoir. With my setup, the three returns shown in the picture all come together. I wonder if that is a problem?

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Post  spence on Sat Jan 05, 2019 6:12 pm

The pump I'm using is actually from a jeep Cherokee, but it's the same style as the ls pump. I ran both return lines separately in the reservoir. One goes thru a cooler and one goes straight in. I bet teeing all the lines together is a bad idea.
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Post  spence on Sun Jan 06, 2019 5:02 am

https://www.ebay.ca/itm/OEM-52089300AB-Fits-Jeep-Grand-Cherokee-WJ-2001-2004-Power-Steering-Pump/323595858859?hash=item4b57d0f3ab:g:uF0AAOSwU65cENQ0

That pump is from a jeep Cherokee that uses a hydraulic powered cooling fan. Its susposed to be a very high flowing pump because of the fan (maybe the guys using both power steering and hydroboost should look into it).
I bet that reservoir would fit on your pump if you wanted two return ports on a stock reservoir mounted on the pump. I'm using a custom remote reservoir that I made out of some stainless pipe.
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Post  87944turbo on Mon Jan 07, 2019 9:09 am

That's really interesting, I have never heard of anything using hydraulic powered fans. I wonder what they use to regulate the speed of the fans? Like you said, a pump designed for that would seemingly easily handle hydroboost and power steering. I wondered with some systems if it is an issue if you are turning and braking simultaneously.

Really appreciate the link, going to look into if that would work with the pump that I have. I also have questions out to this guy. Seems pretty knowledgeable regarding hydroboost and seems to have specific knowledge for the hydroboost setup on 944 LS conversions.

http://www.powerbrakeservice.net/

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Post  spence on Mon Jan 07, 2019 3:08 pm

The only thing I could see being different is the feed inlet diameter on that pump, it may be bigger. Since you have three return lines, you might have to make something or modify your existing reservoir somehow. I dont think teeing three lines together is gonna work.
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Post  kevin924kevin on Thu Oct 24, 2019 10:43 pm

I have a question about this system. As i am running the bmw with out power steering, could you not just plug the port that leads to the power steering at the bomb?
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Post  spence on Fri Oct 25, 2019 3:06 am

No, the pump will not like that at all. You have to run it back to the reservoir
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Post  87944turbo on Fri Oct 25, 2019 7:58 am

No, the pump will not like that at all. You have to run it back to the reservoir

I tried that, Spence is 100% correct, the pump did not like it at all. I spliced in a return line and all was well again.

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Post  kevin924kevin on Fri Oct 25, 2019 11:08 am

Thank you both for the replys. I will plumb as per pic.
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Post  kevin924kevin on Sun Oct 27, 2019 5:08 pm

So can you use the ls reservoir ? If I where to make a 3 headed Y block and run all returns into that and back into the factory unit. What's your thoughts?
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Post  spence on Sun Oct 27, 2019 5:26 pm

Ya, I think he got away with using the stock reservoir by teeing all the return lines together
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Post  kevin924kevin on Mon Oct 28, 2019 9:37 am

Thank you.
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Post  87944turbo on Mon Oct 28, 2019 2:44 pm

Spence is right, that's the setup I have.  I will try and get some pics up for you.  FWIW I tried to put the "T" as close to the inlet to the reservoir as possible.  The hope being that both the return lines would empty into the reservoir (low pressure) instead of possibly back-feeding each other.  

The only issue I have now is that the stock reservoir I have will not hold the contents of the bomb if my reservoir is filled to the recommended level.  So if my bomb dumps its charge (which I think is ~ 0.5 qt), my stock reservoir will overflow.  Mine will dump if I let the car sit for more than a few days (it shouldn't).  But even if it wasn't dumping by itself, it would overflow during an emergency situation where say for example the PS pump died.  

Obviously it's a terrible thing to have your PS pump reservoir dumping PS fluid in the middle of a emergency braking event.  

So far I have been running the PS fluid level on the low side to allow for the extra volume from the bomb.  But I am sure that this is hurting the longevity of the PS pump's life.  

I am still working on a way to get more PS fluid capacity.  Also I have a new bomb to install.  Will be pulling the car off the road for winter here shortly and will have more time to really look at it and come up with the right solution.

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Post  Hotrodz of Dallas on Mon Oct 28, 2019 4:47 pm

Something like this might work well.

https://www.lsxconcepts.com/products/8-25-pro-touring-p-s-remote-reservoir-w-filter-for-hydro-boost-brakes-brushed-aluminum?variant=6236067037227&currency=USD&utm_campaign=gs-2018-09-05&utm_source=google&utm_medium=smart_campaign&gclid=EAIaIQobChMIlojV2_a_5QIVAf7jBx0dWQp8EAQYAiABEgLcCvD_BwE
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Post  kevin924kevin on Mon Oct 28, 2019 4:54 pm

Thank for the reply. Does the height of the reservoir play a factor in any way? I have a friend who is going to machine me a 3 in port single out port Y 3/8"ID ports in side an aluminum hockey puck. This will ensure a non restricted return. Now the next issue is more chamber for expansion if bomb blows. Have to think about that. If the reservoir can sit any where then I will use the BMW can I have. The way I see the GM reservoir is the bottom chamber is a loop in and out you can see it in the bottom when empty. The upper chamber maintains fluid level.
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Post  Hotrodz of Dallas on Mon Oct 28, 2019 5:00 pm

I've never done the BMW HB. Always used the mustang. The GM reservoir is way below the HB. I was worried abut it overfilling the reservoir when not running, but it hasn't been an issue on any I've built so far.
On a racecar i'm building now, I am considering running a remote mounted reservoir with more fluid to help with overheating the fluid. It would be mounted up higher, but again, that doesn't seem to be an issue.
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Post  kevin924kevin on Mon Oct 28, 2019 5:18 pm

So if I an under standing correctly the can can sit at any height in relation to the pump .
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Post  Hotrodz of Dallas on Mon Oct 28, 2019 5:25 pm

Needs to be higher than the pump. But can be lower than the HB itself.
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Post  kevin924kevin on Mon Oct 28, 2019 6:01 pm

Ok. So could I not just  install another gm can in a return line to act as dump can? So use the return line from bomb into second chamber then into The Y. Plumb the so called high pressure return from bomb going into Y an return from booster into Y. If I am not mistaken this would give plenty of fluid to pump no cavitation and added space for fluid to go if bomb blows. Does this make sense. I am going to fill my gm unit with water and see what it holds.
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Post  kevin924kevin on Mon Oct 28, 2019 8:13 pm

So measured gm can 7 oz. Or 220 ml. If the bomb holds roughly 0.5 that equates to just under 16 fluid oz. So need capacity for 24 oz or 3 cups of liquid so 2 gm units no good.
You could also modify a cap with a bleed off port to a catch can. See the problem is space high enough to be above the PS pump to feed.
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Post  kevin924kevin on Mon Oct 28, 2019 9:54 pm

How I learned to stop worrying and love the bomb.
(From Stanley Kubrick's Dr. Strangelove)

This month I want to discuss a somewhat vintage BMW power brake system, the H31 "Hydro Boost" power brakes and steering system. BMW has always been a leader in technology and never was this more evident then when they introduced the H31 system in the E23 seven series cars in 1977. As is still typical the technology that was debut on the flagship Seven series became a proven design and used on various Five, Six and Seven series cars ending on the Eight series before being phased out with the last of the Eight Fifties in the mid nineties. Over the years I have received a great deal of calls and e-mails regarding the diagnosis and repair of this system. I will attempt to clarify some of the misconceptions and advise on accurate, straightforward diagnosis.

Unlike almost every other power assist braking system that uses engine vacuum to create the boost, the H31 system used hydraulic pressure from a special power steering pump to create the assist needed. This system allowed for more available assist that was highly controllable in a smaller package then any vacuum boost system available at that time. Soon after its introduction, BMW coupled its race proven BOSCH ABS technology to offer a braking system that became the performance standard that other manufactures where judged by.

Over the years the H31 system has caused a number of headaches for techs who where attempting to diagnosis this very sophisticated hydraulic system. Most of these headaches are due to a lack of understanding of the basic principles of operation. The original repair information involved the use of very high pressure gauges to test the pump output and the pressure controlled flow regulator known as the DS Regulator with it's attached accumulator better known as "the Bomb" because of it's cannonball shape. I have found the use of these gauges to be unnecessary in all but a few rare cases.

The most common failure of this system is the accumulator (the bomb). It is a round steel chamber with a high-pressure nitrogen filled balloon built inside it. On a normal working system, as the pumps hydraulic pressure builds up it moves fluid into one side of this sphere displacing the balloon and storing pressure and a volume of fluid. Over time the balloon loses its nitrogen charge causing the sphere to lose its spring affect of storing the pressure energy. The simple test of the bomb is to run the car for a minute to allow the pressures to normalize then shut off the engine and then pump the brake pedal until all power assist is lost and the pedal becomes hard. Typically a good accumulator will give you about eight pumps of the brake pedal before you loose assist. A bad one will be hard after one pump and the accumulator needs to be replaced. The second part of the test is to check the DS regulator. Again run the motor briefly to build pressure then shut it off. Now wait five minutes before applying the brakes. You should have at least half the pumps with assist that you had when you did the test the first time. If not the valves in the DS regulator are leaking down to quickly. The DS regulator cannot be serviced and would need to be replaced.

The common symptoms of a failed accumulator can be an intermittent brake warning light that can come on when the brakes are applied, or a too soft brake pedal that does not improve after bleeding the brake hydraulics. A good check for the brake hydraulics is to pump the pedal till all boost is gone, then if the pedal is still spongy then the problem is in the brakes. Other issues common to the booster system are leaking pressure switches at the DS regulator and leaks at the hydraulic booster. The brake booster leaking will vent power steering fluid (either ATF or Pentosin depending on the system) at a drain hole between the booster and the master cylinder.

The power steering pump supplying the pressure for this system has a maximum operating pressure of about 130 bar (1900 psi), however the working pressure for the H31 system is regulated at 35 * 57 bar and only needs about ten percent of the fluid volume that is needed for the power steering. With that in mind it is obvious that any problem with the pump pressure or volume would show itself first as a problem in the power steering.

To properly check the fluid level you must have the engine off, pump the brakes until the assist is gone then remove the cover from the reservoir. The fluid should be at the top of the screen. If not top off with the correct fluid for your car, most early cars used ATF but later BMW's went to Pentosin fluid, do not mix them and NEVER use brake fluid in the pump hydraulics. Brake fluid will destroy the seals in the H31 system and ATF or Pentosin will destroy the seals in the brake hydraulics. They are separate systems and do not share fluids, IF IN DOUBT ADD NOTHING. If either system is contaminated by the other it can be very expensive to fix and potentially dangerous.

My last set of problems, are usually listed as power steering complaints. This system uses a very high-pressure, high volume pump; any leaks in the system can be a big mess fast. Many of these cars develop noises in the pump and the pump is replaced only to find that the noise is still there! The problem is from air being pulled into the pump through loose hose connections on the inlet hose between the pump and the reservoir. The leak can be so small it will not lose any fluid but still allow air to be sucked in when the car is running. This problem is exaggerated by the fact that the filter in the reservoir has probably never been serviced and is plugging up with debris. Finally you must consider the condition of the drive belt, a belt failure will immediately cause a loss of power steering and the brakes will only have the stored pressure of the accumulator to assist you for stopping.

You can only imagine heading to the braking zone at turn three of BIR in your E28 M5 only to find that the belt broke. You would have no power steering and no power brakes if the accumulator were bad. No more M5, Bad day, really, really, bad day.

Until next time,

Paul Dzimian
BMW CCA TSA
Shop Forman
Motorwerks BMW
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