Brakes won't bleed, about to loose my ****

[dude99]

Ok, so in my never ending quest to get my 1983 733i back in the road I have replaced the master cylinder as well as rebuilt the calipers on all 4 corners of the car. I also replaced all 6 brake lines just to be sure that the brake system would be at 100%

How ever I cannot for the life of me get a firm pedal out of it.

I have tried bleeding the entire system:

1. Using my Motive pressure bleeder, I get a steady stream of clear bubbles fluid out of every corner

2. The old fashioned pump and hold method. Pumped pedal 12x, held, opened bleeder and continued. Again on each corner I get a steady stream of clear fluid.


In both cases, the pedal is firm with the engine off, but sinks to the floor with the engine running....


What the heck am I doing wrong? I didn't bench bleed the master, because it didn't come with fitting to do so, but I fail to see how I could be pushing fluid all through the system and still have air in it....

Help!!!

[bigperm206]

This is probably a dumb answer and probably not the solution but are the calipers installed upside down? I made this mistake on my e24 one time and I was getting the same soft pedal like you describe. I couldn't get the system to bleed properly and it drove me nuts.

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[dude99]

Bleeders re pointed up, so I assume that they are on in the correct orientation...

[bigperm206]

Yep, that should be correct.

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[dude99]

Made up an adapter, bench bled the front? Then rest while still on the car. Looped back into the resovoir.

Still the same *pulls what's left of hair out*

WTH, 2 days and I still can't bleed this thing....

[dude99]

So been doing some reading. I found a post that states that a failed brake bomb can lead to a too soft pedal when the engine is running.

I've never actually driven this car so I can't say what normal is, but the pedal is more or less solid once the car is shut off and doesn't sink like it does with the engine running...

Could this be the cause? Need input here, I'm beyond any further ideas...

[8991XJ]

A bad bomb will not affect bleeding as it only supplies power (pressure) to assist the brake application. When it is dead, the brakes operate manually, direct connection between foot and master cylinder without the assistance of the bomb pressure.

You did bench bleed the master cylinder? I had an aftermarket no-name master that did not bench properly and I went through two of those before getting a real ATE or whatever brand master to get the brakes to work properly on my E28.

I don't use pressure bleeders, preferring to do this manually and by myself and have had great luck. Run the hose up a foot of so into the suspension before going down into the collection device.

Maybe you can see if there is any fluid flowing going into the calipers by loosening the hose just a bit. Since you replaced the hoses, I don't think this is the issue that seems common when one can not bleed the brakes. I'm sure you have cleared the bleeder holes and bolts of any debris.

[dude99]

I get lots of flow through all the bleeders so I don't think that's an issue.

New master is an ATE, you can even see where they ground off the BMW emblem after they cast it.

I did bench bleed it in the car, and got no bubbles through either line.

I've been doing a lot of reading and it seems my symptoms are consistent with a bad bomb. All the threads on it I've read describe the condition as a rock hard firm pedal when the car is off, and a spongy pedal, that will slowly sink when the car is in. This is exactly what I'm experiencing.

So when I get back after this weekend I'm going to do the level change test to see if my bomb is shot or not.

On a related note, has anyone used the "Swag" brand of bomb before? It lists as fitting the 1985 e23, but I assume they are all the same???

[m735is]

I'll agree with your bad bomb diagnosis. I have not used a Swag brand, but yes, they should all function the same.

A note about the bomb: you need to discharge the pressure in it before you bleed brakes using the pump the pedal method. Just pump the pedal with the engine not running until the pedal is hard. Watch your power steering level when you do this, it will rise in the canister. I forgot to do this and ruined one.

[dude99]

You ruined your bomb by bleeding before depressurising it? That seems odd. Wonder how that works.

Thanks for weighing in and confirming, always nice to hear someone agree with your diagnosis before taking the parts plunge.

I can't believe the cost of the accumulators. If I want to wait for one to ship from Latvia I can get it for ~$150CAD, but if I want it in a reasonable time frame it's like $250! Someone is making a killing for a little bit of metal+rubber and a whiff of nitrogen.

[8991XJ]

You need to find your Canadian low cost parts distributors. AutohausAZ has em for 86 for a Febi. The pressurized device makes it a hazmat to ship so you might have trouble getting one from outside Canada. But with your friend's Seattle area shipping address you should be able to get one from a US supply.

[dude99]

Sucked it up and bought a new bomb. $$$$$ All back together now and the sinking pedal is gone! Hooray. Still moves much easier than I'm accustomed to, but I'll have to take it out for a drive and see how it feels.

Thanks all for the help