Big brake upgrade!

Sourcing the parts (August ’18)

Just picked up some big brakes for the old girl! i know that buying brakes for a non-running car is an odd choice…but you don’t find a lot of 90s BMWs around any more. I drove out to pull them myself, met a few really nice scrappers, had an all-around good day in fact. It’s a shame this car was scrapped. Engine seemed healthy so I’d presume a dead transmission or an abandoned car. Check out how well preserved those tools are!


Installing the parts

After a little cleaning & lubing, I installed the components today. As advertised, the larger calipers on the 540i 740i are a direct fit. Be sure to grab the carriers as well when you find a set, and you might as well take the front rotors if they look OK. The 740i rear rotor won’t fit, so I left them at the salvage yard and ordered a new set of rear rotors from the ’94-95 E34 540i. I also opted to install a spare set of E24 M6 front rotors, since they’re a bit worn and not really worth selling. The M6 rotors are internally vented and slightly lighter. IMHO a good choice.

Was it worthwhile? I’m told it is, although my lower back grumpily disagrees. I’ll update this page once I get the system purged & bled.

I was curious about how much the E23 540i setup increases sprung weight so I also carefully weighed everything as I did this job. Per each side, the E34 540i front caliper is 13#, E24 M6 rotor is 17#; total weight is 30#. Stock E24 is 23#, so the upgraded front setup is about 30% heavier than the stock E24 setup. The E34 540i rear caliper is 7.5#, rotor is 13#; total weight is 20.5#. Stock is 15#, so the upgraded rear setup is about 33% heavier than the stock E24 setup. We’re also required to run 16″ wheels to clear these larger front brake, so we gain a good bit of sprung weight there as well.

Since I like to think of these projects in a systemic fashion, there are some other considerations. What master cylinder to run, and what other modifications will be required for the suspension. I’m still assembling parts for this part of the project, but here’s a few posts that have helped with my decisions. First off, this long thread over at Bimmerforums has been especially helpful, it’s loaded with good information and really pointed me in the right direction. Here’s one especially helpful post reply:

The biggest thing you NEED to do is go with ATE Typ 200 brake fluid to prevent brake fluid boiling. The fluid with moisture has a higher boiling point that most fluids that are brand new. This will help prevent brake fade.

I’d suggest using new street/track combo pads if you are only doing one track day (like Hawk HP+ or PFC Z Rated), but maybe it’s worth getting track/race pads if you plan to do another couple track days. These pads have better stopping power, but the big advantage is that they won’t overheat from normal use and wear down in a session or two like a stock pad would– they are rated to last at the higher temperatures.

The big issue with E24 M6 brakes is the bias. The stock rear calipers are the same size as a e28 528e (basically) and do almost nothing to help you stop. also the rear rotors are not vented and do not give good heat dissipation as needed in race application.

If you are doing a single track day, the stock front calipers are fine. FYI the fronts do get warped due to poor brake bias from the factory, which is really related to undersized rear brakes. The E32 740i/750i front rotors are a direct fit and are less expensive. They are compatible with both stock calipers or obviously E32 front rotors.

Go with E34 530i rear rotors and calipers if you want even braking but limited heat dissipation. Probably fine for a single day here and there with the right pads. The bonus is they are slightly lighter than the E34 540i/M5 rotors and calipers. I can’t speak to pad selection.

Go with 540i/M5 rear (vented style) for repeated track use. These calipers are the same as the E32 rears, but the rotor is the one from the E34 540i/M5. This caliper allows E36 rear pads to be used, so plenty of street or track pads are available for purchase.

For repeated track use, E32 front calipers are nice because they have only one piston so it is easier to bleed and they are easier to rebuild. They are also cheaper to find and replace. The biggest advantage is the pads are the same as the e36 M3 so you have a broad range of race pads to choose from.

I haven’t upgraded the brake master and I’m not sure I would until you figure which calipers you are changing. On my M5, I added larger M5/540i rears only and I am happy with the pedal travel.

another helpful Bimmerforums post reply:

I tracked my M6 for several years before I thought it wiser to have a disposable M3 instead.

The E32/E34/ setup works great as a substitute for the M6 OE brakes for a number of reasons.
1) Larger rear pad and bore size (the originals are not just the same as a 528, but also an E30)
2) Much better pad selection — these are the same sizes as E36 M3 and E46 M3, so many track pads available. Hawk DTC 60s and PFC08s are my current favorites, but lots of opinions.
3) Much better rotor selection — and cheaper. Fronts especially heat check and frankly compared with pad prices, should be replaced whenever you change pads.

And totally agree on drilled rotors — stay with solid blanks.

On fluid, the Ate200 is good, but some of the newer fluids are better yet — Motul 600 and Redline 600 are a good mid-priced fluid. Bleed every couple of events and replace every 6 months.

As to the 750 master — the reason to use it is the larger displacement of the rear calipers — the fronts are the same size, so if you put E32s on the front and leave the stock rears, there is no reason to change masters.
There are different points of view on the 750 master with the larger rears. The benefit is it matches the displacement, hence firmer pedal. The drawback is less available modulation. For street, I’d keep the original master as firmness isn’t a problem with these brakes — but for track I’d advise the 750 with the E34 rears. Partly for the pedal firmness, but mainly so that you have a new master. Brake failure on track is not fun.

As to the 540/525 rears — the only difference is that the 540s are vented vs the 525 solid rotors. The advantage of the 525s is lower weight (and lower price) which outweighs the vented bling. Rears don’t overheat.

Agree with Tschulz on the camber plates — I ran with the fixed plates and still have them on the car for sharper turn-in and the extra 1.2′ doesn’t really impact street tire wear. I used poly bushings on the control arms, bigger bars, and Mtech springs with Bilstien HD springs. Rear camber becomes more necessary if you significantly lower the car. But with all that, the car still has a lot of lean. I also found that with stickier tires I was regularly breaking front sway bar mounts on the struts — not a problem with most street tires. If you look carefully at my sig picture, you can see the detached sway bar link peeking out on the drivers side. Makes for a real exciting and loose car.

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