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325XI Master Cylinder DIY

28914 Views 13 Replies 9 Participants Last post by  djdonis, 
G
I spent the weekend replacing my wife's 2001 325XI master brake cylinder, brake pads all the way around and rear disk brake rotors.

Key Notes:

Master Cylinder: I ordered an "off" brand from a company in CA and when it arrived they sent me the wrong master cylinder. It was missing a critical port on the bottom of the master cylinder. So I found a re-manufactured OEM part locally. The top one is the correct one in the picture below.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWMasterCylinersWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWMasterCylinersWS.jpg" border="0" alt="Photobucket"></a>

Bleeding Master Cylinder: For some reason I thought when I put on the new master cylinder that bleeding the system would flush out any air. I did not hook up the bleed connections and tubes. After running (3) litres of DOT 4 brake fluid through and still having a soggy brake pedal I had to hook up the bleeder lines while the master cylinder was on the car. A lot of air came out of the master cylinder and then after another full litre the pedal felt great and the system was ready to go. Pic of the bleeding connectors and lines below.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWMSbleedlines.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWMSbleedlines.jpg" border="0" alt="Photobucket"></a>

ABS System: I have read that you cannot bleed the system fully enough to get around the ABS module. I have read that if you change the master cylinder you will need to go to the dealer to pulse the ABS system to get the air out of the ABS system. My solution (not sure if this is the best way) was to put the car up on blocks, turn the car on, put the car in drive and let the wheels spin slowly, then I slammed the brakes, that made the ABS pulse and then I bled a line, then I did it again and bled another line. If this causes damage to the car let me know but it worked well for me. I am not responsible for your car.

Here is the car and parts ready to go:

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWandPartsWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWandPartsWS.jpg" border="0" alt="Photobucket"></a>

Open up your hood, and you should see the brake fluid reservoir.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWMSResivoirWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWMSResivoirWS.jpg" border="0" alt="Photobucket"></a>

I removed the cabin air box, filter and the engine shroud that blocks off the master cylinder.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWMSreinstalledWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWMSreinstalledWS.jpg" border="0" alt="Photobucket"></a>

Then I removed the brake reservoir. The only annoying part about this is the Torx 25 bit that you need to get the reservoir off.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWresremovalWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWresremovalWS.jpg" border="0" alt="Photobucket"></a>

Then use an 11 mm open ended wrench to remove the three brake lines that are coming into the old master cylinder. Then use a deep 13mm socket to remove the master cylinder.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWMasterRemovedWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWMasterRemovedWS.jpg" border="0" alt="Photobucket"></a>

Then use the provided lines and fittings to bleed the new master cylinder. Instructions should be provided for bench bleeding the new one.

Put the new, fully bled, master cylinder on the car and put all the parts back on the car. Then I changed all the brake pads and rear rotors on my wife's car.

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWOldandNewRotorsWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWOldandNewRotorsWS.jpg" border="0" alt="Photobucket"></a>

Now it's time to bleed the system... Nothing really earth shattering here. Start at the rear passenger, go to the rear driver, then front passenger then front driver. Have your helper pump the brakes 5 times then hold the pedal down. Crack the bleeder valve and then close the bleeder. Repeat the process. I ran (4) litres of DOT 4 fluid through for a full flush of all the old stuff and all air.

When the pedal feels good it's time to put the wheels back on and test drive your car. For me the car's brakes felt brand new! :thumbup:

<a href="http://s470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/?action=view&current=BMWNewPadsRotorsBleedWS.jpg" target="_blank"><img src="http://i470.photobucket.com/albums/rr61/glxedwards/BMW%20Master%20Cylinder/BMWNewPadsRotorsBleedWS.jpg" border="0" alt="Photobucket"></a>
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B
awesome DIY...i'll be doing this project this coming weekend.

can you explain bleeding the master cylinder unit itself with a little more detail? i'm a bit confused on what you mean.

Bleeding Master Cylinder: For some reason I thought when I put on the new master cylinder that bleeding the system would flush out any air. I did not hook up the bleed connections and tubes. After running (3) litres of DOT 4 brake fluid through and still having a soggy brake pedal I had to hook up the bleeder lines while the master cylinder was on the car. A lot of air came out of the master cylinder and then after another full litre the pedal felt great and the system was ready to go. Pic of the bleeding connectors and lines below.
Click to expand...

also what method did you use to drain out the resorvoir? and is that the only thing you had to drain to start the project?
thanks!!
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G
To bleed the master cylinder you have to put the reservoir back on the new master cylinder. Once that is secured on the new one you insert the three green plastic threaded fittings into the open holes in the new master cylinder. You attach the clear plastic tubing from the green fittings and stick them into the top of the reservoir. Then with the master cylinder lightly secured in a bench vice you are going to fill the reservoir with fresh new DOT 4 brake fluid. You then use a wrench to move the main piston that makes the master cylinder work. That movement of the piston will push the air out of the master cylinder chambers. So keep moving the piston and watch the lines off the fittings. You will see a lot of air and fluid flowing back to the reservoir. Once you only see fluid flowing back to the reservoir you know you have fully bled the master cylinder and you can install it on the car. This is very similar to bleeding the brakes, make sure you have the tubes submerged in the brake fluid of the reservoir because if you don't you'll just keep sucking air back into the master cylinder.

I didnt bench bleed my new master cylinder because I thought bleeding the brakes a lot would clear any trapped air, I was wrong. After two attempts I still had a spongy pedal and what I did was remove the hard lines from the master cylinder and hook up the plastic fittings and tubes when it was on the car. I used the brake pedal to pulse the master cylinder and watched the lines as described above. It was very difficult to get at the fittings and do this while on the car so save yourself time and aggravation by bench bleeding first.
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N
Great write-up, thanks! Starting this project on my son's car Monday.
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J
Reviving an old thread that I hope the OP is subscribed to. What were the symptoms that prompted you to replace the master cylinder?

I have a 2005 with 85k miles that has been to over 40 track days and tons of autocrosses. I have been having an inconsistent pedal for a very long time. The best way to describe it is during mountain drives I get into the brakes and have a soft pedal, release and immediately reapply and the pedal is firm as I expect. It's not during corners, straights, or anything repeatable, it's just inconsistent. What is consistent is that the first application is soft, but the immediate second application is firm.

I had a shop take a look and they determined it was operating as normal... not much help there. They recommended I replace the rotors and pads as they were well worn, so I did. No change. During that process I noticed cracks in the dust boot on one of my calipers, so I rebuilt all four of them. All four had cracks in the boots, but were not leaking, though I do think the inner seals were a bit worn. Now I have four rebuilt calipers and still the inconsistent pedal remains.

I know the system is air free... not a rookie at this bleeding thing as I flush the system before every track event. I'm open to suggestions, but I'm leaning towards a new master cylinder. I don't know much about them or why they would fail. Inner seals maybe?

Thanks in advance!
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G
@jvr826

You are running out of possible options. You've replaced everything else there isnt much else it can be. The big problem you are having sounds like my VW Touareg I had. The dealer kept trying to tell me they couldn't reproduce the same spongy pedal feel. The Touaregs are notorious for having the master cylinder inner seal leaking so it will just give you a soft feel here and there but not all the time and you wont lose fluid as it just bypasses the the inner seal but stays in the master cylinder. Luckily for me my wife's BMW was obvious, she would totally lose pedal feel, the pedal would go to the floor and she would have to pump the pedal like 20 times to get any braking pressure. It was very obvious. Yours sounds more like a seal that is failing but has not completely gone yet.

It really can only be (2) things, air or master cylinder. If you've bled the heck out of it, just try one more time, it really doesnt cost you anything. If that's not it, then it's time. The cylinder is only $80'ish for a refurbed one, some fluid and elbow grease and you'll have a brand new braking system. The only other possibility would be a cracked line but then you'd see fluid on your driveway. If there was a crack anywhere in the system where it could pull in air (even tiny amounts) you'd get a soft pedal feel. But it would be all the time. Here and there is most likely the master in my opinion.

Good luck!
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J
Thanks! I did more research after posting and I agree. Now to decide between the $80 Metelli or the $400 OE BMW part. That should be an easy choice, no? :)
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G
Seems like an easy choice.
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Sansho
Now to decide between the $80 Metelli or the $400 OE BMW part. That should be an easy choice, no? :)
Click to expand...
A new BMW master cylinder is $284 (with a 2 year warranty) from thebmwpartstore.com (sponsor) or ebmwparts.com (sponsor), and an ATE is about the same. I don't know Metelli brand, but if it were my car being put on the track, I'd pony up for the factory master cylinder. Maybe you know others that use the Metelli on the track?
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P
2nd revival:

Where do you get the green fittings? I am having problems with the master and I am looking to bleed it but no adapters. Thanks.
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L
I like the trick you used to get around the ABS module, it's nice not to have to pay a shop for to do that.
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M
patriot_man said:
2nd revival:

Where do you get the green fittings? I am having problems with the master and I am looking to bleed it but no adapters. Thanks.
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Mflara20 said:
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Go to your nearest auto supply store. You'll probably find one there. Ask for a master cylinder bleed kit.
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D
This DIY is useless, it fails to mention the installation procedure and brake line attachment with the reservoir full of brake fluid that will pour everywhere as you try to attach the lines.
The space is really tight and it is almost impossible to attach brake lines with the fluid in the reservoir, especially the pre-charge pump lines.

The air WILL get introduced into the hydraulic system and the only way to bleed it properly is with BWM GT1 tools, as you need to cycle the Precharge Pump, Rerturn Pump, and activate appropriate valves in the DSC module at the same time.
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