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Discussion Starter #1
Since I have very basic and limited knowledge on this topic, I wanted to start a discussion where more knowledgeable members can chime in.

We all know that E39 across the range has the same MC, from 520i to M5. I recall that my old 530i had better brake pedal feel than all 3 M5's that I've owned. A friend and member here also feels that his 528i and E53 X5 have better pedal feel than his M5. When I say better brake pedal feel, I mean firmer pedal with less travel.

At the moment, I have D2Racing 8 pot front BBK on my M5 installed by the previous owner. Ever since I first test drove the car, I couldn't shake the feeling that my previous M5, which had stock brake setup, had a better pedal feel. I thought it just needed a good flush and system bleed. I completed the setup with SS brake lines all around and bled the system multiple times using DIS and cycling the pump, while the braking power is great I feel the pedal travel is still too long and the pedal could be firmer.

I was browsing the interweb and it appears that the E65 brake MC could be a direct bolt on for E39.

E39 master cylinder - part # 34311165544



E65 master cylinder - part # 34336785926



Spec from ATE catalog.



So front diameter on E65 MC is slightly bigger at 27 mm whereas E39 is 25,4 mm. The obvious difference is that one fitting on E39 MC is M10 while all 3 on E65 are M12 but this could be solved with brake line adapter M12 to M10. Otherwise, they look physically identical.

I understand the principle that larger means decreased pedal travel (firmer pedal) which needs more pressure for the same amount of braking force, but as I lack experience in this area, is this even worth exploring?
Pricewise, both MC's are around $65 from TRW, at least in Europe. Before doing anything else, I'll try new pads likely Ferodo DS2500 as now I have Street/Sport pads that are supplied by default with D2Racing BBK.
 

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Sreten might be onto something here. While BMW does some great engineering sometime it seems that cost cutting department wins over engineering department during production. Especially as E39 seems to be about the last model (with its E46 and E38 brothers) where engineering almost always wins over cost cutting.
I can't add much more to OP topic than this but hopefully some engineering heads here might.
 

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This seems like it would improve the pedal feel on the car. Here are some others that I have found information on as well for discussion.

The Z8 brake cylinder (direct bolt on) is 27/20
E60 25/22
E65 27/20.65
E39. 25.4/20.65
E70. 27/22
- The X5 e70 brake cylinder is 27/22 (ie same as E60 M5)
 

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Discussion Starter #4
Thanks! It looks like only the E65 is the same and plug n play for E39. The E60/E70 MC is different and has only 2 brake line connections so it wouldn't work.

From the research I did, there should be some pedal feel improvement (more stiffness). It's popular with E30 guys to install E32 MC when they install BBK and get long pedal travel, going from 22 or 23.8 mm to 25.4 mm with E32 MC.

I bought Ferodo DS2500 pads which should be delivered today. I'll pop them in first and drive them for a while. If I'm still unhappy with the pedal feel, it's cheap enough for me to try E65 master cylinder. Worst-case scenario, I don't feel any change with it at which point I have brand new MC that can stay on the car.
 

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Discussion Starter #6 (Edited)
I've seen your thread on it a while back. I'm digging that mode and will follow it for updates. It's actually cheaper to do this than to just buy new M5 fan clutch in Europe which I've done twice so far.
 

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Thanks! It looks like only the E65 is the same and plug n play for E39. The E60/E70 MC is different and has only 2 brake line connections so it wouldn't work.

From the research I did, there should be some pedal feel improvement (more stiffness). It's popular with E30 guys to install E32 MC when they install BBK and get long pedal travel, going from 22 or 23.8 mm to 25.4 mm with E32 MC.

I bought Ferodo DS2500 pads which should be delivered today. I'll pop them in first and drive them for a while. If I'm still unhappy with the pedal feel, it's cheap enough for me to try E65 master cylinder. Worst-case scenario, I don't feel any change with it at which point I have brand new MC that can stay on the car.
Please keep us updated. I'm not happy with the brake feel on my M5 either. I'm not sure if it's flexing of the cheapo floating calipers or a too small MC. Before I gamble on a BBK to address potential flexing, it would be nice to know if I can get to where I want to be with an MC change.

Thanks in advance
 

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I just upgraded my pads from factory BMW to EBC red, better pedal feel, more responsive than stock. I am looking forward to upgrading the master cylinder too
 

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If you really want to fine-tune the feel of your brakes (and query whether that REALLY is an endeavor you want to dive into), delete your brake booster and replace it with a dual master cylinder bracket. Then you will have the full selection of aftermarket master cylinder sizes from which to choose AND you can add a brake bias adjuster to the setup for further front to rear fine-tuning. Massive Lee makes a good bracket, though it make take a little fitment work to make it fit. May be more work than you want, but using a booster delete setup such as Massive Lee's is really the only way to get true adjustability for your brakes without going all the way and adding a pedal box. Just my $.02.

--Peter
 

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Discussion Starter #10
Thanks for your input, Peter. That would be the right way to go about it but I don't want to do heavy modding. I suggested E65 MC because it's slightly bigger, cheap and easy bolt-on part.

At the moment, I'm struggling to find brake pads that fit my stupid D2Racing BBK. 2 sets of Ferodo DS2500 delivered and none of the fit in the caliper properly despite proper dimensions and them being listed as correct pads for this application. Looks like I'll have to go with default D2Racing pads.
 

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Thanks for your input, Peter. That would be the right way to go about it but I don't want to do heavy modding. I suggested E65 MC because it's slightly bigger, cheap and easy bolt-on part.

At the moment, I'm struggling to find brake pads that fit my stupid D2Racing BBK. 2 sets of Ferodo DS2500 delivered and none of the fit in the caliper properly despite proper dimensions and them being listed as correct pads for this application. Looks like I'll have to go with default D2Racing pads.
If the plates are in good condition, Carbotech can attach new pad material to them using one of their compounds, matching the profile amd size of the originals. I like the 1512 Bobcat for daily driving. Not sure of cost, though.
 

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Discussion Starter #12
Interesting idea. Although, given that I'm in Europe and Carbotech is in the USA, that would probably take forever.

I'm talking to Ferodo support, few online shops and useless D2Racing customer support to see if there is a pad that would fit.
 

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Waiting with baited breath for the results on this one. I don't think that the stock brakes lack power, they will activate ABS at 140mph... But I have never been happy with the amount of travel or pedal feel.
 

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Mod done, I will write up the details and how to tips later.

Someone please send me a crowbar to remove smile from my face, it exceeded expectations.
 

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Stefan and I swapped out the master cylinder on the e39 M5 with the master cylinder from the e65. The cylinder diameter is increased to 27mm from 25.4mm for the front brakes, the rear remains 20.64mm

Remember - Use Caution, brake fluid eats paint!

Access Brake Master Cylinder by removing Cabin Filter
Drain Master Cylinder
Remove Cover Shelf above the brake Booster in engine bay
Loosen pipes from Brake Master Cylinder
Inside the car, release the brake pedal cross pin from the booster and remove the 2 bolts holding the brake booster to the chassis
Use master cylinder as a lever to raise the assembly, then remove the master cylinder from the booster
Installation is reverse of removal

Raise car, remove wheels
Power bleed braking system, we bled the system twice with engine running, starting from RR, LR, RF, LF.
Torque Wheels
Parts Needed:

• BMW Master cylinder Part Number 34 33 6 785 926 or 34 33 6 797 650
• M10 to M12 Brake line adapter
• ATE SL6 Brake Fluid

In order to make the e65 master cylinder work there are 2 modifications needed:

· The M10/M12 brake line adapter is used in the driver’s side port shown in photos below. The Brake line on the car is M10, the port on the master cylinder is M12.
· The Mounting flange on the new master cylinder must be modified as shown for reservoir mounting clearance. Some material must be removed from the flange by a cutting wheel in order to for the reservoir to mount.





The braking system responded very well to this modification with more response to the brake pedal that is easily modulated. The calipers on my car are stock BMW M5 brakes with Goodridge SS hoses, ATE SL6 fluid, and EBC red pads on the calipers. My car has over 120k on it, so some of the improvement comes from replacing a 17 year old master cylinder, the remainder of the improvement comes from the increased cylinder diameter of the new master cylinder.

I can email photos if someone else can post for me, I cannot post photos to this site.
 

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If you need to just throw the pics up on dropbox or google drive or something and then share the link here. But your problem is probably that you just need to resize them, this site has a really low limit for picture size. I think they can only be 1000x1000 pixels max. You can resize them quickly down to this with Microsoft Picture Manager.
Can you share where you sourced the M10 to M12 adapter from? I only see ones that have a inverted flange on the M10 side, which I don't think is correct. Thanks again!
 
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