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post #1 of 17 (permalink) Old 10-15-2016, 09:46 PM Thread Starter
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Hydroboost Pressure Drop

I started a thread a while back related to a braking issue I was having and I believe I've narrowed it down to the hydroboost system rather than the braking system. I know, I know... the hydroboost IS the braking system, but let me explain ...I believe the problem has something to do with the power steering fluid side of the hydroboost... in other words, the actual pressurizing of the hydroboost.

Here are the symptoms and how I can recreate the problem. If I'm cruising along at low'ish RPMs and I press on the brake, the car stops beautifully. If I'm at a relatively high'sh RPM and go for the brake, the pedal gets somewhat squishy (that's the technical term) and there's a wheezing noise coming from the brake system. Once I let the RPMs come back down, the brakes are back nice and firm. Over time this has gotten worse and worse and it now takes a much lower RPM for the brakes to lose pressure. I have to pretty much wait for the car to come to idle before the brakes come back.

About two months ago, I posted the issue on a different site that seemed to specialize in hydroboost systems. A user there suggested that the problem was that I was blowing the pressure relief valve in my power steering pump when the engine went to high RPMs. The high RPMs built pressure high enough to pop the valve and therefor blow off the pressure... thus losing pressure to my hydroboost. I personally didn't even know the p/s pump had a relief valve, but after some quick research, it sounded like that was the most likely culprit. The user suggested repairing the relief valve... stretching the spring a bit... cleaning the o-rings... etc. But a new p/s pump was only $45, so I just went ahead and replaced the p/s pump all together. I just finished installing the pump, flushing and bleeding the power steering system a couple hours ago. I took it for a test drive and the problem is exactly the same as it was than before replacing the pump.

I suppose I could try a slightly stiffer relief valve spring or possibly a smaller p/s pulley size ratio to decrease the amount of pressure the p/s pump generates... but it seems like I shouldn't have to do all that since there are probably hundreds of FFR's out there with hyrdoboost systems that don't have this problem.

Sooo... I suppose I'm looking for some miracle insight into the problem. Anyone with lots of hydroboost knowledge have any ideas about what might be going on? It's now gotten to a point where I can't drive it without resolving the problem.

Thanks so much for any tips!


~ Dave


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post #2 of 17 (permalink) Old 10-15-2016, 11:06 PM
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Rev it up and look to see if any bubbles in the tank


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post #3 of 17 (permalink) Old 10-15-2016, 11:17 PM
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I run HB and never had that issue. I wonder if the booster unit is the problem?

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post #4 of 17 (permalink) Old 10-16-2016, 08:08 PM
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Where does the low pressure port of your hydrobooster return to? If the backpressure on the low pressure side is to high the booster may not work correctly.
Ideally, it would return to a dedicated return on the reservoir. Mine ties into a shared return with the rack and seems to work.
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post #5 of 17 (permalink) Old 03-06-2017, 03:40 PM Thread Starter
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Alrighty... I figured I should post an update to my ongoing problems with this to see if I can dislodge any additional knowledge that might still exist from anyone out there.

I've been leaning on this site quite a bit to try to understand what's going on: Hydro-Boost Power Assist Systems: Operation Diagnosis and Repair. It's been a great help... but still no resolution unfortunately.

Here's where I'm at currently:
  • I replaced the p/s pump in case it was the relief valve popping too early. The problem was still there afterwards.
  • It was then suggested by someone from the site above that maybe one of the p/s lines was collapsed in the system. So, I replaced ALL of the original p/s hoses with braided stainless steel hoses (used the attached schematic as my guide). While I had all the hoses off, I blew air through the steering rack to make sure it wasn't clogged. After putting it all back together, the problem basically got worse and now there was really no power brake or any power steering. Prior to this, I at least had some power steering, but now that's gone also.
  • I then thought maybe there was something wrong in the hydroboost unit itself, so I replaced that as well this past week. The exact same problem is there still.
  • I then considered that maybe there's just LOTS of air in the system from when I blew it all clear with the compressor and maybe it's trapped in the steering rack or something. I went through just about every bleeding method I could find online and it never seemed like I could get all the air out. With the car off and the reservoir cap off, if I turn the steering wheel lock-to-lock, I'd consistently get air bubble coming up into the reservoir. I probably turned the wheels maybe 500-700 times for over an hour and it wasn't getting any better. I even purchased a Mityvac hand vacuum pump with an adapter for the reservoir cap opening to try to vacuum out all the air like many recommend... but still I always get more and more bubbles coming up with no improvement. I would think that eventually all the air would come out, but it just seems like that should have happened by now.
Basically, at this point, the entire system has been replaced except for the steering rack. Is it at all possible that there's something wrong going on in the steering rack that it could be allowing air back into the system when the wheels are locked to one side or another?

Another odd thing that happens is that when the car is running and we turn the steering wheel lock-to-lock (wheels off the ground), it's more difficult than it should be to turn the wheels... but if we press the brake pedal, the steering gets much easier. Let off the brake pedal and the steering gets harder again. Weird.

The really difficult part of all this is that it's not as if the power brakes are failing back to just "manual"... they are essentially becoming barely existent. That's why I'm wondering if it's possible that maybe the rack is allowing air back in or something. The p/s rack would be a bear to replace and I'd be willing to do it if I had some confidence that it's really the culprit, but I'd rather not just replace it just to "try it" if I don't have to.

With all that said, I'm basically stuck and pretty discouraged about it all. I might need to start looking for a Ford master mechanic or a really good brake specialist in the area that knows about hydroboost systems to help me diagnose at this point.

Again... huge thanks to anyone that might have some additional advice!
Attached Images
File Type: jpg PowerSteeringLineMap.jpg (105.5 KB, 21 views)

~ Dave


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post #6 of 17 (permalink) Old 03-06-2017, 07:04 PM
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Are you sure you have the pressure line to the rack attached to the Pressure In port, and the pressure out port to the reservoir return port ( and not backwards?)
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post #7 of 17 (permalink) Old 03-06-2017, 08:35 PM Thread Starter
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I've checked the placement of the hoses dozens of times so I'd put quite a bit of money down that they're correct. Plus, from the first occurrence of the original problem, I was using all stock p/s hoses from my donor... which can't be hooked up incorrectly since all the fittings are different sizes and there's only one way they can actually be able to be arranged... which matches what's in the schematic attached to my post this morning.

Basically...
- The high pressure P/S pump 16mm fitting goes to top of the Hydroboost on the 18mm fitting
- The high pressure lower/side/back 16mm Hydroboost fitting goes to the lower 14mm steering rack fitting
- The low pressure barb fitting on lower/side/front of the hydroboost goes to reservoir "T"
- The upper 16mm steering rack fitting goes to my p/s cooler and then out of that to the the reservoir "T" also.
- The reservoir "T" then goes to the reservoir obviously.
- The large barb fitting on the reservoir goes to the input of the p/s pump.

I think I can plumb it up in my sleep now that I've had it apart soo many times!

Thanks for the suggestion!

~ Dave


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post #8 of 17 (permalink) Old 03-07-2017, 02:46 PM
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I recall someone having to adjust (shorten) the pushrod length in the hydroboost MC. I believe it was edwardb?

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post #9 of 17 (permalink) Old 03-08-2017, 12:38 AM
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Hydroboost Pressure Drop

The fact that the steering is getting easier with the brake applied sounds to me like the rack may have a problem. With the brake applied you are basically stealing the pressure from the steering system. I know you have stated that it is plumbed correctly but just to verify the return line should be in the top port on the rack. If it is then the rack is most likely the problem. I am running this system on mine and it is well worth the effort to make it work.
I also have a question. Are you running the same year pedal box as the booster? I know mixing the earlier pedals with later hydroboost will cause some fitment issues and possibly performance problems.

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post #10 of 17 (permalink) Old 03-08-2017, 11:50 AM Thread Starter
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Thanks for the insight...

Yup... the top port on the rack is going to the reservoir and the bottom port of the rack goes to the side/rear port of the hydroboost. Last night I pulled back the steering rack boots to see if there was any fluid leaking there (suggestion from a buddy) and there wasn't. If there was, I suppose that would have told me the seals in the rack were shot... but alas.

And yeah, I'm using an '04 GT pedal w/ an '04 GT hydroboost.

Just really seems like I'm sucking air from somewhere. I'm going to go back over all of my fittings to make sure they're all tight for the hundredth time this weekend, but I'd really think they'd leak if they weren't... and if it was a return line that was pulling air, I would think I would see at least some froth in the reservoir tank.

I'm getting more and more worried that it's my steering rack since the original problem emerged somewhat sporadically, got worse and finally was constant... and the fact that I replaced everything else.

Thanks again


~ Dave


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post #11 of 17 (permalink) Old 03-08-2017, 12:00 PM
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It may not be worth the trouble since AZ racks are about $100, but I have a 2.5 turn to turn rack from AZ that you can have if you'll pay shipping. It was on my car for about a year and I just didn't like it on the street.

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post #12 of 17 (permalink) Old 03-09-2017, 01:00 PM
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Lines/systems under pressure (pressure greater than atmospheric pressure) can NOT suck in air. The only point in this system under potential vacuum/pressure below atmospheric is the feed line from the reservoir to the pump inlet. When the pump is running, all other lines will be under some pressure.
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post #13 of 17 (permalink) Old 03-09-2017, 06:43 PM
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If you spent a lot of time and hundreds of turns on the wheel and are still seeing air bubbles I imagine you are sucking air in the reservoir to pump feed line somewhere.
My friend has an issue with the fluid becoming aerated and it causes steering and braking issues similar to what you described but not as bad.
If you look in the reservoir is the returning fluid aerated or foamy?

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post #14 of 17 (permalink) Old 03-09-2017, 06:59 PM
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Go back to the beginning!

Dave,

Can you put all your original stuff back in the car.....as it seems somewhere you induced more issues.

From there, can you bypass or completely remove the rack from the equation and see what happens to brakes?

I know these problems can drive you nuts....... I went thru similar with an old Mark VII, but my problem was not in the pump pressure side of things but rather at the brake fluid out side of business. An internal leak to the booster unit was my issue....

Once you got down to the nitty gritty, they are fairly simple systems to work on. Of course it helps to have all good components!!!

IN your case, the issue is high RPM performance...... It sounds like you've gone over the hose routing......and you're not seeing a foamy mess in the reservoir...... sounds like a supply issue on the pressure side...... I don't know if you are running the steering and brakes in parallel or in series.....but someone is stealing your thunder......somehow. Check valve or something missing???? Just throwing it out there..... Make sure your reservoir is "vented" either by cap or otherwise.....to allow pressure to equalize at high suction times.....don't want to be drawing a vacuum!

Good luck!
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post #15 of 17 (permalink) Old 03-09-2017, 07:32 PM
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Do you still have the factory cooling loop or external cooler? High temp can cause cavitation
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post #16 of 17 (permalink) Old 03-09-2017, 08:14 PM
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Does the return go back into the bottom of the reservoir? It if were returning to the top, I could see agitation of the reservoir fluid occurring, introducing air0in to what gets sucked into the pump. Again, might be worth observing what happens at the reservoir when you rev the engine high.
Which reservoir are you using?

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post #17 of 17 (permalink) Old 03-09-2017, 11:11 PM Thread Starter
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Thanks for all the responses! Greatly appreciate them! I'll try to answer after each quote...

Quote:
Originally Posted by bhuff View Post
Does the return go back into the bottom of the reservoir? It if were returning to the top, I could see agitation of the reservoir fluid occurring, introducing air0in to what gets sucked into the pump. Again, might be worth observing what happens at the reservoir when you rev the engine high.
Which reservoir are you using?
The return line goes to the bottom of the reservoir. I replaced the donor p/s reservoir with a Moroso one (https://www.summitracing.com/parts/mor-63490). When reving the engine... nothing out of the ordinary in the reservoir. No foam. All clear (well... red/clear)

Quote:
Originally Posted by THEDON View Post
If you spent a lot of time and hundreds of turns on the wheel and are still seeing air bubbles I imagine you are sucking air in the reservoir to pump feed line somewhere.
My friend has an issue with the fluid becoming aerated and it causes steering and braking issues similar to what you described but not as bad.
If you look in the reservoir is the returning fluid aerated or foamy?
In my testing and attempts to bleed the system I did use the Mityvac tool in place of the reservoir cap to try to suck all the air out of the system. When I had it under vacuum, the pressure held steady, so I would "think" that if there was some sort of leak between the reservoir & the pump, I would have lost pressure at the reservoir in that case.. at least I would think so. That said, I only did that with the car NOT running since I wasn't sure what would happen if I had a vacuum on the reservoir with the pump running! The fluid in the reservoir has no foam whatsoever... just crystal clear(red).


Quote:
Originally Posted by fastmerc View Post
Dave,

Can you put all your original stuff back in the car.....as it seems somewhere you induced more issues.

From there, can you bypass or completely remove the rack from the equation and see what happens to brakes?

I know these problems can drive you nuts....... I went thru similar with an old Mark VII, but my problem was not in the pump pressure side of things but rather at the brake fluid out side of business. An internal leak to the booster unit was my issue....

Once you got down to the nitty gritty, they are fairly simple systems to work on. Of course it helps to have all good components!!!

IN your case, the issue is high RPM performance...... It sounds like you've gone over the hose routing......and you're not seeing a foamy mess in the reservoir...... sounds like a supply issue on the pressure side...... I don't know if you are running the steering and brakes in parallel or in series.....but someone is stealing your thunder......somehow. Check valve or something missing???? Just throwing it out there..... Make sure your reservoir is "vented" either by cap or otherwise.....to allow pressure to equalize at high suction times.....don't want to be drawing a vacuum!

Good luck!
Steve
I suppose I "could" put the original hoses back in place... and I may try that before deciding to replace the rack. I'm running in series just like the stock setup. From reservoir, to pump, to hydroboost, to steering rack, to cooler, to reservoir. (w/ a return line from HB also). Reservoir is definitely vented... especially since it happens with the cap off!


Quote:
Originally Posted by timbmn12 View Post
Do you still have the factory cooling loop or external cooler? High temp can cause cavitation
I do still have the stock p/s cooler loop in place after the rack before going back to the reservoir. Plus, it starts happening right away before the engine even starts to heat up.


Sorry if I missed any questions, but I think that covers them!

This weekend, I'm going to put stronger hose clamps on all my low pressure connections and I'm going to replace the teflon washers on my high pressure fittings just to make sure none of those are leaking... even though I would think I would be seeing fluid leaking from them if something wasn't sealed.

Keep the questions coming... please!! And thanks again!!

~ Dave


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