Low speed braking
 

Another week another issue with the X

At low speed the brake pedal goes solid and feels like it has no stopping ability. My understanding is that it’s the brake servo unit (34336760461)

Hoping someone can validate this for me and then advise whether I should also change the master cylinder at the same time.

Thanks all

The vacuum pump is where I'd look. For some reason BMW thought the 8 cylinder engine couldn't make enough vacuum so..... let's just say when mine failed after a 4 hour highway trip that in town traffic made my seat change into a traffic cone [emoji28]

If you hear a gurgling like water behind the dash it 100% the pump.

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Low speed braking
 

Thanks for the info - sorry this is a total noob question but I had no idea there was a brake vacuum pump on these, where is it located/what does it look like? If I google I’m seeing this thing - which I know I changed the o rings in a few years back when I had it off for the valve stem seal replacement, had no idea it had anything to do with the brake system though https://uploads.tapatalk-cdn.com/202...e74d33394a.jpg


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Here's the part numbers https://uploads.tapatalk-cdn.com/202...78815c8c42.jpg

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With Valvetronic operating correctly the throttle valve is open so there's not much vacuum in the intake manifold.

I would first check the vacuum pump is producing vacuum and also check the non-return valve on the hose connection. It seems that the valve is not available separately but comes with the hose.

https://www.realoem.com/bmw/enUS/sho...diagId=34_1350

So I started by replacing the hose and clamps as the hose was rock hard no change, changed the pump unit entirely and still no change. I press the brake, hear a whoosh of air and then the pedal goes hard with no brake force.

Any ideas where I should look next?

Thanks


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Check valve?

If the brake booster "whooshes" air that suggests a vacuum leak in the diaphragm side past the valve associated with the brake.

Run the car to build vacuum, turn off the car and have somebody else press the brake while your are under the hood listening to the brake booster to figure out where the air whoosh is coming from.

I have these same symptoms. Vac pump pulls and pulses. I do hear a whoosh sound. Does this point to booster?
Thanks!

I would guess so. I’m waiting for a new booster to arrive. There is very little that can go wrong with the vac pump itself outside of the o rings. The cheapest place to start would be the rubber hoses at each end of the vacuum hose, mine were definitely perished but I’d just be guessing at anything else.

I would suggest following Andrew’s instructions above

Thanks. Maybe important to mention. Symptoms occurred after changing brake light bulbs. I uses a short 2x4 to depress the brake pedal while I checked bulbs. Did I blow a hole in the booster by pressing too hard with the car off?

When do you hear the whoosh? Vac pump pulls air Ina lot of places. I have an internal vacuum leak in my valve cover causing fits.

whooshes sounds = bad brake booster
I did one not too long ago on a different vehicle. Hopefully it's not too hard on a X.

You said "hard on". Bwahhaahhaa

[emoji1787][emoji1787][emoji1787]

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I’ve replaced the booster, I didn’t swap the master cylinder (I actually bought one but got sent one for. LHD which was no good for me)

I’ve run through the bleeding procedure using my foxwell and I’ve gone from having a hard pedal to a completely soft pedal. Guessing the master cylinder needs to be replaced too


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Two separate bleeding functions in foxwell. Did you do them both? Also did you use pressure @ reservoir or vacuum at the wheels? Vacuum method is said not to work.

I’m using NT510 and it only has one function, I was using vacuum at the wheels.

I’ll give it another go today with pressure at the res - would I be better off using INPA for the bleed function or does it not exist in there?

The best way to bleed brakes is with a second person on the pedal. Vacuum won't do it and pressure bleeders are a cheat for when you need to do it alone. You need to get enough flow to force air out of the high spots (like the front brake lines where they go into the hoses.) The scan tool procedure is only to get the last bit of air out that might be trapped in or in front of the ABS valve/pump. When changing the master cylinder it's a good idea to start bleeding there. Sometimes the last bit of air will slowly come out of the compensating port overnight.

Don't forget that the e53 has you do each wheel is a certain order and going out of that order does seem to leave bubbles in the ABS block.

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Low speed braking
 

NT 510 should have both steps one is for abs block one is for pump.

Attachment 83406

Pdf of bleeding procedure. I just realized that's for e70 but most should be the same.

BMW calls for pressing the brake pedal during the process but supplies fresh fluid though a pressure bleeder I wouldn't consider another option. Vacuum can create bubbles.

Thanks Andrew!

The pdf didn’t load - mine has a brake bleed procedure option and a brake line mix up option. I’m running the latest firmware


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Try again I had to edit my post three draft saved didn't save the PDF properly had to re attach

Hero thanks mate, may be a silly question but rear right means if you’re sitting in the car, looking forward right? Should I swap this to rear left for a RHD vehicle this is the calliper furthest from master cylinder


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Best to pull TIS for your model car. Depending how they run the lines for RHD it might still be right rear first.

RHD & LHD should make it clear which side is left and right.

I'm planning to change my brake fluid soon and will have to run the procedure to clear the abs block. I'll look in foxwell for the options and share what I find.

Thanks mate - definitely only seeing one option on my foxwell. I’ve tried with INPA today but I’m getting connection errors when trying to NC onninicate worh the DSC57 module. I’ve also tried needing again today with pressure at the res but still a soft pedal. I’ll try again this evening when I can get someone in the car the old fashioned way

Yeah old fashioned pumping will not help get air out of abs block.

https://uploads.tapatalk-cdn.com/202...abc2f70781.jpg
https://uploads.tapatalk-cdn.com/202...c6df449b6d.jpg
https://uploads.tapatalk-cdn.com/202...537869e060.jpg
https://uploads.tapatalk-cdn.com/202...c99ae61c76.jpg

Interesting I couldn't find the abs block purge on my e70

I have updated the software on my foxwell (I swear I only did this a few weeks ago but maybe not)

Today I am seeing all different menus in my scanner. The bleed procedure in the service menu is now 7 steps (2 days ago it was just activate bleed procedure and the pump would buzz) now the bleed procedure looks kore similar to what I have seen on INPA for other models. Also just found the ABS pump feature on the active test menu. Thanks for this

I’m now seeing this - will go through this in the daylight and report back
https://uploads.tapatalk-cdn.com/202...e8c236ceb8.jpg


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What's the NT 510 software version?

I need to check for updates for my NT520Pro.

Low speed braking
 

Have now run through the brake procedure 4 times and still have a soft pedal.

If I pressurise the system from the red cap I get pressure but as soon as I take the compressor and pressure cap off to replace with the normal cap there’s nothing there. May be an obvious statement but would that mean I possibly just need a new res/cap?


*edit*
I get really good pressure after the bleed procedure until I start the engine then the pedal goes soft.

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Does the pedal stay firm without the vacuum support to it? Or not? If it still feels soft then there’s still air somewhere in the system unfortunately

I have a feeling "goes soft" if just the normal amount of pedal drop when the booster kicks in.

Like mentioned above the pedal should be nigh impossible to push until the engine is started and then you will be able to press the pedal maybe 1-1.5" I never measured.

When the engine's running, there will be some amount of pedal travel from initial engagement until the pedal won't depress more.

Depends on which engine he has.

The 4.8is has a vacuum pump on the right head and when bad there is zero vacuum to power the booster.

Yeah pressure holds after the bleed without the compressor pressurising the res.

As soon as I start the engine pressure goes - guessing this is because there is still air in there somewhere and starting the engine initiates the abs pump? No idea though

I’m half a day away from submission and taking it to the Indy.

How tf can bleeding the brakes on this be more difficult than replacing the valve stem seals [emoji28]


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You know what l, I’ve had this thought too - maybe I don’t know what the normal brake pedal feels like. I had driven it with a bad booster for two weeks then not driven it for almost 6 more and spent 3 days pumping the pedal.

I’m on a fairly steep driveway though so don’t want to take it out and test it until I’m a little more confident


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So the vac pump is new as is the booster and hose - if I connect a pressure gauge up to this does anyone know what pressure the vac pump should be putting out?


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By sounds of the hose failed on ur one which commons check ur booster for oil that hose has one way vavle and it fails then oil can pass into booster it common there was recall but the e53 not in it . I done the repair kit for my vac pump 2 o rings only cost 50 aud and done the save you full cost of new pump .#n6life lol with valve steams mine touch wood at 170,000 kms and still good but I change my oil changes to 6,000-7,000kms done care if clean or not pop cheap steam repair not lol. If need I find the recall info if you want it on booster failed and your brake paddle be hard as mine in the end sound like one them fart jokes that sit on seat before replacement . You need like Ista for bleeding the system after you replace the booster due to dsc /abs .

Low speed braking
 

So for some reason I wasn’t getting notifications on some of these replies.

You were absolutely right though, at some point during the 5/6 bleed cycles the air was out and the brakes were fine I was not understanding what the normal brake pedal should feel like. Took it for a drive earlier and all is well other than the brake rubbing from the surface rust that has now accumulated on the rotor.

Thanks for all your help with this!

Also in case anyone is interested - if you’re running the bleed procedure using foxwell via the OBD port and the battery dies (even though your battery charger is connected to the vehicle) once recharged and connected the scanner won’t find your vin or connect to any modules and your dash display won’t turn on and if you’re anything like me you’ll have dropped a nugget in your pants.

Before panic fully sets in you should remove the battery from the vehicle and short the connections in the boot


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It can take a day or 2 for the last bit of air to bleed out through the compensating port especially if you didn't bench bleed the master cylinder before you installed it.

Sorry, resurrecting the thread. After idling the car to build booster pressure and stopping engine I can hear a whoosh inside the cabin and outside by the booster. I can not feel a rush of air anywhere.

What engine do you have?

My 4.8is had my vacuum pump fail and it sounded like gurgling water behind the dash.

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4.4 n62. No gurgling. Just one big whoosh with pressure built. I've pulled vac l8ne and it had vac.

Does brake pedal go firm after the whoosh? If so the woosh is the booster.

Either the check valve or the diaphragm


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