Brake Cooling - Cheap DIY method

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exdos
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Brake Cooling - Cheap DIY method

Post by exdos » Tue Jun 12, 2012 11:20 am

DIY Brake Cooling.



A number of BMW owners complain about their OEM brakes suffering from brake-fade when they take their cars on track. The problem is unlikely to be out-and-out stopping power of the brakes; instead, it is more likely to be the "duty cycle" between hard braking events is too short to allow sufficient cooling, so that the brakes, pads and fluid become progressively hotter, until they eventually exceed maximum operating temperature. Many owners feel that the only solution is to upgrade to a Big Brake kit (BBK), but these are expensive and can cost upwards of £1.6k for a well-known brand for the front alone. However there is a very cheap alternative, and that is the provision of brake cooling ducts which feeds cold air directly to the OEM brakes, so that there is a stream of cold air being fed to the brake hardware whilst the car is moving so that the temperature of the brakes will run much lower than would otherwise occur. In this way, the brakes are unlikely to overheat and cause brake-fade.

As far as I am aware, there are no aftermarket brake cooling kits, so I have devised a DIY method of brake cooling which can be made for less than £40. I have previously made a DIY brake cooling set up for my Z3 M Coupe, and this DIY set-up for the Z4MC is based on the method I've used for the M Coupe.

The first requirement is a source of cold air which can be forced through ducting whilst the car is in motion. From my datalogging of the Z4MC's air intake system, I know that all area behind the grilles and in front of the radiators receives air under "ram pressure", which will force air through ducting with inlets located in this part of the car. I have examined the structure of the car and discovered 2 places where inlets can be ideally located, with no need to cut holes in the front bumper.

You need to safely lift the car and place on axle stands under the 2 side jacking points and remove the front undertray (8mm socket and Phillips screwdriver required). Once underneath the engine bay, you will see a small plastic shroud at the bottom of the radiator on each side. If you cut a hole in both of these shrouds, then you have access into the area in front of the radiators, but behind the blanked-off section of the lower radiator grille. The fact that there is no forwards direct line of sight through the holes that you cut will NOT stop this acting as a source of ram-air (similar situation exists for the OEM air-intake).

The photo below shows the position on the right side where access to the front of the car to receive cold air under ram pressure.

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The shroud on the right side with a hole cut through showing the blanked off section of the lower front radiator grille.

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A small piece of ducting has been positioned in the hole in the shroud to show the connection to the front of the car.

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For my inlets, as an inveterate hoarder of stuff (just in case it might come in handy!), I already had a few sink outlets, which were just the right size to fit and install in the holes in the shrouds besides the radiator, so I cut holes of the right size to fit the sink outlets. Before I fitted them, I cut out the "star-shaped" centres, so that there was just one hole for my inlet.

The sink outlet before cutting the "star-shaped" centre with the backing nut.

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I intended to fit 2" internal diameter flexible hosing onto the ends of my inlets, but the threaded part of the inlets was a little too small, so I cut off 2" length of 2" diameter aluminium pipe (also in my hoard!) to fit as a sleeve over the threads, and attached the ducting to the aluminium pipe with a stainless steel jubilee clip. To get a tight "push-fit" connection, I needed to grind the screw-thread a little.

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It is much easier to install the ducting on the right hand side, because on the left side, there are 2 pipes to the oil cooler, but I found it was possible to cut the hole in the shroud on the left with a Dremel after ensuring that I had located the best place to centre the inlet.

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Once the holes had been cut and the inlets screwed in place, I could then attach both lengths of ducting on their sleeves, directly onto the inlets with a push-fit to secure. For ducting to be successful, it needs to be just the right extended length when the wheels are turned to maximum lock. I cut my initial lengths of ducting to 1metre per side. For the outlets of the brake ducting, I didn't want to cut the OEM dust-shield, especially since it already has vents in the front section, which I presume BMW had created to function for cooling already. So, I identified that the best place to site the outlets is just in front of the brake calipers, behind the damper, because there is an open space there, which is not covered by the dust shield. I experimented with various ways of routing the ducting to my chosen outlet point with lock-to-lock turning and found that the best route was essentially taking the outside path of the arms of the front ARB. The ducting needs to be tied with cable ties to the Anti-roll bar, just to the outside of the ARB bush and once the length of the ducting had been adjusted for lock-to-lock movement it can be securely fastened with more cable ties to the bottom of the damper, using the damper brackets as points of restraint, after the oulets have been attached to the ducting. The ducting fits between the damper and the drop link, and although there's not a lot of clearance. if the ducting is properly restrained, it makes no contact with any of the parts under movement and does not rub against the tyres.


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For my outlets, I have again used 2" diameter aluminium tube which required cutting to approximately 4" length and shaping so that the tubing would lie right up against the brake caliper and front damper, so that the outlet is right above the opening to the centre of the brakes.


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For the best fit of the aluminium oulet, the end needs to be cut at angle so that the oulet sits as close as possible to the damper leg and is pressed against the brake caliper and fits as flush as possible against the face of the brake bracketry. Once the outlet had been cut and shaped to the required fit, it was attached to the ducting with a jubilee clip, so that there was no twisting of the ducting when the aluminium outlet was properly in position. The outlet and the ducting are then attached to the damper using cable ties wrapped through the brackets on the damper as points of restraint.

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When the ducting is properly adjusted so that it is at full extension with no tension at maximum inward turning, the ducting should lie between the damper and the drop link to the ARB, with no pinching and with no contact with the wheel and tyre. On opposite lock, the ducting recoils and should make no contact with any part to do damage.

In the photographs I've used 300mm X 4.8mm nylon cable ties whilst experimenting, but for final use I will use 300mm X 7.6mm and on my Z3 M Coupe I've found that these will withstand any heat created by the brakes.
Stainless steel jubilee clips can be bought from ebay (require 4 of 50-70mm adjustment) as can flexible neoprene ducting (ebay search under "brake ducting") and 2" aluminium tube/pipe (1mm wall is suitable). Flexible ducting 51mm (2") is the optimum size that will work using the route which I have described; any larger ducting will pinch or require a reduction in lock-to-lock wheel turning which would severely increase the turning circle.

The Z4MC has a jacking-point in the centre of the car which is useful to lift the car so that it can be rested on 2 axle stands positioned on either side of the car on the side jacking-points.

In order to be able to easily move the wheel hubs by hand from lock-to-lock whilst working on them, first insert the ignition key and turn it to undo the steering lock, once this has been done, turn the key to OFF but leave it in the ignition and you can then press against the brake discs to turn the hubs to check for fitting throughout the fabrication and installation of the brake ducting.

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Re: Brake Cooling - Cheap DIY method

Post by Ewazix » Tue Jun 12, 2012 6:53 pm

The Great British tinkerer is alive and well, ingenious :thumbsup:

Does it work? It would be interesting to see some laps then checking the disc temp with a probe, both with/without the vents being blocked.
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Re: Brake Cooling - Cheap DIY method

Post by exdos » Tue Jun 12, 2012 7:15 pm

Ewazix wrote:The Great British tinkerer is alive and well, ingenious :thumbsup:

Does it work? It would be interesting to see some laps then checking the disc temp with a probe, both with/without the vents being blocked.
My DIY brake ducts on my Z3 M Coupe work very well on track and therefore I every reason to expect that they'll work just as well on the Z4MC with this very similar set up. The hottest that I've ever seen the brakes on my Z3 M Coupe with brake cooling is 270 degs C, which is well below the boiling point of DOT 5.1 brake fluid that I use. Whilst experimenting with different routing on side-to-side of my Z4MC, I did some comparative temperature testing after doing multiple braking events with short intervals for cooling, and the routing and siting of the outlets I've described consistently produced the lowest brake disc temperatures.

If you use the calculator here: http://www.1728.org/flowrate.htm you can estimate the flow rate of air at different speeds of the vehicle. If we assume the diameter of the brake ducting is 1.75" (being conservative) then at 50mph over 34 litres/sec of air passes into the centres of the brakes and at 80mph it is 55.47 litres/per second, all that air MUST have more cooling effect on the brakes than with no ducting. :D

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Re: Brake Cooling - Cheap DIY method

Post by Adamski » Tue Jun 12, 2012 8:26 pm

Great effort. How long did it take you to do the whole job? I find that even on a spirited drive my brakes start to fade :(
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Re: Brake Cooling - Cheap DIY method

Post by exdos » Tue Jun 12, 2012 8:41 pm

Adamski wrote: How long did it take you to do the whole job?
I had the car in the air for several days and worked on it piecemeal, so that I had "thinking time" to consider different options and I was also doing another job on the car at the same time. However, if I were now to do the job that I've described and had all the bits to hand, it would take me no more than 2-3 hours.

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Re: Brake Cooling - Cheap DIY method

Post by BMWZ4MC » Tue Jun 12, 2012 10:53 pm

That looks great Exdos. I think you were right about my EBC yellow stuff pads being a faulty batch, but I'll add something to the other thread on brakes once I've finished changing the pads and spoken with EBC.
I'm looking forward to trying this myself when I have more time and better weather in the summer :thumbsup:
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Brake Cooling - Cheap DIY method

Post by aquazi » Wed Jun 13, 2012 12:06 am

This is a genius idea.

I thought The front ducts on the M are meant for cooling the brakes? Yet the air would only cool the tyres. Why didnt they do this from stock?


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Re: Brake Cooling - Cheap DIY method

Post by exdos » Wed Jun 13, 2012 9:54 am

aquazi wrote: I thought The front ducts on the M are meant for cooling the brakes? Yet the air would only cool the tyres. Why didnt they do this from stock?
The air passing through the so-called "brake ducts" in the front bumper of the ///M is directed at the inside edge of the front tyres and so will pass around the inside of tyre and flow over the hub, helping to remove warmer air from the brakes. I think it also helps to prevent turbulence of "stagnant air" in the wheel arches.

I doubt if any manufacturer would fit flexible brake ducting as OEM because it's not really necessary in everyday driving conditions. They're far more likely to fit a multi-pot BBK instead and I think a lot of BMW owners get disappointed that BMW don't do this for their performance cars.

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Re: Brake Cooling - Cheap DIY method

Post by McKoval » Wed Jun 13, 2012 10:12 am

so, basically, cold air is directed to the inner side of brake caliper?
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Re: Brake Cooling - Cheap DIY method

Post by exdos » Wed Jun 13, 2012 10:49 am

McKoval wrote:so, basically, cold air is directed to the inner side of brake caliper?
On the Z4MC there is a visible gap between the brake caliper and the centre of the hub where the outlet is directed. The OEM brake discs are vented, and they act like impellors, drawing air from the centre of the hub and passing it through the vanes between the inner and outer faces of the disc. The brake ducting is feeding air into the region where the impellors can use the cold air supplied. Since the Z4MC's OEM brake discs are also drilled, air passing through the vanes will also pass through the holes, which will also assist cooling of the brake pads and calipers too.

I have no idea what brake configuration exists for other models of Z4 , but any air directed to the brakes will help.

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Re: Brake Cooling - Cheap DIY method

Post by aquazi » Wed Jun 13, 2012 11:28 am

exdos wrote:
aquazi wrote: I thought The front ducts on the M are meant for cooling the brakes? Yet the air would only cool the tyres. Why didnt they do this from stock?
The air passing through the so-called "brake ducts" in the front bumper of the ///M is directed at the inside edge of the front tyres and so will pass around the inside of tyre and flow over the hub, helping to remove warmer air from the brakes. I think it also helps to prevent turbulence of "stagnant air" in the wheel arches.

I doubt if any manufacturer would fit flexible brake ducting as OEM because it's not really necessary in everyday driving conditions. They're far more likely to fit a multi-pot BBK instead and I think a lot of BMW owners get disappointed that BMW don't do this for their performance cars.
good to know :thumbsup:

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Re: Brake Cooling - Cheap DIY method

Post by ga41 » Wed Jun 13, 2012 12:18 pm

Looking good! I might try this at some point. Thanks for posting. :thumbsup:
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Re: Brake Cooling - Cheap DIY method

Post by Lower » Wed Jun 13, 2012 12:48 pm

exdos wrote:My DIY brake ducts on my Z3 M Coupe work very well on track and therefore I every reason to expect that they'll work just as well on the Z4MC with this very similar set up. The hottest that I've ever seen the brakes on my Z3 M Coupe with brake cooling is 270 degs C, which is well below the boiling point of DOT 5.1 brake fluid that I use.
I take it that temperature was measured after the car had stopped rather than using heat paint? If so i'd expect peak temperatures to be much higher.
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Re: Brake Cooling - Cheap DIY method

Post by exdos » Wed Jun 13, 2012 1:22 pm

Lower wrote: I take it that temperature was measured after the car had stopped rather than using heat paint? If so i'd expect peak temperatures to be much higher.
The temperature was taken with a hand-held IR thermometer, immediately on stopping. I'm sure that the actual peak temperature would be higher, but the rate of cooling in still air is pretty slow, so I wouldn't expect that the brakes had cooled from a peak of say, 600 degs C down to 270 degs C before I took the temperature.

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Re: Brake Cooling - Cheap DIY method

Post by Lower » Wed Jun 13, 2012 9:31 pm

I've achieved temperatures in excess of 625 degrees on track and had the brake discs glowing but I only know that from the heat paint and photos taken from outside the car. The cooling rate will be exponential so the greatest cooling rate will be when the temperature is at its highest. I have no doubt that your cooling ducts will be of considerable benefit in cooling th brake discs but it's a dangerous assumption to make that peak temperatures don't exceed the boiling temp of th brake fluid by measuring temps after the car as stopped.

As an aside, there will be very little airflow through the drilled holes in the discs. The holes are there to allow gas build up under the pads to escape rather than aid cooling.
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