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E36 (1991 - 1999)
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  #1  
Old 10-04-2019, 05:50 PM
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dwonda dwonda is offline
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Mein Auto: 1996 328iS
My elusive spongy brake pedal...

Quick summary:

1996 BMW 328iS

- Front calipers replaced with reman M3
- All rubber brake lines replaced with ECS steel braided
- New Centric M3 MC installed
- New DBA front rotors
- New StopTech front Street pads

I've come to the conclusion that I have air ingress in my brake system. I have noticed that when bleeding my brakes from the calipers or as far up as the ABS unit bleed screw, I can get clear fluid if pumping my pedal with the engine off (power bleeder is also attached), but when I perform the same procedure with the engine on, I start seeing foamy air in my lines.

I have decided to replace the remaining components, which would be the brake booster, and the ABS unit. My brake booster definitely has issues at this point, something feels/sounds broken. However sourcing my brake booster will be really difficult unless I want to risk a Cardone reman. I am currently waiting to hear from a company in France that may have some ATE units available, fail that there is a TRW option listed with some company in the UK, all other sources are NLA. I am also going to buy a used ABS unit from an M3 this time. I have no idea what the difference is as they look identical, but if I am replacing it anyways I might as well get one that is supposed to match the rest of my brake system. I am also buying a used M3 ABS control unit just in case that is also necessary. Any coding I should be able to do with DIS if needed.

As I am becoming increasingly observant, and methodical when tackling this problem of spongy brakes for the past year and half or more, I am learning as much as I can. Today I started to remove components in anticipation of replacing them. I have an interest in these 2 screws at the top (highest point) of the ABS unit, but I am not certain of their function and am looking for an engineering perspective. What I can tell you is this, the 2 caps each have a hole in the center and a hole on the side. There is a small spring loaded bearing in the center which would allow travel in the direction of from center hole to side hole. The caps also have rubber o rings. When fully tightened down they form a seal around the center hole of the ABS unit, ensuring 1 way travel of brake fluid from the center hole to the side hole. My question is why does this mechanism exist in a removable cap? Is there any evidence of a design here for the purpose of bleeding air out of the unit? See photos attached.
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1996 328iS OEM Frankenstein
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  #2  
Old 10-09-2019, 11:06 PM
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dwonda dwonda is offline
Insane in the membrane!
Location: North Carolina
 
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Mein Auto: 1996 328iS
What I have noticed is that while I have my MC disconnected from my hard brake lines, and instead have some short clear lines hooked up, and running back into the reservoir, I will get very foamy air in the fluid if I pumped the pedal with the engine running. If I turned off the engine and pumped the pedal then I would get clear fluid again. This was happening despite having the new Centric brand MC installed. I haven't talked to a single person who has been able to explain this behavior.

However I'm at my wits end, and I've already accepted the fact that I'm not going to figure out what has been introducing air into my brake fluid, as I will be replacing all of the components not yet replaced.

Because of pumping on my brake pedal hundreds of times these past several months I have effectively broken my brake booster, not sure if it was a problem before, but it is definitely a problem now. I'm way past the point of taking risks buying remans, and new ones are NLA with a couple exceptions. It seems there are some companies in Europe that have them still.

I ordered my brake booster from a French company: https://www.mecatrouve.com/search?q=10.6360-1903.4 <- which is an ATE part number but same as original part. Ordering from them has been a frustrating experience, has required doing a lot of translating, PayPal won't work, and contacting them via email despite my best French efforts has so far yielded no response. However I was able to make an order after confirming with my CC that it wasn't fraud, and after a few days I got an email from mecatrouve confirming my order and sending me a pdf receipt. They stated that when it ships out I will receive another notification and 3 days later it still has not shipped out apparently.

Shortly after placing my order I did receive a response from another vendor, they are in Germany and a little more pricey, but at least I heard from another human there who said that they did in fact have them. So if mecatrouve doesn't come through perhaps I will try these guys: https://www.teilehaber.de/itm/bremsk...l?id=106463337

I think it is insane that such a critical component on a mass produced car up to 1999 is NLAt, from what I can tell it was used on E36's before 96 including 96, but also used in M3's all the way to 99 even though 328's for example got rid of the brake pedal position sensor.

I got my used ABS unit in the mail today, I figure if the rest of my brake components are from an M3 I may as well continue the trend so I bought an ABS pump with part #34512228225, RealOEM has it listed as 34512228226, but that doesn't seem to actually exist. I also ordered the control module in case it is needed for the different pump, part # 34521164023. These are 96+ M3 numbers which seem to be consistent from 96-99.

Some other NLA brake parts include the "intake manifold" on the back of the ABS unit, this refers to seals and hard plastic nipples that the soft return lines connect to. Strangely RealOEM only lists this part on the M3's even though I've never seen an M3 to have the plastic brace piece pictured, 328's simply don't have a part # listed for this, and neither do they have a part # listed for the soft return lines. They do for the M3 however, but 1 of them is NLA, however I can't imagine they are much different from each other, one is probably slightly longer, I ordered 2 of what they did have. We'll see how it fits when I install it. I decided to replace some pedal hardware as well, but didn't order the plastic bushings the clutch and brake pedal pivot on because I'm ordering some fancier copper ones from Garagistic that should last longer.

Another NLA part was the reservoir cap, but then I realized through ECS's amazing photos of everything, that a new reservoir includes the cap and level sensor. This had to be ordered from Germany however. I don't really understand why the M3 reservoir has the return lines on the driver side, where as the 328 reservoir has the return lines on the passenger side, but whatever. I'm honestly not looking forward to the new return line locations because it will make access to the bleed nipple on the side of the ABS unit more difficult.

Here is a list of the rest of the parts I ordered:

34-32-2-227-296
HOSE
2 $17.55 $35.10
16-12-1-180-240
HOSE CLAMP
2 $0.98 $1.96
16-12-1-180-241
HOSE CLAMP
2 $2.41 $4.82
34-31-1-160-133
SEALING PLUG
2 $9.59 $19.18
07-12-9-906-196
HEX NUT
2 $1.82 $3.64
34-31-1-160-617
BRAKE MASTER CYL
1 $11.02 $11.02
34-32-2-228-163
EXPANSION TANK
1 $154.25 $154.25
07-12-9-952-109
HOSE CLAMP
2 $1.90 $3.80
34-33-6-765-316
GASKET
1 $7.90 $7.90
07-12-9-952-109
HOSE CLAMP
2 $1.90 $3.80
34-33-6-765-316
GASKET
1 $7.90 $7.90
34-33-1-160-183
NON-RETURN VALVE
1 $22.85 $22.85
35-21-1-158-489
RETURN SPRING
2 $2.98 $5.96
35-41-1-113-728
GROMMET
2 $2.58 $5.16
35-31-1-158-661
LOCKING PIN
1 $5.54 $5.54
35-31-1-162-363
BRACKET
1 $3.76 $3.76
35-31-1-157-478
BRACKET
1 $3.89 $3.89
21-52-6-863-043
GROMMET
1 $5.36 $5.36
21-52-1-163-714
HOSE
1 $9.03 $9.03
21-52-2-227-764
COMPRESSION SPRING
1 $6.61 $6.61
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1996 328iS OEM Frankenstein
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  #3  
Old 11-10-2019, 07:39 PM
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dwonda dwonda is offline
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I acquired another used M3 ABS unit, as well as the controller. The controller was not needed but I may still install it as there could be differences in programming which applies to the M3's.

I seem to have stumbled upon a series of unfortunate events, but my guessing days are over...

After installing all of the above parts I could not get air out of my lines. Long story short is I gave up, and decided I needed to to test the components individually. The first component I tested was the ABS pump. I used clear vinyl tubing in place of the hard and soft lines, with the exception of the lines which would go to my calipers, those I blocked off with some short lengths of brake lines I found at Advance. I cut them short, then folded the ends of the lines over themselves for an air tight seal. I then simply applied 12 volts to the motor. After the initial bleed I was able to observe that the pump is consistently injecting very fine air particulates in the fluid, sometimes only visible with a bright flashlight or sunlight. The pump is also leaking around the gasket between the pump and the aluminum block underneath. I took this apart to look at the gasket, and nothing obvious was wrong with it. I swapped the gasket with the one from my 328 pump since they are identical, but it still leaked. Tomorrow I plan to bench test my 328 pump and see if it performs in the same way.

Next component I tested today was the master cylinder. I had previously bench bleed it and didn't have a problem, but somehow it has developed a problem very recently, what happens is if the cylinder is depressed quickly at all, the first port closest to me when pushing the cylinder in, will inject a substantial amount of air into the fluid, also peculiarly there is no fluid which leaks from anywhere from the MC. Luckily I my friend had a spare MC which I was able to bench bleed without issue. So while I am waiting for another used ABS unit, I'll be further tinkering with the ones I have, and if I'm lucky I'll find out where the air is actually coming from.

The next thing I will be testing is each one of my brake lines. I plan to do this by attaching a vacuum pump to each individual line and making sure they can hold 1 bar of vacuum consistently. This should tell me definitively that there are no leaks from the attachment point to the ABS and all the way to and including the calipers. Once this is done I will connect them to my ABS pump assuming I find a good working one.

Also I learned a pro tip for bench bleeding the MC. Instead of having to buy 2 stupid bleed kits because they only include one of each size plastic nipple adapter, and everything else is useless, buy a set of m10x1.0 quick bleeders, I found them at Advance, and if you don't see them on the shelf there is a good chance they have it in the back. Not only is this cheaper, but it works way better because they only allow the fluid to travel in one direction. The problem with the nipples is that if your hoses are too long, you'll never get the air out because as soon as you release the piston/cylinder it just sucks the fluid back, so you need to use super short hoses so one pump can move the bubbles out of the hose. I don't particularly like this because it takes longer, and I always like to do a bit of bench bleeding with it mounted on my car, and when the tubes are so short I can't see whats happening from inside my car. The other nice thing is that you don't have to deal with the stupid square shapes of the nipples, which don't particularly fit any socket very well, and tend to slip. My warning is that you should avoid screwing the quick bleeders in all the way. The ends are not bubble flares which the MC ports are designed for and if they are screwed in with much force you may damage the holes in the MC and cause a leak in your bubble flare seal. I just screwed them in slowly and softly until I felt it bottom out and then backed off one rotation from there.

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1996 328iS OEM Frankenstein

Last edited by dwonda; 11-10-2019 at 08:01 PM.
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  #4  
Old 11-11-2019, 09:03 PM
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dc_wright dc_wright is offline
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Quote:
Originally Posted by dwonda View Post
The caps also have rubber o rings. When fully tightened down they form a seal around the center hole of the ABS unit, ensuring 1 way travel of brake fluid from the center hole to the side hole. My question is why does this mechanism exist in a removable cap? Is there any evidence of a design here for the purpose of bleeding air out of the unit? See photos attached.
There should be a seal on the piston also. It looks like a pressure relief valve, and the spring controls the relief pressure. The holes in the top would be to allow the piston to move without building up air pressure and enabling the spring to be the controlling force. If it was sealed above the piston it would be trapping the air and that would both limit the travel and make the movement pressure temperature sensitive.
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Old 12-08-2019, 02:39 AM
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dwonda dwonda is offline
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Location: North Carolina
 
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Quote:
Originally Posted by dc_wright View Post
There should be a seal on the piston also. It looks like a pressure relief valve, and the spring controls the relief pressure. The holes in the top would be to allow the piston to move without building up air pressure and enabling the spring to be the controlling force. If it was sealed above the piston it would be trapping the air and that would both limit the travel and make the movement pressure temperature sensitive.
I apologize for responding to this so late. I did see it when you originally posted. After trying a few different ABS units I discovered that the air I was seeing come out of the lines when the pump was running was just cavitation, and not actual air bubbles. As I noticed that these particles didn't rise, and actually dissolved over time.

However I am still struggling to get air out of my lines...

I had acquired yet another used M3 MC from a friend, and unless I'm losing my marbles I did have success bench bleeding it. Just before I bench bleed that one, I bench bleed the other one. And what I had noticed with the previous one was that if I pushed on the MC plunger too fast, air would get shot into the fluid. However with the 2nd one, I didn't notice that. So I installed it in my car, and achieved a better feeling pedal than I had felt in a long time, but I knew I must still have some air trapped. So I went to bleed my ABS system again and started noticing that while using my pressure bleeder, every time I pressed on my pedal I would get more air coming out. So I disconnected the MC AGAIN, and did a bench bleed on my car, and the same thing. Unless I stepped on my pedal VERY slowly, it would shoot air into the fluid. So I thought well tough luck, I guess I broke another one and blamed it on the fact that I was not limiting the travel of my pedal with a block of wood. So I ordered another new Centric one, and right out of the box noticed the same thing. I then went back to my old 328 one which I thought was fine, and also noticed the same thing.

So tell me, what are the odds that I have a 328, 2 M3 OEM, and 1 new aftermarket M3 MC that have all failed in the same way? But for the life of me I can't explain why in any case, a MC would shoot air into the fluid, even if an open system situation. Does this sound right to anyone?
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