After upgrading my brakes, I found the pedal a bit soft due to the extra area in the Pistons in the new calipers, not being provided enough hydraulic pressure from the Master Cylinder.

Basically the old Master cylinder was able to keep the right amount of pressure up to the Calipers, you can feel this through the Pedal feel when braking...it will travel alot further to the floor than with stock brakes.

The upgrade for it is a Master cylinder from a BMW E-32 750i (late 80's V12 model)

the Part number is BMW part number is: 34-31-1-156-643 the Manafacturer ATE part number is 03-2125-2802.3

Here in Australia, this master cylinder will cost you around $400 to $500. I bought my from Steve haygood, He is located in the USA, but his prices are that good, that it is worth buying from him, especially for smaller items that do not incur large shipping costs like the master cylinder. and due to the Free trade aggreement no need to pay a Tariff..only GST.

HERE:

Steve Haygood Automobile Soloutions

Or a more direct link to his On-line store:

Steve Haygood On-line store

The diffrence between the new and old Master cylinder is that the old original E28 has a 22mm bore, and the 750i version has a 25mm bore.

Below is a photo of both of them next to each other..no real diffrence in physical appearence...the main casing is wider though..to allow for the 25mm bore inside.

This is quite an easy job, so i dont think you will have any trouble.

1# Remove the Coolant Expansion tank and push the main hose from the tank out the way facing up so as not to lose coolant. remove the Dipstick as well, and any other stuff you feel is in the way. (photo below with the Expansion tank removed)

2# Remove the lid of the Brake Fluid Resovoir etc... Sipion off the brake fluid from the Resovoir, you can use a Turkey baster or syringe...i got an empty plastic 500ml coke bottle and drilled a hole in the lid and put a 10mm PVC hose throuh...squash bottle with hose in Fluid, when you release the squeeze it will suck up the Fluid.

Then Remove the Resovoir, grab hold of it and pull up to remove....some excees brake fluid that was not sipioned may spill as the resovoir can be tight......if any brake fluid gets spilt it can be cleaned up later...Brake fluid will eat paint, but there will be no instant hurry to clean it as long as you not going to leave it for hours on end. you can clean after you have done the repair.

It should look like this now:

Looking at the Photo above you will see Yellow and Red Circles.

3# Give it all a wipe down with a cloth to remove any dirt etc.. so it cant get in the system when you remove it.

Undo the Solid Brake lines (yellow) to the Master cylinder first, they require an 11mm open ender or even better a Ring spanner with a notch taken out to fit over the brake line. These brake lines can be very Tight and hard to undo, so don't go forcing it as you will not want to damage it!!! below some pics of the tools you should have for this job...note the spanner in the photo i am reffering to...Get ONE!

The tools from Top to bottom:

1# A Socket set of the tinyiest proportions, these are great for this job, especially the 13mm bolt on the MC on the brake line side. and a heap of other stuff...i bought this set form Crazy Clints (The Warehouse) for $9.99, and was very happy...It has got me out of so many difficult situations...and changing the Thermostat with out removing the Fan is a breeze. (i went to buy a couple more sets "they are that good"..but they all where gone!!..they are incrediably well made for something made in the PRC for a change)

2# Vice Grips..but not your Vanilla Vice grips....but unique choclate brand..with a unique jaw feature that allows you to remove almost any bolt with a rounded head...excellent if you round the head on one of the brake lines and to undo the grub screw on the bottom of the Brake Booster..more of that further down. (buy some of these...a Must have tool around the home)

3# The Ring Spanner i was reffering to with the bit cut out to fit over the brake lines....you should really always use a spanner like this on any of those rigid hyrdraulic lines so as to limit any chance of rounding the head of the nut. (I didnt have a 11mm one ..i used a open ender...but it would be better to use one)

You should have removed the Hydraulic brake lines now and it should look like it does below:

#4 Now you have to undo the 13mm bolts ("Red circles" refer to two photos above) that attach the Master cylinder to the hydraulic brake booster.

They are quite tight! i used a long extension for one side, and the other my small socket/ratchet due to space restictrictions. ( a 13mm open ender will do, just a little slower)

After you undo the bolts just lift the Master cylinder off and it should look like this:

Looking at the photo above the Master cylinder has been removed.

You can see the power steering fluid leaking from the Hydraulic Brake Booster, this is because of a worn seal in the Hydraulic Brake Booster (brake assist), i suggest while the MC is off, that you replace it....you can find the replacment procedure here:

Hydraulic brake booster main Seal repair

If you decide to do this, it would pay for you to depressurize the Brake Bomb first by pumping the pedal about 20 times with the engine off before removing the MC. (all about brake Bomb here:

Brake Bomb Repair

1# firstly you have to bench bleed the new Master cylinder before fitting, if you dont it will not work, basically you are priming the plunger inside the bore of the MC, similar to how you have to prime some Water pumps before starting them.

The word bench bleed usully means placing the MC in a bench vice and doing it there...No need here.

Get your new 750i MC and put the Old resovoir on it....I suggest you give the resovoir a good clean first with cloth and like i did a blast with an air compressor, then whoosh around some new brake fluid and tip it out.

Put a bit of brake fluid on the MC Rubber seals where the Resovoir sits and then push the resovoir into it.

It should look like this:

#2 Now to Bench bleed it.

Before you start, just get a feel for the master cylinder, push the plunger in to get a feel for its resitance and put your fingers on the outlets where the brake lines go in. as you push the plunger in you will feel pressure on one of the outlets.

now fill the resovoir with a little bit of fluid..50ml to 100ml should be heaps.

Put your fingers on the outlets, and push the plunger in, this should remove the air from the Bore, it will push past your fingers through the outlets.

Now, let the plunger out to draw Brake Fluid into the Bore of the MC, be sure to continue holding your fingers on the outlets to be sure not to let any air back into the MC at the same time.

Now push the plunger back in again while holding your fingers on the outlet still, when you push the plunger back in, it will push the Brake fluid out of the bore through one of the outlets past your finger/s.

You can repeat it a couple of times to be sure no air is in there at all....do this procedure twice to be sure no Air is left in there.

(BE CAREFUL: as brake fluid will shoot out, so do it out of the way where anything could get sprayed and point it away from your body)

This Photo below shows how i done it: Note: i used my palm to hold one of the outlets as it was difficult to grasp both outlets with 2 fingers for me.

Your MC should be Primed/Bench bleed now and full of Brake fluid and ready to be put on.

You will have to remove the Resovoir again so as to be able to bolt the new MC back in place. Just pull it off, and do NOT turn the MC upside down or press in the Plunger.

Place it onto the Hydraulic brake Booster pictured:

Now do up the bolts (a New MC should come with new bolts with Loctite on the thread already in place) Do up the the bolts and Torque them to 29newton meters, you wont be able to Torque both bolts as space wont allow it with most Torque wrench sizes.

Do up the Hydraulic brake lines, besure that you have them located square and true before doing them up, as you dont want to cross thread them into the MC. (do NOT over tighten either)

Place the Resovoir back on to the New MC and fill up with new brake fluid.

Now time to bleed the the brakes.

The E28 has diagonaly Split brakes, meaning that there is a 1 line for 2 of the calipers that run to opposite corners of the car. the reason they do this is that if one of the brake lines fail, when you put your foot on the brakes your car will not spin you around.

The Bleeding procedure goes like this:

1st Right Rear Caliper

2nd Left Front Caliper

3rd Left Rear Caliper

4th Right Front Caliper

Im assuming you already now how to bleed the brakes? if not, it is easy. (sorry no photos here)

Basically get a 7mm open ended spanner, locate the Bleeder screw on the Caliper/s (you can take of the wheels or lay on the ground and reach behind the wheel. (A trolley jack is a good compramise to give you a bit extra room without taking off the Wheels)

Get a Helper to pump the brake pedal a couple of times and hold it down, while he/she is holding it down release the bleeder screw until fluid stops flowing, then retighten. make sure the Helper does not release the brake pedal till you have retightened the Bleeder screw as it will draw air into the brake system...so good communication: ....Shout: Pump the pedal.......Shout: Hold it down... loosen bleeder to release pressure/fluid...Retighten.....then you can Shout to them to let go of the pedal...or go back to pump the pedal and do it again.

(be sure to check the Brake fluid resovoir for brake fluid so it does not get low as you bleed it.)

Do the bleeding once see how the pedal feels, id suggest bleding it twice to get rid of any old fluid.

After bleeding the system, hose the wheels and brakes down with water to iperse any excess brake fluid, do the same in the engine bay around the MC.

Well there is a bit of debate about the 750i MC upgrade as to whether it makes the pedal to HARD. There fore reducing the ability for the driver to modulate the brakes with there foot properly.

For me, the previous MC was just a bit to soft since the brake upgrade.

After installing the 750i MC i have found the brake pedal feel to be very firm, and the abilty to modulate the brakes is alot less.

(prehaps something i just have to get used to.)

Overall It is alot better though. The car stops much better now, and the firm pedal fel does not worry me.

But I would not reccomend this upgrade with stock brakes IMHO. But the mechanical procedure is identical for replacment.

If you have anything to add, feel free to shot me an E-mail.