M front brake ducts - odd

S

stevo///m3

Senior member
 Leeds - you know where it is
Afternoon chaps, I have a query which you could perhaps help me with. Shortly after I bought my M and had it on the drive admiring it, I noticed that the brake duct on one side was not sitting correctly (the black plastic scoop thingy). I tried a bit of manipulation but was not successful in re-seating it in the correct retaining brackets/mounts. I tried a few more times over the course of a couple of weeks - still to no avail and I was worried that I'd have to have the front bumper off. Anyway, I had reason to take it to my local indy who I'm on good terms with and he managed to pop them both back in when it was up on the ramp. Great stuff.

So I had a good look when I got home and they're seated exactly right now BUT - here comes the BUT - BUT, if you get down to the duct level and look through the duct (so looking inwards towards where the tyres are), each side is different in terms of what you see at the far (inner) end of the ducting...

I will do my best to post some pics when I get home to illustrate the difference but I remember how it looks fairly well - and I might not actually need the pics for you to identify the answer in any case. The far end of the ducting - i.e. the inner end, not the exposed hole at the front - meets the wheel arch inner, which is also black plastic (and a bit grubby in my particular case). On the inner wheel arch on one side, there is a black plastic plate which covers the entire place where you would expect the air to exit from - so the duct is basically blocked off from what I can tell! :!: Pretty sure there should be some exit holes as I believe the ducts are intended to cool the brakes. The other side has that same area - would you belive it - half blocked off, or half open if you prefer. I can see this from looking at the back of the ducts from inside the wheel arch. I'm thinking I prob will have to take photos because I remember seeing some louvred openings at the back of the duct but can't remember whether this relates to the blocked- or half-blocked side. Or maybe both ducts have louvres but the one set of louvres are completely blocked by the plate - I admit, I can't remember... :oldman:

Either way, the question is what has yours got (and what is "correct")? Obviously, answers need to come from non-modded front bumper owners... I've looked on RealOEM and didn't turn up anything useful. It shows that there is ducting but does not deal with the specific question I have as far as I can see. RealOEM: http://www.realoem.com/bmw/showparts.do?model=DU92&mospid=49422&btnr=51_5960&hg=51&fg=15 and it is part number 18 on that diagram. Hope that link works.

Once there is a collective answer any advice on how to sort it out would be appreciated. :hattip:

And I'll take comments on my use of the word "louvre" when I get home. :wink:

Cheers. :cheers:

Stevo
 
The ducts have half of the exit blocked off as standard, but you can pop the blanking plate off if you wish.

I assume that they'll also sometimes break/fall off of their own accord.
 
mmm-five said:
The ducts have half of the exit blocked off as standard, but you can pop the blanking plate off if you wish.

I assume that they'll also sometimes break/fall off of their own accord.
Click to expand...


mine don't have this and are fully open, they have never been modified or damaged either, mine is a 2007MY.
 
Mine are about two thirds covered, one third hole, so some air get's through. Always thought it was odd, but dealer assured me it was standard and looks like it's made that way. Have thought about cutting the pretusions off, a few times, but have never had any problems with my brakes, so left alone.
 
Thanks for the replies so far. I have some photos now - not the best but they should illustrate the point:

First driver's side, view up the duct then view from the wheel arch (looking forwards obv)

photo1_zpsba7db81b.jpg[URL]

So, louvres on the top surface - fine. At the back you can see the tyre tread - i.e. there is a gap that air passes through.

photo3_zps79f34579.jpg

Then from the wheel arch, if you look closely (sorry, poor qulity on my phone) there is a big plastic plate (I think this is how you access the headlights) which has a hole in it and part of that hole is filled with a smaller plate on it. Note that the smaller plate does not cover the whole of the hole in the larger plate such that there is a "gap" where the air can pass through - that's what you can see in the first photo. I'm calling this smaller plate the "half plate" for lack of a better term.

Then the passenger side, front then wheel arch:

photo_zpsdcf78292.jpg

You can see the same "half plate" as with the driver's side but the "half" that is not covered shows no tyre tread - it is blocked by another black plastic plate...

photo2_zps2e29490b.jpg

this last photo is shows the one big plate totally covering the half plate.

Beedub - are you saying that yours has no half plates? I think that is what you are saying.... in which case I think that the big plate on the passenger's side is the problem - it should have a hole that would be filled by the half plate and leaving a gap for air to pass through. Or perhaps you don't even have the half plates?

Stevo
 
Beedub said:
mmm-five said:
The ducts have half of the exit blocked off as standard, but you can pop the blanking plate off if you wish.

I assume that they'll also sometimes break/fall off of their own accord.
Click to expand...


mine don't have this and are fully open, they have never been modified or damaged either, mine is a 2007MY.
Click to expand...

I'm with you Beedub - I have fully open ducts with no full or half plates. Mine are unmodified and have always been this way.

Maybe they knew that you and I would be driving that much faster than the others :P
 
The "brake ducts" of my Z4MC are the same on both sides and have blocking plates at the top of the rear end and with an opening which is approximately 25% of the potential fully open duct. Looking through the opening, I can see the front tyre for approximately two-thirds of the width so there's less than 1 square inch of the opening that directs air to the inside of the wheel i.e. for brake cooling, therefore I think these ducts serve another purpose.

I originally thought that the N/S "brake duct" acted as an air-intake source, as it does for the Z3MC, but after close examination, there is no connection with the air intake system. Therefore, I consider that the slotted openings at the top of the "brake ducts" are partly to provide air-cooling to the headlights.

Since the "brake ducts" have a much larger opening aperture than the total of the exits at the back of the ducts, and because the "fangs" on the bumper are immediately in front of the "brake ducts", I think that the ducts might actually be intended to increase static pressure within the "brake ducts" so that the relatively small size of the fangs become more effective as "flippers" for aerodynamic reasons. Before the Z4M was even available, I experimented with blocking off the brake ducts on my Z3MC fitted with AC Schnitzer flippers, and when I measured the static pressure within the brake ducts with a Magnehelic differential pressure gauge I found that the static pressure increases when the ducts are partially blocked, and likewise, when I removed the ACS flippers, the static pressure within the ducts was less. Consequently, I think that the blocking plates might be for aerodynamic reasons, in part, to prevent front-end lift, to which the OEM Z4M is particularly prone.

If you want a cheap and effective brake cooling system, I devised a method described here: http://www.z4-forum.com/forum/viewtopic.php?f=24&t=38775&hilit=brake+cooling+exdos

Likewise, if you want to improve the OEM brakes I've also described the fitting of solid brake bushes here: http://www.z4-forum.com/forum/viewtopic.php?f=24&t=45293
 
OK thanks for the response all. The status quo is not causing me any problems as far as I know; rather, it just struck me as odd that the two sides are not the same. I understand what Exdos is talking about - and thanks for those comments - I tend to agree that the aperture is definitely not pointed at the inside of the wheel so as to materially affect the cooling capability of the airflow - it seems to be pointed directly at the tyre itself so would have some limited cooling effect. It sounds like my passenger side total-plate-block-off is probably not right so either I cut a section out so that it mirros the driver's side or perhaps more wisely a trip to BMW to ask a few more questions is in order.

Stevo
 
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