Low speed braking

[Mistermorgan]

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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[Lucas.ua]

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

[andrewwynn]

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.

[StephenVA]

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.

[Mistermorgan]

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


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[Mistermorgan]

Originally Posted by andrewwynn

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.

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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[Mistermorgan]

Originally Posted by StephenVA

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.

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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[bmw983]

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 .

[Mistermorgan]

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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[80stech]

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.