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E28 535is versus M5 Brake Systems

Discussion in 'E28 (1982-1988)' started by gusgriff, Mar 13, 2010.

    gusgriff guest

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    I hear from all the post an opinion that the brakes are better on the E28 M5 rather than the 535is version. Knowing the M5 is a better performance car. I beleive this in most areas but I could not with the brakes with the data I can gleen from engineering data I had found so far. The E32 735i and E34 540i brakes are to be considered and mentioned in the my future plans. The research done and shown below is not meant argue with anyone who has done these upgrades or to change anyones opinion that is considering these upgrades. This is done for my benefit, to understand the engineering and do a cost benefit study. I am asking for the forum's members to look an my reseach and correct any errors and add any clarifications.

    This is what I have found which is missing specific engineering data and the questions that arise due to this.

    Master Cylinder ( Hydraulic Power Generation) ===========

    What is the difference between the E28 535is and M5 Master Cylinder What is the output pressure and volume differences?

    E28 535is Master Cylinder #34311153053 is different PN from E28 M5 Master Cylinder #34311155270 but same size and type: 23,81MM ATE

    The Brake Servo and Pressure Regulator are the same.

    Do not know brake pedal moment arm differences and how this effects Master Cylinder input pressure.

    Do not know differences in timed flow in cubic centimeter per second or response delay but cannot be significant.

    The front and rear brake bias is not significantly different between the two cars.

    Rotors ============

    Front Rotors are 18mm larger in diameter and 5mm thicker which does improve the heat abatement characteristics thus reducing fade. The larger diameter can improve the brake moment arm but I have no data on the delta distance centerline of wheel relative to centerline of braking force from pistons/pads. If greater distance it may be offset by the increased inertial mass due to the rotors and the added vehicle weight.

    Rear Rotors are the same.

    Brake Calipers =======================

    Saw some info on the forum that can lead one to believe that the 535is have only 1 piston per front caliper and the M5 has 4. The M5 does have 4 pistons but 2 per wheel caliper and the 535is has 2 pistons or 1 per wheel caliper. The piston bore or pressure area of both are virually identical. 535is has a 57mm bore (2550 sq.mm) and the M5 has two 40mm bore pistons (2512 sq.mm)

    The front calipers are #:34111160369/370 for the 535is and the calipers repair kit is #34111153208, (ATE FN-57)

    The front calipers are #:34112225002/003 for the M5 and the calipers repair kit is #34111158692 front and rear

    Rear calipers are different #34211160397/398 and #34211160393/394. The piston bore is the same as both use the same piston repair kit #34211153194.
    NOTE: Though number are the difference the carriers are the same so maybe BMW gave the calipers a different number so they could charge more since it would go on a more expensive car.

    Brake Lines ==================================

    Higher pressure and flow volume at the caliper input port will signicantly change the piston force to the pads negating the fact that the overall piston area is the same. As asked above what are the pressure and flow volume differences between the two systems. The diameter of the brake lines supplying the caliper input ports is identical. If the M5 has a higher flow volume why would be brake line be the same because with increased flow the pressure drop increases. Higher input pressure would be needed to overcome the increase pressure drop but this does not seem the best approach.

    Brakes Pads =================================

    Jurid pads are OEM for both cars but with different compounds. The M5 pads do appear larger by 10-20% and this will increase the fictional drag thus improving stopping power. I question how much if the the hydraulic power supplied by both the 535is and M5 brake systems is the same. The larger M5 pads would be lesser pressure per square mm but the overall force should be the same.
    The formula for frictional stopping power is (Force due to friction = coefficient of friction x Force due to pressure). Assuming the compression force is the same this is not the answer

    The 535is uses JURID 508 #34211157925 and the M5 uses ENERGIT 582 #34212226013 which is also a Jurid and both look identical.

    Do not yet know the difference in the pad compounds. The coefficient of friction may be better on the M5 type and they may have better heat abatement thus resist fade better. The pads with the three gaps between sections does enhance the heat abatement. The main purpose of the pads and rotors outside of stopping the car is this Heat Abatement. With the facts above the larger pads even creating less PSI force on the rotors coupled with the pads four sections and a better compound must abate/dissippate the heat generated more efficiently.

    CONCLUSION =========================================

    I still believe the M5 brakes are better but not that much significantly better, maybe 20%. I believe this improvement is due solely to the front brakes. I could not justify spend the money for front and rear M5 calipers to upgrade my 535is. Even if I raced this car the most I would do is the fronts with the M5 types. The next step would be to upgrade the rears with the e32/e34 types. I did this exercise to justify in my mind if the engineering backed up the desire for the "wizbang gotta have one of those" trap that we motorheads tend to jump into headfirst. If I were a rich man or had no other financial responsiblities, I to would want the best and what the hell if the improvement does not justify the cost.

    As stated several times above some enginnering was not found and assumptions were made as to the significance of said missing data. I am stubborn and anal and maybe to some a little flawed in my approach. If you have solid engineering data to pass on, I would greatly appreciate the education even if it proves me wrong. I promise to admit it in this forum.

    Some of you will disagree and think me an a..hole and a fool. Some of you will argue with me and state this on this forum. Some of you that do this without solid engineering to back your opinion up will do so because of your own agenda. I welcome all data and opinions and my agenda is only knowing the facts.

    CREDITS: My data was gleened from a similar study found on the mye28.com forum, RealOEM.com, online vendors and manufacturer websites.

    NEXT STEP =============================

    I will do this same exercise for the E32 and E34 brake systems. My preliminary opinion based on the reseach does thus far is guarded. The e32 735i & e34 540i front brakes are the same and an improvement over the e28 535is fronts but may be equal with the e28 M5 brakes. Though the e32 735i rear brakes are a slight improvement over the e28 535is rear brakes, the e34 540i rear brake appear to be a much greater improvement. The e34 540i brakes should be an improvement but the e28 535is may not have the hydraulic Power of the e34 540i. The brake lines are smaller on the 535is so voumeric flow and pressure would not be the same. I have yet to determine the Master Cylinder, Brake Servo and Pressure Regualtor differences. I hope this is more positive.
    I am still a "Motorhead and have to fight the attitude of "I gotta have one of these".

    gusgriff guest

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    Another member has on the mye28.com forum has pointed out an error in my reseach. This is the type of information I welcome.

    The M5 Front Caliper does indeed have 4 pistons.

    I was going by the RealOEM.com diagrams which shows 2. I should have checked the part number with a supplier. Four pistons per caliper will double the compression force on the rotors if the pressure supplied is the same. Even at a 25% lower pressure the force would be higher.

    Does anyone know where I could get a better diagram of the M5 caliper? Are pistons on each side of the rotor?

    Though this information changes my conclusion it does not invalididate it. There are questions that still need answering.

    Does anyone know the output pressure to the pistons and if the brake hydraulic are indeed at a higher pressure and volume since the brake lines appear to be the same size?
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    John in VA

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    gusgriff guest

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    Thank you. I had was slightly apprehensive posting these questions. There are some members who are not helpful, argue or make negative comments. I surmise these are the people who do not understand, do not want their opionions questioned or have some other agenda.

    As long as their are members like you and others on this forum and other forums like
    mye28.com, I and others might just learn something. Thanks Again
    • Member
    • Technical Service Advisor


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    Those are E34 M5 brakes, but the E28 M5 brakes are similar- 4 piston caliper fronts, single piston slider rears. The rear calipers have 1mm larger diameter pistons to maintain the brake balance with the higer front brake torque. Everything else in the system is the same as the regular E28 535i. It is still not a bad idea to go ahead and upgrade to the E34 rear calipers with E28 M5 fronts. It prevents the nose dive on hard braking. E28 M5 front brakes have better feel than E32/V8 E34 brakes because of their opposed piston design, but I do not have quantitative data on their stopping abilities with modern pads. I do not know if anyone has done a back to back test.

    E34 and E32 front brakes (US models) are all the same diameter, but the non 540 E34 brakes have a thinner rotor. The piston sizes are the same. The E28 M5 uses a rotor that is nearly the same diameter and thickness as the 540 E34/ all E32 and you can actually use those rotors with E28 M5 front brakes.
    The E32 and 540 E34 have the same size pistons in their rear calipers as the non 540 E34, but again the rear rotors are thinner (in this case, the non 540 cars do not have vented rear rotors.)
    Basically, the braking upgrade between adding E32 brakes to your E28 will be identical to adding non 540 E34 brakes until you get to the point of fading them, which is rare on the street. The lighter weight may be a worthwhile trade off if you don't track the car.

    gusgriff guest

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    Thanks, since most of you follow mye28.com you have seen the other replies. I was trying to find out the mechanism used to set the brake bias. Reading the replies as to the M5 upgrade the 1mm larger rear caliper piston will tend to equalize the bias.

    This may seem a strange question but how much does suspension stiffness front to rear play in reducing nose dive? If brake bias is eqaul its effect should be minimal if none at all. I ask this because if you put brakes from another car on a car but not change the suspension is there an effect? For example; M5 brakes on my 535is will feel different since the suspension is different. I am assuming the M5 is stiffer.

    Comments on the e32 and e34 brakes are appreciated.
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