Whistling noise from brake reservoir/booster area

[JPR10]

Changed out my brake booster due to being water logged... Bought a used brake booster and master cylinder on fleabay.

Here are some details:

• Original master cylinder had rusty water residue. I opted to use the newly acquired brake master instead.
• Brake reservoir on replacement was for manual transmission (had hose for slave). I decided to replace it with original one from car w/ the cap.
• Sounds like air is leaking from somewhere when I press the brakes, but no visible leaks...
• When car is off, pedal firms up after pumping brakes
• When car is on, pedal depresses to the floor making whistling noise (coming from booster/reservoir area)

Some possibilities:

• Replacement master cyl. is no good
• Replacement brake booster is no good
• Check valve, although seems fine, may be no good

Any thoughts? How can I test these components individually?

[Yonkers320is]

Was everything bled properly, including the M/C? Maybe the diaphragm inside the booster is no good?

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[JPR10]

Was everything bled properly, including the M/C? Maybe the diaphragm inside the booster is no good?

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i bled each caliper free of air starting from the one furthest from the MC... How does one bleed the MC? That might've been something I missed...

[Yonkers320is]

i bled each caliper free of air starting from the one furthest from the MC... How does one bleed the MC? That might've been something I missed...

You fill the reservoir with brake fluid, put a hose from one exit to the reservoir capping, the other exit and use something to pump the MC untill you see no more bubbles. Then do the same with the other exit...

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[Yonkers320is]

https://m.youtube.com/watch?v=523fHbmbdsQ

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[jclausen]

Is the booster supposed to move around so much when pressing the pedal

[JPR10]

Is the booster supposed to move around so much when pressing the pedal

Maybe not. I need to tighten those nuts a bit more... it felt like it kept on spinning so I didn't want to strip the threads.

[geargrinder]

All the vac lines and the 'sucky jet pump' thing are all good? Like I just posted yesterday, the jetsuckypump thing (the Y-shaped checkvalve dingus) is notorious for half breaking and leaking while still looking OK to a casual eyeball.

[JPR10]

All the vac lines and the 'sucky jet pump' thing are all good? Like I just posted yesterday, the jetsuckypump thing (the Y-shaped checkvalve dingus) is notorious for half breaking and leaking while still looking OK to a casual eyeball.

sucky jet pump? lol I believe the check valve is OK... any tips on checking for cracks? Maybe soapy water?

[geargrinder]

Yes I’m being silly as usual but the actual part is really a “sucking jet pump”. You didn’t get it reversed by mistake or anything? It is more than just a check valve, it’s a Venturi vac amplifier.

[bjornk]

hoping this doesn't constitute resurrecting a dead post.. but I need a new sucky jet pump and can't help but notice that all the places I look for one with an e 39 based on my vin they are 150 bucks but a damn near similar looking sucky jet pump on any other vehicle is under 50$ so am I a victim of price fixing here? or simply that I have a m52tu that had a production run of 2 years? do you think the intake and out put volumes on these pumps is actually different? is it simply a matter of the labor it takes a German to crimp a few hoses on with a living wage? I mean I just want the correct sucky jet pump so I can give the jb weld one I have a proper burial.


according to real oem, this is the part number:11611439025 for the 150$ part

fcp and pelican both sell it with a few hoses and fittings which granted, may put the price up.

but I see this part number all over eBay which is from an z3 or 323 for 50$ 11617503621 and im willing to cut and clamp my own hoses.....

[geargrinder]

Hmmm. Perfect situation for an FCP “unlimited guarantee”. Get the cheapo. See if it’s same. If not, send her back.

I won’t be surprised if it is. With luck there will be PNs on the plastic that might confirm the standalone suckyjet is same and the $100 extra indeed just pays for the hoses which are made from extruded unicorn scrotums. Even if it’s different I also tend to agree, doubt the flow difference between those motors can be really major. Some V8 guys have ditched the suckysucksuckthing and reported no real impact. Of course the V8 has loads more vac power to supply so maybe the jet pump is more useful on the smaller motors...

[JPR10]

Btw, my original problem was solved... I didn’t tighten down 1 or 2 of the bolts in the footwell which was allowing air to leak between the seal.

Stupid mistake but easy fix.


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[StephenVA]

Congrats!