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      09-28-2012, 07:52 AM   #1
Some say...
GuidoK's Avatar
Drives: Z4 3.0i ESS TS2+
Join Date: Jul 2012
Location: Netherlands

Posts: 352
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DIY custom OEM Rear BBK

After installing the ECS front OEM big brake kit for the E85 Z4 (non /m), I also wanted a matching BBK for the rear of course..

When I bought the ECS kit they also had this crazy sale for matching rear calipers (135i performance calipers in phoenix yellow) for only $99 /piece, so I took advantage of that

This is how I designed my BBK:

initial fitting on the stock rotor and stock mounting points showed that this had potential:

You can clearly see that the caliper was designed for much lager rotors.

Offset would require some adaptation:

Lots of room between caliper and rotor on the inside

Not so much room between caliper and rotor on the outside

In -c-'s thread about Z4, 2.5, 3.0 easy cheap brake upgrade's I already wrote that E46 330i rotors would never fit and that the best options would be an E90 rotor (320i) which is roughly the same size or an X3 rotor if you like a challenge. The X3 rotor is 320mm (vs. stock 297mm), so much larger, and in combination with the ECS front BBK a well used combination size wise (front 325mm rear 320mm; eg. used in a 330i etc).
Also the x3 rotors are thicker, so overall they can handle more forces and dissipate more heat.

But the X3 uses a larger diameter e-brake than the stock z4 (185mm vs. 160mm). But I decided to go for the x3 rotors after all

First of all the x3 rotors have a ridge on the inside which had to be removed with a lathe:

About 9mm has to be taken of.

Then I had to fit and measure the offset from the rotors compared to the calipers. Between the caliper and caliper mounting points on the suspensionarm aluminium bushes can be fitted to place the caliper more outwards. After fitting some testbushes and measuring the space between caliper and rotor with some feeler gages I found that the bushes should be 7,65mm thick:

So the final size of the aluminium bushes I made on the lathe is 7,65x30mm and the hole is m10 (a bit over 10mm).

To fit the calipers you need longer bolts:

I used the same blots as the rear bolts from the underside pullrods. (M10X35-10.9ZNS3 part nr.: 31 10 6 772 199).
Be sure to use 10.9 bolts in this application

After that came the adaptation of the e-brake, protection plate etc.
I used the protection plate from the e46 330i (34 21 1 166 107 and 34 21 1 166 108) which had to be modified to fit the larger calipers and different z4 hub:

The red lines & holes is where I cut the plate and drilled some holes. The holes are for mounting an 'elevation' mountingplate to fit the e-brake shoes. These brake shoes cannot be fitted directly on the protection plate because they will then touch the brake caliper and they will not fit properly in the brake rotor. The mountingplate for the brake shoes is fitted with m6 bolts where the elevation is done by a washer and a nut between protection plate and mounting plate (washer and nut obviously on the m6 bolts)

The yellow area on the plate is where you have to bend it a little.

Next the mounting plate for the brake shoes. For that I used the "Supporting ring brake shoe" as bmw call it from the 130i (34 21 6 771 430). (the e60 has a similar construction but these mounting plates are too fragile and narrow to modify for fitting on the protection plate as I experienced).
This is how the final brake shoe mounting plate looks like:

The red lines indicate where I cut/drilled the plate, and the yellow corner indicates where I bent the plate a little bit upwards to support the brake shoe on that spot.

Next is fittng the protection plate:

Fitting the caliper:

Fitting the brake shoe mounting plate:

The brake shoes themselves also have to be modified.
I used brake shoes from the e46 330i. (185mmx20mm)
I chose to adapt only the side where the expanding lock is located:

I cut away a piece on the expanding lock side and welded the corresponding piece of metal from the original brake shoes in place.
3 area's should be aligned to the original z4 e-brake (all on the expanding lock side):
1. The holes where the spring fits. (use the original spring; it fits between the expanding lock and the bearinghousing)
2. The little slot where the expanding lock fits into
3. The 'pins' which push against the metal piece form the suspension arm which lock the brake shoes in place.

When all is fitted it looks like this:

Final results....
Front original:


Rear original:

Rear custom OEM BBK:

The only thing now on the list is fitting some decent brake lines. The rear calipers have a mounting point for the lines which is coming straight out of the cilinder and the original brake lines come out on the underside, so regular kits dont fit. I have a temporary piece of copper line flaired on the caliper and hose (in a 90 degree angle) but that is a bit flimsy. I probably need to use a banjo bolt and an an3 to m10 adapter or someting like that.
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