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E39 M5 Brakes- OEM piston sizes?

2K views 3 replies 3 participants last post by  fvicente 
#1 ·
Anyone know this spec or suggest where to find answer? Looking for front and rear OEM piston specs for calipers.

Interested in comparing with E39 540i data, if you have that.

Thanks for any repies
 
#3 · (Edited)
So far I know that E39 540i and M5 share the same front caliper piston dia and pads, based upon service part#'s.

M5 brake torque leverage on the front rotor will be a bit higher due to larger diameter rotor, but this difference will not be huge. I assume that the simple T = r x F formula can be applied to the "center" of the swept areas to come up with a rough percentage torque difference between the two systems. I will likely come out to something in the range 5-10%.

I find my OEM 540i brake system has too much front bias. The front ABS always engages first, even with matching pads f->r. On the track with HT10 race pads in front and premium street pads in the rear, the rear brakes do almost nothing and the fronts become grossly overworked. A bit more rear brake function on my 540i will improve bias and reduce heat buildup in the front.

In conclusion, it sounds like a conversion to M5 rear brakes is feasible for use with OEM 540i fronts. I realize heat buildup in front brakes will still be a limiting factor for severe duty. The next logical step for track use will be BBK for the front only.
 
#4 · (Edited)
I did the upgrade to M5 brakes in two stages because UPS lost my front calipers, and with just the M5 rears on the car, I barely noticed a difference. Granted, I don't track the car or threshold brake very often, but I did notice an improvement when I put the M5 fronts in. back-to-back driving of that car and a stock 540 there was a marked improvement in initial bite, but not a whole lot else. I did it because the car needed pads and rotors anyhow so "while I was at it...."

of course, I ended up having to replace my beloved Style 19s to do the upgrade...so much for a cheap brake upgrade.

also, the ETK shows different part #s for the 540 pads and the M5 ones...perhaps some aftermarket manufacturers use the same pad for both.

-f
 
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