My definition of small changes are that the the rear rotors are shared with regular E28 518-520-630-633 etc...off the shelf from BMW assembly parts bin, E34 M5 had its own brakes system front and rear in diameter. BMW upgrade the front brakes on E28 M5 using 4pot ATE cast caliper and left the rear complete stock, porque ?. The rear trailing arms bushings are shared again from the regular production line E28 518i up to M5. The Oil Temp gage is missing bloody critical option for our S38/M88! and BMW left the door open in Oil Filter housing so I can put the E34 M5/E30 M3 150C sensor to read as accurate as it could be! My personal Oil Temp Gauge I created till today people are confused that this option was available up to special order when they see my gage in my E24 M6. On my E24E28 I do miss the rear to be more tight!!! and that is why plan is to adapt a good set of trailing arms from E34 M5 with the unique slide bearing bushing with adjustable camber option. No downs side on that upgrade either. Just make a personal note when you driving your E34 M5 those rear bushings makes the car rear end one pice with your butt on the seat. On the E28/E24 you can feel the rear mushy specially on the twists were the side load is mandatory. Control arm bushings Upper and lower....Let me remind you that if you give your car to the local BMW authorized dealership they will replace the Upper Control arm bushings with the Black regular bushings because according to the ETK catalog these are the proper bushings and then you upgraded to the aka green E34 M5 design. E31 Lower control arm is one of the best upgrade Factory Upgrade on E28E24 with spherical bearings makes the side load one to one with the car chassis. Only one thing will move is the tire side wall, not the suspension etc..etc....That depends on what your definition of small changes is and to that we may agree that we can both disagree.
Above are the small changes I wanted do direct with particular your car and also from being in your shoes like kind of ala OEM upgrade. Because I do agree with you restoring the car back to its original condition and I do support that but again these small changes I was referring as I call it "Hidden Upgrades" will make the car more pleasant to handle in the next level of handling.
There is no owner of E28 M5 nor E24 M6 who sad one bad word with this upgrade rear brakes to E34 M5. You can hear only very good comments and its desirable upgrade. No down site for this upgrade.
I am aware of when buying a stainless steel brake lines it comes as a package front and back but I never ever thought that you will be changing the brake lines in the back as well. I tough you will separate the rear complete brake overhaul in separate day order. Doing rear lines will even the brake bias design and will make the pedal travel and will apply more brake pads torque than from before front and back.
When I do break job on any E28 M5 or E24 M6 and the owner wants stock replacement I always order the E32 750 front rotors, they they are 302mm and yes they do clear the caliper. But the real benefit is that the rotor cooling is from behind ! I hate what BMW did with E28 M5 rotors made then cool down from inside, having BBS mesh/cross spoke complete closed wheel design when the wheel is in motion it becomes like a solid wall. Their is no way the rotor to be cooled down and thus causes the rotor to overheat. When I used to have on my E24 M6 stock system I always had a problem with the Original design...changed to E32 and my problems got away with warped rotors. Yea I do get the idea of having the wholes inside the hub in order to cool it down but were the air is coming from with 16inch closed BBS cross spoke...There is a lot more air traveling underneath the car than the wheel in motion form outside.
In my opinion E32 750 Front brakes are upgrade over the stoke E28 M5 and its proven with my money and my personal experience. I have put over 100k miles on my DD E24 M6 and have leared a lot over that period of time from my pocket!
Just sharing what works for me.
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