E36 - ABS Brake Bleeding Issue

[TipsyMcStagger]

This is a non standard scenario. I and doing an engine swap on my '98 328iS and have installed a hydroboost and master cylinder from a 2004 Mustang. I've pressure bled the system and see no air bubbles but the pedal goes to the floor.

I've tried cycling the ABS pump by jumping pins 87 & 30 on the ASC relay to no avail. The Bentley seemingly has no listed procedure for brake bleeding ASC equipped cars. I found the following procedure in another post:

"Prerequisite:
- Motive bleeder or equivalent and able to go up to 29psi as per BMW spec.[/COLOR]
- Fluid collector and tube to be connected to bleeding nipples.[/COLOR]

1. Pressurise to 29psi.
2. Look for 'Ventilation' in Service Functions - DSC and follow the instructions. It will ask if it's a fluid chance, bleeding, unit replacement etc. and then prompt you to go to each wheel, starting with rear right.

Sequence is as follows:

- insert tube from collecting jar
- release bleeder screw until you see a reasonable flow (you won't have a mighty fast flow like manual bleeding)
- click to acknowledge in DIS
- hear pump activating and wait for the 2 cycles to end
- pump the pedal 5 times (bleeder screw still open)
- close bleeder screw
- go to next wheel indicated by DIS
- insert tube from collecting jar
... and so on.

It's very important to pump the pedal as per instructions otherwise it's very possible you will still have air trapped in the system."


Since I will be attempting to replicate this procedure without DIS (by manually activating the ABS pump), I'm wondering if anyone knows how long the pump would normally activate for each of the two cycles?

Also, the procedure says to "go to the next wheel indicated by DIS." Obviously, the normal sequence would be right rear, left rear, right front, left front. Is it safe to assume the sequence directed by the DIS would be the same?

TIA.

TIpsy

[328 Power 04]

You cannot replicate the procedure without DIS, or similar.

When you bridge the relay, all you are doing is running the electric motor, but doing nothing with the valves. The info online is false. DIS has a specific sequence of events to turn on the pump and cycle the input and output valves. It's impossible manually.

The best you can do, since the pump is not brand new and completely dry, is bleed from longest tract to shortest, then drive and activate ABS, then bleed some more. You will clear out bubbles. The surface tension of the fluid already on the walls of the fluid tract should allow for full bleeding after a few good rebleeds.

[TipsyMcStagger]

You cannot replicate the procedure without DIS, or similar.

When you bridge the relay, all you are doing is running the electric motor, but doing nothing with the valves. The info online is false. DIS has a specific sequence of events to turn on the pump and cycle the input and output valves. It's impossible manually.

The best you can do, since the pump is not brand new and completely dry, is bleed from longest tract to shortest, then drive and activate ABS, then bleed some more. You will clear out bubbles. The surface tension of the fluid already on the walls of the fluid tract should allow for full bleeding after a few good rebleeds.

That makes sense. I was unaware that powering the pump would simply activate the motor without actuating the valves.

After posting, I tired to replicate the procedure and still have no pedal. Unfortunately, since this is an engine swap project, I can't currently drive the car. And there is no harness in the car through which to connect DIS.

I was thinking the MC might be faulty (it's a used MC) and it might be. If the issue is air, I'm just wondering why the pedal doesn't firm-up with repeated application? No matter how many times I pump, it goes to the floor.

Thanks again.

Tipsy

[pbonsalb]

Are the line sizes the same? I tried different size clutch lines and got strange pedal results. Seems like with hydraulic systems the pedal travel limits displacement any changes affecting fluid have to stay within certain parameters or you hsve to compensate some other way. You might be able to play with master sizes to get it back in range.

[TipsyMcStagger]

Are the line sizes the same? I tried different size clutch lines and got strange pedal results. Seems like hydraulic systems in which the decks limited displacement have to stay within certain parameters. You might be able to play with master sizes to get it back in range.

The line sizes are the same but I think the MC bore is slightly larger than the stock 328iS MC.

Tipsy

[MIKYZZ4]

I was thinking the MC might be faulty (it's a used MC) and it might be. If the issue is air, I'm just wondering why the pedal doesn't firm-up with repeated application? No matter how many times I pump, it goes to the floor.

The rare time or two that I have experienced these symptoms, the MC was to blame.
I would make sure that a simply low reservoir or a major leak in the system was not the cause of the low pedal,
before removing and replacing the MC.

[TipsyMcStagger]

The rare time or two that I have experienced these symptoms, the MC was to blame.
I would make sure that a simply low reservoir or a major leak in the system was not the cause of the low pedal,
before removing and replacing the MC.

The reservoir is filled to the top and I have a Motive bleeder holding 15 PSI on the system, which would not be possible if there were a leak.

Tipsy

[328 Power 04]

Not that I'm assuming that this happened here... but last time I saw a master cylinder being blamed, the calipers were mounted on opposite sides after a caliper rebuild, with bleeder down. Simple thing to check.

[TipsyMcStagger]

Not that I'm assuming that this happened here... but last time I saw a master cylinder being blamed, the calipers were mounted on opposite sides after a caliper rebuild, with bleeder down. Simple thing to check.

Thanks for the suggestion. Bleeders are on top.

Tipsy

[TipsyMcStagger]

I just read this note in the Cardone bench bleeding instructions:

NOTE: If firm pedalaction results from benchbleeding but becomes soft afterinstallation in vehicle, the problemis not the replacement mastercylinder.

So, I guess it stands to reason that if I remove the MC and bench bleed it, if it builds resistance on the bench, the MC is not the issue.

Tipsy

[MIKYZZ4]

Yes, that would be a logical assumption.
Maybe the brake booster is to blame?
Here is an informative article:https://www.eeuroparts.com/blog/7994...e-booster-diy/

[TipsyMcStagger]

Maybe the brake booster is to blame?

I'm not an expert on hydroboost units but I don't see how the booster could be to blame. With no hydraulic pressure to the booster, it's simply acting as a pushrod between the pedal and the MC.

There is no engine in the car at present.

Tipsy

[TipsyMcStagger]

This probably won't be much help for the BMW crowd but I hate that forums across the internet are filled with OP's seeking help with a problem, who never come back to post a resolution;

Success! This Mustang MC is a little different - at least by my experience. The lines to the ABS module exit on the bottom (red arrows). But on the side, there are two bleeders (green arrows). I hadn't messed with these previously and I'm not really sure exactly what they are for. But I figured they have to be there for a reason.

So, I hooked a length of hose to each bleeder, looped it back into the reservoir, opened each bleeder one at at time and gave the pedal a few pumps. I was doing it myself so I couldn't see how much air, if any, was escaping. But after just a few applications on each bleeder, I have pedal!

Tipsy

[WadiM3]

That's because because your on a BMW forum and 90% of the people and techs are only familiar with BMW parts as they are BMW specialists.. if you asked this question in a GM forum I'm sure you would have got more quicker answered but thanks for sharing with us the should be useful to anyone who ends up doing your mod

[MauiM3Mania]

...if you asked this question in a GM forum I'm sure you would have got more quicker answered

We all know that GM had a winner when they introduced the Mustang. Ignore Wadi, Tipsy.

[bmwdirtracer]

Yeah, um I do not believe that the OP would have gotten any help asking about a Ford part in a General Motors forum. I think people would have thrown shoes.

Damned good job, Tipsy. I love hydroboost, but did not have an answer for you....glad you found it yourself!

[WadiM3]

Ha sorry OP I'm just overly excited as I installed a very rare set of us m3 spec cams and my car is absolutely flying !!!

[bmwdirtracer]

Speaking of throwing shoes, Tipsy....you know BMW had hydroboost too? '83 533i, and many others.

[TipsyMcStagger]

Speaking of throwing shoes, Tipsy....you know BMW had hydroboost too? '83 533i, and many others.

I knew there were some hydroboost applications in years past, but I'm not familiar with the specifics.

With regard to asking my original question on this forum vs. a Ford forum; at the time I posted, I thought the air was in the ABS pump, hence the reason I was seeking information from those familiar with the BMW ABS system.

Thanks to all who offered advice.

Tipsy