DIY: 28i to 35i Brake Upgrade

[outlawdevil]

Originally Posted by vstolpner

Well you could always just place a starting marker, and start breaking at that market and then measure (the most obvious way).

Otherwise you can measure using an OBD adapter. This would be either via stopping time or stopping distance, depending on the phone app you're using. Torque, for example, gives me stopping time.

For example mine shows 3.3 seconds. Assuming a straight line deceleration, that works out to be about 44m (144 feet). If adding bigger breaks then reduces it to 3.1 seconds(again, as example) then the stopping distance is reduced to 41.3m or 135 feet, or about 9 feet improvement.

awesome, thanks.

[D Unit]

Subscribed!

[kiloTHREE]

We'll I've collected all the parts I need, but we have deer hunting the next two weekends here so all I need now is a free weekend.

Even though I went with coated rotors, I still might go in and have the hats powdercoated black.

[PrematureApex]

Originally Posted by vstolpner

Hope your wedding planning is going well. Just had a thought that it would be great to see the stopping distance improvement before and after the upgrade.

I don't think one should expect any stopping distance improvement, at least when talking about single hard stop, where brake fade isn't an issue.

Want shorter stopping distance? Get stickier tires.

The stock brakes are strong enough to engage the ABS, at least on the stock tires. So what does that mean? It means you already have more brake torque than you do available traction. That means adding more stopping power isn't going to gain you anything. Big brake kits, for example, don't always actually increase brake torque (or at least not a huge amount). They do however add heat capacity. So when you're tracking, you fend off brake fade longer.

Dare I say it, this "upgrade" may actually marginally INCREASE stopping distances, as you've increased your unsprung weight and rotating mass at the wheels.

Again, on a stock car in a single-stop scenario, available traction is the limiting factor in stopping distances, not braking power.

Where this upgrade will shine is under heavy, repeated use (like on a track)where the added thermal capacity will keep stopping distances more consistent.

1) The brakes don't stop the vehicle - the tires do. The brakes slow the rotation of the wheels and tires. This means that braking distance measured on a single stop from a highway legal speed or higher is almost totally dependent upon the stopping ability of the tires in use - which, in the case of aftermarket advertising, may or may not be the ones originally fitted to the car by the OE manufacturer.

http://www.stoptech.com/technical-su...rade-selection

[kiloTHREE]

Originally Posted by PrematureApex

I don't think one should expect any stopping distance improvement, at least when talking about single hard stop, where brake fade isn't an issue.

Want shorter stopping distance? Get stickier tires.

Truth, my dedicated summers should help.

Originally Posted by PrematureApex

The stock brakes are strong enough to engage the ABS, at least on the stock tires. So what does that mean? It means you already have more brake torque than you do available traction. That means adding more stopping power isn't going to gain you anything. Big brake kits, for example, don't always actually increase brake torque (or at least not a huge amount). They do however add heat capacity. So when you're tracking, you fend off brake fade longer.

Dare I say it, this "upgrade" may actually marginally INCREASE stopping distances, as you've increased your unsprung weight and rotating mass at the wheels.

This is countered by loosing 12lb's per corner by ditching the stock anchor wheels/ RFT's. The stock wheels are just over 32 lb's and cripes are run flats tires heavy!

I'll have a full weight difference when I actually get around to doing it.

Originally Posted by PrematureApex

Again, on a stock car in a single-stop scenario, available traction is the limiting factor in stopping distances, not braking power.

Where this upgrade will shine is under heavy, repeated use (like on a track)where the added thermal capacity will keep stopping distances more consistent.

What I'm actually striving for is decreased brake pressure, primarily at full stop. The amount of braking force to hold the 28i w/automatic stopped, is strangely bizarre to me. Often I find myself slowly creeping at a stop.

This is my first automatic car that I've owned so maybe it's me.

Also note that when cross shopping 28i vs 35i rotors/pads, the 35i items are about $8 dollars cheaper per item, per corner. My guess would be since they are used on more cars. 3 series..ect

I hope I'm not trying to convey that this will be a massive upgrade.
These ain't no 6 pot calipers with two piece carbon rotors that i'm only buying for status points at a car show, but for the cost, and lets face it, looks; it's damn cheap.

[vstolpner]

I understand from a physics perspective why these shouldn't decrease breaking distance much, I'm more curious if the physics match real life performance. There are other aspects play, such as ability to better modulate torque with a longer lever thanks to the bigger rotors.
Again, I'm curious from an experimental perspective.

[kiloTHREE]

All done.
Good news, everything bolts right up, front and rears.

Some stats:
Stock rear caliper weight: 7.2 lb
35i rear caliper weight: 7.2 lb

Stock rotor weight: 14.6 lb
35i rear rotor weight 18.0 lb

Stock front caliper weight: 12.2 lb
35i front caliper weight: 11.0 lb

Stock front rotor weight: 19.8 lb
35i front rotor weight: 23.8 lb

Total weight gained rear per corner: 3.4 lb
Total weight gained front per corner: 2.8 lb

While it's nothing to snear at gaining ~13 lb of unsprung weight, the benefits I believe are worth it.
The surprising part was the larger calipers up front were lighter than stock, pig iron vs aluminum.

Two annoying parts:
Bleeding the system (more on that later).
Rear brake pad sensor, you have to get behind the passenger rear fender liner:


Reach up in here and disconnect the white connector.


You'll be eating gravel for a couple hours.

Rear done:


Same thing driver side, no sensor to dick with on this side.


Rear done:


People with 17" wheels be wary, they may not fit. that rear is very close. My one set of 17"s did not, but my other set did. YMMV.


Sorry forgot before picture for rears.

Front before:


Front after:


Front brake sensor is on the drivers side:
Very easy to get to.


I had everything done hardware wise within 2 hours.
Left the brake bleeding for the morning.


This is where things got "FUN".
Bleeding was straight forward like any other car, however I think I got some air into the ABS system. This surprised me since I was super quick about changing the lines to the new calipers. Bled the brakes 3 separate times with no luck.

Long story short, I don't have any computer equipment to cycle the ABS, so after a few quick braking maneuvers down a gravel road, I bled the system again and even though no bubbles came out, the brake pedal firmed right up.

After a quick break in:




Old pile:


Forgot to remove my wood block spacers, felt kinda dumb but they didn't fall out after gravel road hoonage.


I'll have a performance report after break in, but so far very impressed with clamping pressure when stopped, and much more linear braking.

[Njerts]

Great post!

[vstolpner]

Looks absolutely amazing!! Any chance you can measure the inner diameter of the wheels that didn't fit and of those that did? I have two sets of 17" wheels that I would prefer not to change...

[kiloTHREE]

Originally Posted by vstolpner

Looks absolutely amazing!! Any chance you can measure the inner diameter of the wheels that didn't fit and of those that did? I have two sets of 17" wheels that I would prefer not to change...

Thanks, yep I'll grab a measurement this week.

I forgot to mention the emergency brake.
There are two ways to get the rotors off:

1. Enable the service position under the hand brake. You have to pull the boot up and with a long flat head screwdriver, push the spring down into the service position.


2. Just pull the rotor off at an angle. The pads are located on the top of the hub so you can just tilt the rotor down a little and slide it over the pads, not a big deal but worth mentioning.

I had read incorrectly somewhere the rear e brake needed additional parts to make it work, this is false. The new rotors fit perfectly, I didn't even have to adjust the parking brake.

[fiehlsport]

If any air got in the ABS system, it was because the level got too low in the reservoir while you were bleeding. The speed at which you changed the lines/calipers over would've made no difference.

Sometimes, finding some wet grass and engaging the ABS pump for a few seconds at a time will allow the air to bleed out of the pump. Sounds like it firmed up though after a bit, good thing!!

[kiloTHREE]

Originally Posted by burnout8488

If any air got in the ABS system, it was because the level got too low in the reservoir while you were bleeding. The speed at which you changed the lines/calipers over would've made no difference.

That's what I thought too, but my reservoir was always topped off.
I know you can introduce a lot of air swapping lines, and the calipers were dry/new so maybe it was just that much air?

Originally Posted by burnout8488

Sometimes, finding some wet grass and engaging the ABS pump for a few seconds at a time will allow the air to bleed out of the pump. Sounds like it firmed up though after a bit, good thing!!

Yep, I'm going to bleed them again this weekend just to be sure all the air pockets got shaken out after driving for a bit.

[kiloTHREE]

Well everything is shaken out. I did end up having my local BMW dealer run the ABS modules and bleed the brakes again. Honestly I don't think it did much but they did it the same time as my bmw assist retro so why not.

The feel is great, they are broken in now and perform well. Clamping pressure at full stop is greatly reduced and it is a much better feel. Not sure how much of this has to do with the pads or the caliper upgrade but I'm quite pleased.
Stopping distance, no idea, but it takes much less pedal effort to stop than it did before.
Always felt like I was fighting the engine when it downshifts when slowing down, no longer do I have this feeling.

If I were to do it again; and I would in a heart beat; I would probably get a set of braided brake lines as well while your in there.

[DUI Elite]

Nice glad it feels better. Did you use factory brake fluid?

I've always swapped to ATE Typ 200 in my cars and notice a small but good difference in pedal feel

[kiloTHREE]

Used Pentosin LV, something about the abs and cold weather.

[Gamb1t]

I'm gonna speculate the improvements are largely due to fluid bleed and pads. BBKs will have little to no gain for street applications per the prior poster. For every lb of unsprung weight it is roughly 3-4lb of sprung weight that your suspension has to deal with....Per corner.

Fwiw l looks like a fun activity. Thanks for sharing.

[kiloTHREE]

Originally Posted by Gamb1t

I'm gonna speculate the improvements are largely due to fluid bleed and pads. BBKs will have little to no gain for street applications per the prior poster. For every lb of unsprung weight it is roughly 3-4lb of sprung weight that your suspension has to deal with....Per corner.

Which is laughable since stock non M BMW wheels are ridiculously heavy.
I measured my new setup and I drop 12 lbs a corner with non runflats and M wheels this spring.
I was surprised that runflats were not that much heavier than non runflat tires. (about 2-3 lbs) But I was comparing different brands as well so maybe they aren't much of a difference at all.

Originally Posted by Gamb1t

Fwiw l looks like a fun activity. Thanks for sharing.

It was easier than most brakes I've done. I like the rattle clips on the BMW; sooo much easier to work with than VW. I scrapped my R brakes to hell replacing pads with the stupid rattle clips. Looked terrible.

[Gamb1t]

Originally Posted by kiloTHREE

Which is laughable since stock non M BMW wheels are ridiculously heavy.
I measured my new setup and I drop 12 lbs a corner with non runflats and M wheels this spring.
I was surprised that runflats were not that much heavier than non runflat tires. (about 2-3 lbs) But I was comparing different brands as well so maybe they aren't much of a difference at all.

Which M wheels did you get? I quite like the Sportline's Style 421 18x8s personally.
RFTs are generally heavier because of the strengthened sidewalls. But some brands are worse....Bridgestones S001.

[kiloTHREE]

Originally Posted by Gamb1t

Which M wheels did you get? I quite like the Sportline's Style 421 18x8s personally.

Funny you mention those, I'm replacing those since they're 32lb's each.
Got some parallel m's

[Gamb1t]

Originally Posted by kiloTHREE

Funny you mention those, I'm replacing those since they're 32lb's each.

I find that hard to believe so I went and weighed the 421s. With the Continental SSR rft it came to 56lbs. The SSRs in 225/45/18 are rated at 26lbs. That's 30lbs for an 18x8 wheel! In contrast my RX-8s 19x8.5 RAYS Eng. wheels are 20lbs.

That's disappointing as I quite like the 421s.

Nice M deep dishes. Going staggered eh?

[jazredgt]

Rear calipers still available?

[kiloTHREE]

PM Sent