Project E39 M5: Part 1 - Stopping the Ultimate Driving Machine

by Martin Gonzales


With almost 400 horsepower and weighing in at a little over two tons, slowing down the hefty BMW E39 M5 safely and consistently is definitely no easy task. Aside ensuring all stock braking components are in tip top shape before we start on the inevitable road of power and handling mods, we will also be making a few improvements to the already well engineered braking system of our new/used Bavarian fun machine.

The story of how we came about getting our hands on what is commonly referred to as the perfect M5 is one of pure unfiltered WANT. Avid MotoIQ readers will remember a story we posted late last year about the sweet plug-n-play solution available from AEM's Infinity stand alone ECU for the E46 M3. What they won't remember is how we left that very day with a new project car. That was the first time we met Daniel Wennerberg and the team of BMW specialists over at Pure Performance and we were seriously taken back by the amount of go-fast hardware at the shop. After just a few minutes of talking shop with Daniel, it was blatantly apparent we had just made a new best friend! As he continued to give us a tour of Pure Performance we ran into a beautiful carbon black (midnight blue really) E39 M5 on one of the service lifts. Turns out Daniel had bought himself the M5 to replace his current E39 wagon family-hauler. The story quickly took a turn for the unexpected when he began to tell me about how the WAR department (Women Against Racing) was completely against the idea of adding "another" gas guzzling, manual transmission vehicle to their arsenal. As the ol' saying goes, "One man's tragedy is another man's treasure". Being the optimist that I am, I quickly began thinking of ways I could help my new best friend out of this bind he was in. We decided to go to lunch to think about our options over some calzones. Like a good sales man, Daniel asked that I drive the M5 to lunch. Before we even got to our lunch destination, the solution was clear...I needed to buy this car. Well, didn't really need to. I wanted to! The rational side of me peeked its little head for a few minutes, but all that led to were a few phone calls to car buddies. And no way they were going to talk me out of buying this vehicle. The sheer acceleration is enough to make any grown man giggle like a little girl. Couple that with a chassis that is fast to respond to driver inputs, and any real driver would be hard pressed to turn down an opportunity to own one. After a very quick lunch, Daniel and I were back at Pure Performance printing out the necessary documents to finalize the ultimate impulse buy.

Not wanting to waste any time before getting acquainted with our newly acquired project, I immediately started planning a spirited drive to give the M5 a thorough "evaluation". We bought the car towards the end of the very short California winter, but there was still a little snow to be seen on our local mountain tops. Which meant it was the perfect time to take a cruise up to Bear Mountain, as the roads would be completely clear and I could still get some snowboarding in while I was at it! The drive up to Bear Mountain through highway 18 is a 40 mile series of twisties and elevation changes that when driven at a spirited pace, can be quite the stress test on any vehicle's braking system. Halfway up the mountain I started experiencing brake fade, and right before reaching the top I was already feeling a slight shimmy from the rotors...wtf?!


A quick look at the chart above clearly shows just how much larger the brake components in the E39 M5 are when compared to its other E39 siblings. Caliper part numbers are included to show that though all E39 models may share the same front caliper bore size, they do not share the same front calipers or brake pads. Interesting note - all E39s with DSC (Dynamic Stability Control) do however share the same master cylinder. 


The stock E39 M5 is equipped with a pretty beefy brake package from the factory. As a matter of fact the front and rear rotors, measuring in at 345mm x 32mm and 328mm x 20mm respectively, are the largest offered in any E39. The brake package may not be optimal for sustained track use, but it should be up to the task of handling a few spirited laps/drives without exhibiting fade as quickly as we experienced. Due to the shimmy we could feel through the brake pedal and steering wheel it was pretty safe to assume the rotors must have been well below the recommended minimum thickness before we started our evaluation. They would need to be replaced immediately. Taking our usual "while we're in there" approach, we will also be adding steel braided brake lines in order to give our M5 that confidence inspiring pedal feel we're all after. The pedal was not horribly mushy, but it did leave much to be desired in regards to feel and feedback.


stoptech, carpartkings, powerslot, brake rotors, brake pads, steel braided lines, brake hardware

After the first "evaluation" of our new BMW E39 Project we identified some key shortcomings in the stock braking components and were ready for our first round of parts. The first item on the list would be a StopTech Sport Kit which we ordered from our online friends over at CarPartKings.com. The StopTech Sport Kit includes slotted rotors, street performance brake pads, and steel braided brake lines. The Sport Kit uses all stock sized components which will make installation a snap. The goal here is to get the most out of the stock braking components without needing larger wheels or extensive modifications. 


The StopTech Sport Kit can come with either slotted, drilled or drilled & slotted rotors. We chose to go with the slotted option. The slots will help evacuate vaporized pad material created during hard braking which will in turn help braking performance. Though the StopTech slotted rotors are sure to provide some performance gains, one cannot overlook the end results you get from a premier manufacturing process. We've never had a single issue with StopTech rotors and this is due largely in part to their machining and treatment process. The rotors are machined to very close tolerances for better balancing that ensures vibration free operation. The e-coating on the rotors will prevent them from rusting and will keep them looking good throughout their entire service life. 


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Tuesday, September 30, 2014 3:10 AM
"If you're looking to get the most performance out of your stock brake components, the StopTech Sport Kit is hands down the way to go."

I'd argue that Performance Friction is a better option for pads though, sadly, they don't seem to make a drop-in two-piece rotor for the stock E39 M5 brake system like they do for the M3.

Nice write-up either way. It is often surprising how much you can get out of the stock braking system from a variety of performance cars through simple upgrades such as those seen in this article. Some folks think you need to go straight to a Big Brake Kit, but that often isn't the case.

For instance, I've been *amazed* at how much performance you can get out of the stock brake calipers on the E36 M3 with a simple bolt-on rebuild of the stock braking system.
Dusty Duster
Dusty Dusterlink
Tuesday, September 30, 2014 5:29 AM
I pulled up the Google to look up highway 18, and I now want to know why the heck we don't have sweet roads like that over here.
Tuesday, September 30, 2014 6:36 AM
"finally come to a complete stop."

While most manufacturers and distributors have varying procedures for brake bedding, the one thing that is nearly universal is never come to a complete stop and never lock up the brakes.

One of many articles you can find:

I'm also glad you didn't go straight for a BBK. The stock system is good with a little refreshing and improving. I would've considered a solid brake guide kit instead of the rubber, but otherwise very nice start.
Tuesday, September 30, 2014 6:40 AM
"There is one pitfall in this process, however, which must be avoided. The rotor and, therefore, the vehicle should not be brought to a complete stop, with the brakes still applied, as this risks the non-uniform transfer of pad material onto the friction surface."

Source: http://www.stoptech.com/technical-support/technical-white-papers/bed-in-theory-definitions-and-procedures/stock-brake-system-bed-in
Mike Kojima
Mike Kojimalink
Tuesday, September 30, 2014 7:08 AM
This brake bedding procedure is ok. When Martin releases the brakes, he drives for a bit like a few blocks before the next stage and he didn't completely elaborate this. He also comes to a stop for only a fraction of a second. This is different than how I do it for instance but he's been doing it for years and it works fine every time with many different kinds of pads from race to street. Most modern brake pads don't need a super elaborate and anal bedding procedures like they used to. As long as you don't come to a complete stop and sit there heat soaking in your first initial stops you are ok and won't get material transfer. If you experience transfer juddering, it is easy to get it off by letting the brakes cool and then drive lightly dragging them for a bit, then do a few hard stops to almost zero.
Martin Gonzales
Martin Gonzaleslink
Tuesday, September 30, 2014 7:58 AM
@StrangeLiForm - As a matter of fact, PFC makes absolutely nothing for the BMW E39 M5. Something else I learned while I was planning out the first round of brake upgrades is that the euro model E39 M5 came with floating rotors with aluminum top hats. These rotors were identical in size, but were much lighter...and twice the cost.

@MDR - Thanks for reading and adding some clarification/detail to "my" bedding process. You bring up a very good point, as locking up the brakes or coming to a complete stop can cause an uneven transfer layer. Though like Mike stated above, the real danger is when you're coming to a complete stop and letting the pads sit on the rotor for more than a second or two. My procedure has yielded great results for me, but your point is valid and I've added a little more detail to not confuse the novices. Thanks for keeping me on my toes!
Friday, October 10, 2014 10:35 AM
Ultimate Depreciation Machine!

Absolutely amazing that average Joes like us can afford to buy what was the pinnacle of uber-sedan performance 10 years ago. Hrrrm.... Ford Focus or M5...? Fack it, I've got a killer set of tools, I can fix it!
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